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<span class="siteTitle">NYTProf Performance Profile</span>
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<span class="siteSubtitle">Run on Tue May 4 15:25:55 2010<br />Reported on Tue May 4 15:26:18 2010</span>
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<table>
<tr>
<td class="h" align="right">File</td>
<td align="left">/usr/local/lib/perl5/5.10.1/overload.pm</td>
</tr>
<tr>
<td class="h" align="right">Statements Executed</td>
<td align="left">112</td>
</tr>
<tr>
<td class="h" align="right">Statement Execution Time</td>
<td align="left">674µs</td>
</tr>
</table>
<table id="subs_table" border="1" cellpadding="0" class="tablesorter">
<caption>Subroutines — ordered by exclusive time</caption>
<thead>
<tr>
<th>Calls</th>
<th><span title="Number of Places sub is called from">P</span></th>
<th><span title="Number of Files sub is called from">F</span></th>
<th>Exclusive<br />Time</th>
<th>Inclusive<br />Time</th>
<th>Subroutine</th>
</tr>
</thead>
<tbody>
<tr><td class="c3">6</td><td class="c3">1</td><td class="c3">1</td><td class="c1"><span title="0.0%">212µs</span></td><td class="c3"><span title="0.0%">214µs</span></td><td class="sub_name"><span style="display: none;">overload::::OVERLOAD</span>overload::<a href="overload-pm-line.html#7">OVERLOAD</a></span></td></tr>
<tr><td class="c3">6</td><td class="c0">6</td><td class="c0">6</td><td class="c3"><span title="0.0%">81µs</span></td><td class="c1"><span title="0.0%">295µs</span></td><td class="sub_name"><span style="display: none;">overload::::import</span>overload::<a href="overload-pm-line.html#29">import</a></span></td></tr>
<tr><td class="c3">1</td><td class="c3">1</td><td class="c3">1</td><td class="c3"><span title="0.0%">25µs</span></td><td class="c3"><span title="0.0%">140µs</span></td><td class="sub_name"><span style="display: none;">overload::::BEGIN@139</span>overload::<a href="overload-pm-line.html#139">BEGIN@139</a></span></td></tr>
<tr><td class="c3">1</td><td class="c3">1</td><td class="c3">2</td><td class="c3"><span title="0.0%">2µs</span></td><td class="c3"><span title="0.0%">2µs</span></td><td class="sub_name"><span style="display: none;">overload::::CORE:match</span>overload::<a href="overload-pm-line.html#overload__CORE_match">CORE:match</a> (opcode)</span></td></tr>
<tr><td class="c3">0</td><td class="c3">0</td><td class="c3">0</td><td class="c3"><span title="0.0%">0s</span></td><td class="c3"><span title="0.0%">0s</span></td><td class="sub_name"><span style="display: none;">overload::::AddrRef</span>overload::<a href="overload-pm-line.html#88">AddrRef</a></span></td></tr>
<tr><td class="c3">0</td><td class="c3">0</td><td class="c3">0</td><td class="c3"><span title="0.0%">0s</span></td><td class="c3"><span title="0.0%">0s</span></td><td class="sub_name"><span style="display: none;">overload::::Method</span>overload::<a href="overload-pm-line.html#73">Method</a></span></td></tr>
<tr><td class="c3">0</td><td class="c3">0</td><td class="c3">0</td><td class="c3"><span title="0.0%">0s</span></td><td class="c3"><span title="0.0%">0s</span></td><td class="sub_name"><span style="display: none;">overload::::Overloaded</span>overload::<a href="overload-pm-line.html#49">Overloaded</a></span></td></tr>
<tr><td class="c3">0</td><td class="c3">0</td><td class="c3">0</td><td class="c3"><span title="0.0%">0s</span></td><td class="c3"><span title="0.0%">0s</span></td><td class="sub_name"><span style="display: none;">overload::::OverloadedStringify</span>overload::<a href="overload-pm-line.html#63">OverloadedStringify</a></span></td></tr>
<tr><td class="c3">0</td><td class="c3">0</td><td class="c3">0</td><td class="c3"><span title="0.0%">0s</span></td><td class="c3"><span title="0.0%">0s</span></td><td class="sub_name"><span style="display: none;">overload::::constant</span>overload::<a href="overload-pm-line.html#140">constant</a></span></td></tr>
<tr><td class="c3">0</td><td class="c3">0</td><td class="c3">0</td><td class="c3"><span title="0.0%">0s</span></td><td class="c3"><span title="0.0%">0s</span></td><td class="sub_name"><span style="display: none;">overload::::mycan</span>overload::<a href="overload-pm-line.html#104">mycan</a></span></td></tr>
<tr><td class="c3">0</td><td class="c3">0</td><td class="c3">0</td><td class="c3"><span title="0.0%">0s</span></td><td class="c3"><span title="0.0%">0s</span></td><td class="sub_name"><span style="display: none;">overload::::nil</span>overload::<a href="overload-pm-line.html#5">nil</a></span></td></tr>
<tr><td class="c3">0</td><td class="c3">0</td><td class="c3">0</td><td class="c3"><span title="0.0%">0s</span></td><td class="c3"><span title="0.0%">0s</span></td><td class="sub_name"><span style="display: none;">overload::::ov_method</span>overload::<a href="overload-pm-line.html#55">ov_method</a></span></td></tr>
<tr><td class="c3">0</td><td class="c3">0</td><td class="c3">0</td><td class="c3"><span title="0.0%">0s</span></td><td class="c3"><span title="0.0%">0s</span></td><td class="sub_name"><span style="display: none;">overload::::remove_constant</span>overload::<a href="overload-pm-line.html#166">remove_constant</a></span></td></tr>
<tr><td class="c3">0</td><td class="c3">0</td><td class="c3">0</td><td class="c3"><span title="0.0%">0s</span></td><td class="c3"><span title="0.0%">0s</span></td><td class="sub_name"><span style="display: none;">overload::::unimport</span>overload::<a href="overload-pm-line.html#36">unimport</a></span></td></tr>
</tbody>
</table>
Call graph for these subroutines as a <a href="http://en.wikipedia.org/wiki/Graphviz">Graphviz</a> <a href="usr-local-lib-perl5-5-10-1-overload-pm.dot">dot language file</a>.
<table border="1" cellpadding="0">
<thead>
<tr><th>Line</th>
<th><span title="Number of statements executed">State<br />ments</span></th>
<th><span title="Time spend executing statements on the line,
excluding time spent executing statements in any called subroutines">Time<br />on line</span></th>
<th><span title="Number of subroutines calls">Calls</span></th>
<th><span title="Time spent in subroutines called">Time<br />in subs</span></th>
<th class="left_indent_header">Code</th>
</tr>
</thead>
<tbody>
<tr><td class="h"><a name="1"></a>1</td><td></td><td></td><td></td><td></td><td class="s">package overload;</td></tr>
<tr><td class="h"><a name="2"></a>2</td><td></td><td></td><td></td><td></td><td class="s"></td></tr>
<tr><td class="h"><a name="3"></a>3</td><td class="c3">1</td><td class="c3"><span title="Avg 1µs">1µs</span></td><td></td><td></td><td class="s">our $VERSION = '1.07';</td></tr>
<tr><td class="h"><a name="4"></a>4</td><td></td><td></td><td></td><td></td><td class="s"></td></tr>
<tr><td class="h"><a name="5"></a>5</td><td></td><td></td><td></td><td></td><td class="s">sub nil {}</td></tr>
<tr><td class="h"><a name="6"></a>6</td><td></td><td></td><td></td><td></td><td class="s"></td></tr>
<tr><td class="h"><a name="7"></a>7</td><td></td><td></td><td></td><td></td><td class="s"><div class="calls"><div class="calls_in"># spent 214µs (212+2) within overload::OVERLOAD which was called 6 times, avg 36µs/call:
# 6 times (212µs+2µs) by overload::import at <a href="overload-pm-line.html#33">line 33</a>, avg 36µs/call</div></div>sub OVERLOAD {</td></tr>
<tr><td class="h"><a name="8"></a>8</td><td class="c3">6</td><td class="c3"><span title="Avg 417ns">2µs</span></td><td></td><td></td><td class="s"> $package = shift;</td></tr>
<tr><td class="h"><a name="9"></a>9</td><td class="c3">6</td><td class="c3"><span title="Avg 3µs">17µs</span></td><td></td><td></td><td class="s"> my %arg = @_;</td></tr>
<tr><td class="h"><a name="10"></a>10</td><td class="c3">6</td><td class="c3"><span title="Avg 500ns">3µs</span></td><td></td><td></td><td class="s"> my ($sub, $fb);</td></tr>
<tr><td class="h"><a name="11"></a>11</td><td class="c3">6</td><td class="c1"><span title="Avg 7µs">42µs</span></td><td></td><td></td><td class="s"> $ {$package . "::OVERLOAD"}{dummy}++; # Register with magic by touching.</td></tr>
<tr><td class="h"><a name="12"></a>12</td><td class="c3">6</td><td class="c3"><span title="Avg 4µs">24µs</span></td><td></td><td></td><td class="s"> *{$package . "::()"} = \&nil; # Make it findable via fetchmethod.</td></tr>
<tr><td class="h"><a name="13"></a>13</td><td class="c3">6</td><td class="c3"><span title="Avg 3µs">19µs</span></td><td></td><td></td><td class="s"> for (keys %arg) {</td></tr>
<tr><td class="h"><a name="14"></a>14</td><td class="c0">15</td><td class="c3"><span title="Avg 1µs">18µs</span></td><td></td><td></td><td class="s"> if ($_ eq 'fallback') {</td></tr>
<tr><td class="h"><a name="15"></a>15</td><td></td><td></td><td></td><td></td><td class="s"> $fb = $arg{$_};</td></tr>
<tr><td class="h"><a name="16"></a>16</td><td></td><td></td><td></td><td></td><td class="s"> } else {</td></tr>
<tr><td class="h"><a name="17"></a>17</td><td class="c1">9</td><td class="c3"><span title="Avg 600ns">5µs</span></td><td></td><td></td><td class="s"> $sub = $arg{$_};</td></tr>
<tr><td class="h"><a name="18"></a>18</td><td class="c1">9</td><td class="c3"><span title="Avg 2µs">17µs</span></td><td class="c3">1</td><td class="c3">2µs</td><td class="s"> if (not ref $sub and $sub !~ /::/) {<div class="calls"><div class="calls_out"> # spent 2µs making 1 call to <a href="overload-pm-line.html#overload__CORE_match">overload::CORE:match</a></div></div></td></tr>
<tr><td class="h"><a name="19"></a>19</td><td class="c3">1</td><td class="c3"><span title="Avg 4µs">4µs</span></td><td></td><td></td><td class="s"> $ {$package . "::(" . $_} = $sub;</td></tr>
<tr><td class="h"><a name="20"></a>20</td><td class="c3">1</td><td class="c3"><span title="Avg 1µs">1µs</span></td><td></td><td></td><td class="s"> $sub = \&nil;</td></tr>
<tr><td class="h"><a name="21"></a>21</td><td></td><td></td><td></td><td></td><td class="s"> }</td></tr>
<tr><td class="h"><a name="22"></a>22</td><td></td><td></td><td></td><td></td><td class="s"> #print STDERR "Setting `$ {'package'}::\cO$_' to \\&`$sub'.\n";</td></tr>
<tr><td class="h"><a name="23"></a>23</td><td class="c1">9</td><td class="c3"><span title="Avg 3µs">23µs</span></td><td></td><td></td><td class="s"> *{$package . "::(" . $_} = \&{ $sub };</td></tr>
<tr><td class="h"><a name="24"></a>24</td><td></td><td></td><td></td><td></td><td class="s"> }</td></tr>
<tr><td class="h"><a name="25"></a>25</td><td></td><td></td><td></td><td></td><td class="s"> }</td></tr>
<tr><td class="h"><a name="26"></a>26</td><td class="c3">6</td><td class="c1"><span title="Avg 7µs">45µs</span></td><td></td><td></td><td class="s"> ${$package . "::()"} = $fb; # Make it findable too (fallback only).</td></tr>
<tr><td class="h"><a name="27"></a>27</td><td></td><td></td><td></td><td></td><td class="s">}</td></tr>
<tr><td class="h"><a name="28"></a>28</td><td></td><td></td><td></td><td></td><td class="s"></td></tr>
<tr><td class="h"><a name="29"></a>29</td><td></td><td></td><td></td><td></td><td class="s"><div class="calls"><div class="calls_in"># spent 295µs (81+214) within overload::import which was called 6 times, avg 49µs/call:
# once (19µs+42µs) by Devel::StackTrace::BEGIN@12 at <a href="Devel-StackTrace-pm-line.html#12">line 12 of Devel/StackTrace.pm</a>
# once (9µs+48µs) by Exception::Class::Base::BEGIN@30 at <a href="Exception-Class-Base-pm-line.html#31">line 31 of Exception/Class/Base.pm</a>
# once (14µs+37µs) by URI::BEGIN@24 at <a href="URI-pm-line.html#27">line 27 of URI.pm</a>
# once (14µs+30µs) by Class::MOP::Method::BEGIN@19 at <a href="Class-MOP-Method-pm-line.html#19">line 19 of Class/MOP/Method.pm</a>
# once (13µs+29µs) by Moose::Meta::TypeConstraint::BEGIN@8 at <a href="Moose-Meta-TypeConstraint-pm-line.html#9">line 9 of Moose/Meta/TypeConstraint.pm</a>
# once (13µs+28µs) by Moose::Meta::Role::Method::Required::BEGIN@8 at <a href="Moose-Meta-Role-Method-Required-pm-line.html#9">line 9 of Moose/Meta/Role/Method/Required.pm</a></div></div>sub import {</td></tr>
<tr><td class="h"><a name="30"></a>30</td><td class="c3">6</td><td class="c3"><span title="Avg 3µs">16µs</span></td><td></td><td></td><td class="s"> $package = (caller())[0];</td></tr>
<tr><td class="h"><a name="31"></a>31</td><td></td><td></td><td></td><td></td><td class="s"> # *{$package . "::OVERLOAD"} = \&OVERLOAD;</td></tr>
<tr><td class="h"><a name="32"></a>32</td><td class="c3">6</td><td class="c3"><span title="Avg 450ns">3µs</span></td><td></td><td></td><td class="s"> shift;</td></tr>
<tr><td class="h"><a name="33"></a>33</td><td class="c3">6</td><td class="c0"><span title="Avg 9µs">53µs</span></td><td class="c0">6</td><td class="c3">214µs</td><td class="s"> $package->overload::OVERLOAD(@_);<div class="calls"><div class="calls_out"> # spent 214µs making 6 calls to <a href="overload-pm-line.html#7">overload::OVERLOAD</a>, avg 36µs/call</div></div></td></tr>
<tr><td class="h"><a name="34"></a>34</td><td></td><td></td><td></td><td></td><td class="s">}</td></tr>
<tr><td class="h"><a name="35"></a>35</td><td></td><td></td><td></td><td></td><td class="s"></td></tr>
<tr><td class="h"><a name="36"></a>36</td><td></td><td></td><td></td><td></td><td class="s">sub unimport {</td></tr>
<tr><td class="h"><a name="37"></a>37</td><td></td><td></td><td></td><td></td><td class="s"> $package = (caller())[0];</td></tr>
<tr><td class="h"><a name="38"></a>38</td><td></td><td></td><td></td><td></td><td class="s"> ${$package . "::OVERLOAD"}{dummy}++; # Upgrade the table</td></tr>
<tr><td class="h"><a name="39"></a>39</td><td></td><td></td><td></td><td></td><td class="s"> shift;</td></tr>
<tr><td class="h"><a name="40"></a>40</td><td></td><td></td><td></td><td></td><td class="s"> for (@_) {</td></tr>
<tr><td class="h"><a name="41"></a>41</td><td></td><td></td><td></td><td></td><td class="s"> if ($_ eq 'fallback') {</td></tr>
<tr><td class="h"><a name="42"></a>42</td><td></td><td></td><td></td><td></td><td class="s"> undef $ {$package . "::()"};</td></tr>
<tr><td class="h"><a name="43"></a>43</td><td></td><td></td><td></td><td></td><td class="s"> } else {</td></tr>
<tr><td class="h"><a name="44"></a>44</td><td></td><td></td><td></td><td></td><td class="s"> delete $ {$package . "::"}{"(" . $_};</td></tr>
<tr><td class="h"><a name="45"></a>45</td><td></td><td></td><td></td><td></td><td class="s"> }</td></tr>
<tr><td class="h"><a name="46"></a>46</td><td></td><td></td><td></td><td></td><td class="s"> }</td></tr>
<tr><td class="h"><a name="47"></a>47</td><td></td><td></td><td></td><td></td><td class="s">}</td></tr>
<tr><td class="h"><a name="48"></a>48</td><td></td><td></td><td></td><td></td><td class="s"></td></tr>
<tr><td class="h"><a name="49"></a>49</td><td></td><td></td><td></td><td></td><td class="s">sub Overloaded {</td></tr>
<tr><td class="h"><a name="50"></a>50</td><td></td><td></td><td></td><td></td><td class="s"> my $package = shift;</td></tr>
<tr><td class="h"><a name="51"></a>51</td><td></td><td></td><td></td><td></td><td class="s"> $package = ref $package if ref $package;</td></tr>
<tr><td class="h"><a name="52"></a>52</td><td></td><td></td><td></td><td></td><td class="s"> $package->can('()');</td></tr>
<tr><td class="h"><a name="53"></a>53</td><td></td><td></td><td></td><td></td><td class="s">}</td></tr>
<tr><td class="h"><a name="54"></a>54</td><td></td><td></td><td></td><td></td><td class="s"></td></tr>
<tr><td class="h"><a name="55"></a>55</td><td></td><td></td><td></td><td></td><td class="s">sub ov_method {</td></tr>
<tr><td class="h"><a name="56"></a>56</td><td></td><td></td><td></td><td></td><td class="s"> my $globref = shift;</td></tr>
<tr><td class="h"><a name="57"></a>57</td><td></td><td></td><td></td><td></td><td class="s"> return undef unless $globref;</td></tr>
<tr><td class="h"><a name="58"></a>58</td><td></td><td></td><td></td><td></td><td class="s"> my $sub = \&{*$globref};</td></tr>
<tr><td class="h"><a name="59"></a>59</td><td></td><td></td><td></td><td></td><td class="s"> return $sub if $sub ne \&nil;</td></tr>
<tr><td class="h"><a name="60"></a>60</td><td></td><td></td><td></td><td></td><td class="s"> return shift->can($ {*$globref});</td></tr>
<tr><td class="h"><a name="61"></a>61</td><td></td><td></td><td></td><td></td><td class="s">}</td></tr>
<tr><td class="h"><a name="62"></a>62</td><td></td><td></td><td></td><td></td><td class="s"></td></tr>
<tr><td class="h"><a name="63"></a>63</td><td></td><td></td><td></td><td></td><td class="s">sub OverloadedStringify {</td></tr>
<tr><td class="h"><a name="64"></a>64</td><td></td><td></td><td></td><td></td><td class="s"> my $package = shift;</td></tr>
<tr><td class="h"><a name="65"></a>65</td><td></td><td></td><td></td><td></td><td class="s"> $package = ref $package if ref $package;</td></tr>
<tr><td class="h"><a name="66"></a>66</td><td></td><td></td><td></td><td></td><td class="s"> #$package->can('(""')</td></tr>
<tr><td class="h"><a name="67"></a>67</td><td></td><td></td><td></td><td></td><td class="s"> ov_method mycan($package, '(""'), $package</td></tr>
<tr><td class="h"><a name="68"></a>68</td><td></td><td></td><td></td><td></td><td class="s"> or ov_method mycan($package, '(0+'), $package</td></tr>
<tr><td class="h"><a name="69"></a>69</td><td></td><td></td><td></td><td></td><td class="s"> or ov_method mycan($package, '(bool'), $package</td></tr>
<tr><td class="h"><a name="70"></a>70</td><td></td><td></td><td></td><td></td><td class="s"> or ov_method mycan($package, '(nomethod'), $package;</td></tr>
<tr><td class="h"><a name="71"></a>71</td><td></td><td></td><td></td><td></td><td class="s">}</td></tr>
<tr><td class="h"><a name="72"></a>72</td><td></td><td></td><td></td><td></td><td class="s"></td></tr>
<tr><td class="h"><a name="73"></a>73</td><td></td><td></td><td></td><td></td><td class="s">sub Method {</td></tr>
<tr><td class="h"><a name="74"></a>74</td><td></td><td></td><td></td><td></td><td class="s"> my $package = shift;</td></tr>
<tr><td class="h"><a name="75"></a>75</td><td></td><td></td><td></td><td></td><td class="s"> if(ref $package) {</td></tr>
<tr><td class="h"><a name="76"></a>76</td><td></td><td></td><td></td><td></td><td class="s"> local $@;</td></tr>
<tr><td class="h"><a name="77"></a>77</td><td></td><td></td><td></td><td></td><td class="s"> local $!;</td></tr>
<tr><td class="h"><a name="78"></a>78</td><td></td><td></td><td></td><td></td><td class="s"> require Scalar::Util;</td></tr>
<tr><td class="h"><a name="79"></a>79</td><td></td><td></td><td></td><td></td><td class="s"> $package = Scalar::Util::blessed($package);</td></tr>
<tr><td class="h"><a name="80"></a>80</td><td></td><td></td><td></td><td></td><td class="s"> return undef if !defined $package;</td></tr>
<tr><td class="h"><a name="81"></a>81</td><td></td><td></td><td></td><td></td><td class="s"> }</td></tr>
<tr><td class="h"><a name="82"></a>82</td><td></td><td></td><td></td><td></td><td class="s"> #my $meth = $package->can('(' . shift);</td></tr>
<tr><td class="h"><a name="83"></a>83</td><td></td><td></td><td></td><td></td><td class="s"> ov_method mycan($package, '(' . shift), $package;</td></tr>
<tr><td class="h"><a name="84"></a>84</td><td></td><td></td><td></td><td></td><td class="s"> #return $meth if $meth ne \&nil;</td></tr>
<tr><td class="h"><a name="85"></a>85</td><td></td><td></td><td></td><td></td><td class="s"> #return $ {*{$meth}};</td></tr>
<tr><td class="h"><a name="86"></a>86</td><td></td><td></td><td></td><td></td><td class="s">}</td></tr>
<tr><td class="h"><a name="87"></a>87</td><td></td><td></td><td></td><td></td><td class="s"></td></tr>
<tr><td class="h"><a name="88"></a>88</td><td></td><td></td><td></td><td></td><td class="s">sub AddrRef {</td></tr>
<tr><td class="h"><a name="89"></a>89</td><td></td><td></td><td></td><td></td><td class="s"> my $package = ref $_[0];</td></tr>
<tr><td class="h"><a name="90"></a>90</td><td></td><td></td><td></td><td></td><td class="s"> return "$_[0]" unless $package;</td></tr>
<tr><td class="h"><a name="91"></a>91</td><td></td><td></td><td></td><td></td><td class="s"></td></tr>
<tr><td class="h"><a name="92"></a>92</td><td></td><td></td><td></td><td></td><td class="s"> local $@;</td></tr>
<tr><td class="h"><a name="93"></a>93</td><td></td><td></td><td></td><td></td><td class="s"> local $!;</td></tr>
<tr><td class="h"><a name="94"></a>94</td><td></td><td></td><td></td><td></td><td class="s"> require Scalar::Util;</td></tr>
<tr><td class="h"><a name="95"></a>95</td><td></td><td></td><td></td><td></td><td class="s"> my $class = Scalar::Util::blessed($_[0]);</td></tr>
<tr><td class="h"><a name="96"></a>96</td><td></td><td></td><td></td><td></td><td class="s"> my $class_prefix = defined($class) ? "$class=" : "";</td></tr>
<tr><td class="h"><a name="97"></a>97</td><td></td><td></td><td></td><td></td><td class="s"> my $type = Scalar::Util::reftype($_[0]);</td></tr>
<tr><td class="h"><a name="98"></a>98</td><td></td><td></td><td></td><td></td><td class="s"> my $addr = Scalar::Util::refaddr($_[0]);</td></tr>
<tr><td class="h"><a name="99"></a>99</td><td></td><td></td><td></td><td></td><td class="s"> return sprintf("$class_prefix$type(0x%x)", $addr);</td></tr>
<tr><td class="h"><a name="100"></a>100</td><td></td><td></td><td></td><td></td><td class="s">}</td></tr>
<tr><td class="h"><a name="101"></a>101</td><td></td><td></td><td></td><td></td><td class="s"></td></tr>
<tr><td class="h"><a name="102"></a>102</td><td class="c3">1</td><td class="c3"><span title="Avg 2µs">2µs</span></td><td></td><td></td><td class="s">*StrVal = *AddrRef;</td></tr>
<tr><td class="h"><a name="103"></a>103</td><td></td><td></td><td></td><td></td><td class="s"></td></tr>
<tr><td class="h"><a name="104"></a>104</td><td></td><td></td><td></td><td></td><td class="s">sub mycan { # Real can would leave stubs.</td></tr>
<tr><td class="h"><a name="105"></a>105</td><td></td><td></td><td></td><td></td><td class="s"> my ($package, $meth) = @_;</td></tr>
<tr><td class="h"><a name="106"></a>106</td><td></td><td></td><td></td><td></td><td class="s"></td></tr>
<tr><td class="h"><a name="107"></a>107</td><td></td><td></td><td></td><td></td><td class="s"> my $mro = mro::get_linear_isa($package);</td></tr>
<tr><td class="h"><a name="108"></a>108</td><td></td><td></td><td></td><td></td><td class="s"> foreach my $p (@$mro) {</td></tr>
<tr><td class="h"><a name="109"></a>109</td><td></td><td></td><td></td><td></td><td class="s"> my $fqmeth = $p . q{::} . $meth;</td></tr>
<tr><td class="h"><a name="110"></a>110</td><td></td><td></td><td></td><td></td><td class="s"> return \*{$fqmeth} if defined &{$fqmeth};</td></tr>
<tr><td class="h"><a name="111"></a>111</td><td></td><td></td><td></td><td></td><td class="s"> }</td></tr>
<tr><td class="h"><a name="112"></a>112</td><td></td><td></td><td></td><td></td><td class="s"></td></tr>
<tr><td class="h"><a name="113"></a>113</td><td></td><td></td><td></td><td></td><td class="s"> return undef;</td></tr>
<tr><td class="h"><a name="114"></a>114</td><td></td><td></td><td></td><td></td><td class="s">}</td></tr>
<tr><td class="h"><a name="115"></a>115</td><td></td><td></td><td></td><td></td><td class="s"></td></tr>
<tr><td class="h"><a name="116"></a>116</td><td class="c3">1</td><td class="c3"><span title="Avg 4µs">4µs</span></td><td></td><td></td><td class="s">%constants = (</td></tr>
<tr><td class="h"><a name="117"></a>117</td><td></td><td></td><td></td><td></td><td class="s"> 'integer' => 0x1000, # HINT_NEW_INTEGER</td></tr>
<tr><td class="h"><a name="118"></a>118</td><td></td><td></td><td></td><td></td><td class="s"> 'float' => 0x2000, # HINT_NEW_FLOAT</td></tr>
<tr><td class="h"><a name="119"></a>119</td><td></td><td></td><td></td><td></td><td class="s"> 'binary' => 0x4000, # HINT_NEW_BINARY</td></tr>
<tr><td class="h"><a name="120"></a>120</td><td></td><td></td><td></td><td></td><td class="s"> 'q' => 0x8000, # HINT_NEW_STRING</td></tr>
<tr><td class="h"><a name="121"></a>121</td><td></td><td></td><td></td><td></td><td class="s"> 'qr' => 0x10000, # HINT_NEW_RE</td></tr>
<tr><td class="h"><a name="122"></a>122</td><td></td><td></td><td></td><td></td><td class="s"> );</td></tr>
<tr><td class="h"><a name="123"></a>123</td><td></td><td></td><td></td><td></td><td class="s"></td></tr>
<tr><td class="h"><a name="124"></a>124</td><td class="c3">1</td><td class="c3"><span title="Avg 11µs">11µs</span></td><td></td><td></td><td class="s">%ops = ( with_assign => "+ - * / % ** << >> x .",</td></tr>
<tr><td class="h"><a name="125"></a>125</td><td></td><td></td><td></td><td></td><td class="s"> assign => "+= -= *= /= %= **= <<= >>= x= .=",</td></tr>
<tr><td class="h"><a name="126"></a>126</td><td></td><td></td><td></td><td></td><td class="s"> num_comparison => "< <= > >= == !=",</td></tr>
<tr><td class="h"><a name="127"></a>127</td><td></td><td></td><td></td><td></td><td class="s"> '3way_comparison'=> "<=> cmp",</td></tr>
<tr><td class="h"><a name="128"></a>128</td><td></td><td></td><td></td><td></td><td class="s"> str_comparison => "lt le gt ge eq ne",</td></tr>
<tr><td class="h"><a name="129"></a>129</td><td></td><td></td><td></td><td></td><td class="s"> binary => '& &= | |= ^ ^=',</td></tr>
<tr><td class="h"><a name="130"></a>130</td><td></td><td></td><td></td><td></td><td class="s"> unary => "neg ! ~",</td></tr>
<tr><td class="h"><a name="131"></a>131</td><td></td><td></td><td></td><td></td><td class="s"> mutators => '++ --',</td></tr>
<tr><td class="h"><a name="132"></a>132</td><td></td><td></td><td></td><td></td><td class="s"> func => "atan2 cos sin exp abs log sqrt int",</td></tr>
<tr><td class="h"><a name="133"></a>133</td><td></td><td></td><td></td><td></td><td class="s"> conversion => 'bool "" 0+',</td></tr>
<tr><td class="h"><a name="134"></a>134</td><td></td><td></td><td></td><td></td><td class="s"> iterators => '<>',</td></tr>
<tr><td class="h"><a name="135"></a>135</td><td></td><td></td><td></td><td></td><td class="s"> dereferencing => '${} @{} %{} &{} *{}',</td></tr>
<tr><td class="h"><a name="136"></a>136</td><td></td><td></td><td></td><td></td><td class="s"> matching => '~~',</td></tr>
<tr><td class="h"><a name="137"></a>137</td><td></td><td></td><td></td><td></td><td class="s"> special => 'nomethod fallback =');</td></tr>
<tr><td class="h"><a name="138"></a>138</td><td></td><td></td><td></td><td></td><td class="s"></td></tr>
<tr><td class="h"><a name="139"></a>139</td><td class="c3">3</td><td class="c0"><span title="Avg 113µs">338µs</span></td><td class="c3">2</td><td class="c1">254µs</td><td class="s"><div class="calls"><div class="calls_in"># spent 140µs (25+115) within overload::BEGIN@139 which was called
# once (25µs+115µs) by Class::MOP::Method::BEGIN@19 at <a href="overload-pm-line.html#139">line 139</a></div></div>use warnings::register;<div class="calls"><div class="calls_out"># spent 140µs making 1 call to <a href="overload-pm-line.html#139">overload::BEGIN@139</a>
# spent 114µs making 1 call to <a href="warnings-register-pm-line.html#36">warnings::register::import</a></div></div></td></tr>
<tr><td class="h"><a name="140"></a>140</td><td></td><td></td><td></td><td></td><td class="s">sub constant {</td></tr>
<tr><td class="h"><a name="141"></a>141</td><td></td><td></td><td></td><td></td><td class="s"> # Arguments: what, sub</td></tr>
<tr><td class="h"><a name="142"></a>142</td><td></td><td></td><td></td><td></td><td class="s"> while (@_) {</td></tr>
<tr><td class="h"><a name="143"></a>143</td><td></td><td></td><td></td><td></td><td class="s"> if (@_ == 1) {</td></tr>
<tr><td class="h"><a name="144"></a>144</td><td></td><td></td><td></td><td></td><td class="s"> warnings::warnif ("Odd number of arguments for overload::constant");</td></tr>
<tr><td class="h"><a name="145"></a>145</td><td></td><td></td><td></td><td></td><td class="s"> last;</td></tr>
<tr><td class="h"><a name="146"></a>146</td><td></td><td></td><td></td><td></td><td class="s"> }</td></tr>
<tr><td class="h"><a name="147"></a>147</td><td></td><td></td><td></td><td></td><td class="s"> elsif (!exists $constants {$_ [0]}) {</td></tr>
<tr><td class="h"><a name="148"></a>148</td><td></td><td></td><td></td><td></td><td class="s"> warnings::warnif ("`$_[0]' is not an overloadable type");</td></tr>
<tr><td class="h"><a name="149"></a>149</td><td></td><td></td><td></td><td></td><td class="s"> }</td></tr>
<tr><td class="h"><a name="150"></a>150</td><td></td><td></td><td></td><td></td><td class="s"> elsif (!ref $_ [1] || "$_[1]" !~ /(^|=)CODE\(0x[0-9a-f]+\)$/) {</td></tr>
<tr><td class="h"><a name="151"></a>151</td><td></td><td></td><td></td><td></td><td class="s"> # Can't use C<ref $_[1] eq "CODE"> above as code references can be</td></tr>
<tr><td class="h"><a name="152"></a>152</td><td></td><td></td><td></td><td></td><td class="s"> # blessed, and C<ref> would return the package the ref is blessed into.</td></tr>
<tr><td class="h"><a name="153"></a>153</td><td></td><td></td><td></td><td></td><td class="s"> if (warnings::enabled) {</td></tr>
<tr><td class="h"><a name="154"></a>154</td><td></td><td></td><td></td><td></td><td class="s"> $_ [1] = "undef" unless defined $_ [1];</td></tr>
<tr><td class="h"><a name="155"></a>155</td><td></td><td></td><td></td><td></td><td class="s"> warnings::warn ("`$_[1]' is not a code reference");</td></tr>
<tr><td class="h"><a name="156"></a>156</td><td></td><td></td><td></td><td></td><td class="s"> }</td></tr>
<tr><td class="h"><a name="157"></a>157</td><td></td><td></td><td></td><td></td><td class="s"> }</td></tr>
<tr><td class="h"><a name="158"></a>158</td><td></td><td></td><td></td><td></td><td class="s"> else {</td></tr>
<tr><td class="h"><a name="159"></a>159</td><td></td><td></td><td></td><td></td><td class="s"> $^H{$_[0]} = $_[1];</td></tr>
<tr><td class="h"><a name="160"></a>160</td><td></td><td></td><td></td><td></td><td class="s"> $^H |= $constants{$_[0]};</td></tr>
<tr><td class="h"><a name="161"></a>161</td><td></td><td></td><td></td><td></td><td class="s"> }</td></tr>
<tr><td class="h"><a name="162"></a>162</td><td></td><td></td><td></td><td></td><td class="s"> shift, shift;</td></tr>
<tr><td class="h"><a name="163"></a>163</td><td></td><td></td><td></td><td></td><td class="s"> }</td></tr>
<tr><td class="h"><a name="164"></a>164</td><td></td><td></td><td></td><td></td><td class="s">}</td></tr>
<tr><td class="h"><a name="165"></a>165</td><td></td><td></td><td></td><td></td><td class="s"></td></tr>
<tr><td class="h"><a name="166"></a>166</td><td></td><td></td><td></td><td></td><td class="s">sub remove_constant {</td></tr>
<tr><td class="h"><a name="167"></a>167</td><td></td><td></td><td></td><td></td><td class="s"> # Arguments: what, sub</td></tr>
<tr><td class="h"><a name="168"></a>168</td><td></td><td></td><td></td><td></td><td class="s"> while (@_) {</td></tr>
<tr><td class="h"><a name="169"></a>169</td><td></td><td></td><td></td><td></td><td class="s"> delete $^H{$_[0]};</td></tr>
<tr><td class="h"><a name="170"></a>170</td><td></td><td></td><td></td><td></td><td class="s"> $^H &= ~ $constants{$_[0]};</td></tr>
<tr><td class="h"><a name="171"></a>171</td><td></td><td></td><td></td><td></td><td class="s"> shift, shift;</td></tr>
<tr><td class="h"><a name="172"></a>172</td><td></td><td></td><td></td><td></td><td class="s"> }</td></tr>
<tr><td class="h"><a name="173"></a>173</td><td></td><td></td><td></td><td></td><td class="s">}</td></tr>
<tr><td class="h"><a name="174"></a>174</td><td></td><td></td><td></td><td></td><td class="s"></td></tr>
<tr><td class="h"><a name="175"></a>175</td><td class="c3">1</td><td class="c3"><span title="Avg 24µs">24µs</span></td><td></td><td></td><td class="s">1;</td></tr>
<tr><td class="h"><a name="176"></a>176</td><td></td><td></td><td></td><td></td><td class="s"></td></tr>
<tr><td class="h"><a name="177"></a>177</td><td></td><td></td><td></td><td></td><td class="s">__END__</td></tr>
<tr><td class="h"><a name="178"></a>178</td><td></td><td></td><td></td><td></td><td class="s"></td></tr>
<tr><td class="h"><a name="179"></a>179</td><td></td><td></td><td></td><td></td><td class="s">=head1 NAME</td></tr>
<tr><td class="h"><a name="180"></a>180</td><td></td><td></td><td></td><td></td><td class="s"></td></tr>
<tr><td class="h"><a name="181"></a>181</td><td></td><td></td><td></td><td></td><td class="s">overload - Package for overloading Perl operations</td></tr>
<tr><td class="h"><a name="182"></a>182</td><td></td><td></td><td></td><td></td><td class="s"></td></tr>
<tr><td class="h"><a name="183"></a>183</td><td></td><td></td><td></td><td></td><td class="s">=head1 SYNOPSIS</td></tr>
<tr><td class="h"><a name="184"></a>184</td><td></td><td></td><td></td><td></td><td class="s"></td></tr>
<tr><td class="h"><a name="185"></a>185</td><td></td><td></td><td></td><td></td><td class="s"> package SomeThing;</td></tr>
<tr><td class="h"><a name="186"></a>186</td><td></td><td></td><td></td><td></td><td class="s"></td></tr>
<tr><td class="h"><a name="187"></a>187</td><td></td><td></td><td></td><td></td><td class="s"> use overload</td></tr>
<tr><td class="h"><a name="188"></a>188</td><td></td><td></td><td></td><td></td><td class="s"> '+' => \&myadd,</td></tr>
<tr><td class="h"><a name="189"></a>189</td><td></td><td></td><td></td><td></td><td class="s"> '-' => \&mysub;</td></tr>
<tr><td class="h"><a name="190"></a>190</td><td></td><td></td><td></td><td></td><td class="s"> # etc</td></tr>
<tr><td class="h"><a name="191"></a>191</td><td></td><td></td><td></td><td></td><td class="s"> ...</td></tr>
<tr><td class="h"><a name="192"></a>192</td><td></td><td></td><td></td><td></td><td class="s"></td></tr>
<tr><td class="h"><a name="193"></a>193</td><td></td><td></td><td></td><td></td><td class="s"> package main;</td></tr>
<tr><td class="h"><a name="194"></a>194</td><td></td><td></td><td></td><td></td><td class="s"> $a = SomeThing->new( 57 );</td></tr>
<tr><td class="h"><a name="195"></a>195</td><td></td><td></td><td></td><td></td><td class="s"> $b=5+$a;</td></tr>
<tr><td class="h"><a name="196"></a>196</td><td></td><td></td><td></td><td></td><td class="s"> ...</td></tr>
<tr><td class="h"><a name="197"></a>197</td><td></td><td></td><td></td><td></td><td class="s"> if (overload::Overloaded $b) {...}</td></tr>
<tr><td class="h"><a name="198"></a>198</td><td></td><td></td><td></td><td></td><td class="s"> ...</td></tr>
<tr><td class="h"><a name="199"></a>199</td><td></td><td></td><td></td><td></td><td class="s"> $strval = overload::StrVal $b;</td></tr>
<tr><td class="h"><a name="200"></a>200</td><td></td><td></td><td></td><td></td><td class="s"></td></tr>
<tr><td class="h"><a name="201"></a>201</td><td></td><td></td><td></td><td></td><td class="s">=head1 DESCRIPTION</td></tr>
<tr><td class="h"><a name="202"></a>202</td><td></td><td></td><td></td><td></td><td class="s"></td></tr>
<tr><td class="h"><a name="203"></a>203</td><td></td><td></td><td></td><td></td><td class="s">This pragma allows overloading of Perl's operators for a class.</td></tr>
<tr><td class="h"><a name="204"></a>204</td><td></td><td></td><td></td><td></td><td class="s">To overload built-in functions, see L<perlsub/Overriding Built-in Functions> instead.</td></tr>
<tr><td class="h"><a name="205"></a>205</td><td></td><td></td><td></td><td></td><td class="s"></td></tr>
<tr><td class="h"><a name="206"></a>206</td><td></td><td></td><td></td><td></td><td class="s">=head2 Declaration of overloaded functions</td></tr>
<tr><td class="h"><a name="207"></a>207</td><td></td><td></td><td></td><td></td><td class="s"></td></tr>
<tr><td class="h"><a name="208"></a>208</td><td></td><td></td><td></td><td></td><td class="s">The compilation directive</td></tr>
<tr><td class="h"><a name="209"></a>209</td><td></td><td></td><td></td><td></td><td class="s"></td></tr>
<tr><td class="h"><a name="210"></a>210</td><td></td><td></td><td></td><td></td><td class="s"> package Number;</td></tr>
<tr><td class="h"><a name="211"></a>211</td><td></td><td></td><td></td><td></td><td class="s"> use overload</td></tr>
<tr><td class="h"><a name="212"></a>212</td><td></td><td></td><td></td><td></td><td class="s"> "+" => \&add,</td></tr>
<tr><td class="h"><a name="213"></a>213</td><td></td><td></td><td></td><td></td><td class="s"> "*=" => "muas";</td></tr>
<tr><td class="h"><a name="214"></a>214</td><td></td><td></td><td></td><td></td><td class="s"></td></tr>
<tr><td class="h"><a name="215"></a>215</td><td></td><td></td><td></td><td></td><td class="s">declares function Number::add() for addition, and method muas() in</td></tr>
<tr><td class="h"><a name="216"></a>216</td><td></td><td></td><td></td><td></td><td class="s">the "class" C<Number> (or one of its base classes)</td></tr>
<tr><td class="h"><a name="217"></a>217</td><td></td><td></td><td></td><td></td><td class="s">for the assignment form C<*=> of multiplication.</td></tr>
<tr><td class="h"><a name="218"></a>218</td><td></td><td></td><td></td><td></td><td class="s"></td></tr>
<tr><td class="h"><a name="219"></a>219</td><td></td><td></td><td></td><td></td><td class="s">Arguments of this directive come in (key, value) pairs. Legal values</td></tr>
<tr><td class="h"><a name="220"></a>220</td><td></td><td></td><td></td><td></td><td class="s">are values legal inside a C<&{ ... }> call, so the name of a</td></tr>
<tr><td class="h"><a name="221"></a>221</td><td></td><td></td><td></td><td></td><td class="s">subroutine, a reference to a subroutine, or an anonymous subroutine</td></tr>
<tr><td class="h"><a name="222"></a>222</td><td></td><td></td><td></td><td></td><td class="s">will all work. Note that values specified as strings are</td></tr>
<tr><td class="h"><a name="223"></a>223</td><td></td><td></td><td></td><td></td><td class="s">interpreted as methods, not subroutines. Legal keys are listed below.</td></tr>
<tr><td class="h"><a name="224"></a>224</td><td></td><td></td><td></td><td></td><td class="s"></td></tr>
<tr><td class="h"><a name="225"></a>225</td><td></td><td></td><td></td><td></td><td class="s">The subroutine C<add> will be called to execute C<$a+$b> if $a</td></tr>
<tr><td class="h"><a name="226"></a>226</td><td></td><td></td><td></td><td></td><td class="s">is a reference to an object blessed into the package C<Number>, or if $a is</td></tr>
<tr><td class="h"><a name="227"></a>227</td><td></td><td></td><td></td><td></td><td class="s">not an object from a package with defined mathemagic addition, but $b is a</td></tr>
<tr><td class="h"><a name="228"></a>228</td><td></td><td></td><td></td><td></td><td class="s">reference to a C<Number>. It can also be called in other situations, like</td></tr>
<tr><td class="h"><a name="229"></a>229</td><td></td><td></td><td></td><td></td><td class="s">C<$a+=7>, or C<$a++>. See L<MAGIC AUTOGENERATION>. (Mathemagical</td></tr>
<tr><td class="h"><a name="230"></a>230</td><td></td><td></td><td></td><td></td><td class="s">methods refer to methods triggered by an overloaded mathematical</td></tr>
<tr><td class="h"><a name="231"></a>231</td><td></td><td></td><td></td><td></td><td class="s">operator.)</td></tr>
<tr><td class="h"><a name="232"></a>232</td><td></td><td></td><td></td><td></td><td class="s"></td></tr>
<tr><td class="h"><a name="233"></a>233</td><td></td><td></td><td></td><td></td><td class="s">Since overloading respects inheritance via the @ISA hierarchy, the</td></tr>
<tr><td class="h"><a name="234"></a>234</td><td></td><td></td><td></td><td></td><td class="s">above declaration would also trigger overloading of C<+> and C<*=> in</td></tr>
<tr><td class="h"><a name="235"></a>235</td><td></td><td></td><td></td><td></td><td class="s">all the packages which inherit from C<Number>.</td></tr>
<tr><td class="h"><a name="236"></a>236</td><td></td><td></td><td></td><td></td><td class="s"></td></tr>
<tr><td class="h"><a name="237"></a>237</td><td></td><td></td><td></td><td></td><td class="s">=head2 Calling Conventions for Binary Operations</td></tr>
<tr><td class="h"><a name="238"></a>238</td><td></td><td></td><td></td><td></td><td class="s"></td></tr>
<tr><td class="h"><a name="239"></a>239</td><td></td><td></td><td></td><td></td><td class="s">The functions specified in the C<use overload ...> directive are called</td></tr>
<tr><td class="h"><a name="240"></a>240</td><td></td><td></td><td></td><td></td><td class="s">with three (in one particular case with four, see L<Last Resort>)</td></tr>
<tr><td class="h"><a name="241"></a>241</td><td></td><td></td><td></td><td></td><td class="s">arguments. If the corresponding operation is binary, then the first</td></tr>
<tr><td class="h"><a name="242"></a>242</td><td></td><td></td><td></td><td></td><td class="s">two arguments are the two arguments of the operation. However, due to</td></tr>
<tr><td class="h"><a name="243"></a>243</td><td></td><td></td><td></td><td></td><td class="s">general object calling conventions, the first argument should always be</td></tr>
<tr><td class="h"><a name="244"></a>244</td><td></td><td></td><td></td><td></td><td class="s">an object in the package, so in the situation of C<7+$a>, the</td></tr>
<tr><td class="h"><a name="245"></a>245</td><td></td><td></td><td></td><td></td><td class="s">order of the arguments is interchanged. It probably does not matter</td></tr>
<tr><td class="h"><a name="246"></a>246</td><td></td><td></td><td></td><td></td><td class="s">when implementing the addition method, but whether the arguments</td></tr>
<tr><td class="h"><a name="247"></a>247</td><td></td><td></td><td></td><td></td><td class="s">are reversed is vital to the subtraction method. The method can</td></tr>
<tr><td class="h"><a name="248"></a>248</td><td></td><td></td><td></td><td></td><td class="s">query this information by examining the third argument, which can take</td></tr>
<tr><td class="h"><a name="249"></a>249</td><td></td><td></td><td></td><td></td><td class="s">three different values:</td></tr>
<tr><td class="h"><a name="250"></a>250</td><td></td><td></td><td></td><td></td><td class="s"></td></tr>
<tr><td class="h"><a name="251"></a>251</td><td></td><td></td><td></td><td></td><td class="s">=over 7</td></tr>
<tr><td class="h"><a name="252"></a>252</td><td></td><td></td><td></td><td></td><td class="s"></td></tr>
<tr><td class="h"><a name="253"></a>253</td><td></td><td></td><td></td><td></td><td class="s">=item FALSE</td></tr>
<tr><td class="h"><a name="254"></a>254</td><td></td><td></td><td></td><td></td><td class="s"></td></tr>
<tr><td class="h"><a name="255"></a>255</td><td></td><td></td><td></td><td></td><td class="s">the order of arguments is as in the current operation.</td></tr>
<tr><td class="h"><a name="256"></a>256</td><td></td><td></td><td></td><td></td><td class="s"></td></tr>
<tr><td class="h"><a name="257"></a>257</td><td></td><td></td><td></td><td></td><td class="s">=item TRUE</td></tr>
<tr><td class="h"><a name="258"></a>258</td><td></td><td></td><td></td><td></td><td class="s"></td></tr>
<tr><td class="h"><a name="259"></a>259</td><td></td><td></td><td></td><td></td><td class="s">the arguments are reversed.</td></tr>
<tr><td class="h"><a name="260"></a>260</td><td></td><td></td><td></td><td></td><td class="s"></td></tr>
<tr><td class="h"><a name="261"></a>261</td><td></td><td></td><td></td><td></td><td class="s">=item C<undef></td></tr>
<tr><td class="h"><a name="262"></a>262</td><td></td><td></td><td></td><td></td><td class="s"></td></tr>
<tr><td class="h"><a name="263"></a>263</td><td></td><td></td><td></td><td></td><td class="s">the current operation is an assignment variant (as in</td></tr>
<tr><td class="h"><a name="264"></a>264</td><td></td><td></td><td></td><td></td><td class="s">C<$a+=7>), but the usual function is called instead. This additional</td></tr>
<tr><td class="h"><a name="265"></a>265</td><td></td><td></td><td></td><td></td><td class="s">information can be used to generate some optimizations. Compare</td></tr>
<tr><td class="h"><a name="266"></a>266</td><td></td><td></td><td></td><td></td><td class="s">L<Calling Conventions for Mutators>.</td></tr>
<tr><td class="h"><a name="267"></a>267</td><td></td><td></td><td></td><td></td><td class="s"></td></tr>
<tr><td class="h"><a name="268"></a>268</td><td></td><td></td><td></td><td></td><td class="s">=back</td></tr>
<tr><td class="h"><a name="269"></a>269</td><td></td><td></td><td></td><td></td><td class="s"></td></tr>
<tr><td class="h"><a name="270"></a>270</td><td></td><td></td><td></td><td></td><td class="s">=head2 Calling Conventions for Unary Operations</td></tr>
<tr><td class="h"><a name="271"></a>271</td><td></td><td></td><td></td><td></td><td class="s"></td></tr>
<tr><td class="h"><a name="272"></a>272</td><td></td><td></td><td></td><td></td><td class="s">Unary operation are considered binary operations with the second</td></tr>
<tr><td class="h"><a name="273"></a>273</td><td></td><td></td><td></td><td></td><td class="s">argument being C<undef>. Thus the functions that overloads C<{"++"}></td></tr>
<tr><td class="h"><a name="274"></a>274</td><td></td><td></td><td></td><td></td><td class="s">is called with arguments C<($a,undef,'')> when $a++ is executed.</td></tr>
<tr><td class="h"><a name="275"></a>275</td><td></td><td></td><td></td><td></td><td class="s"></td></tr>
<tr><td class="h"><a name="276"></a>276</td><td></td><td></td><td></td><td></td><td class="s">=head2 Calling Conventions for Mutators</td></tr>
<tr><td class="h"><a name="277"></a>277</td><td></td><td></td><td></td><td></td><td class="s"></td></tr>
<tr><td class="h"><a name="278"></a>278</td><td></td><td></td><td></td><td></td><td class="s">Two types of mutators have different calling conventions:</td></tr>
<tr><td class="h"><a name="279"></a>279</td><td></td><td></td><td></td><td></td><td class="s"></td></tr>
<tr><td class="h"><a name="280"></a>280</td><td></td><td></td><td></td><td></td><td class="s">=over</td></tr>
<tr><td class="h"><a name="281"></a>281</td><td></td><td></td><td></td><td></td><td class="s"></td></tr>
<tr><td class="h"><a name="282"></a>282</td><td></td><td></td><td></td><td></td><td class="s">=item C<++> and C<--></td></tr>
<tr><td class="h"><a name="283"></a>283</td><td></td><td></td><td></td><td></td><td class="s"></td></tr>
<tr><td class="h"><a name="284"></a>284</td><td></td><td></td><td></td><td></td><td class="s">The routines which implement these operators are expected to actually</td></tr>
<tr><td class="h"><a name="285"></a>285</td><td></td><td></td><td></td><td></td><td class="s">I<mutate> their arguments. So, assuming that $obj is a reference to a</td></tr>
<tr><td class="h"><a name="286"></a>286</td><td></td><td></td><td></td><td></td><td class="s">number,</td></tr>
<tr><td class="h"><a name="287"></a>287</td><td></td><td></td><td></td><td></td><td class="s"></td></tr>
<tr><td class="h"><a name="288"></a>288</td><td></td><td></td><td></td><td></td><td class="s"> sub incr { my $n = $ {$_[0]}; ++$n; $_[0] = bless \$n}</td></tr>
<tr><td class="h"><a name="289"></a>289</td><td></td><td></td><td></td><td></td><td class="s"></td></tr>
<tr><td class="h"><a name="290"></a>290</td><td></td><td></td><td></td><td></td><td class="s">is an appropriate implementation of overloaded C<++>. Note that</td></tr>
<tr><td class="h"><a name="291"></a>291</td><td></td><td></td><td></td><td></td><td class="s"></td></tr>
<tr><td class="h"><a name="292"></a>292</td><td></td><td></td><td></td><td></td><td class="s"> sub incr { ++$ {$_[0]} ; shift }</td></tr>
<tr><td class="h"><a name="293"></a>293</td><td></td><td></td><td></td><td></td><td class="s"></td></tr>
<tr><td class="h"><a name="294"></a>294</td><td></td><td></td><td></td><td></td><td class="s">is OK if used with preincrement and with postincrement. (In the case</td></tr>
<tr><td class="h"><a name="295"></a>295</td><td></td><td></td><td></td><td></td><td class="s">of postincrement a copying will be performed, see L<Copy Constructor>.)</td></tr>
<tr><td class="h"><a name="296"></a>296</td><td></td><td></td><td></td><td></td><td class="s"></td></tr>
<tr><td class="h"><a name="297"></a>297</td><td></td><td></td><td></td><td></td><td class="s">=item C<x=> and other assignment versions</td></tr>
<tr><td class="h"><a name="298"></a>298</td><td></td><td></td><td></td><td></td><td class="s"></td></tr>
<tr><td class="h"><a name="299"></a>299</td><td></td><td></td><td></td><td></td><td class="s">There is nothing special about these methods. They may change the</td></tr>
<tr><td class="h"><a name="300"></a>300</td><td></td><td></td><td></td><td></td><td class="s">value of their arguments, and may leave it as is. The result is going</td></tr>
<tr><td class="h"><a name="301"></a>301</td><td></td><td></td><td></td><td></td><td class="s">to be assigned to the value in the left-hand-side if different from</td></tr>
<tr><td class="h"><a name="302"></a>302</td><td></td><td></td><td></td><td></td><td class="s">this value.</td></tr>
<tr><td class="h"><a name="303"></a>303</td><td></td><td></td><td></td><td></td><td class="s"></td></tr>
<tr><td class="h"><a name="304"></a>304</td><td></td><td></td><td></td><td></td><td class="s">This allows for the same method to be used as overloaded C<+=> and</td></tr>
<tr><td class="h"><a name="305"></a>305</td><td></td><td></td><td></td><td></td><td class="s">C<+>. Note that this is I<allowed>, but not recommended, since by the</td></tr>
<tr><td class="h"><a name="306"></a>306</td><td></td><td></td><td></td><td></td><td class="s">semantic of L<"Fallback"> Perl will call the method for C<+> anyway,</td></tr>
<tr><td class="h"><a name="307"></a>307</td><td></td><td></td><td></td><td></td><td class="s">if C<+=> is not overloaded.</td></tr>
<tr><td class="h"><a name="308"></a>308</td><td></td><td></td><td></td><td></td><td class="s"></td></tr>
<tr><td class="h"><a name="309"></a>309</td><td></td><td></td><td></td><td></td><td class="s">=back</td></tr>
<tr><td class="h"><a name="310"></a>310</td><td></td><td></td><td></td><td></td><td class="s"></td></tr>
<tr><td class="h"><a name="311"></a>311</td><td></td><td></td><td></td><td></td><td class="s">B<Warning.> Due to the presence of assignment versions of operations,</td></tr>
<tr><td class="h"><a name="312"></a>312</td><td></td><td></td><td></td><td></td><td class="s">routines which may be called in assignment context may create</td></tr>
<tr><td class="h"><a name="313"></a>313</td><td></td><td></td><td></td><td></td><td class="s">self-referential structures. Currently Perl will not free self-referential</td></tr>
<tr><td class="h"><a name="314"></a>314</td><td></td><td></td><td></td><td></td><td class="s">structures until cycles are C<explicitly> broken. You may get problems</td></tr>
<tr><td class="h"><a name="315"></a>315</td><td></td><td></td><td></td><td></td><td class="s">when traversing your structures too.</td></tr>
<tr><td class="h"><a name="316"></a>316</td><td></td><td></td><td></td><td></td><td class="s"></td></tr>
<tr><td class="h"><a name="317"></a>317</td><td></td><td></td><td></td><td></td><td class="s">Say,</td></tr>
<tr><td class="h"><a name="318"></a>318</td><td></td><td></td><td></td><td></td><td class="s"></td></tr>
<tr><td class="h"><a name="319"></a>319</td><td></td><td></td><td></td><td></td><td class="s"> use overload '+' => sub { bless [ \$_[0], \$_[1] ] };</td></tr>
<tr><td class="h"><a name="320"></a>320</td><td></td><td></td><td></td><td></td><td class="s"></td></tr>
<tr><td class="h"><a name="321"></a>321</td><td></td><td></td><td></td><td></td><td class="s">is asking for trouble, since for code C<$obj += $foo> the subroutine</td></tr>
<tr><td class="h"><a name="322"></a>322</td><td></td><td></td><td></td><td></td><td class="s">is called as C<$obj = add($obj, $foo, undef)>, or C<$obj = [\$obj,</td></tr>
<tr><td class="h"><a name="323"></a>323</td><td></td><td></td><td></td><td></td><td class="s">\$foo]>. If using such a subroutine is an important optimization, one</td></tr>
<tr><td class="h"><a name="324"></a>324</td><td></td><td></td><td></td><td></td><td class="s">can overload C<+=> explicitly by a non-"optimized" version, or switch</td></tr>
<tr><td class="h"><a name="325"></a>325</td><td></td><td></td><td></td><td></td><td class="s">to non-optimized version if C<not defined $_[2]> (see</td></tr>
<tr><td class="h"><a name="326"></a>326</td><td></td><td></td><td></td><td></td><td class="s">L<Calling Conventions for Binary Operations>).</td></tr>
<tr><td class="h"><a name="327"></a>327</td><td></td><td></td><td></td><td></td><td class="s"></td></tr>
<tr><td class="h"><a name="328"></a>328</td><td></td><td></td><td></td><td></td><td class="s">Even if no I<explicit> assignment-variants of operators are present in</td></tr>
<tr><td class="h"><a name="329"></a>329</td><td></td><td></td><td></td><td></td><td class="s">the script, they may be generated by the optimizer. Say, C<",$obj,"> or</td></tr>
<tr><td class="h"><a name="330"></a>330</td><td></td><td></td><td></td><td></td><td class="s">C<',' . $obj . ','> may be both optimized to</td></tr>
<tr><td class="h"><a name="331"></a>331</td><td></td><td></td><td></td><td></td><td class="s"></td></tr>
<tr><td class="h"><a name="332"></a>332</td><td></td><td></td><td></td><td></td><td class="s"> my $tmp = ',' . $obj; $tmp .= ',';</td></tr>
<tr><td class="h"><a name="333"></a>333</td><td></td><td></td><td></td><td></td><td class="s"></td></tr>
<tr><td class="h"><a name="334"></a>334</td><td></td><td></td><td></td><td></td><td class="s">=head2 Overloadable Operations</td></tr>
<tr><td class="h"><a name="335"></a>335</td><td></td><td></td><td></td><td></td><td class="s"></td></tr>
<tr><td class="h"><a name="336"></a>336</td><td></td><td></td><td></td><td></td><td class="s">The following symbols can be specified in C<use overload> directive:</td></tr>
<tr><td class="h"><a name="337"></a>337</td><td></td><td></td><td></td><td></td><td class="s"></td></tr>
<tr><td class="h"><a name="338"></a>338</td><td></td><td></td><td></td><td></td><td class="s">=over 5</td></tr>
<tr><td class="h"><a name="339"></a>339</td><td></td><td></td><td></td><td></td><td class="s"></td></tr>
<tr><td class="h"><a name="340"></a>340</td><td></td><td></td><td></td><td></td><td class="s">=item * I<Arithmetic operations></td></tr>
<tr><td class="h"><a name="341"></a>341</td><td></td><td></td><td></td><td></td><td class="s"></td></tr>
<tr><td class="h"><a name="342"></a>342</td><td></td><td></td><td></td><td></td><td class="s"> "+", "+=", "-", "-=", "*", "*=", "/", "/=", "%", "%=",</td></tr>
<tr><td class="h"><a name="343"></a>343</td><td></td><td></td><td></td><td></td><td class="s"> "**", "**=", "<<", "<<=", ">>", ">>=", "x", "x=", ".", ".=",</td></tr>
<tr><td class="h"><a name="344"></a>344</td><td></td><td></td><td></td><td></td><td class="s"></td></tr>
<tr><td class="h"><a name="345"></a>345</td><td></td><td></td><td></td><td></td><td class="s">For these operations a substituted non-assignment variant can be called if</td></tr>
<tr><td class="h"><a name="346"></a>346</td><td></td><td></td><td></td><td></td><td class="s">the assignment variant is not available. Methods for operations C<+>,</td></tr>
<tr><td class="h"><a name="347"></a>347</td><td></td><td></td><td></td><td></td><td class="s">C<->, C<+=>, and C<-=> can be called to automatically generate</td></tr>
<tr><td class="h"><a name="348"></a>348</td><td></td><td></td><td></td><td></td><td class="s">increment and decrement methods. The operation C<-> can be used to</td></tr>
<tr><td class="h"><a name="349"></a>349</td><td></td><td></td><td></td><td></td><td class="s">autogenerate missing methods for unary minus or C<abs>.</td></tr>
<tr><td class="h"><a name="350"></a>350</td><td></td><td></td><td></td><td></td><td class="s"></td></tr>
<tr><td class="h"><a name="351"></a>351</td><td></td><td></td><td></td><td></td><td class="s">See L<"MAGIC AUTOGENERATION">, L<"Calling Conventions for Mutators"> and</td></tr>
<tr><td class="h"><a name="352"></a>352</td><td></td><td></td><td></td><td></td><td class="s">L<"Calling Conventions for Binary Operations">) for details of these</td></tr>
<tr><td class="h"><a name="353"></a>353</td><td></td><td></td><td></td><td></td><td class="s">substitutions.</td></tr>
<tr><td class="h"><a name="354"></a>354</td><td></td><td></td><td></td><td></td><td class="s"></td></tr>
<tr><td class="h"><a name="355"></a>355</td><td></td><td></td><td></td><td></td><td class="s">=item * I<Comparison operations></td></tr>
<tr><td class="h"><a name="356"></a>356</td><td></td><td></td><td></td><td></td><td class="s"></td></tr>
<tr><td class="h"><a name="357"></a>357</td><td></td><td></td><td></td><td></td><td class="s"> "<", "<=", ">", ">=", "==", "!=", "<=>",</td></tr>
<tr><td class="h"><a name="358"></a>358</td><td></td><td></td><td></td><td></td><td class="s"> "lt", "le", "gt", "ge", "eq", "ne", "cmp",</td></tr>
<tr><td class="h"><a name="359"></a>359</td><td></td><td></td><td></td><td></td><td class="s"></td></tr>
<tr><td class="h"><a name="360"></a>360</td><td></td><td></td><td></td><td></td><td class="s">If the corresponding "spaceship" variant is available, it can be</td></tr>
<tr><td class="h"><a name="361"></a>361</td><td></td><td></td><td></td><td></td><td class="s">used to substitute for the missing operation. During C<sort>ing</td></tr>
<tr><td class="h"><a name="362"></a>362</td><td></td><td></td><td></td><td></td><td class="s">arrays, C<cmp> is used to compare values subject to C<use overload>.</td></tr>
<tr><td class="h"><a name="363"></a>363</td><td></td><td></td><td></td><td></td><td class="s"></td></tr>
<tr><td class="h"><a name="364"></a>364</td><td></td><td></td><td></td><td></td><td class="s">=item * I<Bit operations></td></tr>
<tr><td class="h"><a name="365"></a>365</td><td></td><td></td><td></td><td></td><td class="s"></td></tr>
<tr><td class="h"><a name="366"></a>366</td><td></td><td></td><td></td><td></td><td class="s"> "&", "&=", "^", "^=", "|", "|=", "neg", "!", "~",</td></tr>
<tr><td class="h"><a name="367"></a>367</td><td></td><td></td><td></td><td></td><td class="s"></td></tr>
<tr><td class="h"><a name="368"></a>368</td><td></td><td></td><td></td><td></td><td class="s">C<neg> stands for unary minus. If the method for C<neg> is not</td></tr>
<tr><td class="h"><a name="369"></a>369</td><td></td><td></td><td></td><td></td><td class="s">specified, it can be autogenerated using the method for</td></tr>
<tr><td class="h"><a name="370"></a>370</td><td></td><td></td><td></td><td></td><td class="s">subtraction. If the method for C<!> is not specified, it can be</td></tr>
<tr><td class="h"><a name="371"></a>371</td><td></td><td></td><td></td><td></td><td class="s">autogenerated using the methods for C<bool>, or C<"">, or C<0+>.</td></tr>
<tr><td class="h"><a name="372"></a>372</td><td></td><td></td><td></td><td></td><td class="s"></td></tr>
<tr><td class="h"><a name="373"></a>373</td><td></td><td></td><td></td><td></td><td class="s">The same remarks in L<"Arithmetic operations"> about</td></tr>
<tr><td class="h"><a name="374"></a>374</td><td></td><td></td><td></td><td></td><td class="s">assignment-variants and autogeneration apply for</td></tr>
<tr><td class="h"><a name="375"></a>375</td><td></td><td></td><td></td><td></td><td class="s">bit operations C<"&">, C<"^">, and C<"|"> as well.</td></tr>
<tr><td class="h"><a name="376"></a>376</td><td></td><td></td><td></td><td></td><td class="s"></td></tr>
<tr><td class="h"><a name="377"></a>377</td><td></td><td></td><td></td><td></td><td class="s">=item * I<Increment and decrement></td></tr>
<tr><td class="h"><a name="378"></a>378</td><td></td><td></td><td></td><td></td><td class="s"></td></tr>
<tr><td class="h"><a name="379"></a>379</td><td></td><td></td><td></td><td></td><td class="s"> "++", "--",</td></tr>
<tr><td class="h"><a name="380"></a>380</td><td></td><td></td><td></td><td></td><td class="s"></td></tr>
<tr><td class="h"><a name="381"></a>381</td><td></td><td></td><td></td><td></td><td class="s">If undefined, addition and subtraction methods can be</td></tr>
<tr><td class="h"><a name="382"></a>382</td><td></td><td></td><td></td><td></td><td class="s">used instead. These operations are called both in prefix and</td></tr>
<tr><td class="h"><a name="383"></a>383</td><td></td><td></td><td></td><td></td><td class="s">postfix form.</td></tr>
<tr><td class="h"><a name="384"></a>384</td><td></td><td></td><td></td><td></td><td class="s"></td></tr>
<tr><td class="h"><a name="385"></a>385</td><td></td><td></td><td></td><td></td><td class="s">=item * I<Transcendental functions></td></tr>
<tr><td class="h"><a name="386"></a>386</td><td></td><td></td><td></td><td></td><td class="s"></td></tr>
<tr><td class="h"><a name="387"></a>387</td><td></td><td></td><td></td><td></td><td class="s"> "atan2", "cos", "sin", "exp", "abs", "log", "sqrt", "int"</td></tr>
<tr><td class="h"><a name="388"></a>388</td><td></td><td></td><td></td><td></td><td class="s"></td></tr>
<tr><td class="h"><a name="389"></a>389</td><td></td><td></td><td></td><td></td><td class="s">If C<abs> is unavailable, it can be autogenerated using methods</td></tr>
<tr><td class="h"><a name="390"></a>390</td><td></td><td></td><td></td><td></td><td class="s">for "E<lt>" or "E<lt>=E<gt>" combined with either unary minus or subtraction.</td></tr>
<tr><td class="h"><a name="391"></a>391</td><td></td><td></td><td></td><td></td><td class="s"></td></tr>
<tr><td class="h"><a name="392"></a>392</td><td></td><td></td><td></td><td></td><td class="s">Note that traditionally the Perl function L<int> rounds to 0, thus for</td></tr>
<tr><td class="h"><a name="393"></a>393</td><td></td><td></td><td></td><td></td><td class="s">floating-point-like types one should follow the same semantic. If</td></tr>
<tr><td class="h"><a name="394"></a>394</td><td></td><td></td><td></td><td></td><td class="s">C<int> is unavailable, it can be autogenerated using the overloading of</td></tr>
<tr><td class="h"><a name="395"></a>395</td><td></td><td></td><td></td><td></td><td class="s">C<0+>.</td></tr>
<tr><td class="h"><a name="396"></a>396</td><td></td><td></td><td></td><td></td><td class="s"></td></tr>
<tr><td class="h"><a name="397"></a>397</td><td></td><td></td><td></td><td></td><td class="s">=item * I<Boolean, string and numeric conversion></td></tr>
<tr><td class="h"><a name="398"></a>398</td><td></td><td></td><td></td><td></td><td class="s"></td></tr>
<tr><td class="h"><a name="399"></a>399</td><td></td><td></td><td></td><td></td><td class="s"> 'bool', '""', '0+',</td></tr>
<tr><td class="h"><a name="400"></a>400</td><td></td><td></td><td></td><td></td><td class="s"></td></tr>
<tr><td class="h"><a name="401"></a>401</td><td></td><td></td><td></td><td></td><td class="s">If one or two of these operations are not overloaded, the remaining ones can</td></tr>
<tr><td class="h"><a name="402"></a>402</td><td></td><td></td><td></td><td></td><td class="s">be used instead. C<bool> is used in the flow control operators</td></tr>
<tr><td class="h"><a name="403"></a>403</td><td></td><td></td><td></td><td></td><td class="s">(like C<while>) and for the ternary C<?:> operation. These functions can</td></tr>
<tr><td class="h"><a name="404"></a>404</td><td></td><td></td><td></td><td></td><td class="s">return any arbitrary Perl value. If the corresponding operation for this value</td></tr>
<tr><td class="h"><a name="405"></a>405</td><td></td><td></td><td></td><td></td><td class="s">is overloaded too, that operation will be called again with this value.</td></tr>
<tr><td class="h"><a name="406"></a>406</td><td></td><td></td><td></td><td></td><td class="s"></td></tr>
<tr><td class="h"><a name="407"></a>407</td><td></td><td></td><td></td><td></td><td class="s">As a special case if the overload returns the object itself then it will</td></tr>
<tr><td class="h"><a name="408"></a>408</td><td></td><td></td><td></td><td></td><td class="s">be used directly. An overloaded conversion returning the object is</td></tr>
<tr><td class="h"><a name="409"></a>409</td><td></td><td></td><td></td><td></td><td class="s">probably a bug, because you're likely to get something that looks like</td></tr>
<tr><td class="h"><a name="410"></a>410</td><td></td><td></td><td></td><td></td><td class="s">C<YourPackage=HASH(0x8172b34)>.</td></tr>
<tr><td class="h"><a name="411"></a>411</td><td></td><td></td><td></td><td></td><td class="s"></td></tr>
<tr><td class="h"><a name="412"></a>412</td><td></td><td></td><td></td><td></td><td class="s">=item * I<Iteration></td></tr>
<tr><td class="h"><a name="413"></a>413</td><td></td><td></td><td></td><td></td><td class="s"></td></tr>
<tr><td class="h"><a name="414"></a>414</td><td></td><td></td><td></td><td></td><td class="s"> "<>"</td></tr>
<tr><td class="h"><a name="415"></a>415</td><td></td><td></td><td></td><td></td><td class="s"></td></tr>
<tr><td class="h"><a name="416"></a>416</td><td></td><td></td><td></td><td></td><td class="s">If not overloaded, the argument will be converted to a filehandle or</td></tr>
<tr><td class="h"><a name="417"></a>417</td><td></td><td></td><td></td><td></td><td class="s">glob (which may require a stringification). The same overloading</td></tr>
<tr><td class="h"><a name="418"></a>418</td><td></td><td></td><td></td><td></td><td class="s">happens both for the I<read-filehandle> syntax C<E<lt>$varE<gt>> and</td></tr>
<tr><td class="h"><a name="419"></a>419</td><td></td><td></td><td></td><td></td><td class="s">I<globbing> syntax C<E<lt>${var}E<gt>>.</td></tr>
<tr><td class="h"><a name="420"></a>420</td><td></td><td></td><td></td><td></td><td class="s"></td></tr>
<tr><td class="h"><a name="421"></a>421</td><td></td><td></td><td></td><td></td><td class="s">B<BUGS> Even in list context, the iterator is currently called only</td></tr>
<tr><td class="h"><a name="422"></a>422</td><td></td><td></td><td></td><td></td><td class="s">once and with scalar context.</td></tr>
<tr><td class="h"><a name="423"></a>423</td><td></td><td></td><td></td><td></td><td class="s"></td></tr>
<tr><td class="h"><a name="424"></a>424</td><td></td><td></td><td></td><td></td><td class="s">=item * I<Matching></td></tr>
<tr><td class="h"><a name="425"></a>425</td><td></td><td></td><td></td><td></td><td class="s"></td></tr>
<tr><td class="h"><a name="426"></a>426</td><td></td><td></td><td></td><td></td><td class="s">The key C<"~~"> allows you to override the smart matching logic used by</td></tr>
<tr><td class="h"><a name="427"></a>427</td><td></td><td></td><td></td><td></td><td class="s">the C<~~> operator and the switch construct (C<given>/C<when>). See</td></tr>
<tr><td class="h"><a name="428"></a>428</td><td></td><td></td><td></td><td></td><td class="s">L<perlsyn/switch> and L<feature>.</td></tr>
<tr><td class="h"><a name="429"></a>429</td><td></td><td></td><td></td><td></td><td class="s"></td></tr>
<tr><td class="h"><a name="430"></a>430</td><td></td><td></td><td></td><td></td><td class="s">Unusually, overloading of the smart match operator does not automatically</td></tr>
<tr><td class="h"><a name="431"></a>431</td><td></td><td></td><td></td><td></td><td class="s">take precedence over normal smart match behaviour. In particular, in the</td></tr>
<tr><td class="h"><a name="432"></a>432</td><td></td><td></td><td></td><td></td><td class="s">following code:</td></tr>
<tr><td class="h"><a name="433"></a>433</td><td></td><td></td><td></td><td></td><td class="s"></td></tr>
<tr><td class="h"><a name="434"></a>434</td><td></td><td></td><td></td><td></td><td class="s"> package Foo;</td></tr>
<tr><td class="h"><a name="435"></a>435</td><td></td><td></td><td></td><td></td><td class="s"> use overload '~~' => 'match';</td></tr>
<tr><td class="h"><a name="436"></a>436</td><td></td><td></td><td></td><td></td><td class="s"></td></tr>
<tr><td class="h"><a name="437"></a>437</td><td></td><td></td><td></td><td></td><td class="s"> my $obj = Foo->new();</td></tr>
<tr><td class="h"><a name="438"></a>438</td><td></td><td></td><td></td><td></td><td class="s"> $obj ~~ [ 1,2,3 ];</td></tr>
<tr><td class="h"><a name="439"></a>439</td><td></td><td></td><td></td><td></td><td class="s"></td></tr>
<tr><td class="h"><a name="440"></a>440</td><td></td><td></td><td></td><td></td><td class="s">the smart match does I<not> invoke the method call like this:</td></tr>
<tr><td class="h"><a name="441"></a>441</td><td></td><td></td><td></td><td></td><td class="s"></td></tr>
<tr><td class="h"><a name="442"></a>442</td><td></td><td></td><td></td><td></td><td class="s"> $obj->match([1,2,3],0);</td></tr>
<tr><td class="h"><a name="443"></a>443</td><td></td><td></td><td></td><td></td><td class="s"></td></tr>
<tr><td class="h"><a name="444"></a>444</td><td></td><td></td><td></td><td></td><td class="s">rather, the smart match distributive rule takes precedence, so $obj is</td></tr>
<tr><td class="h"><a name="445"></a>445</td><td></td><td></td><td></td><td></td><td class="s">smart matched against each array element in turn until a match is found,</td></tr>
<tr><td class="h"><a name="446"></a>446</td><td></td><td></td><td></td><td></td><td class="s">so you may see between one and three of these calls instead:</td></tr>
<tr><td class="h"><a name="447"></a>447</td><td></td><td></td><td></td><td></td><td class="s"></td></tr>
<tr><td class="h"><a name="448"></a>448</td><td></td><td></td><td></td><td></td><td class="s"> $obj->match(1,0);</td></tr>
<tr><td class="h"><a name="449"></a>449</td><td></td><td></td><td></td><td></td><td class="s"> $obj->match(2,0);</td></tr>
<tr><td class="h"><a name="450"></a>450</td><td></td><td></td><td></td><td></td><td class="s"> $obj->match(3,0);</td></tr>
<tr><td class="h"><a name="451"></a>451</td><td></td><td></td><td></td><td></td><td class="s"></td></tr>
<tr><td class="h"><a name="452"></a>452</td><td></td><td></td><td></td><td></td><td class="s">Consult the match table in L<perlsyn/"Smart matching in detail"> for</td></tr>
<tr><td class="h"><a name="453"></a>453</td><td></td><td></td><td></td><td></td><td class="s">details of when overloading is invoked.</td></tr>
<tr><td class="h"><a name="454"></a>454</td><td></td><td></td><td></td><td></td><td class="s"></td></tr>
<tr><td class="h"><a name="455"></a>455</td><td></td><td></td><td></td><td></td><td class="s">=item * I<Dereferencing></td></tr>
<tr><td class="h"><a name="456"></a>456</td><td></td><td></td><td></td><td></td><td class="s"></td></tr>
<tr><td class="h"><a name="457"></a>457</td><td></td><td></td><td></td><td></td><td class="s"> '${}', '@{}', '%{}', '&{}', '*{}'.</td></tr>
<tr><td class="h"><a name="458"></a>458</td><td></td><td></td><td></td><td></td><td class="s"></td></tr>
<tr><td class="h"><a name="459"></a>459</td><td></td><td></td><td></td><td></td><td class="s">If not overloaded, the argument will be dereferenced I<as is>, thus</td></tr>
<tr><td class="h"><a name="460"></a>460</td><td></td><td></td><td></td><td></td><td class="s">should be of correct type. These functions should return a reference</td></tr>
<tr><td class="h"><a name="461"></a>461</td><td></td><td></td><td></td><td></td><td class="s">of correct type, or another object with overloaded dereferencing.</td></tr>
<tr><td class="h"><a name="462"></a>462</td><td></td><td></td><td></td><td></td><td class="s"></td></tr>
<tr><td class="h"><a name="463"></a>463</td><td></td><td></td><td></td><td></td><td class="s">As a special case if the overload returns the object itself then it</td></tr>
<tr><td class="h"><a name="464"></a>464</td><td></td><td></td><td></td><td></td><td class="s">will be used directly (provided it is the correct type).</td></tr>
<tr><td class="h"><a name="465"></a>465</td><td></td><td></td><td></td><td></td><td class="s"></td></tr>
<tr><td class="h"><a name="466"></a>466</td><td></td><td></td><td></td><td></td><td class="s">The dereference operators must be specified explicitly they will not be passed to</td></tr>
<tr><td class="h"><a name="467"></a>467</td><td></td><td></td><td></td><td></td><td class="s">"nomethod".</td></tr>
<tr><td class="h"><a name="468"></a>468</td><td></td><td></td><td></td><td></td><td class="s"></td></tr>
<tr><td class="h"><a name="469"></a>469</td><td></td><td></td><td></td><td></td><td class="s">=item * I<Special></td></tr>
<tr><td class="h"><a name="470"></a>470</td><td></td><td></td><td></td><td></td><td class="s"></td></tr>
<tr><td class="h"><a name="471"></a>471</td><td></td><td></td><td></td><td></td><td class="s"> "nomethod", "fallback", "=".</td></tr>
<tr><td class="h"><a name="472"></a>472</td><td></td><td></td><td></td><td></td><td class="s"></td></tr>
<tr><td class="h"><a name="473"></a>473</td><td></td><td></td><td></td><td></td><td class="s">see L<SPECIAL SYMBOLS FOR C<use overload>>.</td></tr>
<tr><td class="h"><a name="474"></a>474</td><td></td><td></td><td></td><td></td><td class="s"></td></tr>
<tr><td class="h"><a name="475"></a>475</td><td></td><td></td><td></td><td></td><td class="s">=back</td></tr>
<tr><td class="h"><a name="476"></a>476</td><td></td><td></td><td></td><td></td><td class="s"></td></tr>
<tr><td class="h"><a name="477"></a>477</td><td></td><td></td><td></td><td></td><td class="s">See L<"Fallback"> for an explanation of when a missing method can be</td></tr>
<tr><td class="h"><a name="478"></a>478</td><td></td><td></td><td></td><td></td><td class="s">autogenerated.</td></tr>
<tr><td class="h"><a name="479"></a>479</td><td></td><td></td><td></td><td></td><td class="s"></td></tr>
<tr><td class="h"><a name="480"></a>480</td><td></td><td></td><td></td><td></td><td class="s">A computer-readable form of the above table is available in the hash</td></tr>
<tr><td class="h"><a name="481"></a>481</td><td></td><td></td><td></td><td></td><td class="s">%overload::ops, with values being space-separated lists of names:</td></tr>
<tr><td class="h"><a name="482"></a>482</td><td></td><td></td><td></td><td></td><td class="s"></td></tr>
<tr><td class="h"><a name="483"></a>483</td><td></td><td></td><td></td><td></td><td class="s"> with_assign => '+ - * / % ** << >> x .',</td></tr>
<tr><td class="h"><a name="484"></a>484</td><td></td><td></td><td></td><td></td><td class="s"> assign => '+= -= *= /= %= **= <<= >>= x= .=',</td></tr>
<tr><td class="h"><a name="485"></a>485</td><td></td><td></td><td></td><td></td><td class="s"> num_comparison => '< <= > >= == !=',</td></tr>
<tr><td class="h"><a name="486"></a>486</td><td></td><td></td><td></td><td></td><td class="s"> '3way_comparison'=> '<=> cmp',</td></tr>
<tr><td class="h"><a name="487"></a>487</td><td></td><td></td><td></td><td></td><td class="s"> str_comparison => 'lt le gt ge eq ne',</td></tr>
<tr><td class="h"><a name="488"></a>488</td><td></td><td></td><td></td><td></td><td class="s"> binary => '& &= | |= ^ ^=',</td></tr>
<tr><td class="h"><a name="489"></a>489</td><td></td><td></td><td></td><td></td><td class="s"> unary => 'neg ! ~',</td></tr>
<tr><td class="h"><a name="490"></a>490</td><td></td><td></td><td></td><td></td><td class="s"> mutators => '++ --',</td></tr>
<tr><td class="h"><a name="491"></a>491</td><td></td><td></td><td></td><td></td><td class="s"> func => 'atan2 cos sin exp abs log sqrt',</td></tr>
<tr><td class="h"><a name="492"></a>492</td><td></td><td></td><td></td><td></td><td class="s"> conversion => 'bool "" 0+',</td></tr>
<tr><td class="h"><a name="493"></a>493</td><td></td><td></td><td></td><td></td><td class="s"> iterators => '<>',</td></tr>
<tr><td class="h"><a name="494"></a>494</td><td></td><td></td><td></td><td></td><td class="s"> dereferencing => '${} @{} %{} &{} *{}',</td></tr>
<tr><td class="h"><a name="495"></a>495</td><td></td><td></td><td></td><td></td><td class="s"> matching => '~~',</td></tr>
<tr><td class="h"><a name="496"></a>496</td><td></td><td></td><td></td><td></td><td class="s"> special => 'nomethod fallback ='</td></tr>
<tr><td class="h"><a name="497"></a>497</td><td></td><td></td><td></td><td></td><td class="s"></td></tr>
<tr><td class="h"><a name="498"></a>498</td><td></td><td></td><td></td><td></td><td class="s">=head2 Inheritance and overloading</td></tr>
<tr><td class="h"><a name="499"></a>499</td><td></td><td></td><td></td><td></td><td class="s"></td></tr>
<tr><td class="h"><a name="500"></a>500</td><td></td><td></td><td></td><td></td><td class="s">Inheritance interacts with overloading in two ways.</td></tr>
<tr><td class="h"><a name="501"></a>501</td><td></td><td></td><td></td><td></td><td class="s"></td></tr>
<tr><td class="h"><a name="502"></a>502</td><td></td><td></td><td></td><td></td><td class="s">=over</td></tr>
<tr><td class="h"><a name="503"></a>503</td><td></td><td></td><td></td><td></td><td class="s"></td></tr>
<tr><td class="h"><a name="504"></a>504</td><td></td><td></td><td></td><td></td><td class="s">=item Strings as values of C<use overload> directive</td></tr>
<tr><td class="h"><a name="505"></a>505</td><td></td><td></td><td></td><td></td><td class="s"></td></tr>
<tr><td class="h"><a name="506"></a>506</td><td></td><td></td><td></td><td></td><td class="s">If C<value> in</td></tr>
<tr><td class="h"><a name="507"></a>507</td><td></td><td></td><td></td><td></td><td class="s"></td></tr>
<tr><td class="h"><a name="508"></a>508</td><td></td><td></td><td></td><td></td><td class="s"> use overload key => value;</td></tr>
<tr><td class="h"><a name="509"></a>509</td><td></td><td></td><td></td><td></td><td class="s"></td></tr>
<tr><td class="h"><a name="510"></a>510</td><td></td><td></td><td></td><td></td><td class="s">is a string, it is interpreted as a method name.</td></tr>
<tr><td class="h"><a name="511"></a>511</td><td></td><td></td><td></td><td></td><td class="s"></td></tr>
<tr><td class="h"><a name="512"></a>512</td><td></td><td></td><td></td><td></td><td class="s">=item Overloading of an operation is inherited by derived classes</td></tr>
<tr><td class="h"><a name="513"></a>513</td><td></td><td></td><td></td><td></td><td class="s"></td></tr>
<tr><td class="h"><a name="514"></a>514</td><td></td><td></td><td></td><td></td><td class="s">Any class derived from an overloaded class is also overloaded. The</td></tr>
<tr><td class="h"><a name="515"></a>515</td><td></td><td></td><td></td><td></td><td class="s">set of overloaded methods is the union of overloaded methods of all</td></tr>
<tr><td class="h"><a name="516"></a>516</td><td></td><td></td><td></td><td></td><td class="s">the ancestors. If some method is overloaded in several ancestor, then</td></tr>
<tr><td class="h"><a name="517"></a>517</td><td></td><td></td><td></td><td></td><td class="s">which description will be used is decided by the usual inheritance</td></tr>
<tr><td class="h"><a name="518"></a>518</td><td></td><td></td><td></td><td></td><td class="s">rules:</td></tr>
<tr><td class="h"><a name="519"></a>519</td><td></td><td></td><td></td><td></td><td class="s"></td></tr>
<tr><td class="h"><a name="520"></a>520</td><td></td><td></td><td></td><td></td><td class="s">If C<A> inherits from C<B> and C<C> (in this order), C<B> overloads</td></tr>
<tr><td class="h"><a name="521"></a>521</td><td></td><td></td><td></td><td></td><td class="s">C<+> with C<\&D::plus_sub>, and C<C> overloads C<+> by C<"plus_meth">,</td></tr>
<tr><td class="h"><a name="522"></a>522</td><td></td><td></td><td></td><td></td><td class="s">then the subroutine C<D::plus_sub> will be called to implement</td></tr>
<tr><td class="h"><a name="523"></a>523</td><td></td><td></td><td></td><td></td><td class="s">operation C<+> for an object in package C<A>.</td></tr>
<tr><td class="h"><a name="524"></a>524</td><td></td><td></td><td></td><td></td><td class="s"></td></tr>
<tr><td class="h"><a name="525"></a>525</td><td></td><td></td><td></td><td></td><td class="s">=back</td></tr>
<tr><td class="h"><a name="526"></a>526</td><td></td><td></td><td></td><td></td><td class="s"></td></tr>
<tr><td class="h"><a name="527"></a>527</td><td></td><td></td><td></td><td></td><td class="s">Note that since the value of the C<fallback> key is not a subroutine,</td></tr>
<tr><td class="h"><a name="528"></a>528</td><td></td><td></td><td></td><td></td><td class="s">its inheritance is not governed by the above rules. In the current</td></tr>
<tr><td class="h"><a name="529"></a>529</td><td></td><td></td><td></td><td></td><td class="s">implementation, the value of C<fallback> in the first overloaded</td></tr>
<tr><td class="h"><a name="530"></a>530</td><td></td><td></td><td></td><td></td><td class="s">ancestor is used, but this is accidental and subject to change.</td></tr>
<tr><td class="h"><a name="531"></a>531</td><td></td><td></td><td></td><td></td><td class="s"></td></tr>
<tr><td class="h"><a name="532"></a>532</td><td></td><td></td><td></td><td></td><td class="s">=head1 SPECIAL SYMBOLS FOR C<use overload></td></tr>
<tr><td class="h"><a name="533"></a>533</td><td></td><td></td><td></td><td></td><td class="s"></td></tr>
<tr><td class="h"><a name="534"></a>534</td><td></td><td></td><td></td><td></td><td class="s">Three keys are recognized by Perl that are not covered by the above</td></tr>
<tr><td class="h"><a name="535"></a>535</td><td></td><td></td><td></td><td></td><td class="s">description.</td></tr>
<tr><td class="h"><a name="536"></a>536</td><td></td><td></td><td></td><td></td><td class="s"></td></tr>
<tr><td class="h"><a name="537"></a>537</td><td></td><td></td><td></td><td></td><td class="s">=head2 Last Resort</td></tr>
<tr><td class="h"><a name="538"></a>538</td><td></td><td></td><td></td><td></td><td class="s"></td></tr>
<tr><td class="h"><a name="539"></a>539</td><td></td><td></td><td></td><td></td><td class="s">C<"nomethod"> should be followed by a reference to a function of four</td></tr>
<tr><td class="h"><a name="540"></a>540</td><td></td><td></td><td></td><td></td><td class="s">parameters. If defined, it is called when the overloading mechanism</td></tr>
<tr><td class="h"><a name="541"></a>541</td><td></td><td></td><td></td><td></td><td class="s">cannot find a method for some operation. The first three arguments of</td></tr>
<tr><td class="h"><a name="542"></a>542</td><td></td><td></td><td></td><td></td><td class="s">this function coincide with the arguments for the corresponding method if</td></tr>
<tr><td class="h"><a name="543"></a>543</td><td></td><td></td><td></td><td></td><td class="s">it were found, the fourth argument is the symbol</td></tr>
<tr><td class="h"><a name="544"></a>544</td><td></td><td></td><td></td><td></td><td class="s">corresponding to the missing method. If several methods are tried,</td></tr>
<tr><td class="h"><a name="545"></a>545</td><td></td><td></td><td></td><td></td><td class="s">the last one is used. Say, C<1-$a> can be equivalent to</td></tr>
<tr><td class="h"><a name="546"></a>546</td><td></td><td></td><td></td><td></td><td class="s"></td></tr>
<tr><td class="h"><a name="547"></a>547</td><td></td><td></td><td></td><td></td><td class="s"> &nomethodMethod($a,1,1,"-")</td></tr>
<tr><td class="h"><a name="548"></a>548</td><td></td><td></td><td></td><td></td><td class="s"></td></tr>
<tr><td class="h"><a name="549"></a>549</td><td></td><td></td><td></td><td></td><td class="s">if the pair C<"nomethod" =E<gt> "nomethodMethod"> was specified in the</td></tr>
<tr><td class="h"><a name="550"></a>550</td><td></td><td></td><td></td><td></td><td class="s">C<use overload> directive.</td></tr>
<tr><td class="h"><a name="551"></a>551</td><td></td><td></td><td></td><td></td><td class="s"></td></tr>
<tr><td class="h"><a name="552"></a>552</td><td></td><td></td><td></td><td></td><td class="s">The C<"nomethod"> mechanism is I<not> used for the dereference operators</td></tr>
<tr><td class="h"><a name="553"></a>553</td><td></td><td></td><td></td><td></td><td class="s">( ${} @{} %{} &{} *{} ).</td></tr>
<tr><td class="h"><a name="554"></a>554</td><td></td><td></td><td></td><td></td><td class="s"></td></tr>
<tr><td class="h"><a name="555"></a>555</td><td></td><td></td><td></td><td></td><td class="s"></td></tr>
<tr><td class="h"><a name="556"></a>556</td><td></td><td></td><td></td><td></td><td class="s">If some operation cannot be resolved, and there is no function</td></tr>
<tr><td class="h"><a name="557"></a>557</td><td></td><td></td><td></td><td></td><td class="s">assigned to C<"nomethod">, then an exception will be raised via die()--</td></tr>
<tr><td class="h"><a name="558"></a>558</td><td></td><td></td><td></td><td></td><td class="s">unless C<"fallback"> was specified as a key in C<use overload> directive.</td></tr>
<tr><td class="h"><a name="559"></a>559</td><td></td><td></td><td></td><td></td><td class="s"></td></tr>
<tr><td class="h"><a name="560"></a>560</td><td></td><td></td><td></td><td></td><td class="s"></td></tr>
<tr><td class="h"><a name="561"></a>561</td><td></td><td></td><td></td><td></td><td class="s">=head2 Fallback</td></tr>
<tr><td class="h"><a name="562"></a>562</td><td></td><td></td><td></td><td></td><td class="s"></td></tr>
<tr><td class="h"><a name="563"></a>563</td><td></td><td></td><td></td><td></td><td class="s">The key C<"fallback"> governs what to do if a method for a particular</td></tr>
<tr><td class="h"><a name="564"></a>564</td><td></td><td></td><td></td><td></td><td class="s">operation is not found. Three different cases are possible depending on</td></tr>
<tr><td class="h"><a name="565"></a>565</td><td></td><td></td><td></td><td></td><td class="s">the value of C<"fallback">:</td></tr>
<tr><td class="h"><a name="566"></a>566</td><td></td><td></td><td></td><td></td><td class="s"></td></tr>
<tr><td class="h"><a name="567"></a>567</td><td></td><td></td><td></td><td></td><td class="s">=over 16</td></tr>
<tr><td class="h"><a name="568"></a>568</td><td></td><td></td><td></td><td></td><td class="s"></td></tr>
<tr><td class="h"><a name="569"></a>569</td><td></td><td></td><td></td><td></td><td class="s">=item * C<undef></td></tr>
<tr><td class="h"><a name="570"></a>570</td><td></td><td></td><td></td><td></td><td class="s"></td></tr>
<tr><td class="h"><a name="571"></a>571</td><td></td><td></td><td></td><td></td><td class="s">Perl tries to use a</td></tr>
<tr><td class="h"><a name="572"></a>572</td><td></td><td></td><td></td><td></td><td class="s">substituted method (see L<MAGIC AUTOGENERATION>). If this fails, it</td></tr>
<tr><td class="h"><a name="573"></a>573</td><td></td><td></td><td></td><td></td><td class="s">then tries to calls C<"nomethod"> value; if missing, an exception</td></tr>
<tr><td class="h"><a name="574"></a>574</td><td></td><td></td><td></td><td></td><td class="s">will be raised.</td></tr>
<tr><td class="h"><a name="575"></a>575</td><td></td><td></td><td></td><td></td><td class="s"></td></tr>
<tr><td class="h"><a name="576"></a>576</td><td></td><td></td><td></td><td></td><td class="s">=item * TRUE</td></tr>
<tr><td class="h"><a name="577"></a>577</td><td></td><td></td><td></td><td></td><td class="s"></td></tr>
<tr><td class="h"><a name="578"></a>578</td><td></td><td></td><td></td><td></td><td class="s">The same as for the C<undef> value, but no exception is raised. Instead,</td></tr>
<tr><td class="h"><a name="579"></a>579</td><td></td><td></td><td></td><td></td><td class="s">it silently reverts to what it would have done were there no C<use overload></td></tr>
<tr><td class="h"><a name="580"></a>580</td><td></td><td></td><td></td><td></td><td class="s">present.</td></tr>
<tr><td class="h"><a name="581"></a>581</td><td></td><td></td><td></td><td></td><td class="s"></td></tr>
<tr><td class="h"><a name="582"></a>582</td><td></td><td></td><td></td><td></td><td class="s">=item * defined, but FALSE</td></tr>
<tr><td class="h"><a name="583"></a>583</td><td></td><td></td><td></td><td></td><td class="s"></td></tr>
<tr><td class="h"><a name="584"></a>584</td><td></td><td></td><td></td><td></td><td class="s">No autogeneration is tried. Perl tries to call</td></tr>
<tr><td class="h"><a name="585"></a>585</td><td></td><td></td><td></td><td></td><td class="s">C<"nomethod"> value, and if this is missing, raises an exception.</td></tr>
<tr><td class="h"><a name="586"></a>586</td><td></td><td></td><td></td><td></td><td class="s"></td></tr>
<tr><td class="h"><a name="587"></a>587</td><td></td><td></td><td></td><td></td><td class="s">=back</td></tr>
<tr><td class="h"><a name="588"></a>588</td><td></td><td></td><td></td><td></td><td class="s"></td></tr>
<tr><td class="h"><a name="589"></a>589</td><td></td><td></td><td></td><td></td><td class="s">B<Note.> C<"fallback"> inheritance via @ISA is not carved in stone</td></tr>
<tr><td class="h"><a name="590"></a>590</td><td></td><td></td><td></td><td></td><td class="s">yet, see L<"Inheritance and overloading">.</td></tr>
<tr><td class="h"><a name="591"></a>591</td><td></td><td></td><td></td><td></td><td class="s"></td></tr>
<tr><td class="h"><a name="592"></a>592</td><td></td><td></td><td></td><td></td><td class="s">=head2 Copy Constructor</td></tr>
<tr><td class="h"><a name="593"></a>593</td><td></td><td></td><td></td><td></td><td class="s"></td></tr>
<tr><td class="h"><a name="594"></a>594</td><td></td><td></td><td></td><td></td><td class="s">The value for C<"="> is a reference to a function with three</td></tr>
<tr><td class="h"><a name="595"></a>595</td><td></td><td></td><td></td><td></td><td class="s">arguments, i.e., it looks like the other values in C<use</td></tr>
<tr><td class="h"><a name="596"></a>596</td><td></td><td></td><td></td><td></td><td class="s">overload>. However, it does not overload the Perl assignment</td></tr>
<tr><td class="h"><a name="597"></a>597</td><td></td><td></td><td></td><td></td><td class="s">operator. This would go against Camel hair.</td></tr>
<tr><td class="h"><a name="598"></a>598</td><td></td><td></td><td></td><td></td><td class="s"></td></tr>
<tr><td class="h"><a name="599"></a>599</td><td></td><td></td><td></td><td></td><td class="s">This operation is called in the situations when a mutator is applied</td></tr>
<tr><td class="h"><a name="600"></a>600</td><td></td><td></td><td></td><td></td><td class="s">to a reference that shares its object with some other reference, such</td></tr>
<tr><td class="h"><a name="601"></a>601</td><td></td><td></td><td></td><td></td><td class="s">as</td></tr>
<tr><td class="h"><a name="602"></a>602</td><td></td><td></td><td></td><td></td><td class="s"></td></tr>
<tr><td class="h"><a name="603"></a>603</td><td></td><td></td><td></td><td></td><td class="s"> $a=$b;</td></tr>
<tr><td class="h"><a name="604"></a>604</td><td></td><td></td><td></td><td></td><td class="s"> ++$a;</td></tr>
<tr><td class="h"><a name="605"></a>605</td><td></td><td></td><td></td><td></td><td class="s"></td></tr>
<tr><td class="h"><a name="606"></a>606</td><td></td><td></td><td></td><td></td><td class="s">To make this change $a and not change $b, a copy of C<$$a> is made,</td></tr>
<tr><td class="h"><a name="607"></a>607</td><td></td><td></td><td></td><td></td><td class="s">and $a is assigned a reference to this new object. This operation is</td></tr>
<tr><td class="h"><a name="608"></a>608</td><td></td><td></td><td></td><td></td><td class="s">done during execution of the C<++$a>, and not during the assignment,</td></tr>
<tr><td class="h"><a name="609"></a>609</td><td></td><td></td><td></td><td></td><td class="s">(so before the increment C<$$a> coincides with C<$$b>). This is only</td></tr>
<tr><td class="h"><a name="610"></a>610</td><td></td><td></td><td></td><td></td><td class="s">done if C<++> is expressed via a method for C<'++'> or C<'+='> (or</td></tr>
<tr><td class="h"><a name="611"></a>611</td><td></td><td></td><td></td><td></td><td class="s">C<nomethod>). Note that if this operation is expressed via C<'+'></td></tr>
<tr><td class="h"><a name="612"></a>612</td><td></td><td></td><td></td><td></td><td class="s">a nonmutator, i.e., as in</td></tr>
<tr><td class="h"><a name="613"></a>613</td><td></td><td></td><td></td><td></td><td class="s"></td></tr>
<tr><td class="h"><a name="614"></a>614</td><td></td><td></td><td></td><td></td><td class="s"> $a=$b;</td></tr>
<tr><td class="h"><a name="615"></a>615</td><td></td><td></td><td></td><td></td><td class="s"> $a=$a+1;</td></tr>
<tr><td class="h"><a name="616"></a>616</td><td></td><td></td><td></td><td></td><td class="s"></td></tr>
<tr><td class="h"><a name="617"></a>617</td><td></td><td></td><td></td><td></td><td class="s">then C<$a> does not reference a new copy of C<$$a>, since $$a does not</td></tr>
<tr><td class="h"><a name="618"></a>618</td><td></td><td></td><td></td><td></td><td class="s">appear as lvalue when the above code is executed.</td></tr>
<tr><td class="h"><a name="619"></a>619</td><td></td><td></td><td></td><td></td><td class="s"></td></tr>
<tr><td class="h"><a name="620"></a>620</td><td></td><td></td><td></td><td></td><td class="s">If the copy constructor is required during the execution of some mutator,</td></tr>
<tr><td class="h"><a name="621"></a>621</td><td></td><td></td><td></td><td></td><td class="s">but a method for C<'='> was not specified, it can be autogenerated as a</td></tr>
<tr><td class="h"><a name="622"></a>622</td><td></td><td></td><td></td><td></td><td class="s">string copy if the object is a plain scalar or a simple assignment if it</td></tr>
<tr><td class="h"><a name="623"></a>623</td><td></td><td></td><td></td><td></td><td class="s">is not.</td></tr>
<tr><td class="h"><a name="624"></a>624</td><td></td><td></td><td></td><td></td><td class="s"></td></tr>
<tr><td class="h"><a name="625"></a>625</td><td></td><td></td><td></td><td></td><td class="s">=over 5</td></tr>
<tr><td class="h"><a name="626"></a>626</td><td></td><td></td><td></td><td></td><td class="s"></td></tr>
<tr><td class="h"><a name="627"></a>627</td><td></td><td></td><td></td><td></td><td class="s">=item B<Example></td></tr>
<tr><td class="h"><a name="628"></a>628</td><td></td><td></td><td></td><td></td><td class="s"></td></tr>
<tr><td class="h"><a name="629"></a>629</td><td></td><td></td><td></td><td></td><td class="s">The actually executed code for</td></tr>
<tr><td class="h"><a name="630"></a>630</td><td></td><td></td><td></td><td></td><td class="s"></td></tr>
<tr><td class="h"><a name="631"></a>631</td><td></td><td></td><td></td><td></td><td class="s"> $a=$b;</td></tr>
<tr><td class="h"><a name="632"></a>632</td><td></td><td></td><td></td><td></td><td class="s"> Something else which does not modify $a or $b....</td></tr>
<tr><td class="h"><a name="633"></a>633</td><td></td><td></td><td></td><td></td><td class="s"> ++$a;</td></tr>
<tr><td class="h"><a name="634"></a>634</td><td></td><td></td><td></td><td></td><td class="s"></td></tr>
<tr><td class="h"><a name="635"></a>635</td><td></td><td></td><td></td><td></td><td class="s">may be</td></tr>
<tr><td class="h"><a name="636"></a>636</td><td></td><td></td><td></td><td></td><td class="s"></td></tr>
<tr><td class="h"><a name="637"></a>637</td><td></td><td></td><td></td><td></td><td class="s"> $a=$b;</td></tr>
<tr><td class="h"><a name="638"></a>638</td><td></td><td></td><td></td><td></td><td class="s"> Something else which does not modify $a or $b....</td></tr>
<tr><td class="h"><a name="639"></a>639</td><td></td><td></td><td></td><td></td><td class="s"> $a = $a->clone(undef,"");</td></tr>
<tr><td class="h"><a name="640"></a>640</td><td></td><td></td><td></td><td></td><td class="s"> $a->incr(undef,"");</td></tr>
<tr><td class="h"><a name="641"></a>641</td><td></td><td></td><td></td><td></td><td class="s"></td></tr>
<tr><td class="h"><a name="642"></a>642</td><td></td><td></td><td></td><td></td><td class="s">if $b was mathemagical, and C<'++'> was overloaded with C<\&incr>,</td></tr>
<tr><td class="h"><a name="643"></a>643</td><td></td><td></td><td></td><td></td><td class="s">C<'='> was overloaded with C<\&clone>.</td></tr>
<tr><td class="h"><a name="644"></a>644</td><td></td><td></td><td></td><td></td><td class="s"></td></tr>
<tr><td class="h"><a name="645"></a>645</td><td></td><td></td><td></td><td></td><td class="s">=back</td></tr>
<tr><td class="h"><a name="646"></a>646</td><td></td><td></td><td></td><td></td><td class="s"></td></tr>
<tr><td class="h"><a name="647"></a>647</td><td></td><td></td><td></td><td></td><td class="s">Same behaviour is triggered by C<$b = $a++>, which is consider a synonym for</td></tr>
<tr><td class="h"><a name="648"></a>648</td><td></td><td></td><td></td><td></td><td class="s">C<$b = $a; ++$a>.</td></tr>
<tr><td class="h"><a name="649"></a>649</td><td></td><td></td><td></td><td></td><td class="s"></td></tr>
<tr><td class="h"><a name="650"></a>650</td><td></td><td></td><td></td><td></td><td class="s">=head1 MAGIC AUTOGENERATION</td></tr>
<tr><td class="h"><a name="651"></a>651</td><td></td><td></td><td></td><td></td><td class="s"></td></tr>
<tr><td class="h"><a name="652"></a>652</td><td></td><td></td><td></td><td></td><td class="s">If a method for an operation is not found, and the value for C<"fallback"> is</td></tr>
<tr><td class="h"><a name="653"></a>653</td><td></td><td></td><td></td><td></td><td class="s">TRUE or undefined, Perl tries to autogenerate a substitute method for</td></tr>
<tr><td class="h"><a name="654"></a>654</td><td></td><td></td><td></td><td></td><td class="s">the missing operation based on the defined operations. Autogenerated method</td></tr>
<tr><td class="h"><a name="655"></a>655</td><td></td><td></td><td></td><td></td><td class="s">substitutions are possible for the following operations:</td></tr>
<tr><td class="h"><a name="656"></a>656</td><td></td><td></td><td></td><td></td><td class="s"></td></tr>
<tr><td class="h"><a name="657"></a>657</td><td></td><td></td><td></td><td></td><td class="s">=over 16</td></tr>
<tr><td class="h"><a name="658"></a>658</td><td></td><td></td><td></td><td></td><td class="s"></td></tr>
<tr><td class="h"><a name="659"></a>659</td><td></td><td></td><td></td><td></td><td class="s">=item I<Assignment forms of arithmetic operations></td></tr>
<tr><td class="h"><a name="660"></a>660</td><td></td><td></td><td></td><td></td><td class="s"></td></tr>
<tr><td class="h"><a name="661"></a>661</td><td></td><td></td><td></td><td></td><td class="s">C<$a+=$b> can use the method for C<"+"> if the method for C<"+="></td></tr>
<tr><td class="h"><a name="662"></a>662</td><td></td><td></td><td></td><td></td><td class="s">is not defined.</td></tr>
<tr><td class="h"><a name="663"></a>663</td><td></td><td></td><td></td><td></td><td class="s"></td></tr>
<tr><td class="h"><a name="664"></a>664</td><td></td><td></td><td></td><td></td><td class="s">=item I<Conversion operations></td></tr>
<tr><td class="h"><a name="665"></a>665</td><td></td><td></td><td></td><td></td><td class="s"></td></tr>
<tr><td class="h"><a name="666"></a>666</td><td></td><td></td><td></td><td></td><td class="s">String, numeric, and boolean conversion are calculated in terms of one</td></tr>
<tr><td class="h"><a name="667"></a>667</td><td></td><td></td><td></td><td></td><td class="s">another if not all of them are defined.</td></tr>
<tr><td class="h"><a name="668"></a>668</td><td></td><td></td><td></td><td></td><td class="s"></td></tr>
<tr><td class="h"><a name="669"></a>669</td><td></td><td></td><td></td><td></td><td class="s">=item I<Increment and decrement></td></tr>
<tr><td class="h"><a name="670"></a>670</td><td></td><td></td><td></td><td></td><td class="s"></td></tr>
<tr><td class="h"><a name="671"></a>671</td><td></td><td></td><td></td><td></td><td class="s">The C<++$a> operation can be expressed in terms of C<$a+=1> or C<$a+1>,</td></tr>
<tr><td class="h"><a name="672"></a>672</td><td></td><td></td><td></td><td></td><td class="s">and C<$a--> in terms of C<$a-=1> and C<$a-1>.</td></tr>
<tr><td class="h"><a name="673"></a>673</td><td></td><td></td><td></td><td></td><td class="s"></td></tr>
<tr><td class="h"><a name="674"></a>674</td><td></td><td></td><td></td><td></td><td class="s">=item C<abs($a)></td></tr>
<tr><td class="h"><a name="675"></a>675</td><td></td><td></td><td></td><td></td><td class="s"></td></tr>
<tr><td class="h"><a name="676"></a>676</td><td></td><td></td><td></td><td></td><td class="s">can be expressed in terms of C<$aE<lt>0> and C<-$a> (or C<0-$a>).</td></tr>
<tr><td class="h"><a name="677"></a>677</td><td></td><td></td><td></td><td></td><td class="s"></td></tr>
<tr><td class="h"><a name="678"></a>678</td><td></td><td></td><td></td><td></td><td class="s">=item I<Unary minus></td></tr>
<tr><td class="h"><a name="679"></a>679</td><td></td><td></td><td></td><td></td><td class="s"></td></tr>
<tr><td class="h"><a name="680"></a>680</td><td></td><td></td><td></td><td></td><td class="s">can be expressed in terms of subtraction.</td></tr>
<tr><td class="h"><a name="681"></a>681</td><td></td><td></td><td></td><td></td><td class="s"></td></tr>
<tr><td class="h"><a name="682"></a>682</td><td></td><td></td><td></td><td></td><td class="s">=item I<Negation></td></tr>
<tr><td class="h"><a name="683"></a>683</td><td></td><td></td><td></td><td></td><td class="s"></td></tr>
<tr><td class="h"><a name="684"></a>684</td><td></td><td></td><td></td><td></td><td class="s">C<!> and C<not> can be expressed in terms of boolean conversion, or</td></tr>
<tr><td class="h"><a name="685"></a>685</td><td></td><td></td><td></td><td></td><td class="s">string or numerical conversion.</td></tr>
<tr><td class="h"><a name="686"></a>686</td><td></td><td></td><td></td><td></td><td class="s"></td></tr>
<tr><td class="h"><a name="687"></a>687</td><td></td><td></td><td></td><td></td><td class="s">=item I<Concatenation></td></tr>
<tr><td class="h"><a name="688"></a>688</td><td></td><td></td><td></td><td></td><td class="s"></td></tr>
<tr><td class="h"><a name="689"></a>689</td><td></td><td></td><td></td><td></td><td class="s">can be expressed in terms of string conversion.</td></tr>
<tr><td class="h"><a name="690"></a>690</td><td></td><td></td><td></td><td></td><td class="s"></td></tr>
<tr><td class="h"><a name="691"></a>691</td><td></td><td></td><td></td><td></td><td class="s">=item I<Comparison operations></td></tr>
<tr><td class="h"><a name="692"></a>692</td><td></td><td></td><td></td><td></td><td class="s"></td></tr>
<tr><td class="h"><a name="693"></a>693</td><td></td><td></td><td></td><td></td><td class="s">can be expressed in terms of its "spaceship" counterpart: either</td></tr>
<tr><td class="h"><a name="694"></a>694</td><td></td><td></td><td></td><td></td><td class="s">C<E<lt>=E<gt>> or C<cmp>:</td></tr>
<tr><td class="h"><a name="695"></a>695</td><td></td><td></td><td></td><td></td><td class="s"></td></tr>
<tr><td class="h"><a name="696"></a>696</td><td></td><td></td><td></td><td></td><td class="s"> <, >, <=, >=, ==, != in terms of <=></td></tr>
<tr><td class="h"><a name="697"></a>697</td><td></td><td></td><td></td><td></td><td class="s"> lt, gt, le, ge, eq, ne in terms of cmp</td></tr>
<tr><td class="h"><a name="698"></a>698</td><td></td><td></td><td></td><td></td><td class="s"></td></tr>
<tr><td class="h"><a name="699"></a>699</td><td></td><td></td><td></td><td></td><td class="s">=item I<Iterator></td></tr>
<tr><td class="h"><a name="700"></a>700</td><td></td><td></td><td></td><td></td><td class="s"></td></tr>
<tr><td class="h"><a name="701"></a>701</td><td></td><td></td><td></td><td></td><td class="s"> <> in terms of builtin operations</td></tr>
<tr><td class="h"><a name="702"></a>702</td><td></td><td></td><td></td><td></td><td class="s"></td></tr>
<tr><td class="h"><a name="703"></a>703</td><td></td><td></td><td></td><td></td><td class="s">=item I<Dereferencing></td></tr>
<tr><td class="h"><a name="704"></a>704</td><td></td><td></td><td></td><td></td><td class="s"></td></tr>
<tr><td class="h"><a name="705"></a>705</td><td></td><td></td><td></td><td></td><td class="s"> ${} @{} %{} &{} *{} in terms of builtin operations</td></tr>
<tr><td class="h"><a name="706"></a>706</td><td></td><td></td><td></td><td></td><td class="s"></td></tr>
<tr><td class="h"><a name="707"></a>707</td><td></td><td></td><td></td><td></td><td class="s">=item I<Copy operator></td></tr>
<tr><td class="h"><a name="708"></a>708</td><td></td><td></td><td></td><td></td><td class="s"></td></tr>
<tr><td class="h"><a name="709"></a>709</td><td></td><td></td><td></td><td></td><td class="s">can be expressed in terms of an assignment to the dereferenced value, if this</td></tr>
<tr><td class="h"><a name="710"></a>710</td><td></td><td></td><td></td><td></td><td class="s">value is a scalar and not a reference, or simply a reference assignment</td></tr>
<tr><td class="h"><a name="711"></a>711</td><td></td><td></td><td></td><td></td><td class="s">otherwise.</td></tr>
<tr><td class="h"><a name="712"></a>712</td><td></td><td></td><td></td><td></td><td class="s"></td></tr>
<tr><td class="h"><a name="713"></a>713</td><td></td><td></td><td></td><td></td><td class="s">=back</td></tr>
<tr><td class="h"><a name="714"></a>714</td><td></td><td></td><td></td><td></td><td class="s"></td></tr>
<tr><td class="h"><a name="715"></a>715</td><td></td><td></td><td></td><td></td><td class="s">=head1 Minimal set of overloaded operations</td></tr>
<tr><td class="h"><a name="716"></a>716</td><td></td><td></td><td></td><td></td><td class="s"></td></tr>
<tr><td class="h"><a name="717"></a>717</td><td></td><td></td><td></td><td></td><td class="s">Since some operations can be automatically generated from others, there is</td></tr>
<tr><td class="h"><a name="718"></a>718</td><td></td><td></td><td></td><td></td><td class="s">a minimal set of operations that need to be overloaded in order to have</td></tr>
<tr><td class="h"><a name="719"></a>719</td><td></td><td></td><td></td><td></td><td class="s">the complete set of overloaded operations at one's disposal.</td></tr>
<tr><td class="h"><a name="720"></a>720</td><td></td><td></td><td></td><td></td><td class="s">Of course, the autogenerated operations may not do exactly what the user</td></tr>
<tr><td class="h"><a name="721"></a>721</td><td></td><td></td><td></td><td></td><td class="s">expects. See L<MAGIC AUTOGENERATION> above. The minimal set is:</td></tr>
<tr><td class="h"><a name="722"></a>722</td><td></td><td></td><td></td><td></td><td class="s"></td></tr>
<tr><td class="h"><a name="723"></a>723</td><td></td><td></td><td></td><td></td><td class="s"> + - * / % ** << >> x</td></tr>
<tr><td class="h"><a name="724"></a>724</td><td></td><td></td><td></td><td></td><td class="s"> <=> cmp</td></tr>
<tr><td class="h"><a name="725"></a>725</td><td></td><td></td><td></td><td></td><td class="s"> & | ^ ~</td></tr>
<tr><td class="h"><a name="726"></a>726</td><td></td><td></td><td></td><td></td><td class="s"> atan2 cos sin exp log sqrt int</td></tr>
<tr><td class="h"><a name="727"></a>727</td><td></td><td></td><td></td><td></td><td class="s"></td></tr>
<tr><td class="h"><a name="728"></a>728</td><td></td><td></td><td></td><td></td><td class="s">Additionally, you need to define at least one of string, boolean or</td></tr>
<tr><td class="h"><a name="729"></a>729</td><td></td><td></td><td></td><td></td><td class="s">numeric conversions because any one can be used to emulate the others.</td></tr>
<tr><td class="h"><a name="730"></a>730</td><td></td><td></td><td></td><td></td><td class="s">The string conversion can also be used to emulate concatenation.</td></tr>
<tr><td class="h"><a name="731"></a>731</td><td></td><td></td><td></td><td></td><td class="s"></td></tr>
<tr><td class="h"><a name="732"></a>732</td><td></td><td></td><td></td><td></td><td class="s">=head1 Losing overloading</td></tr>
<tr><td class="h"><a name="733"></a>733</td><td></td><td></td><td></td><td></td><td class="s"></td></tr>
<tr><td class="h"><a name="734"></a>734</td><td></td><td></td><td></td><td></td><td class="s">The restriction for the comparison operation is that even if, for example,</td></tr>
<tr><td class="h"><a name="735"></a>735</td><td></td><td></td><td></td><td></td><td class="s">`C<cmp>' should return a blessed reference, the autogenerated `C<lt>'</td></tr>
<tr><td class="h"><a name="736"></a>736</td><td></td><td></td><td></td><td></td><td class="s">function will produce only a standard logical value based on the</td></tr>
<tr><td class="h"><a name="737"></a>737</td><td></td><td></td><td></td><td></td><td class="s">numerical value of the result of `C<cmp>'. In particular, a working</td></tr>
<tr><td class="h"><a name="738"></a>738</td><td></td><td></td><td></td><td></td><td class="s">numeric conversion is needed in this case (possibly expressed in terms of</td></tr>
<tr><td class="h"><a name="739"></a>739</td><td></td><td></td><td></td><td></td><td class="s">other conversions).</td></tr>
<tr><td class="h"><a name="740"></a>740</td><td></td><td></td><td></td><td></td><td class="s"></td></tr>
<tr><td class="h"><a name="741"></a>741</td><td></td><td></td><td></td><td></td><td class="s">Similarly, C<.=> and C<x=> operators lose their mathemagical properties</td></tr>
<tr><td class="h"><a name="742"></a>742</td><td></td><td></td><td></td><td></td><td class="s">if the string conversion substitution is applied.</td></tr>
<tr><td class="h"><a name="743"></a>743</td><td></td><td></td><td></td><td></td><td class="s"></td></tr>
<tr><td class="h"><a name="744"></a>744</td><td></td><td></td><td></td><td></td><td class="s">When you chop() a mathemagical object it is promoted to a string and its</td></tr>
<tr><td class="h"><a name="745"></a>745</td><td></td><td></td><td></td><td></td><td class="s">mathemagical properties are lost. The same can happen with other</td></tr>
<tr><td class="h"><a name="746"></a>746</td><td></td><td></td><td></td><td></td><td class="s">operations as well.</td></tr>
<tr><td class="h"><a name="747"></a>747</td><td></td><td></td><td></td><td></td><td class="s"></td></tr>
<tr><td class="h"><a name="748"></a>748</td><td></td><td></td><td></td><td></td><td class="s">=head1 Run-time Overloading</td></tr>
<tr><td class="h"><a name="749"></a>749</td><td></td><td></td><td></td><td></td><td class="s"></td></tr>
<tr><td class="h"><a name="750"></a>750</td><td></td><td></td><td></td><td></td><td class="s">Since all C<use> directives are executed at compile-time, the only way to</td></tr>
<tr><td class="h"><a name="751"></a>751</td><td></td><td></td><td></td><td></td><td class="s">change overloading during run-time is to</td></tr>
<tr><td class="h"><a name="752"></a>752</td><td></td><td></td><td></td><td></td><td class="s"></td></tr>
<tr><td class="h"><a name="753"></a>753</td><td></td><td></td><td></td><td></td><td class="s"> eval 'use overload "+" => \&addmethod';</td></tr>
<tr><td class="h"><a name="754"></a>754</td><td></td><td></td><td></td><td></td><td class="s"></td></tr>
<tr><td class="h"><a name="755"></a>755</td><td></td><td></td><td></td><td></td><td class="s">You can also use</td></tr>
<tr><td class="h"><a name="756"></a>756</td><td></td><td></td><td></td><td></td><td class="s"></td></tr>
<tr><td class="h"><a name="757"></a>757</td><td></td><td></td><td></td><td></td><td class="s"> eval 'no overload "+", "--", "<="';</td></tr>
<tr><td class="h"><a name="758"></a>758</td><td></td><td></td><td></td><td></td><td class="s"></td></tr>
<tr><td class="h"><a name="759"></a>759</td><td></td><td></td><td></td><td></td><td class="s">though the use of these constructs during run-time is questionable.</td></tr>
<tr><td class="h"><a name="760"></a>760</td><td></td><td></td><td></td><td></td><td class="s"></td></tr>
<tr><td class="h"><a name="761"></a>761</td><td></td><td></td><td></td><td></td><td class="s">=head1 Public functions</td></tr>
<tr><td class="h"><a name="762"></a>762</td><td></td><td></td><td></td><td></td><td class="s"></td></tr>
<tr><td class="h"><a name="763"></a>763</td><td></td><td></td><td></td><td></td><td class="s">Package C<overload.pm> provides the following public functions:</td></tr>
<tr><td class="h"><a name="764"></a>764</td><td></td><td></td><td></td><td></td><td class="s"></td></tr>
<tr><td class="h"><a name="765"></a>765</td><td></td><td></td><td></td><td></td><td class="s">=over 5</td></tr>
<tr><td class="h"><a name="766"></a>766</td><td></td><td></td><td></td><td></td><td class="s"></td></tr>
<tr><td class="h"><a name="767"></a>767</td><td></td><td></td><td></td><td></td><td class="s">=item overload::StrVal(arg)</td></tr>
<tr><td class="h"><a name="768"></a>768</td><td></td><td></td><td></td><td></td><td class="s"></td></tr>
<tr><td class="h"><a name="769"></a>769</td><td></td><td></td><td></td><td></td><td class="s">Gives string value of C<arg> as in absence of stringify overloading. If you</td></tr>
<tr><td class="h"><a name="770"></a>770</td><td></td><td></td><td></td><td></td><td class="s">are using this to get the address of a reference (useful for checking if two</td></tr>
<tr><td class="h"><a name="771"></a>771</td><td></td><td></td><td></td><td></td><td class="s">references point to the same thing) then you may be better off using</td></tr>
<tr><td class="h"><a name="772"></a>772</td><td></td><td></td><td></td><td></td><td class="s">C<Scalar::Util::refaddr()>, which is faster.</td></tr>
<tr><td class="h"><a name="773"></a>773</td><td></td><td></td><td></td><td></td><td class="s"></td></tr>
<tr><td class="h"><a name="774"></a>774</td><td></td><td></td><td></td><td></td><td class="s">=item overload::Overloaded(arg)</td></tr>
<tr><td class="h"><a name="775"></a>775</td><td></td><td></td><td></td><td></td><td class="s"></td></tr>
<tr><td class="h"><a name="776"></a>776</td><td></td><td></td><td></td><td></td><td class="s">Returns true if C<arg> is subject to overloading of some operations.</td></tr>
<tr><td class="h"><a name="777"></a>777</td><td></td><td></td><td></td><td></td><td class="s"></td></tr>
<tr><td class="h"><a name="778"></a>778</td><td></td><td></td><td></td><td></td><td class="s">=item overload::Method(obj,op)</td></tr>
<tr><td class="h"><a name="779"></a>779</td><td></td><td></td><td></td><td></td><td class="s"></td></tr>
<tr><td class="h"><a name="780"></a>780</td><td></td><td></td><td></td><td></td><td class="s">Returns C<undef> or a reference to the method that implements C<op>.</td></tr>
<tr><td class="h"><a name="781"></a>781</td><td></td><td></td><td></td><td></td><td class="s"></td></tr>
<tr><td class="h"><a name="782"></a>782</td><td></td><td></td><td></td><td></td><td class="s">=back</td></tr>
<tr><td class="h"><a name="783"></a>783</td><td></td><td></td><td></td><td></td><td class="s"></td></tr>
<tr><td class="h"><a name="784"></a>784</td><td></td><td></td><td></td><td></td><td class="s">=head1 Overloading constants</td></tr>
<tr><td class="h"><a name="785"></a>785</td><td></td><td></td><td></td><td></td><td class="s"></td></tr>
<tr><td class="h"><a name="786"></a>786</td><td></td><td></td><td></td><td></td><td class="s">For some applications, the Perl parser mangles constants too much.</td></tr>
<tr><td class="h"><a name="787"></a>787</td><td></td><td></td><td></td><td></td><td class="s">It is possible to hook into this process via C<overload::constant()></td></tr>
<tr><td class="h"><a name="788"></a>788</td><td></td><td></td><td></td><td></td><td class="s">and C<overload::remove_constant()> functions.</td></tr>
<tr><td class="h"><a name="789"></a>789</td><td></td><td></td><td></td><td></td><td class="s"></td></tr>
<tr><td class="h"><a name="790"></a>790</td><td></td><td></td><td></td><td></td><td class="s">These functions take a hash as an argument. The recognized keys of this hash</td></tr>
<tr><td class="h"><a name="791"></a>791</td><td></td><td></td><td></td><td></td><td class="s">are:</td></tr>
<tr><td class="h"><a name="792"></a>792</td><td></td><td></td><td></td><td></td><td class="s"></td></tr>
<tr><td class="h"><a name="793"></a>793</td><td></td><td></td><td></td><td></td><td class="s">=over 8</td></tr>
<tr><td class="h"><a name="794"></a>794</td><td></td><td></td><td></td><td></td><td class="s"></td></tr>
<tr><td class="h"><a name="795"></a>795</td><td></td><td></td><td></td><td></td><td class="s">=item integer</td></tr>
<tr><td class="h"><a name="796"></a>796</td><td></td><td></td><td></td><td></td><td class="s"></td></tr>
<tr><td class="h"><a name="797"></a>797</td><td></td><td></td><td></td><td></td><td class="s">to overload integer constants,</td></tr>
<tr><td class="h"><a name="798"></a>798</td><td></td><td></td><td></td><td></td><td class="s"></td></tr>
<tr><td class="h"><a name="799"></a>799</td><td></td><td></td><td></td><td></td><td class="s">=item float</td></tr>
<tr><td class="h"><a name="800"></a>800</td><td></td><td></td><td></td><td></td><td class="s"></td></tr>
<tr><td class="h"><a name="801"></a>801</td><td></td><td></td><td></td><td></td><td class="s">to overload floating point constants,</td></tr>
<tr><td class="h"><a name="802"></a>802</td><td></td><td></td><td></td><td></td><td class="s"></td></tr>
<tr><td class="h"><a name="803"></a>803</td><td></td><td></td><td></td><td></td><td class="s">=item binary</td></tr>
<tr><td class="h"><a name="804"></a>804</td><td></td><td></td><td></td><td></td><td class="s"></td></tr>
<tr><td class="h"><a name="805"></a>805</td><td></td><td></td><td></td><td></td><td class="s">to overload octal and hexadecimal constants,</td></tr>
<tr><td class="h"><a name="806"></a>806</td><td></td><td></td><td></td><td></td><td class="s"></td></tr>
<tr><td class="h"><a name="807"></a>807</td><td></td><td></td><td></td><td></td><td class="s">=item q</td></tr>
<tr><td class="h"><a name="808"></a>808</td><td></td><td></td><td></td><td></td><td class="s"></td></tr>
<tr><td class="h"><a name="809"></a>809</td><td></td><td></td><td></td><td></td><td class="s">to overload C<q>-quoted strings, constant pieces of C<qq>- and C<qx>-quoted</td></tr>
<tr><td class="h"><a name="810"></a>810</td><td></td><td></td><td></td><td></td><td class="s">strings and here-documents,</td></tr>
<tr><td class="h"><a name="811"></a>811</td><td></td><td></td><td></td><td></td><td class="s"></td></tr>
<tr><td class="h"><a name="812"></a>812</td><td></td><td></td><td></td><td></td><td class="s">=item qr</td></tr>
<tr><td class="h"><a name="813"></a>813</td><td></td><td></td><td></td><td></td><td class="s"></td></tr>
<tr><td class="h"><a name="814"></a>814</td><td></td><td></td><td></td><td></td><td class="s">to overload constant pieces of regular expressions.</td></tr>
<tr><td class="h"><a name="815"></a>815</td><td></td><td></td><td></td><td></td><td class="s"></td></tr>
<tr><td class="h"><a name="816"></a>816</td><td></td><td></td><td></td><td></td><td class="s">=back</td></tr>
<tr><td class="h"><a name="817"></a>817</td><td></td><td></td><td></td><td></td><td class="s"></td></tr>
<tr><td class="h"><a name="818"></a>818</td><td></td><td></td><td></td><td></td><td class="s">The corresponding values are references to functions which take three arguments:</td></tr>
<tr><td class="h"><a name="819"></a>819</td><td></td><td></td><td></td><td></td><td class="s">the first one is the I<initial> string form of the constant, the second one</td></tr>
<tr><td class="h"><a name="820"></a>820</td><td></td><td></td><td></td><td></td><td class="s">is how Perl interprets this constant, the third one is how the constant is used.</td></tr>
<tr><td class="h"><a name="821"></a>821</td><td></td><td></td><td></td><td></td><td class="s">Note that the initial string form does not</td></tr>
<tr><td class="h"><a name="822"></a>822</td><td></td><td></td><td></td><td></td><td class="s">contain string delimiters, and has backslashes in backslash-delimiter</td></tr>
<tr><td class="h"><a name="823"></a>823</td><td></td><td></td><td></td><td></td><td class="s">combinations stripped (thus the value of delimiter is not relevant for</td></tr>
<tr><td class="h"><a name="824"></a>824</td><td></td><td></td><td></td><td></td><td class="s">processing of this string). The return value of this function is how this</td></tr>
<tr><td class="h"><a name="825"></a>825</td><td></td><td></td><td></td><td></td><td class="s">constant is going to be interpreted by Perl. The third argument is undefined</td></tr>
<tr><td class="h"><a name="826"></a>826</td><td></td><td></td><td></td><td></td><td class="s">unless for overloaded C<q>- and C<qr>- constants, it is C<q> in single-quote</td></tr>
<tr><td class="h"><a name="827"></a>827</td><td></td><td></td><td></td><td></td><td class="s">context (comes from strings, regular expressions, and single-quote HERE</td></tr>
<tr><td class="h"><a name="828"></a>828</td><td></td><td></td><td></td><td></td><td class="s">documents), it is C<tr> for arguments of C<tr>/C<y> operators,</td></tr>
<tr><td class="h"><a name="829"></a>829</td><td></td><td></td><td></td><td></td><td class="s">it is C<s> for right-hand side of C<s>-operator, and it is C<qq> otherwise.</td></tr>
<tr><td class="h"><a name="830"></a>830</td><td></td><td></td><td></td><td></td><td class="s"></td></tr>
<tr><td class="h"><a name="831"></a>831</td><td></td><td></td><td></td><td></td><td class="s">Since an expression C<"ab$cd,,"> is just a shortcut for C<'ab' . $cd . ',,'>,</td></tr>
<tr><td class="h"><a name="832"></a>832</td><td></td><td></td><td></td><td></td><td class="s">it is expected that overloaded constant strings are equipped with reasonable</td></tr>
<tr><td class="h"><a name="833"></a>833</td><td></td><td></td><td></td><td></td><td class="s">overloaded catenation operator, otherwise absurd results will result.</td></tr>
<tr><td class="h"><a name="834"></a>834</td><td></td><td></td><td></td><td></td><td class="s">Similarly, negative numbers are considered as negations of positive constants.</td></tr>
<tr><td class="h"><a name="835"></a>835</td><td></td><td></td><td></td><td></td><td class="s"></td></tr>
<tr><td class="h"><a name="836"></a>836</td><td></td><td></td><td></td><td></td><td class="s">Note that it is probably meaningless to call the functions overload::constant()</td></tr>
<tr><td class="h"><a name="837"></a>837</td><td></td><td></td><td></td><td></td><td class="s">and overload::remove_constant() from anywhere but import() and unimport() methods.</td></tr>
<tr><td class="h"><a name="838"></a>838</td><td></td><td></td><td></td><td></td><td class="s">From these methods they may be called as</td></tr>
<tr><td class="h"><a name="839"></a>839</td><td></td><td></td><td></td><td></td><td class="s"></td></tr>
<tr><td class="h"><a name="840"></a>840</td><td></td><td></td><td></td><td></td><td class="s"> sub import {</td></tr>
<tr><td class="h"><a name="841"></a>841</td><td></td><td></td><td></td><td></td><td class="s"> shift;</td></tr>
<tr><td class="h"><a name="842"></a>842</td><td></td><td></td><td></td><td></td><td class="s"> return unless @_;</td></tr>
<tr><td class="h"><a name="843"></a>843</td><td></td><td></td><td></td><td></td><td class="s"> die "unknown import: @_" unless @_ == 1 and $_[0] eq ':constant';</td></tr>
<tr><td class="h"><a name="844"></a>844</td><td></td><td></td><td></td><td></td><td class="s"> overload::constant integer => sub {Math::BigInt->new(shift)};</td></tr>
<tr><td class="h"><a name="845"></a>845</td><td></td><td></td><td></td><td></td><td class="s"> }</td></tr>
<tr><td class="h"><a name="846"></a>846</td><td></td><td></td><td></td><td></td><td class="s"></td></tr>
<tr><td class="h"><a name="847"></a>847</td><td></td><td></td><td></td><td></td><td class="s">=head1 IMPLEMENTATION</td></tr>
<tr><td class="h"><a name="848"></a>848</td><td></td><td></td><td></td><td></td><td class="s"></td></tr>
<tr><td class="h"><a name="849"></a>849</td><td></td><td></td><td></td><td></td><td class="s">What follows is subject to change RSN.</td></tr>
<tr><td class="h"><a name="850"></a>850</td><td></td><td></td><td></td><td></td><td class="s"></td></tr>
<tr><td class="h"><a name="851"></a>851</td><td></td><td></td><td></td><td></td><td class="s">The table of methods for all operations is cached in magic for the</td></tr>
<tr><td class="h"><a name="852"></a>852</td><td></td><td></td><td></td><td></td><td class="s">symbol table hash for the package. The cache is invalidated during</td></tr>
<tr><td class="h"><a name="853"></a>853</td><td></td><td></td><td></td><td></td><td class="s">processing of C<use overload>, C<no overload>, new function</td></tr>
<tr><td class="h"><a name="854"></a>854</td><td></td><td></td><td></td><td></td><td class="s">definitions, and changes in @ISA. However, this invalidation remains</td></tr>
<tr><td class="h"><a name="855"></a>855</td><td></td><td></td><td></td><td></td><td class="s">unprocessed until the next C<bless>ing into the package. Hence if you</td></tr>
<tr><td class="h"><a name="856"></a>856</td><td></td><td></td><td></td><td></td><td class="s">want to change overloading structure dynamically, you'll need an</td></tr>
<tr><td class="h"><a name="857"></a>857</td><td></td><td></td><td></td><td></td><td class="s">additional (fake) C<bless>ing to update the table.</td></tr>
<tr><td class="h"><a name="858"></a>858</td><td></td><td></td><td></td><td></td><td class="s"></td></tr>
<tr><td class="h"><a name="859"></a>859</td><td></td><td></td><td></td><td></td><td class="s">(Every SVish thing has a magic queue, and magic is an entry in that</td></tr>
<tr><td class="h"><a name="860"></a>860</td><td></td><td></td><td></td><td></td><td class="s">queue. This is how a single variable may participate in multiple</td></tr>
<tr><td class="h"><a name="861"></a>861</td><td></td><td></td><td></td><td></td><td class="s">forms of magic simultaneously. For instance, environment variables</td></tr>
<tr><td class="h"><a name="862"></a>862</td><td></td><td></td><td></td><td></td><td class="s">regularly have two forms at once: their %ENV magic and their taint</td></tr>
<tr><td class="h"><a name="863"></a>863</td><td></td><td></td><td></td><td></td><td class="s">magic. However, the magic which implements overloading is applied to</td></tr>
<tr><td class="h"><a name="864"></a>864</td><td></td><td></td><td></td><td></td><td class="s">the stashes, which are rarely used directly, thus should not slow down</td></tr>
<tr><td class="h"><a name="865"></a>865</td><td></td><td></td><td></td><td></td><td class="s">Perl.)</td></tr>
<tr><td class="h"><a name="866"></a>866</td><td></td><td></td><td></td><td></td><td class="s"></td></tr>
<tr><td class="h"><a name="867"></a>867</td><td></td><td></td><td></td><td></td><td class="s">If an object belongs to a package using overload, it carries a special</td></tr>
<tr><td class="h"><a name="868"></a>868</td><td></td><td></td><td></td><td></td><td class="s">flag. Thus the only speed penalty during arithmetic operations without</td></tr>
<tr><td class="h"><a name="869"></a>869</td><td></td><td></td><td></td><td></td><td class="s">overloading is the checking of this flag.</td></tr>
<tr><td class="h"><a name="870"></a>870</td><td></td><td></td><td></td><td></td><td class="s"></td></tr>
<tr><td class="h"><a name="871"></a>871</td><td></td><td></td><td></td><td></td><td class="s">In fact, if C<use overload> is not present, there is almost no overhead</td></tr>
<tr><td class="h"><a name="872"></a>872</td><td></td><td></td><td></td><td></td><td class="s">for overloadable operations, so most programs should not suffer</td></tr>
<tr><td class="h"><a name="873"></a>873</td><td></td><td></td><td></td><td></td><td class="s">measurable performance penalties. A considerable effort was made to</td></tr>
<tr><td class="h"><a name="874"></a>874</td><td></td><td></td><td></td><td></td><td class="s">minimize the overhead when overload is used in some package, but the</td></tr>
<tr><td class="h"><a name="875"></a>875</td><td></td><td></td><td></td><td></td><td class="s">arguments in question do not belong to packages using overload. When</td></tr>
<tr><td class="h"><a name="876"></a>876</td><td></td><td></td><td></td><td></td><td class="s">in doubt, test your speed with C<use overload> and without it. So far</td></tr>
<tr><td class="h"><a name="877"></a>877</td><td></td><td></td><td></td><td></td><td class="s">there have been no reports of substantial speed degradation if Perl is</td></tr>
<tr><td class="h"><a name="878"></a>878</td><td></td><td></td><td></td><td></td><td class="s">compiled with optimization turned on.</td></tr>
<tr><td class="h"><a name="879"></a>879</td><td></td><td></td><td></td><td></td><td class="s"></td></tr>
<tr><td class="h"><a name="880"></a>880</td><td></td><td></td><td></td><td></td><td class="s">There is no size penalty for data if overload is not used. The only</td></tr>
<tr><td class="h"><a name="881"></a>881</td><td></td><td></td><td></td><td></td><td class="s">size penalty if overload is used in some package is that I<all> the</td></tr>
<tr><td class="h"><a name="882"></a>882</td><td></td><td></td><td></td><td></td><td class="s">packages acquire a magic during the next C<bless>ing into the</td></tr>
<tr><td class="h"><a name="883"></a>883</td><td></td><td></td><td></td><td></td><td class="s">package. This magic is three-words-long for packages without</td></tr>
<tr><td class="h"><a name="884"></a>884</td><td></td><td></td><td></td><td></td><td class="s">overloading, and carries the cache table if the package is overloaded.</td></tr>
<tr><td class="h"><a name="885"></a>885</td><td></td><td></td><td></td><td></td><td class="s"></td></tr>
<tr><td class="h"><a name="886"></a>886</td><td></td><td></td><td></td><td></td><td class="s">Copying (C<$a=$b>) is shallow; however, a one-level-deep copying is</td></tr>
<tr><td class="h"><a name="887"></a>887</td><td></td><td></td><td></td><td></td><td class="s">carried out before any operation that can imply an assignment to the</td></tr>
<tr><td class="h"><a name="888"></a>888</td><td></td><td></td><td></td><td></td><td class="s">object $a (or $b) refers to, like C<$a++>. You can override this</td></tr>
<tr><td class="h"><a name="889"></a>889</td><td></td><td></td><td></td><td></td><td class="s">behavior by defining your own copy constructor (see L<"Copy Constructor">).</td></tr>
<tr><td class="h"><a name="890"></a>890</td><td></td><td></td><td></td><td></td><td class="s"></td></tr>
<tr><td class="h"><a name="891"></a>891</td><td></td><td></td><td></td><td></td><td class="s">It is expected that arguments to methods that are not explicitly supposed</td></tr>
<tr><td class="h"><a name="892"></a>892</td><td></td><td></td><td></td><td></td><td class="s">to be changed are constant (but this is not enforced).</td></tr>
<tr><td class="h"><a name="893"></a>893</td><td></td><td></td><td></td><td></td><td class="s"></td></tr>
<tr><td class="h"><a name="894"></a>894</td><td></td><td></td><td></td><td></td><td class="s">=head1 Metaphor clash</td></tr>
<tr><td class="h"><a name="895"></a>895</td><td></td><td></td><td></td><td></td><td class="s"></td></tr>
<tr><td class="h"><a name="896"></a>896</td><td></td><td></td><td></td><td></td><td class="s">One may wonder why the semantic of overloaded C<=> is so counter intuitive.</td></tr>
<tr><td class="h"><a name="897"></a>897</td><td></td><td></td><td></td><td></td><td class="s">If it I<looks> counter intuitive to you, you are subject to a metaphor</td></tr>
<tr><td class="h"><a name="898"></a>898</td><td></td><td></td><td></td><td></td><td class="s">clash.</td></tr>
<tr><td class="h"><a name="899"></a>899</td><td></td><td></td><td></td><td></td><td class="s"></td></tr>
<tr><td class="h"><a name="900"></a>900</td><td></td><td></td><td></td><td></td><td class="s">Here is a Perl object metaphor:</td></tr>
<tr><td class="h"><a name="901"></a>901</td><td></td><td></td><td></td><td></td><td class="s"></td></tr>
<tr><td class="h"><a name="902"></a>902</td><td></td><td></td><td></td><td></td><td class="s">I< object is a reference to blessed data></td></tr>
<tr><td class="h"><a name="903"></a>903</td><td></td><td></td><td></td><td></td><td class="s"></td></tr>
<tr><td class="h"><a name="904"></a>904</td><td></td><td></td><td></td><td></td><td class="s">and an arithmetic metaphor:</td></tr>
<tr><td class="h"><a name="905"></a>905</td><td></td><td></td><td></td><td></td><td class="s"></td></tr>
<tr><td class="h"><a name="906"></a>906</td><td></td><td></td><td></td><td></td><td class="s">I< object is a thing by itself>.</td></tr>
<tr><td class="h"><a name="907"></a>907</td><td></td><td></td><td></td><td></td><td class="s"></td></tr>
<tr><td class="h"><a name="908"></a>908</td><td></td><td></td><td></td><td></td><td class="s">The I<main> problem of overloading C<=> is the fact that these metaphors</td></tr>
<tr><td class="h"><a name="909"></a>909</td><td></td><td></td><td></td><td></td><td class="s">imply different actions on the assignment C<$a = $b> if $a and $b are</td></tr>
<tr><td class="h"><a name="910"></a>910</td><td></td><td></td><td></td><td></td><td class="s">objects. Perl-think implies that $a becomes a reference to whatever</td></tr>
<tr><td class="h"><a name="911"></a>911</td><td></td><td></td><td></td><td></td><td class="s">$b was referencing. Arithmetic-think implies that the value of "object"</td></tr>
<tr><td class="h"><a name="912"></a>912</td><td></td><td></td><td></td><td></td><td class="s">$a is changed to become the value of the object $b, preserving the fact</td></tr>
<tr><td class="h"><a name="913"></a>913</td><td></td><td></td><td></td><td></td><td class="s">that $a and $b are separate entities.</td></tr>
<tr><td class="h"><a name="914"></a>914</td><td></td><td></td><td></td><td></td><td class="s"></td></tr>
<tr><td class="h"><a name="915"></a>915</td><td></td><td></td><td></td><td></td><td class="s">The difference is not relevant in the absence of mutators. After</td></tr>
<tr><td class="h"><a name="916"></a>916</td><td></td><td></td><td></td><td></td><td class="s">a Perl-way assignment an operation which mutates the data referenced by $a</td></tr>
<tr><td class="h"><a name="917"></a>917</td><td></td><td></td><td></td><td></td><td class="s">would change the data referenced by $b too. Effectively, after</td></tr>
<tr><td class="h"><a name="918"></a>918</td><td></td><td></td><td></td><td></td><td class="s">C<$a = $b> values of $a and $b become I<indistinguishable>.</td></tr>
<tr><td class="h"><a name="919"></a>919</td><td></td><td></td><td></td><td></td><td class="s"></td></tr>
<tr><td class="h"><a name="920"></a>920</td><td></td><td></td><td></td><td></td><td class="s">On the other hand, anyone who has used algebraic notation knows the</td></tr>
<tr><td class="h"><a name="921"></a>921</td><td></td><td></td><td></td><td></td><td class="s">expressive power of the arithmetic metaphor. Overloading works hard</td></tr>
<tr><td class="h"><a name="922"></a>922</td><td></td><td></td><td></td><td></td><td class="s">to enable this metaphor while preserving the Perlian way as far as</td></tr>
<tr><td class="h"><a name="923"></a>923</td><td></td><td></td><td></td><td></td><td class="s">possible. Since it is not possible to freely mix two contradicting</td></tr>
<tr><td class="h"><a name="924"></a>924</td><td></td><td></td><td></td><td></td><td class="s">metaphors, overloading allows the arithmetic way to write things I<as</td></tr>
<tr><td class="h"><a name="925"></a>925</td><td></td><td></td><td></td><td></td><td class="s">far as all the mutators are called via overloaded access only>. The</td></tr>
<tr><td class="h"><a name="926"></a>926</td><td></td><td></td><td></td><td></td><td class="s">way it is done is described in L<Copy Constructor>.</td></tr>
<tr><td class="h"><a name="927"></a>927</td><td></td><td></td><td></td><td></td><td class="s"></td></tr>
<tr><td class="h"><a name="928"></a>928</td><td></td><td></td><td></td><td></td><td class="s">If some mutator methods are directly applied to the overloaded values,</td></tr>
<tr><td class="h"><a name="929"></a>929</td><td></td><td></td><td></td><td></td><td class="s">one may need to I<explicitly unlink> other values which references the</td></tr>
<tr><td class="h"><a name="930"></a>930</td><td></td><td></td><td></td><td></td><td class="s">same value:</td></tr>
<tr><td class="h"><a name="931"></a>931</td><td></td><td></td><td></td><td></td><td class="s"></td></tr>
<tr><td class="h"><a name="932"></a>932</td><td></td><td></td><td></td><td></td><td class="s"> $a = Data->new(23);</td></tr>
<tr><td class="h"><a name="933"></a>933</td><td></td><td></td><td></td><td></td><td class="s"> ...</td></tr>
<tr><td class="h"><a name="934"></a>934</td><td></td><td></td><td></td><td></td><td class="s"> $b = $a; # $b is "linked" to $a</td></tr>
<tr><td class="h"><a name="935"></a>935</td><td></td><td></td><td></td><td></td><td class="s"> ...</td></tr>
<tr><td class="h"><a name="936"></a>936</td><td></td><td></td><td></td><td></td><td class="s"> $a = $a->clone; # Unlink $b from $a</td></tr>
<tr><td class="h"><a name="937"></a>937</td><td></td><td></td><td></td><td></td><td class="s"> $a->increment_by(4);</td></tr>
<tr><td class="h"><a name="938"></a>938</td><td></td><td></td><td></td><td></td><td class="s"></td></tr>
<tr><td class="h"><a name="939"></a>939</td><td></td><td></td><td></td><td></td><td class="s">Note that overloaded access makes this transparent:</td></tr>
<tr><td class="h"><a name="940"></a>940</td><td></td><td></td><td></td><td></td><td class="s"></td></tr>
<tr><td class="h"><a name="941"></a>941</td><td></td><td></td><td></td><td></td><td class="s"> $a = Data->new(23);</td></tr>
<tr><td class="h"><a name="942"></a>942</td><td></td><td></td><td></td><td></td><td class="s"> $b = $a; # $b is "linked" to $a</td></tr>
<tr><td class="h"><a name="943"></a>943</td><td></td><td></td><td></td><td></td><td class="s"> $a += 4; # would unlink $b automagically</td></tr>
<tr><td class="h"><a name="944"></a>944</td><td></td><td></td><td></td><td></td><td class="s"></td></tr>
<tr><td class="h"><a name="945"></a>945</td><td></td><td></td><td></td><td></td><td class="s">However, it would not make</td></tr>
<tr><td class="h"><a name="946"></a>946</td><td></td><td></td><td></td><td></td><td class="s"></td></tr>
<tr><td class="h"><a name="947"></a>947</td><td></td><td></td><td></td><td></td><td class="s"> $a = Data->new(23);</td></tr>
<tr><td class="h"><a name="948"></a>948</td><td></td><td></td><td></td><td></td><td class="s"> $a = 4; # Now $a is a plain 4, not 'Data'</td></tr>
<tr><td class="h"><a name="949"></a>949</td><td></td><td></td><td></td><td></td><td class="s"></td></tr>
<tr><td class="h"><a name="950"></a>950</td><td></td><td></td><td></td><td></td><td class="s">preserve "objectness" of $a. But Perl I<has> a way to make assignments</td></tr>
<tr><td class="h"><a name="951"></a>951</td><td></td><td></td><td></td><td></td><td class="s">to an object do whatever you want. It is just not the overload, but</td></tr>
<tr><td class="h"><a name="952"></a>952</td><td></td><td></td><td></td><td></td><td class="s">tie()ing interface (see L<perlfunc/tie>). Adding a FETCH() method</td></tr>
<tr><td class="h"><a name="953"></a>953</td><td></td><td></td><td></td><td></td><td class="s">which returns the object itself, and STORE() method which changes the</td></tr>
<tr><td class="h"><a name="954"></a>954</td><td></td><td></td><td></td><td></td><td class="s">value of the object, one can reproduce the arithmetic metaphor in its</td></tr>
<tr><td class="h"><a name="955"></a>955</td><td></td><td></td><td></td><td></td><td class="s">completeness, at least for variables which were tie()d from the start.</td></tr>
<tr><td class="h"><a name="956"></a>956</td><td></td><td></td><td></td><td></td><td class="s"></td></tr>
<tr><td class="h"><a name="957"></a>957</td><td></td><td></td><td></td><td></td><td class="s">(Note that a workaround for a bug may be needed, see L<"BUGS">.)</td></tr>
<tr><td class="h"><a name="958"></a>958</td><td></td><td></td><td></td><td></td><td class="s"></td></tr>
<tr><td class="h"><a name="959"></a>959</td><td></td><td></td><td></td><td></td><td class="s">=head1 Cookbook</td></tr>
<tr><td class="h"><a name="960"></a>960</td><td></td><td></td><td></td><td></td><td class="s"></td></tr>
<tr><td class="h"><a name="961"></a>961</td><td></td><td></td><td></td><td></td><td class="s">Please add examples to what follows!</td></tr>
<tr><td class="h"><a name="962"></a>962</td><td></td><td></td><td></td><td></td><td class="s"></td></tr>
<tr><td class="h"><a name="963"></a>963</td><td></td><td></td><td></td><td></td><td class="s">=head2 Two-face scalars</td></tr>
<tr><td class="h"><a name="964"></a>964</td><td></td><td></td><td></td><td></td><td class="s"></td></tr>
<tr><td class="h"><a name="965"></a>965</td><td></td><td></td><td></td><td></td><td class="s">Put this in F<two_face.pm> in your Perl library directory:</td></tr>
<tr><td class="h"><a name="966"></a>966</td><td></td><td></td><td></td><td></td><td class="s"></td></tr>
<tr><td class="h"><a name="967"></a>967</td><td></td><td></td><td></td><td></td><td class="s"> package two_face; # Scalars with separate string and</td></tr>
<tr><td class="h"><a name="968"></a>968</td><td></td><td></td><td></td><td></td><td class="s"> # numeric values.</td></tr>
<tr><td class="h"><a name="969"></a>969</td><td></td><td></td><td></td><td></td><td class="s"> sub new { my $p = shift; bless [@_], $p }</td></tr>
<tr><td class="h"><a name="970"></a>970</td><td></td><td></td><td></td><td></td><td class="s"> use overload '""' => \&str, '0+' => \&num, fallback => 1;</td></tr>
<tr><td class="h"><a name="971"></a>971</td><td></td><td></td><td></td><td></td><td class="s"> sub num {shift->[1]}</td></tr>
<tr><td class="h"><a name="972"></a>972</td><td></td><td></td><td></td><td></td><td class="s"> sub str {shift->[0]}</td></tr>
<tr><td class="h"><a name="973"></a>973</td><td></td><td></td><td></td><td></td><td class="s"></td></tr>
<tr><td class="h"><a name="974"></a>974</td><td></td><td></td><td></td><td></td><td class="s">Use it as follows:</td></tr>
<tr><td class="h"><a name="975"></a>975</td><td></td><td></td><td></td><td></td><td class="s"></td></tr>
<tr><td class="h"><a name="976"></a>976</td><td></td><td></td><td></td><td></td><td class="s"> require two_face;</td></tr>
<tr><td class="h"><a name="977"></a>977</td><td></td><td></td><td></td><td></td><td class="s"> my $seven = two_face->new("vii", 7);</td></tr>
<tr><td class="h"><a name="978"></a>978</td><td></td><td></td><td></td><td></td><td class="s"> printf "seven=$seven, seven=%d, eight=%d\n", $seven, $seven+1;</td></tr>
<tr><td class="h"><a name="979"></a>979</td><td></td><td></td><td></td><td></td><td class="s"> print "seven contains `i'\n" if $seven =~ /i/;</td></tr>
<tr><td class="h"><a name="980"></a>980</td><td></td><td></td><td></td><td></td><td class="s"></td></tr>
<tr><td class="h"><a name="981"></a>981</td><td></td><td></td><td></td><td></td><td class="s">(The second line creates a scalar which has both a string value, and a</td></tr>
<tr><td class="h"><a name="982"></a>982</td><td></td><td></td><td></td><td></td><td class="s">numeric value.) This prints:</td></tr>
<tr><td class="h"><a name="983"></a>983</td><td></td><td></td><td></td><td></td><td class="s"></td></tr>
<tr><td class="h"><a name="984"></a>984</td><td></td><td></td><td></td><td></td><td class="s"> seven=vii, seven=7, eight=8</td></tr>
<tr><td class="h"><a name="985"></a>985</td><td></td><td></td><td></td><td></td><td class="s"> seven contains `i'</td></tr>
<tr><td class="h"><a name="986"></a>986</td><td></td><td></td><td></td><td></td><td class="s"></td></tr>
<tr><td class="h"><a name="987"></a>987</td><td></td><td></td><td></td><td></td><td class="s">=head2 Two-face references</td></tr>
<tr><td class="h"><a name="988"></a>988</td><td></td><td></td><td></td><td></td><td class="s"></td></tr>
<tr><td class="h"><a name="989"></a>989</td><td></td><td></td><td></td><td></td><td class="s">Suppose you want to create an object which is accessible as both an</td></tr>
<tr><td class="h"><a name="990"></a>990</td><td></td><td></td><td></td><td></td><td class="s">array reference and a hash reference.</td></tr>
<tr><td class="h"><a name="991"></a>991</td><td></td><td></td><td></td><td></td><td class="s"></td></tr>
<tr><td class="h"><a name="992"></a>992</td><td></td><td></td><td></td><td></td><td class="s"> package two_refs;</td></tr>
<tr><td class="h"><a name="993"></a>993</td><td></td><td></td><td></td><td></td><td class="s"> use overload '%{}' => \&gethash, '@{}' => sub { $ {shift()} };</td></tr>
<tr><td class="h"><a name="994"></a>994</td><td></td><td></td><td></td><td></td><td class="s"> sub new {</td></tr>
<tr><td class="h"><a name="995"></a>995</td><td></td><td></td><td></td><td></td><td class="s"> my $p = shift;</td></tr>
<tr><td class="h"><a name="996"></a>996</td><td></td><td></td><td></td><td></td><td class="s"> bless \ [@_], $p;</td></tr>
<tr><td class="h"><a name="997"></a>997</td><td></td><td></td><td></td><td></td><td class="s"> }</td></tr>
<tr><td class="h"><a name="998"></a>998</td><td></td><td></td><td></td><td></td><td class="s"> sub gethash {</td></tr>
<tr><td class="h"><a name="999"></a>999</td><td></td><td></td><td></td><td></td><td class="s"> my %h;</td></tr>
<tr><td class="h"><a name="1000"></a>1000</td><td></td><td></td><td></td><td></td><td class="s"> my $self = shift;</td></tr>
<tr><td class="h"><a name="1001"></a>1001</td><td></td><td></td><td></td><td></td><td class="s"> tie %h, ref $self, $self;</td></tr>
<tr><td class="h"><a name="1002"></a>1002</td><td></td><td></td><td></td><td></td><td class="s"> \%h;</td></tr>
<tr><td class="h"><a name="1003"></a>1003</td><td></td><td></td><td></td><td></td><td class="s"> }</td></tr>
<tr><td class="h"><a name="1004"></a>1004</td><td></td><td></td><td></td><td></td><td class="s"></td></tr>
<tr><td class="h"><a name="1005"></a>1005</td><td></td><td></td><td></td><td></td><td class="s"> sub TIEHASH { my $p = shift; bless \ shift, $p }</td></tr>
<tr><td class="h"><a name="1006"></a>1006</td><td></td><td></td><td></td><td></td><td class="s"> my %fields;</td></tr>
<tr><td class="h"><a name="1007"></a>1007</td><td></td><td></td><td></td><td></td><td class="s"> my $i = 0;</td></tr>
<tr><td class="h"><a name="1008"></a>1008</td><td></td><td></td><td></td><td></td><td class="s"> $fields{$_} = $i++ foreach qw{zero one two three};</td></tr>
<tr><td class="h"><a name="1009"></a>1009</td><td></td><td></td><td></td><td></td><td class="s"> sub STORE {</td></tr>
<tr><td class="h"><a name="1010"></a>1010</td><td></td><td></td><td></td><td></td><td class="s"> my $self = ${shift()};</td></tr>
<tr><td class="h"><a name="1011"></a>1011</td><td></td><td></td><td></td><td></td><td class="s"> my $key = $fields{shift()};</td></tr>
<tr><td class="h"><a name="1012"></a>1012</td><td></td><td></td><td></td><td></td><td class="s"> defined $key or die "Out of band access";</td></tr>
<tr><td class="h"><a name="1013"></a>1013</td><td></td><td></td><td></td><td></td><td class="s"> $$self->[$key] = shift;</td></tr>
<tr><td class="h"><a name="1014"></a>1014</td><td></td><td></td><td></td><td></td><td class="s"> }</td></tr>
<tr><td class="h"><a name="1015"></a>1015</td><td></td><td></td><td></td><td></td><td class="s"> sub FETCH {</td></tr>
<tr><td class="h"><a name="1016"></a>1016</td><td></td><td></td><td></td><td></td><td class="s"> my $self = ${shift()};</td></tr>
<tr><td class="h"><a name="1017"></a>1017</td><td></td><td></td><td></td><td></td><td class="s"> my $key = $fields{shift()};</td></tr>
<tr><td class="h"><a name="1018"></a>1018</td><td></td><td></td><td></td><td></td><td class="s"> defined $key or die "Out of band access";</td></tr>
<tr><td class="h"><a name="1019"></a>1019</td><td></td><td></td><td></td><td></td><td class="s"> $$self->[$key];</td></tr>
<tr><td class="h"><a name="1020"></a>1020</td><td></td><td></td><td></td><td></td><td class="s"> }</td></tr>
<tr><td class="h"><a name="1021"></a>1021</td><td></td><td></td><td></td><td></td><td class="s"></td></tr>
<tr><td class="h"><a name="1022"></a>1022</td><td></td><td></td><td></td><td></td><td class="s">Now one can access an object using both the array and hash syntax:</td></tr>
<tr><td class="h"><a name="1023"></a>1023</td><td></td><td></td><td></td><td></td><td class="s"></td></tr>
<tr><td class="h"><a name="1024"></a>1024</td><td></td><td></td><td></td><td></td><td class="s"> my $bar = two_refs->new(3,4,5,6);</td></tr>
<tr><td class="h"><a name="1025"></a>1025</td><td></td><td></td><td></td><td></td><td class="s"> $bar->[2] = 11;</td></tr>
<tr><td class="h"><a name="1026"></a>1026</td><td></td><td></td><td></td><td></td><td class="s"> $bar->{two} == 11 or die 'bad hash fetch';</td></tr>
<tr><td class="h"><a name="1027"></a>1027</td><td></td><td></td><td></td><td></td><td class="s"></td></tr>
<tr><td class="h"><a name="1028"></a>1028</td><td></td><td></td><td></td><td></td><td class="s">Note several important features of this example. First of all, the</td></tr>
<tr><td class="h"><a name="1029"></a>1029</td><td></td><td></td><td></td><td></td><td class="s">I<actual> type of $bar is a scalar reference, and we do not overload</td></tr>
<tr><td class="h"><a name="1030"></a>1030</td><td></td><td></td><td></td><td></td><td class="s">the scalar dereference. Thus we can get the I<actual> non-overloaded</td></tr>
<tr><td class="h"><a name="1031"></a>1031</td><td></td><td></td><td></td><td></td><td class="s">contents of $bar by just using C<$$bar> (what we do in functions which</td></tr>
<tr><td class="h"><a name="1032"></a>1032</td><td></td><td></td><td></td><td></td><td class="s">overload dereference). Similarly, the object returned by the</td></tr>
<tr><td class="h"><a name="1033"></a>1033</td><td></td><td></td><td></td><td></td><td class="s">TIEHASH() method is a scalar reference.</td></tr>
<tr><td class="h"><a name="1034"></a>1034</td><td></td><td></td><td></td><td></td><td class="s"></td></tr>
<tr><td class="h"><a name="1035"></a>1035</td><td></td><td></td><td></td><td></td><td class="s">Second, we create a new tied hash each time the hash syntax is used.</td></tr>
<tr><td class="h"><a name="1036"></a>1036</td><td></td><td></td><td></td><td></td><td class="s">This allows us not to worry about a possibility of a reference loop,</td></tr>
<tr><td class="h"><a name="1037"></a>1037</td><td></td><td></td><td></td><td></td><td class="s">which would lead to a memory leak.</td></tr>
<tr><td class="h"><a name="1038"></a>1038</td><td></td><td></td><td></td><td></td><td class="s"></td></tr>
<tr><td class="h"><a name="1039"></a>1039</td><td></td><td></td><td></td><td></td><td class="s">Both these problems can be cured. Say, if we want to overload hash</td></tr>
<tr><td class="h"><a name="1040"></a>1040</td><td></td><td></td><td></td><td></td><td class="s">dereference on a reference to an object which is I<implemented> as a</td></tr>
<tr><td class="h"><a name="1041"></a>1041</td><td></td><td></td><td></td><td></td><td class="s">hash itself, the only problem one has to circumvent is how to access</td></tr>
<tr><td class="h"><a name="1042"></a>1042</td><td></td><td></td><td></td><td></td><td class="s">this I<actual> hash (as opposed to the I<virtual> hash exhibited by the</td></tr>
<tr><td class="h"><a name="1043"></a>1043</td><td></td><td></td><td></td><td></td><td class="s">overloaded dereference operator). Here is one possible fetching routine:</td></tr>
<tr><td class="h"><a name="1044"></a>1044</td><td></td><td></td><td></td><td></td><td class="s"></td></tr>
<tr><td class="h"><a name="1045"></a>1045</td><td></td><td></td><td></td><td></td><td class="s"> sub access_hash {</td></tr>
<tr><td class="h"><a name="1046"></a>1046</td><td></td><td></td><td></td><td></td><td class="s"> my ($self, $key) = (shift, shift);</td></tr>
<tr><td class="h"><a name="1047"></a>1047</td><td></td><td></td><td></td><td></td><td class="s"> my $class = ref $self;</td></tr>
<tr><td class="h"><a name="1048"></a>1048</td><td></td><td></td><td></td><td></td><td class="s"> bless $self, 'overload::dummy'; # Disable overloading of %{}</td></tr>
<tr><td class="h"><a name="1049"></a>1049</td><td></td><td></td><td></td><td></td><td class="s"> my $out = $self->{$key};</td></tr>
<tr><td class="h"><a name="1050"></a>1050</td><td></td><td></td><td></td><td></td><td class="s"> bless $self, $class; # Restore overloading</td></tr>
<tr><td class="h"><a name="1051"></a>1051</td><td></td><td></td><td></td><td></td><td class="s"> $out;</td></tr>
<tr><td class="h"><a name="1052"></a>1052</td><td></td><td></td><td></td><td></td><td class="s"> }</td></tr>
<tr><td class="h"><a name="1053"></a>1053</td><td></td><td></td><td></td><td></td><td class="s"></td></tr>
<tr><td class="h"><a name="1054"></a>1054</td><td></td><td></td><td></td><td></td><td class="s">To remove creation of the tied hash on each access, one may an extra</td></tr>
<tr><td class="h"><a name="1055"></a>1055</td><td></td><td></td><td></td><td></td><td class="s">level of indirection which allows a non-circular structure of references:</td></tr>
<tr><td class="h"><a name="1056"></a>1056</td><td></td><td></td><td></td><td></td><td class="s"></td></tr>
<tr><td class="h"><a name="1057"></a>1057</td><td></td><td></td><td></td><td></td><td class="s"> package two_refs1;</td></tr>
<tr><td class="h"><a name="1058"></a>1058</td><td></td><td></td><td></td><td></td><td class="s"> use overload '%{}' => sub { ${shift()}->[1] },</td></tr>
<tr><td class="h"><a name="1059"></a>1059</td><td></td><td></td><td></td><td></td><td class="s"> '@{}' => sub { ${shift()}->[0] };</td></tr>
<tr><td class="h"><a name="1060"></a>1060</td><td></td><td></td><td></td><td></td><td class="s"> sub new {</td></tr>
<tr><td class="h"><a name="1061"></a>1061</td><td></td><td></td><td></td><td></td><td class="s"> my $p = shift;</td></tr>
<tr><td class="h"><a name="1062"></a>1062</td><td></td><td></td><td></td><td></td><td class="s"> my $a = [@_];</td></tr>
<tr><td class="h"><a name="1063"></a>1063</td><td></td><td></td><td></td><td></td><td class="s"> my %h;</td></tr>
<tr><td class="h"><a name="1064"></a>1064</td><td></td><td></td><td></td><td></td><td class="s"> tie %h, $p, $a;</td></tr>
<tr><td class="h"><a name="1065"></a>1065</td><td></td><td></td><td></td><td></td><td class="s"> bless \ [$a, \%h], $p;</td></tr>
<tr><td class="h"><a name="1066"></a>1066</td><td></td><td></td><td></td><td></td><td class="s"> }</td></tr>
<tr><td class="h"><a name="1067"></a>1067</td><td></td><td></td><td></td><td></td><td class="s"> sub gethash {</td></tr>
<tr><td class="h"><a name="1068"></a>1068</td><td></td><td></td><td></td><td></td><td class="s"> my %h;</td></tr>
<tr><td class="h"><a name="1069"></a>1069</td><td></td><td></td><td></td><td></td><td class="s"> my $self = shift;</td></tr>
<tr><td class="h"><a name="1070"></a>1070</td><td></td><td></td><td></td><td></td><td class="s"> tie %h, ref $self, $self;</td></tr>
<tr><td class="h"><a name="1071"></a>1071</td><td></td><td></td><td></td><td></td><td class="s"> \%h;</td></tr>
<tr><td class="h"><a name="1072"></a>1072</td><td></td><td></td><td></td><td></td><td class="s"> }</td></tr>
<tr><td class="h"><a name="1073"></a>1073</td><td></td><td></td><td></td><td></td><td class="s"></td></tr>
<tr><td class="h"><a name="1074"></a>1074</td><td></td><td></td><td></td><td></td><td class="s"> sub TIEHASH { my $p = shift; bless \ shift, $p }</td></tr>
<tr><td class="h"><a name="1075"></a>1075</td><td></td><td></td><td></td><td></td><td class="s"> my %fields;</td></tr>
<tr><td class="h"><a name="1076"></a>1076</td><td></td><td></td><td></td><td></td><td class="s"> my $i = 0;</td></tr>
<tr><td class="h"><a name="1077"></a>1077</td><td></td><td></td><td></td><td></td><td class="s"> $fields{$_} = $i++ foreach qw{zero one two three};</td></tr>
<tr><td class="h"><a name="1078"></a>1078</td><td></td><td></td><td></td><td></td><td class="s"> sub STORE {</td></tr>
<tr><td class="h"><a name="1079"></a>1079</td><td></td><td></td><td></td><td></td><td class="s"> my $a = ${shift()};</td></tr>
<tr><td class="h"><a name="1080"></a>1080</td><td></td><td></td><td></td><td></td><td class="s"> my $key = $fields{shift()};</td></tr>
<tr><td class="h"><a name="1081"></a>1081</td><td></td><td></td><td></td><td></td><td class="s"> defined $key or die "Out of band access";</td></tr>
<tr><td class="h"><a name="1082"></a>1082</td><td></td><td></td><td></td><td></td><td class="s"> $a->[$key] = shift;</td></tr>
<tr><td class="h"><a name="1083"></a>1083</td><td></td><td></td><td></td><td></td><td class="s"> }</td></tr>
<tr><td class="h"><a name="1084"></a>1084</td><td></td><td></td><td></td><td></td><td class="s"> sub FETCH {</td></tr>
<tr><td class="h"><a name="1085"></a>1085</td><td></td><td></td><td></td><td></td><td class="s"> my $a = ${shift()};</td></tr>
<tr><td class="h"><a name="1086"></a>1086</td><td></td><td></td><td></td><td></td><td class="s"> my $key = $fields{shift()};</td></tr>
<tr><td class="h"><a name="1087"></a>1087</td><td></td><td></td><td></td><td></td><td class="s"> defined $key or die "Out of band access";</td></tr>
<tr><td class="h"><a name="1088"></a>1088</td><td></td><td></td><td></td><td></td><td class="s"> $a->[$key];</td></tr>
<tr><td class="h"><a name="1089"></a>1089</td><td></td><td></td><td></td><td></td><td class="s"> }</td></tr>
<tr><td class="h"><a name="1090"></a>1090</td><td></td><td></td><td></td><td></td><td class="s"></td></tr>
<tr><td class="h"><a name="1091"></a>1091</td><td></td><td></td><td></td><td></td><td class="s">Now if $baz is overloaded like this, then C<$baz> is a reference to a</td></tr>
<tr><td class="h"><a name="1092"></a>1092</td><td></td><td></td><td></td><td></td><td class="s">reference to the intermediate array, which keeps a reference to an</td></tr>
<tr><td class="h"><a name="1093"></a>1093</td><td></td><td></td><td></td><td></td><td class="s">actual array, and the access hash. The tie()ing object for the access</td></tr>
<tr><td class="h"><a name="1094"></a>1094</td><td></td><td></td><td></td><td></td><td class="s">hash is a reference to a reference to the actual array, so</td></tr>
<tr><td class="h"><a name="1095"></a>1095</td><td></td><td></td><td></td><td></td><td class="s"></td></tr>
<tr><td class="h"><a name="1096"></a>1096</td><td></td><td></td><td></td><td></td><td class="s">=over</td></tr>
<tr><td class="h"><a name="1097"></a>1097</td><td></td><td></td><td></td><td></td><td class="s"></td></tr>
<tr><td class="h"><a name="1098"></a>1098</td><td></td><td></td><td></td><td></td><td class="s">=item *</td></tr>
<tr><td class="h"><a name="1099"></a>1099</td><td></td><td></td><td></td><td></td><td class="s"></td></tr>
<tr><td class="h"><a name="1100"></a>1100</td><td></td><td></td><td></td><td></td><td class="s">There are no loops of references.</td></tr>
<tr><td class="h"><a name="1101"></a>1101</td><td></td><td></td><td></td><td></td><td class="s"></td></tr>
<tr><td class="h"><a name="1102"></a>1102</td><td></td><td></td><td></td><td></td><td class="s">=item *</td></tr>
<tr><td class="h"><a name="1103"></a>1103</td><td></td><td></td><td></td><td></td><td class="s"></td></tr>
<tr><td class="h"><a name="1104"></a>1104</td><td></td><td></td><td></td><td></td><td class="s">Both "objects" which are blessed into the class C<two_refs1> are</td></tr>
<tr><td class="h"><a name="1105"></a>1105</td><td></td><td></td><td></td><td></td><td class="s">references to a reference to an array, thus references to a I<scalar>.</td></tr>
<tr><td class="h"><a name="1106"></a>1106</td><td></td><td></td><td></td><td></td><td class="s">Thus the accessor expression C<$$foo-E<gt>[$ind]> involves no</td></tr>
<tr><td class="h"><a name="1107"></a>1107</td><td></td><td></td><td></td><td></td><td class="s">overloaded operations.</td></tr>
<tr><td class="h"><a name="1108"></a>1108</td><td></td><td></td><td></td><td></td><td class="s"></td></tr>
<tr><td class="h"><a name="1109"></a>1109</td><td></td><td></td><td></td><td></td><td class="s">=back</td></tr>
<tr><td class="h"><a name="1110"></a>1110</td><td></td><td></td><td></td><td></td><td class="s"></td></tr>
<tr><td class="h"><a name="1111"></a>1111</td><td></td><td></td><td></td><td></td><td class="s">=head2 Symbolic calculator</td></tr>
<tr><td class="h"><a name="1112"></a>1112</td><td></td><td></td><td></td><td></td><td class="s"></td></tr>
<tr><td class="h"><a name="1113"></a>1113</td><td></td><td></td><td></td><td></td><td class="s">Put this in F<symbolic.pm> in your Perl library directory:</td></tr>
<tr><td class="h"><a name="1114"></a>1114</td><td></td><td></td><td></td><td></td><td class="s"></td></tr>
<tr><td class="h"><a name="1115"></a>1115</td><td></td><td></td><td></td><td></td><td class="s"> package symbolic; # Primitive symbolic calculator</td></tr>
<tr><td class="h"><a name="1116"></a>1116</td><td></td><td></td><td></td><td></td><td class="s"> use overload nomethod => \&wrap;</td></tr>
<tr><td class="h"><a name="1117"></a>1117</td><td></td><td></td><td></td><td></td><td class="s"></td></tr>
<tr><td class="h"><a name="1118"></a>1118</td><td></td><td></td><td></td><td></td><td class="s"> sub new { shift; bless ['n', @_] }</td></tr>
<tr><td class="h"><a name="1119"></a>1119</td><td></td><td></td><td></td><td></td><td class="s"> sub wrap {</td></tr>
<tr><td class="h"><a name="1120"></a>1120</td><td></td><td></td><td></td><td></td><td class="s"> my ($obj, $other, $inv, $meth) = @_;</td></tr>
<tr><td class="h"><a name="1121"></a>1121</td><td></td><td></td><td></td><td></td><td class="s"> ($obj, $other) = ($other, $obj) if $inv;</td></tr>
<tr><td class="h"><a name="1122"></a>1122</td><td></td><td></td><td></td><td></td><td class="s"> bless [$meth, $obj, $other];</td></tr>
<tr><td class="h"><a name="1123"></a>1123</td><td></td><td></td><td></td><td></td><td class="s"> }</td></tr>
<tr><td class="h"><a name="1124"></a>1124</td><td></td><td></td><td></td><td></td><td class="s"></td></tr>
<tr><td class="h"><a name="1125"></a>1125</td><td></td><td></td><td></td><td></td><td class="s">This module is very unusual as overloaded modules go: it does not</td></tr>
<tr><td class="h"><a name="1126"></a>1126</td><td></td><td></td><td></td><td></td><td class="s">provide any usual overloaded operators, instead it provides the L<Last</td></tr>
<tr><td class="h"><a name="1127"></a>1127</td><td></td><td></td><td></td><td></td><td class="s">Resort> operator C<nomethod>. In this example the corresponding</td></tr>
<tr><td class="h"><a name="1128"></a>1128</td><td></td><td></td><td></td><td></td><td class="s">subroutine returns an object which encapsulates operations done over</td></tr>
<tr><td class="h"><a name="1129"></a>1129</td><td></td><td></td><td></td><td></td><td class="s">the objects: C<< symbolic->new(3) >> contains C<['n', 3]>, C<< 2 +</td></tr>
<tr><td class="h"><a name="1130"></a>1130</td><td></td><td></td><td></td><td></td><td class="s">symbolic->new(3) >> contains C<['+', 2, ['n', 3]]>.</td></tr>
<tr><td class="h"><a name="1131"></a>1131</td><td></td><td></td><td></td><td></td><td class="s"></td></tr>
<tr><td class="h"><a name="1132"></a>1132</td><td></td><td></td><td></td><td></td><td class="s">Here is an example of the script which "calculates" the side of</td></tr>
<tr><td class="h"><a name="1133"></a>1133</td><td></td><td></td><td></td><td></td><td class="s">circumscribed octagon using the above package:</td></tr>
<tr><td class="h"><a name="1134"></a>1134</td><td></td><td></td><td></td><td></td><td class="s"></td></tr>
<tr><td class="h"><a name="1135"></a>1135</td><td></td><td></td><td></td><td></td><td class="s"> require symbolic;</td></tr>
<tr><td class="h"><a name="1136"></a>1136</td><td></td><td></td><td></td><td></td><td class="s"> my $iter = 1; # 2**($iter+2) = 8</td></tr>
<tr><td class="h"><a name="1137"></a>1137</td><td></td><td></td><td></td><td></td><td class="s"> my $side = symbolic->new(1);</td></tr>
<tr><td class="h"><a name="1138"></a>1138</td><td></td><td></td><td></td><td></td><td class="s"> my $cnt = $iter;</td></tr>
<tr><td class="h"><a name="1139"></a>1139</td><td></td><td></td><td></td><td></td><td class="s"></td></tr>
<tr><td class="h"><a name="1140"></a>1140</td><td></td><td></td><td></td><td></td><td class="s"> while ($cnt--) {</td></tr>
<tr><td class="h"><a name="1141"></a>1141</td><td></td><td></td><td></td><td></td><td class="s"> $side = (sqrt(1 + $side**2) - 1)/$side;</td></tr>
<tr><td class="h"><a name="1142"></a>1142</td><td></td><td></td><td></td><td></td><td class="s"> }</td></tr>
<tr><td class="h"><a name="1143"></a>1143</td><td></td><td></td><td></td><td></td><td class="s"> print "OK\n";</td></tr>
<tr><td class="h"><a name="1144"></a>1144</td><td></td><td></td><td></td><td></td><td class="s"></td></tr>
<tr><td class="h"><a name="1145"></a>1145</td><td></td><td></td><td></td><td></td><td class="s">The value of $side is</td></tr>
<tr><td class="h"><a name="1146"></a>1146</td><td></td><td></td><td></td><td></td><td class="s"></td></tr>
<tr><td class="h"><a name="1147"></a>1147</td><td></td><td></td><td></td><td></td><td class="s"> ['/', ['-', ['sqrt', ['+', 1, ['**', ['n', 1], 2]],</td></tr>
<tr><td class="h"><a name="1148"></a>1148</td><td></td><td></td><td></td><td></td><td class="s"> undef], 1], ['n', 1]]</td></tr>
<tr><td class="h"><a name="1149"></a>1149</td><td></td><td></td><td></td><td></td><td class="s"></td></tr>
<tr><td class="h"><a name="1150"></a>1150</td><td></td><td></td><td></td><td></td><td class="s">Note that while we obtained this value using a nice little script,</td></tr>
<tr><td class="h"><a name="1151"></a>1151</td><td></td><td></td><td></td><td></td><td class="s">there is no simple way to I<use> this value. In fact this value may</td></tr>
<tr><td class="h"><a name="1152"></a>1152</td><td></td><td></td><td></td><td></td><td class="s">be inspected in debugger (see L<perldebug>), but only if</td></tr>
<tr><td class="h"><a name="1153"></a>1153</td><td></td><td></td><td></td><td></td><td class="s">C<bareStringify> B<O>ption is set, and not via C<p> command.</td></tr>
<tr><td class="h"><a name="1154"></a>1154</td><td></td><td></td><td></td><td></td><td class="s"></td></tr>
<tr><td class="h"><a name="1155"></a>1155</td><td></td><td></td><td></td><td></td><td class="s">If one attempts to print this value, then the overloaded operator</td></tr>
<tr><td class="h"><a name="1156"></a>1156</td><td></td><td></td><td></td><td></td><td class="s">C<""> will be called, which will call C<nomethod> operator. The</td></tr>
<tr><td class="h"><a name="1157"></a>1157</td><td></td><td></td><td></td><td></td><td class="s">result of this operator will be stringified again, but this result is</td></tr>
<tr><td class="h"><a name="1158"></a>1158</td><td></td><td></td><td></td><td></td><td class="s">again of type C<symbolic>, which will lead to an infinite loop.</td></tr>
<tr><td class="h"><a name="1159"></a>1159</td><td></td><td></td><td></td><td></td><td class="s"></td></tr>
<tr><td class="h"><a name="1160"></a>1160</td><td></td><td></td><td></td><td></td><td class="s">Add a pretty-printer method to the module F<symbolic.pm>:</td></tr>
<tr><td class="h"><a name="1161"></a>1161</td><td></td><td></td><td></td><td></td><td class="s"></td></tr>
<tr><td class="h"><a name="1162"></a>1162</td><td></td><td></td><td></td><td></td><td class="s"> sub pretty {</td></tr>
<tr><td class="h"><a name="1163"></a>1163</td><td></td><td></td><td></td><td></td><td class="s"> my ($meth, $a, $b) = @{+shift};</td></tr>
<tr><td class="h"><a name="1164"></a>1164</td><td></td><td></td><td></td><td></td><td class="s"> $a = 'u' unless defined $a;</td></tr>
<tr><td class="h"><a name="1165"></a>1165</td><td></td><td></td><td></td><td></td><td class="s"> $b = 'u' unless defined $b;</td></tr>
<tr><td class="h"><a name="1166"></a>1166</td><td></td><td></td><td></td><td></td><td class="s"> $a = $a->pretty if ref $a;</td></tr>
<tr><td class="h"><a name="1167"></a>1167</td><td></td><td></td><td></td><td></td><td class="s"> $b = $b->pretty if ref $b;</td></tr>
<tr><td class="h"><a name="1168"></a>1168</td><td></td><td></td><td></td><td></td><td class="s"> "[$meth $a $b]";</td></tr>
<tr><td class="h"><a name="1169"></a>1169</td><td></td><td></td><td></td><td></td><td class="s"> }</td></tr>
<tr><td class="h"><a name="1170"></a>1170</td><td></td><td></td><td></td><td></td><td class="s"></td></tr>
<tr><td class="h"><a name="1171"></a>1171</td><td></td><td></td><td></td><td></td><td class="s">Now one can finish the script by</td></tr>
<tr><td class="h"><a name="1172"></a>1172</td><td></td><td></td><td></td><td></td><td class="s"></td></tr>
<tr><td class="h"><a name="1173"></a>1173</td><td></td><td></td><td></td><td></td><td class="s"> print "side = ", $side->pretty, "\n";</td></tr>
<tr><td class="h"><a name="1174"></a>1174</td><td></td><td></td><td></td><td></td><td class="s"></td></tr>
<tr><td class="h"><a name="1175"></a>1175</td><td></td><td></td><td></td><td></td><td class="s">The method C<pretty> is doing object-to-string conversion, so it</td></tr>
<tr><td class="h"><a name="1176"></a>1176</td><td></td><td></td><td></td><td></td><td class="s">is natural to overload the operator C<""> using this method. However,</td></tr>
<tr><td class="h"><a name="1177"></a>1177</td><td></td><td></td><td></td><td></td><td class="s">inside such a method it is not necessary to pretty-print the</td></tr>
<tr><td class="h"><a name="1178"></a>1178</td><td></td><td></td><td></td><td></td><td class="s">I<components> $a and $b of an object. In the above subroutine</td></tr>
<tr><td class="h"><a name="1179"></a>1179</td><td></td><td></td><td></td><td></td><td class="s">C<"[$meth $a $b]"> is a catenation of some strings and components $a</td></tr>
<tr><td class="h"><a name="1180"></a>1180</td><td></td><td></td><td></td><td></td><td class="s">and $b. If these components use overloading, the catenation operator</td></tr>
<tr><td class="h"><a name="1181"></a>1181</td><td></td><td></td><td></td><td></td><td class="s">will look for an overloaded operator C<.>; if not present, it will</td></tr>
<tr><td class="h"><a name="1182"></a>1182</td><td></td><td></td><td></td><td></td><td class="s">look for an overloaded operator C<"">. Thus it is enough to use</td></tr>
<tr><td class="h"><a name="1183"></a>1183</td><td></td><td></td><td></td><td></td><td class="s"></td></tr>
<tr><td class="h"><a name="1184"></a>1184</td><td></td><td></td><td></td><td></td><td class="s"> use overload nomethod => \&wrap, '""' => \&str;</td></tr>
<tr><td class="h"><a name="1185"></a>1185</td><td></td><td></td><td></td><td></td><td class="s"> sub str {</td></tr>
<tr><td class="h"><a name="1186"></a>1186</td><td></td><td></td><td></td><td></td><td class="s"> my ($meth, $a, $b) = @{+shift};</td></tr>
<tr><td class="h"><a name="1187"></a>1187</td><td></td><td></td><td></td><td></td><td class="s"> $a = 'u' unless defined $a;</td></tr>
<tr><td class="h"><a name="1188"></a>1188</td><td></td><td></td><td></td><td></td><td class="s"> $b = 'u' unless defined $b;</td></tr>
<tr><td class="h"><a name="1189"></a>1189</td><td></td><td></td><td></td><td></td><td class="s"> "[$meth $a $b]";</td></tr>
<tr><td class="h"><a name="1190"></a>1190</td><td></td><td></td><td></td><td></td><td class="s"> }</td></tr>
<tr><td class="h"><a name="1191"></a>1191</td><td></td><td></td><td></td><td></td><td class="s"></td></tr>
<tr><td class="h"><a name="1192"></a>1192</td><td></td><td></td><td></td><td></td><td class="s">Now one can change the last line of the script to</td></tr>
<tr><td class="h"><a name="1193"></a>1193</td><td></td><td></td><td></td><td></td><td class="s"></td></tr>
<tr><td class="h"><a name="1194"></a>1194</td><td></td><td></td><td></td><td></td><td class="s"> print "side = $side\n";</td></tr>
<tr><td class="h"><a name="1195"></a>1195</td><td></td><td></td><td></td><td></td><td class="s"></td></tr>
<tr><td class="h"><a name="1196"></a>1196</td><td></td><td></td><td></td><td></td><td class="s">which outputs</td></tr>
<tr><td class="h"><a name="1197"></a>1197</td><td></td><td></td><td></td><td></td><td class="s"></td></tr>
<tr><td class="h"><a name="1198"></a>1198</td><td></td><td></td><td></td><td></td><td class="s"> side = [/ [- [sqrt [+ 1 [** [n 1 u] 2]] u] 1] [n 1 u]]</td></tr>
<tr><td class="h"><a name="1199"></a>1199</td><td></td><td></td><td></td><td></td><td class="s"></td></tr>
<tr><td class="h"><a name="1200"></a>1200</td><td></td><td></td><td></td><td></td><td class="s">and one can inspect the value in debugger using all the possible</td></tr>
<tr><td class="h"><a name="1201"></a>1201</td><td></td><td></td><td></td><td></td><td class="s">methods.</td></tr>
<tr><td class="h"><a name="1202"></a>1202</td><td></td><td></td><td></td><td></td><td class="s"></td></tr>
<tr><td class="h"><a name="1203"></a>1203</td><td></td><td></td><td></td><td></td><td class="s">Something is still amiss: consider the loop variable $cnt of the</td></tr>
<tr><td class="h"><a name="1204"></a>1204</td><td></td><td></td><td></td><td></td><td class="s">script. It was a number, not an object. We cannot make this value of</td></tr>
<tr><td class="h"><a name="1205"></a>1205</td><td></td><td></td><td></td><td></td><td class="s">type C<symbolic>, since then the loop will not terminate.</td></tr>
<tr><td class="h"><a name="1206"></a>1206</td><td></td><td></td><td></td><td></td><td class="s"></td></tr>
<tr><td class="h"><a name="1207"></a>1207</td><td></td><td></td><td></td><td></td><td class="s">Indeed, to terminate the cycle, the $cnt should become false.</td></tr>
<tr><td class="h"><a name="1208"></a>1208</td><td></td><td></td><td></td><td></td><td class="s">However, the operator C<bool> for checking falsity is overloaded (this</td></tr>
<tr><td class="h"><a name="1209"></a>1209</td><td></td><td></td><td></td><td></td><td class="s">time via overloaded C<"">), and returns a long string, thus any object</td></tr>
<tr><td class="h"><a name="1210"></a>1210</td><td></td><td></td><td></td><td></td><td class="s">of type C<symbolic> is true. To overcome this, we need a way to</td></tr>
<tr><td class="h"><a name="1211"></a>1211</td><td></td><td></td><td></td><td></td><td class="s">compare an object to 0. In fact, it is easier to write a numeric</td></tr>
<tr><td class="h"><a name="1212"></a>1212</td><td></td><td></td><td></td><td></td><td class="s">conversion routine.</td></tr>
<tr><td class="h"><a name="1213"></a>1213</td><td></td><td></td><td></td><td></td><td class="s"></td></tr>
<tr><td class="h"><a name="1214"></a>1214</td><td></td><td></td><td></td><td></td><td class="s">Here is the text of F<symbolic.pm> with such a routine added (and</td></tr>
<tr><td class="h"><a name="1215"></a>1215</td><td></td><td></td><td></td><td></td><td class="s">slightly modified str()):</td></tr>
<tr><td class="h"><a name="1216"></a>1216</td><td></td><td></td><td></td><td></td><td class="s"></td></tr>
<tr><td class="h"><a name="1217"></a>1217</td><td></td><td></td><td></td><td></td><td class="s"> package symbolic; # Primitive symbolic calculator</td></tr>
<tr><td class="h"><a name="1218"></a>1218</td><td></td><td></td><td></td><td></td><td class="s"> use overload</td></tr>
<tr><td class="h"><a name="1219"></a>1219</td><td></td><td></td><td></td><td></td><td class="s"> nomethod => \&wrap, '""' => \&str, '0+' => \&num;</td></tr>
<tr><td class="h"><a name="1220"></a>1220</td><td></td><td></td><td></td><td></td><td class="s"></td></tr>
<tr><td class="h"><a name="1221"></a>1221</td><td></td><td></td><td></td><td></td><td class="s"> sub new { shift; bless ['n', @_] }</td></tr>
<tr><td class="h"><a name="1222"></a>1222</td><td></td><td></td><td></td><td></td><td class="s"> sub wrap {</td></tr>
<tr><td class="h"><a name="1223"></a>1223</td><td></td><td></td><td></td><td></td><td class="s"> my ($obj, $other, $inv, $meth) = @_;</td></tr>
<tr><td class="h"><a name="1224"></a>1224</td><td></td><td></td><td></td><td></td><td class="s"> ($obj, $other) = ($other, $obj) if $inv;</td></tr>
<tr><td class="h"><a name="1225"></a>1225</td><td></td><td></td><td></td><td></td><td class="s"> bless [$meth, $obj, $other];</td></tr>
<tr><td class="h"><a name="1226"></a>1226</td><td></td><td></td><td></td><td></td><td class="s"> }</td></tr>
<tr><td class="h"><a name="1227"></a>1227</td><td></td><td></td><td></td><td></td><td class="s"> sub str {</td></tr>
<tr><td class="h"><a name="1228"></a>1228</td><td></td><td></td><td></td><td></td><td class="s"> my ($meth, $a, $b) = @{+shift};</td></tr>
<tr><td class="h"><a name="1229"></a>1229</td><td></td><td></td><td></td><td></td><td class="s"> $a = 'u' unless defined $a;</td></tr>
<tr><td class="h"><a name="1230"></a>1230</td><td></td><td></td><td></td><td></td><td class="s"> if (defined $b) {</td></tr>
<tr><td class="h"><a name="1231"></a>1231</td><td></td><td></td><td></td><td></td><td class="s"> "[$meth $a $b]";</td></tr>
<tr><td class="h"><a name="1232"></a>1232</td><td></td><td></td><td></td><td></td><td class="s"> } else {</td></tr>
<tr><td class="h"><a name="1233"></a>1233</td><td></td><td></td><td></td><td></td><td class="s"> "[$meth $a]";</td></tr>
<tr><td class="h"><a name="1234"></a>1234</td><td></td><td></td><td></td><td></td><td class="s"> }</td></tr>
<tr><td class="h"><a name="1235"></a>1235</td><td></td><td></td><td></td><td></td><td class="s"> }</td></tr>
<tr><td class="h"><a name="1236"></a>1236</td><td></td><td></td><td></td><td></td><td class="s"> my %subr = ( n => sub {$_[0]},</td></tr>
<tr><td class="h"><a name="1237"></a>1237</td><td></td><td></td><td></td><td></td><td class="s"> sqrt => sub {sqrt $_[0]},</td></tr>
<tr><td class="h"><a name="1238"></a>1238</td><td></td><td></td><td></td><td></td><td class="s"> '-' => sub {shift() - shift()},</td></tr>
<tr><td class="h"><a name="1239"></a>1239</td><td></td><td></td><td></td><td></td><td class="s"> '+' => sub {shift() + shift()},</td></tr>
<tr><td class="h"><a name="1240"></a>1240</td><td></td><td></td><td></td><td></td><td class="s"> '/' => sub {shift() / shift()},</td></tr>
<tr><td class="h"><a name="1241"></a>1241</td><td></td><td></td><td></td><td></td><td class="s"> '*' => sub {shift() * shift()},</td></tr>
<tr><td class="h"><a name="1242"></a>1242</td><td></td><td></td><td></td><td></td><td class="s"> '**' => sub {shift() ** shift()},</td></tr>
<tr><td class="h"><a name="1243"></a>1243</td><td></td><td></td><td></td><td></td><td class="s"> );</td></tr>
<tr><td class="h"><a name="1244"></a>1244</td><td></td><td></td><td></td><td></td><td class="s"> sub num {</td></tr>
<tr><td class="h"><a name="1245"></a>1245</td><td></td><td></td><td></td><td></td><td class="s"> my ($meth, $a, $b) = @{+shift};</td></tr>
<tr><td class="h"><a name="1246"></a>1246</td><td></td><td></td><td></td><td></td><td class="s"> my $subr = $subr{$meth}</td></tr>
<tr><td class="h"><a name="1247"></a>1247</td><td></td><td></td><td></td><td></td><td class="s"> or die "Do not know how to ($meth) in symbolic";</td></tr>
<tr><td class="h"><a name="1248"></a>1248</td><td></td><td></td><td></td><td></td><td class="s"> $a = $a->num if ref $a eq __PACKAGE__;</td></tr>
<tr><td class="h"><a name="1249"></a>1249</td><td></td><td></td><td></td><td></td><td class="s"> $b = $b->num if ref $b eq __PACKAGE__;</td></tr>
<tr><td class="h"><a name="1250"></a>1250</td><td></td><td></td><td></td><td></td><td class="s"> $subr->($a,$b);</td></tr>
<tr><td class="h"><a name="1251"></a>1251</td><td></td><td></td><td></td><td></td><td class="s"> }</td></tr>
<tr><td class="h"><a name="1252"></a>1252</td><td></td><td></td><td></td><td></td><td class="s"></td></tr>
<tr><td class="h"><a name="1253"></a>1253</td><td></td><td></td><td></td><td></td><td class="s">All the work of numeric conversion is done in %subr and num(). Of</td></tr>
<tr><td class="h"><a name="1254"></a>1254</td><td></td><td></td><td></td><td></td><td class="s">course, %subr is not complete, it contains only operators used in the</td></tr>
<tr><td class="h"><a name="1255"></a>1255</td><td></td><td></td><td></td><td></td><td class="s">example below. Here is the extra-credit question: why do we need an</td></tr>
<tr><td class="h"><a name="1256"></a>1256</td><td></td><td></td><td></td><td></td><td class="s">explicit recursion in num()? (Answer is at the end of this section.)</td></tr>
<tr><td class="h"><a name="1257"></a>1257</td><td></td><td></td><td></td><td></td><td class="s"></td></tr>
<tr><td class="h"><a name="1258"></a>1258</td><td></td><td></td><td></td><td></td><td class="s">Use this module like this:</td></tr>
<tr><td class="h"><a name="1259"></a>1259</td><td></td><td></td><td></td><td></td><td class="s"></td></tr>
<tr><td class="h"><a name="1260"></a>1260</td><td></td><td></td><td></td><td></td><td class="s"> require symbolic;</td></tr>
<tr><td class="h"><a name="1261"></a>1261</td><td></td><td></td><td></td><td></td><td class="s"> my $iter = symbolic->new(2); # 16-gon</td></tr>
<tr><td class="h"><a name="1262"></a>1262</td><td></td><td></td><td></td><td></td><td class="s"> my $side = symbolic->new(1);</td></tr>
<tr><td class="h"><a name="1263"></a>1263</td><td></td><td></td><td></td><td></td><td class="s"> my $cnt = $iter;</td></tr>
<tr><td class="h"><a name="1264"></a>1264</td><td></td><td></td><td></td><td></td><td class="s"></td></tr>
<tr><td class="h"><a name="1265"></a>1265</td><td></td><td></td><td></td><td></td><td class="s"> while ($cnt) {</td></tr>
<tr><td class="h"><a name="1266"></a>1266</td><td></td><td></td><td></td><td></td><td class="s"> $cnt = $cnt - 1; # Mutator `--' not implemented</td></tr>
<tr><td class="h"><a name="1267"></a>1267</td><td></td><td></td><td></td><td></td><td class="s"> $side = (sqrt(1 + $side**2) - 1)/$side;</td></tr>
<tr><td class="h"><a name="1268"></a>1268</td><td></td><td></td><td></td><td></td><td class="s"> }</td></tr>
<tr><td class="h"><a name="1269"></a>1269</td><td></td><td></td><td></td><td></td><td class="s"> printf "%s=%f\n", $side, $side;</td></tr>
<tr><td class="h"><a name="1270"></a>1270</td><td></td><td></td><td></td><td></td><td class="s"> printf "pi=%f\n", $side*(2**($iter+2));</td></tr>
<tr><td class="h"><a name="1271"></a>1271</td><td></td><td></td><td></td><td></td><td class="s"></td></tr>
<tr><td class="h"><a name="1272"></a>1272</td><td></td><td></td><td></td><td></td><td class="s">It prints (without so many line breaks)</td></tr>
<tr><td class="h"><a name="1273"></a>1273</td><td></td><td></td><td></td><td></td><td class="s"></td></tr>
<tr><td class="h"><a name="1274"></a>1274</td><td></td><td></td><td></td><td></td><td class="s"> [/ [- [sqrt [+ 1 [** [/ [- [sqrt [+ 1 [** [n 1] 2]]] 1]</td></tr>
<tr><td class="h"><a name="1275"></a>1275</td><td></td><td></td><td></td><td></td><td class="s"> [n 1]] 2]]] 1]</td></tr>
<tr><td class="h"><a name="1276"></a>1276</td><td></td><td></td><td></td><td></td><td class="s"> [/ [- [sqrt [+ 1 [** [n 1] 2]]] 1] [n 1]]]=0.198912</td></tr>
<tr><td class="h"><a name="1277"></a>1277</td><td></td><td></td><td></td><td></td><td class="s"> pi=3.182598</td></tr>
<tr><td class="h"><a name="1278"></a>1278</td><td></td><td></td><td></td><td></td><td class="s"></td></tr>
<tr><td class="h"><a name="1279"></a>1279</td><td></td><td></td><td></td><td></td><td class="s">The above module is very primitive. It does not implement</td></tr>
<tr><td class="h"><a name="1280"></a>1280</td><td></td><td></td><td></td><td></td><td class="s">mutator methods (C<++>, C<-=> and so on), does not do deep copying</td></tr>
<tr><td class="h"><a name="1281"></a>1281</td><td></td><td></td><td></td><td></td><td class="s">(not required without mutators!), and implements only those arithmetic</td></tr>
<tr><td class="h"><a name="1282"></a>1282</td><td></td><td></td><td></td><td></td><td class="s">operations which are used in the example.</td></tr>
<tr><td class="h"><a name="1283"></a>1283</td><td></td><td></td><td></td><td></td><td class="s"></td></tr>
<tr><td class="h"><a name="1284"></a>1284</td><td></td><td></td><td></td><td></td><td class="s">To implement most arithmetic operations is easy; one should just use</td></tr>
<tr><td class="h"><a name="1285"></a>1285</td><td></td><td></td><td></td><td></td><td class="s">the tables of operations, and change the code which fills %subr to</td></tr>
<tr><td class="h"><a name="1286"></a>1286</td><td></td><td></td><td></td><td></td><td class="s"></td></tr>
<tr><td class="h"><a name="1287"></a>1287</td><td></td><td></td><td></td><td></td><td class="s"> my %subr = ( 'n' => sub {$_[0]} );</td></tr>
<tr><td class="h"><a name="1288"></a>1288</td><td></td><td></td><td></td><td></td><td class="s"> foreach my $op (split " ", $overload::ops{with_assign}) {</td></tr>
<tr><td class="h"><a name="1289"></a>1289</td><td></td><td></td><td></td><td></td><td class="s"> $subr{$op} = $subr{"$op="} = eval "sub {shift() $op shift()}";</td></tr>
<tr><td class="h"><a name="1290"></a>1290</td><td></td><td></td><td></td><td></td><td class="s"> }</td></tr>
<tr><td class="h"><a name="1291"></a>1291</td><td></td><td></td><td></td><td></td><td class="s"> my @bins = qw(binary 3way_comparison num_comparison str_comparison);</td></tr>
<tr><td class="h"><a name="1292"></a>1292</td><td></td><td></td><td></td><td></td><td class="s"> foreach my $op (split " ", "@overload::ops{ @bins }") {</td></tr>
<tr><td class="h"><a name="1293"></a>1293</td><td></td><td></td><td></td><td></td><td class="s"> $subr{$op} = eval "sub {shift() $op shift()}";</td></tr>
<tr><td class="h"><a name="1294"></a>1294</td><td></td><td></td><td></td><td></td><td class="s"> }</td></tr>
<tr><td class="h"><a name="1295"></a>1295</td><td></td><td></td><td></td><td></td><td class="s"> foreach my $op (split " ", "@overload::ops{qw(unary func)}") {</td></tr>
<tr><td class="h"><a name="1296"></a>1296</td><td></td><td></td><td></td><td></td><td class="s"> print "defining `$op'\n";</td></tr>
<tr><td class="h"><a name="1297"></a>1297</td><td></td><td></td><td></td><td></td><td class="s"> $subr{$op} = eval "sub {$op shift()}";</td></tr>
<tr><td class="h"><a name="1298"></a>1298</td><td></td><td></td><td></td><td></td><td class="s"> }</td></tr>
<tr><td class="h"><a name="1299"></a>1299</td><td></td><td></td><td></td><td></td><td class="s"></td></tr>
<tr><td class="h"><a name="1300"></a>1300</td><td></td><td></td><td></td><td></td><td class="s">Due to L<Calling Conventions for Mutators>, we do not need anything</td></tr>
<tr><td class="h"><a name="1301"></a>1301</td><td></td><td></td><td></td><td></td><td class="s">special to make C<+=> and friends work, except filling C<+=> entry of</td></tr>
<tr><td class="h"><a name="1302"></a>1302</td><td></td><td></td><td></td><td></td><td class="s">%subr, and defining a copy constructor (needed since Perl has no</td></tr>
<tr><td class="h"><a name="1303"></a>1303</td><td></td><td></td><td></td><td></td><td class="s">way to know that the implementation of C<'+='> does not mutate</td></tr>
<tr><td class="h"><a name="1304"></a>1304</td><td></td><td></td><td></td><td></td><td class="s">the argument, compare L<Copy Constructor>).</td></tr>
<tr><td class="h"><a name="1305"></a>1305</td><td></td><td></td><td></td><td></td><td class="s"></td></tr>
<tr><td class="h"><a name="1306"></a>1306</td><td></td><td></td><td></td><td></td><td class="s">To implement a copy constructor, add C<< '=' => \&cpy >> to C<use overload></td></tr>
<tr><td class="h"><a name="1307"></a>1307</td><td></td><td></td><td></td><td></td><td class="s">line, and code (this code assumes that mutators change things one level</td></tr>
<tr><td class="h"><a name="1308"></a>1308</td><td></td><td></td><td></td><td></td><td class="s">deep only, so recursive copying is not needed):</td></tr>
<tr><td class="h"><a name="1309"></a>1309</td><td></td><td></td><td></td><td></td><td class="s"></td></tr>
<tr><td class="h"><a name="1310"></a>1310</td><td></td><td></td><td></td><td></td><td class="s"> sub cpy {</td></tr>
<tr><td class="h"><a name="1311"></a>1311</td><td></td><td></td><td></td><td></td><td class="s"> my $self = shift;</td></tr>
<tr><td class="h"><a name="1312"></a>1312</td><td></td><td></td><td></td><td></td><td class="s"> bless [@$self], ref $self;</td></tr>
<tr><td class="h"><a name="1313"></a>1313</td><td></td><td></td><td></td><td></td><td class="s"> }</td></tr>
<tr><td class="h"><a name="1314"></a>1314</td><td></td><td></td><td></td><td></td><td class="s"></td></tr>
<tr><td class="h"><a name="1315"></a>1315</td><td></td><td></td><td></td><td></td><td class="s">To make C<++> and C<--> work, we need to implement actual mutators,</td></tr>
<tr><td class="h"><a name="1316"></a>1316</td><td></td><td></td><td></td><td></td><td class="s">either directly, or in C<nomethod>. We continue to do things inside</td></tr>
<tr><td class="h"><a name="1317"></a>1317</td><td></td><td></td><td></td><td></td><td class="s">C<nomethod>, thus add</td></tr>
<tr><td class="h"><a name="1318"></a>1318</td><td></td><td></td><td></td><td></td><td class="s"></td></tr>
<tr><td class="h"><a name="1319"></a>1319</td><td></td><td></td><td></td><td></td><td class="s"> if ($meth eq '++' or $meth eq '--') {</td></tr>
<tr><td class="h"><a name="1320"></a>1320</td><td></td><td></td><td></td><td></td><td class="s"> @$obj = ($meth, (bless [@$obj]), 1); # Avoid circular reference</td></tr>
<tr><td class="h"><a name="1321"></a>1321</td><td></td><td></td><td></td><td></td><td class="s"> return $obj;</td></tr>
<tr><td class="h"><a name="1322"></a>1322</td><td></td><td></td><td></td><td></td><td class="s"> }</td></tr>
<tr><td class="h"><a name="1323"></a>1323</td><td></td><td></td><td></td><td></td><td class="s"></td></tr>
<tr><td class="h"><a name="1324"></a>1324</td><td></td><td></td><td></td><td></td><td class="s">after the first line of wrap(). This is not a most effective</td></tr>
<tr><td class="h"><a name="1325"></a>1325</td><td></td><td></td><td></td><td></td><td class="s">implementation, one may consider</td></tr>
<tr><td class="h"><a name="1326"></a>1326</td><td></td><td></td><td></td><td></td><td class="s"></td></tr>
<tr><td class="h"><a name="1327"></a>1327</td><td></td><td></td><td></td><td></td><td class="s"> sub inc { $_[0] = bless ['++', shift, 1]; }</td></tr>
<tr><td class="h"><a name="1328"></a>1328</td><td></td><td></td><td></td><td></td><td class="s"></td></tr>
<tr><td class="h"><a name="1329"></a>1329</td><td></td><td></td><td></td><td></td><td class="s">instead.</td></tr>
<tr><td class="h"><a name="1330"></a>1330</td><td></td><td></td><td></td><td></td><td class="s"></td></tr>
<tr><td class="h"><a name="1331"></a>1331</td><td></td><td></td><td></td><td></td><td class="s">As a final remark, note that one can fill %subr by</td></tr>
<tr><td class="h"><a name="1332"></a>1332</td><td></td><td></td><td></td><td></td><td class="s"></td></tr>
<tr><td class="h"><a name="1333"></a>1333</td><td></td><td></td><td></td><td></td><td class="s"> my %subr = ( 'n' => sub {$_[0]} );</td></tr>
<tr><td class="h"><a name="1334"></a>1334</td><td></td><td></td><td></td><td></td><td class="s"> foreach my $op (split " ", $overload::ops{with_assign}) {</td></tr>
<tr><td class="h"><a name="1335"></a>1335</td><td></td><td></td><td></td><td></td><td class="s"> $subr{$op} = $subr{"$op="} = eval "sub {shift() $op shift()}";</td></tr>
<tr><td class="h"><a name="1336"></a>1336</td><td></td><td></td><td></td><td></td><td class="s"> }</td></tr>
<tr><td class="h"><a name="1337"></a>1337</td><td></td><td></td><td></td><td></td><td class="s"> my @bins = qw(binary 3way_comparison num_comparison str_comparison);</td></tr>
<tr><td class="h"><a name="1338"></a>1338</td><td></td><td></td><td></td><td></td><td class="s"> foreach my $op (split " ", "@overload::ops{ @bins }") {</td></tr>
<tr><td class="h"><a name="1339"></a>1339</td><td></td><td></td><td></td><td></td><td class="s"> $subr{$op} = eval "sub {shift() $op shift()}";</td></tr>
<tr><td class="h"><a name="1340"></a>1340</td><td></td><td></td><td></td><td></td><td class="s"> }</td></tr>
<tr><td class="h"><a name="1341"></a>1341</td><td></td><td></td><td></td><td></td><td class="s"> foreach my $op (split " ", "@overload::ops{qw(unary func)}") {</td></tr>
<tr><td class="h"><a name="1342"></a>1342</td><td></td><td></td><td></td><td></td><td class="s"> $subr{$op} = eval "sub {$op shift()}";</td></tr>
<tr><td class="h"><a name="1343"></a>1343</td><td></td><td></td><td></td><td></td><td class="s"> }</td></tr>
<tr><td class="h"><a name="1344"></a>1344</td><td></td><td></td><td></td><td></td><td class="s"> $subr{'++'} = $subr{'+'};</td></tr>
<tr><td class="h"><a name="1345"></a>1345</td><td></td><td></td><td></td><td></td><td class="s"> $subr{'--'} = $subr{'-'};</td></tr>
<tr><td class="h"><a name="1346"></a>1346</td><td></td><td></td><td></td><td></td><td class="s"></td></tr>
<tr><td class="h"><a name="1347"></a>1347</td><td></td><td></td><td></td><td></td><td class="s">This finishes implementation of a primitive symbolic calculator in</td></tr>
<tr><td class="h"><a name="1348"></a>1348</td><td></td><td></td><td></td><td></td><td class="s">50 lines of Perl code. Since the numeric values of subexpressions</td></tr>
<tr><td class="h"><a name="1349"></a>1349</td><td></td><td></td><td></td><td></td><td class="s">are not cached, the calculator is very slow.</td></tr>
<tr><td class="h"><a name="1350"></a>1350</td><td></td><td></td><td></td><td></td><td class="s"></td></tr>
<tr><td class="h"><a name="1351"></a>1351</td><td></td><td></td><td></td><td></td><td class="s">Here is the answer for the exercise: In the case of str(), we need no</td></tr>
<tr><td class="h"><a name="1352"></a>1352</td><td></td><td></td><td></td><td></td><td class="s">explicit recursion since the overloaded C<.>-operator will fall back</td></tr>
<tr><td class="h"><a name="1353"></a>1353</td><td></td><td></td><td></td><td></td><td class="s">to an existing overloaded operator C<"">. Overloaded arithmetic</td></tr>
<tr><td class="h"><a name="1354"></a>1354</td><td></td><td></td><td></td><td></td><td class="s">operators I<do not> fall back to numeric conversion if C<fallback> is</td></tr>
<tr><td class="h"><a name="1355"></a>1355</td><td></td><td></td><td></td><td></td><td class="s">not explicitly requested. Thus without an explicit recursion num()</td></tr>
<tr><td class="h"><a name="1356"></a>1356</td><td></td><td></td><td></td><td></td><td class="s">would convert C<['+', $a, $b]> to C<$a + $b>, which would just rebuild</td></tr>
<tr><td class="h"><a name="1357"></a>1357</td><td></td><td></td><td></td><td></td><td class="s">the argument of num().</td></tr>
<tr><td class="h"><a name="1358"></a>1358</td><td></td><td></td><td></td><td></td><td class="s"></td></tr>
<tr><td class="h"><a name="1359"></a>1359</td><td></td><td></td><td></td><td></td><td class="s">If you wonder why defaults for conversion are different for str() and</td></tr>
<tr><td class="h"><a name="1360"></a>1360</td><td></td><td></td><td></td><td></td><td class="s">num(), note how easy it was to write the symbolic calculator. This</td></tr>
<tr><td class="h"><a name="1361"></a>1361</td><td></td><td></td><td></td><td></td><td class="s">simplicity is due to an appropriate choice of defaults. One extra</td></tr>
<tr><td class="h"><a name="1362"></a>1362</td><td></td><td></td><td></td><td></td><td class="s">note: due to the explicit recursion num() is more fragile than sym():</td></tr>
<tr><td class="h"><a name="1363"></a>1363</td><td></td><td></td><td></td><td></td><td class="s">we need to explicitly check for the type of $a and $b. If components</td></tr>
<tr><td class="h"><a name="1364"></a>1364</td><td></td><td></td><td></td><td></td><td class="s">$a and $b happen to be of some related type, this may lead to problems.</td></tr>
<tr><td class="h"><a name="1365"></a>1365</td><td></td><td></td><td></td><td></td><td class="s"></td></tr>
<tr><td class="h"><a name="1366"></a>1366</td><td></td><td></td><td></td><td></td><td class="s">=head2 I<Really> symbolic calculator</td></tr>
<tr><td class="h"><a name="1367"></a>1367</td><td></td><td></td><td></td><td></td><td class="s"></td></tr>
<tr><td class="h"><a name="1368"></a>1368</td><td></td><td></td><td></td><td></td><td class="s">One may wonder why we call the above calculator symbolic. The reason</td></tr>
<tr><td class="h"><a name="1369"></a>1369</td><td></td><td></td><td></td><td></td><td class="s">is that the actual calculation of the value of expression is postponed</td></tr>
<tr><td class="h"><a name="1370"></a>1370</td><td></td><td></td><td></td><td></td><td class="s">until the value is I<used>.</td></tr>
<tr><td class="h"><a name="1371"></a>1371</td><td></td><td></td><td></td><td></td><td class="s"></td></tr>
<tr><td class="h"><a name="1372"></a>1372</td><td></td><td></td><td></td><td></td><td class="s">To see it in action, add a method</td></tr>
<tr><td class="h"><a name="1373"></a>1373</td><td></td><td></td><td></td><td></td><td class="s"></td></tr>
<tr><td class="h"><a name="1374"></a>1374</td><td></td><td></td><td></td><td></td><td class="s"> sub STORE {</td></tr>
<tr><td class="h"><a name="1375"></a>1375</td><td></td><td></td><td></td><td></td><td class="s"> my $obj = shift;</td></tr>
<tr><td class="h"><a name="1376"></a>1376</td><td></td><td></td><td></td><td></td><td class="s"> $#$obj = 1;</td></tr>
<tr><td class="h"><a name="1377"></a>1377</td><td></td><td></td><td></td><td></td><td class="s"> @$obj->[0,1] = ('=', shift);</td></tr>
<tr><td class="h"><a name="1378"></a>1378</td><td></td><td></td><td></td><td></td><td class="s"> }</td></tr>
<tr><td class="h"><a name="1379"></a>1379</td><td></td><td></td><td></td><td></td><td class="s"></td></tr>
<tr><td class="h"><a name="1380"></a>1380</td><td></td><td></td><td></td><td></td><td class="s">to the package C<symbolic>. After this change one can do</td></tr>
<tr><td class="h"><a name="1381"></a>1381</td><td></td><td></td><td></td><td></td><td class="s"></td></tr>
<tr><td class="h"><a name="1382"></a>1382</td><td></td><td></td><td></td><td></td><td class="s"> my $a = symbolic->new(3);</td></tr>
<tr><td class="h"><a name="1383"></a>1383</td><td></td><td></td><td></td><td></td><td class="s"> my $b = symbolic->new(4);</td></tr>
<tr><td class="h"><a name="1384"></a>1384</td><td></td><td></td><td></td><td></td><td class="s"> my $c = sqrt($a**2 + $b**2);</td></tr>
<tr><td class="h"><a name="1385"></a>1385</td><td></td><td></td><td></td><td></td><td class="s"></td></tr>
<tr><td class="h"><a name="1386"></a>1386</td><td></td><td></td><td></td><td></td><td class="s">and the numeric value of $c becomes 5. However, after calling</td></tr>
<tr><td class="h"><a name="1387"></a>1387</td><td></td><td></td><td></td><td></td><td class="s"></td></tr>
<tr><td class="h"><a name="1388"></a>1388</td><td></td><td></td><td></td><td></td><td class="s"> $a->STORE(12); $b->STORE(5);</td></tr>
<tr><td class="h"><a name="1389"></a>1389</td><td></td><td></td><td></td><td></td><td class="s"></td></tr>
<tr><td class="h"><a name="1390"></a>1390</td><td></td><td></td><td></td><td></td><td class="s">the numeric value of $c becomes 13. There is no doubt now that the module</td></tr>
<tr><td class="h"><a name="1391"></a>1391</td><td></td><td></td><td></td><td></td><td class="s">symbolic provides a I<symbolic> calculator indeed.</td></tr>
<tr><td class="h"><a name="1392"></a>1392</td><td></td><td></td><td></td><td></td><td class="s"></td></tr>
<tr><td class="h"><a name="1393"></a>1393</td><td></td><td></td><td></td><td></td><td class="s">To hide the rough edges under the hood, provide a tie()d interface to the</td></tr>
<tr><td class="h"><a name="1394"></a>1394</td><td></td><td></td><td></td><td></td><td class="s">package C<symbolic> (compare with L<Metaphor clash>). Add methods</td></tr>
<tr><td class="h"><a name="1395"></a>1395</td><td></td><td></td><td></td><td></td><td class="s"></td></tr>
<tr><td class="h"><a name="1396"></a>1396</td><td></td><td></td><td></td><td></td><td class="s"> sub TIESCALAR { my $pack = shift; $pack->new(@_) }</td></tr>
<tr><td class="h"><a name="1397"></a>1397</td><td></td><td></td><td></td><td></td><td class="s"> sub FETCH { shift }</td></tr>
<tr><td class="h"><a name="1398"></a>1398</td><td></td><td></td><td></td><td></td><td class="s"> sub nop { } # Around a bug</td></tr>
<tr><td class="h"><a name="1399"></a>1399</td><td></td><td></td><td></td><td></td><td class="s"></td></tr>
<tr><td class="h"><a name="1400"></a>1400</td><td></td><td></td><td></td><td></td><td class="s">(the bug is described in L<"BUGS">). One can use this new interface as</td></tr>
<tr><td class="h"><a name="1401"></a>1401</td><td></td><td></td><td></td><td></td><td class="s"></td></tr>
<tr><td class="h"><a name="1402"></a>1402</td><td></td><td></td><td></td><td></td><td class="s"> tie $a, 'symbolic', 3;</td></tr>
<tr><td class="h"><a name="1403"></a>1403</td><td></td><td></td><td></td><td></td><td class="s"> tie $b, 'symbolic', 4;</td></tr>
<tr><td class="h"><a name="1404"></a>1404</td><td></td><td></td><td></td><td></td><td class="s"> $a->nop; $b->nop; # Around a bug</td></tr>
<tr><td class="h"><a name="1405"></a>1405</td><td></td><td></td><td></td><td></td><td class="s"></td></tr>
<tr><td class="h"><a name="1406"></a>1406</td><td></td><td></td><td></td><td></td><td class="s"> my $c = sqrt($a**2 + $b**2);</td></tr>
<tr><td class="h"><a name="1407"></a>1407</td><td></td><td></td><td></td><td></td><td class="s"></td></tr>
<tr><td class="h"><a name="1408"></a>1408</td><td></td><td></td><td></td><td></td><td class="s">Now numeric value of $c is 5. After C<$a = 12; $b = 5> the numeric value</td></tr>
<tr><td class="h"><a name="1409"></a>1409</td><td></td><td></td><td></td><td></td><td class="s">of $c becomes 13. To insulate the user of the module add a method</td></tr>
<tr><td class="h"><a name="1410"></a>1410</td><td></td><td></td><td></td><td></td><td class="s"></td></tr>
<tr><td class="h"><a name="1411"></a>1411</td><td></td><td></td><td></td><td></td><td class="s"> sub vars { my $p = shift; tie($_, $p), $_->nop foreach @_; }</td></tr>
<tr><td class="h"><a name="1412"></a>1412</td><td></td><td></td><td></td><td></td><td class="s"></td></tr>
<tr><td class="h"><a name="1413"></a>1413</td><td></td><td></td><td></td><td></td><td class="s">Now</td></tr>
<tr><td class="h"><a name="1414"></a>1414</td><td></td><td></td><td></td><td></td><td class="s"></td></tr>
<tr><td class="h"><a name="1415"></a>1415</td><td></td><td></td><td></td><td></td><td class="s"> my ($a, $b);</td></tr>
<tr><td class="h"><a name="1416"></a>1416</td><td></td><td></td><td></td><td></td><td class="s"> symbolic->vars($a, $b);</td></tr>
<tr><td class="h"><a name="1417"></a>1417</td><td></td><td></td><td></td><td></td><td class="s"> my $c = sqrt($a**2 + $b**2);</td></tr>
<tr><td class="h"><a name="1418"></a>1418</td><td></td><td></td><td></td><td></td><td class="s"></td></tr>
<tr><td class="h"><a name="1419"></a>1419</td><td></td><td></td><td></td><td></td><td class="s"> $a = 3; $b = 4;</td></tr>
<tr><td class="h"><a name="1420"></a>1420</td><td></td><td></td><td></td><td></td><td class="s"> printf "c5 %s=%f\n", $c, $c;</td></tr>
<tr><td class="h"><a name="1421"></a>1421</td><td></td><td></td><td></td><td></td><td class="s"></td></tr>
<tr><td class="h"><a name="1422"></a>1422</td><td></td><td></td><td></td><td></td><td class="s"> $a = 12; $b = 5;</td></tr>
<tr><td class="h"><a name="1423"></a>1423</td><td></td><td></td><td></td><td></td><td class="s"> printf "c13 %s=%f\n", $c, $c;</td></tr>
<tr><td class="h"><a name="1424"></a>1424</td><td></td><td></td><td></td><td></td><td class="s"></td></tr>
<tr><td class="h"><a name="1425"></a>1425</td><td></td><td></td><td></td><td></td><td class="s">shows that the numeric value of $c follows changes to the values of $a</td></tr>
<tr><td class="h"><a name="1426"></a>1426</td><td></td><td></td><td></td><td></td><td class="s">and $b.</td></tr>
<tr><td class="h"><a name="1427"></a>1427</td><td></td><td></td><td></td><td></td><td class="s"></td></tr>
<tr><td class="h"><a name="1428"></a>1428</td><td></td><td></td><td></td><td></td><td class="s">=head1 AUTHOR</td></tr>
<tr><td class="h"><a name="1429"></a>1429</td><td></td><td></td><td></td><td></td><td class="s"></td></tr>
<tr><td class="h"><a name="1430"></a>1430</td><td></td><td></td><td></td><td></td><td class="s">Ilya Zakharevich E<lt>F<ilya@math.mps.ohio-state.edu>E<gt>.</td></tr>
<tr><td class="h"><a name="1431"></a>1431</td><td></td><td></td><td></td><td></td><td class="s"></td></tr>
<tr><td class="h"><a name="1432"></a>1432</td><td></td><td></td><td></td><td></td><td class="s">=head1 SEE ALSO</td></tr>
<tr><td class="h"><a name="1433"></a>1433</td><td></td><td></td><td></td><td></td><td class="s"></td></tr>
<tr><td class="h"><a name="1434"></a>1434</td><td></td><td></td><td></td><td></td><td class="s">The L<overloading> pragma can be used to enable or disable overloaded</td></tr>
<tr><td class="h"><a name="1435"></a>1435</td><td></td><td></td><td></td><td></td><td class="s">operations within a lexical scope.</td></tr>
<tr><td class="h"><a name="1436"></a>1436</td><td></td><td></td><td></td><td></td><td class="s"></td></tr>
<tr><td class="h"><a name="1437"></a>1437</td><td></td><td></td><td></td><td></td><td class="s">=head1 DIAGNOSTICS</td></tr>
<tr><td class="h"><a name="1438"></a>1438</td><td></td><td></td><td></td><td></td><td class="s"></td></tr>
<tr><td class="h"><a name="1439"></a>1439</td><td></td><td></td><td></td><td></td><td class="s">When Perl is run with the B<-Do> switch or its equivalent, overloading</td></tr>
<tr><td class="h"><a name="1440"></a>1440</td><td></td><td></td><td></td><td></td><td class="s">induces diagnostic messages.</td></tr>
<tr><td class="h"><a name="1441"></a>1441</td><td></td><td></td><td></td><td></td><td class="s"></td></tr>
<tr><td class="h"><a name="1442"></a>1442</td><td></td><td></td><td></td><td></td><td class="s">Using the C<m> command of Perl debugger (see L<perldebug>) one can</td></tr>
<tr><td class="h"><a name="1443"></a>1443</td><td></td><td></td><td></td><td></td><td class="s">deduce which operations are overloaded (and which ancestor triggers</td></tr>
<tr><td class="h"><a name="1444"></a>1444</td><td></td><td></td><td></td><td></td><td class="s">this overloading). Say, if C<eq> is overloaded, then the method C<(eq></td></tr>
<tr><td class="h"><a name="1445"></a>1445</td><td></td><td></td><td></td><td></td><td class="s">is shown by debugger. The method C<()> corresponds to the C<fallback></td></tr>
<tr><td class="h"><a name="1446"></a>1446</td><td></td><td></td><td></td><td></td><td class="s">key (in fact a presence of this method shows that this package has</td></tr>
<tr><td class="h"><a name="1447"></a>1447</td><td></td><td></td><td></td><td></td><td class="s">overloading enabled, and it is what is used by the C<Overloaded></td></tr>
<tr><td class="h"><a name="1448"></a>1448</td><td></td><td></td><td></td><td></td><td class="s">function of module C<overload>).</td></tr>
<tr><td class="h"><a name="1449"></a>1449</td><td></td><td></td><td></td><td></td><td class="s"></td></tr>
<tr><td class="h"><a name="1450"></a>1450</td><td></td><td></td><td></td><td></td><td class="s">The module might issue the following warnings:</td></tr>
<tr><td class="h"><a name="1451"></a>1451</td><td></td><td></td><td></td><td></td><td class="s"></td></tr>
<tr><td class="h"><a name="1452"></a>1452</td><td></td><td></td><td></td><td></td><td class="s">=over 4</td></tr>
<tr><td class="h"><a name="1453"></a>1453</td><td></td><td></td><td></td><td></td><td class="s"></td></tr>
<tr><td class="h"><a name="1454"></a>1454</td><td></td><td></td><td></td><td></td><td class="s">=item Odd number of arguments for overload::constant</td></tr>
<tr><td class="h"><a name="1455"></a>1455</td><td></td><td></td><td></td><td></td><td class="s"></td></tr>
<tr><td class="h"><a name="1456"></a>1456</td><td></td><td></td><td></td><td></td><td class="s">(W) The call to overload::constant contained an odd number of arguments.</td></tr>
<tr><td class="h"><a name="1457"></a>1457</td><td></td><td></td><td></td><td></td><td class="s">The arguments should come in pairs.</td></tr>
<tr><td class="h"><a name="1458"></a>1458</td><td></td><td></td><td></td><td></td><td class="s"></td></tr>
<tr><td class="h"><a name="1459"></a>1459</td><td></td><td></td><td></td><td></td><td class="s">=item `%s' is not an overloadable type</td></tr>
<tr><td class="h"><a name="1460"></a>1460</td><td></td><td></td><td></td><td></td><td class="s"></td></tr>
<tr><td class="h"><a name="1461"></a>1461</td><td></td><td></td><td></td><td></td><td class="s">(W) You tried to overload a constant type the overload package is unaware of.</td></tr>
<tr><td class="h"><a name="1462"></a>1462</td><td></td><td></td><td></td><td></td><td class="s"></td></tr>
<tr><td class="h"><a name="1463"></a>1463</td><td></td><td></td><td></td><td></td><td class="s">=item `%s' is not a code reference</td></tr>
<tr><td class="h"><a name="1464"></a>1464</td><td></td><td></td><td></td><td></td><td class="s"></td></tr>
<tr><td class="h"><a name="1465"></a>1465</td><td></td><td></td><td></td><td></td><td class="s">(W) The second (fourth, sixth, ...) argument of overload::constant needs</td></tr>
<tr><td class="h"><a name="1466"></a>1466</td><td></td><td></td><td></td><td></td><td class="s">to be a code reference. Either an anonymous subroutine, or a reference</td></tr>
<tr><td class="h"><a name="1467"></a>1467</td><td></td><td></td><td></td><td></td><td class="s">to a subroutine.</td></tr>
<tr><td class="h"><a name="1468"></a>1468</td><td></td><td></td><td></td><td></td><td class="s"></td></tr>
<tr><td class="h"><a name="1469"></a>1469</td><td></td><td></td><td></td><td></td><td class="s">=back</td></tr>
<tr><td class="h"><a name="1470"></a>1470</td><td></td><td></td><td></td><td></td><td class="s"></td></tr>
<tr><td class="h"><a name="1471"></a>1471</td><td></td><td></td><td></td><td></td><td class="s">=head1 BUGS</td></tr>
<tr><td class="h"><a name="1472"></a>1472</td><td></td><td></td><td></td><td></td><td class="s"></td></tr>
<tr><td class="h"><a name="1473"></a>1473</td><td></td><td></td><td></td><td></td><td class="s">Because it is used for overloading, the per-package hash %OVERLOAD now</td></tr>
<tr><td class="h"><a name="1474"></a>1474</td><td></td><td></td><td></td><td></td><td class="s">has a special meaning in Perl. The symbol table is filled with names</td></tr>
<tr><td class="h"><a name="1475"></a>1475</td><td></td><td></td><td></td><td></td><td class="s">looking like line-noise.</td></tr>
<tr><td class="h"><a name="1476"></a>1476</td><td></td><td></td><td></td><td></td><td class="s"></td></tr>
<tr><td class="h"><a name="1477"></a>1477</td><td></td><td></td><td></td><td></td><td class="s">For the purpose of inheritance every overloaded package behaves as if</td></tr>
<tr><td class="h"><a name="1478"></a>1478</td><td></td><td></td><td></td><td></td><td class="s">C<fallback> is present (possibly undefined). This may create</td></tr>
<tr><td class="h"><a name="1479"></a>1479</td><td></td><td></td><td></td><td></td><td class="s">interesting effects if some package is not overloaded, but inherits</td></tr>
<tr><td class="h"><a name="1480"></a>1480</td><td></td><td></td><td></td><td></td><td class="s">from two overloaded packages.</td></tr>
<tr><td class="h"><a name="1481"></a>1481</td><td></td><td></td><td></td><td></td><td class="s"></td></tr>
<tr><td class="h"><a name="1482"></a>1482</td><td></td><td></td><td></td><td></td><td class="s">Relation between overloading and tie()ing is broken. Overloading is</td></tr>
<tr><td class="h"><a name="1483"></a>1483</td><td></td><td></td><td></td><td></td><td class="s">triggered or not basing on the I<previous> class of tie()d value.</td></tr>
<tr><td class="h"><a name="1484"></a>1484</td><td></td><td></td><td></td><td></td><td class="s"></td></tr>
<tr><td class="h"><a name="1485"></a>1485</td><td></td><td></td><td></td><td></td><td class="s">This happens because the presence of overloading is checked too early,</td></tr>
<tr><td class="h"><a name="1486"></a>1486</td><td></td><td></td><td></td><td></td><td class="s">before any tie()d access is attempted. If the FETCH()ed class of the</td></tr>
<tr><td class="h"><a name="1487"></a>1487</td><td></td><td></td><td></td><td></td><td class="s">tie()d value does not change, a simple workaround is to access the value</td></tr>
<tr><td class="h"><a name="1488"></a>1488</td><td></td><td></td><td></td><td></td><td class="s">immediately after tie()ing, so that after this call the I<previous> class</td></tr>
<tr><td class="h"><a name="1489"></a>1489</td><td></td><td></td><td></td><td></td><td class="s">coincides with the current one.</td></tr>
<tr><td class="h"><a name="1490"></a>1490</td><td></td><td></td><td></td><td></td><td class="s"></td></tr>
<tr><td class="h"><a name="1491"></a>1491</td><td></td><td></td><td></td><td></td><td class="s">B<Needed:> a way to fix this without a speed penalty.</td></tr>
<tr><td class="h"><a name="1492"></a>1492</td><td></td><td></td><td></td><td></td><td class="s"></td></tr>
<tr><td class="h"><a name="1493"></a>1493</td><td></td><td></td><td></td><td></td><td class="s">Barewords are not covered by overloaded string constants.</td></tr>
<tr><td class="h"><a name="1494"></a>1494</td><td></td><td></td><td></td><td></td><td class="s"></td></tr>
<tr><td class="h"><a name="1495"></a>1495</td><td></td><td></td><td></td><td></td><td class="s">This document is confusing. There are grammos and misleading language</td></tr>
<tr><td class="h"><a name="1496"></a>1496</td><td></td><td></td><td></td><td></td><td class="s">used in places. It would seem a total rewrite is needed.</td></tr>
<tr><td class="h"><a name="1497"></a>1497</td><td></td><td></td><td></td><td></td><td class="s"></td></tr>
<tr><td class="h"><a name="1498"></a>1498</td><td></td><td></td><td></td><td></td><td class="s">=cut</td></tr>
<tr><td class="h"><a name="1499"></a>1499</td><td></td><td></td><td></td><td></td><td class="s"></td></tr>
<tr><td class="h"><a name="overload__CORE_match"></a></td><td></td><td></td><td></td><td></td><td class="s"><div class="calls"><div class="calls_in"># spent 2µs within overload::CORE:match which was called
# once (2µs+0s) by overload::OVERLOAD at <a href="overload-pm-line.html#18">line 18 of overload.pm</a></div></div>sub overload::CORE:match; # xsub<br /> </td></tr>
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