override(3)    User Contributed Perl Documentation    override(3)



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       ex::override - Perl pragma to override core functions

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         use ex::override ucfirst => sub {
                                          # make sure only the first
                                          # letter is uppercased
                                          ucfirst( lc( shift ) );
                                         };

         ucfirst( 'MAKE THIS RIGHT' );
         # Make this right

         no ex::override 'ucfirst';

         ucfirst( 'MAKE THIS RIGHT' );
         # MAKE THIS RIGHT


DDDDEEEESSSSCCCCRRRRIIIIPPPPTTTTIIIIOOOONNNN
       "ex::override" is an easy way to override core perl func-
       tions.

       OOOOvvvveeeerrrrrrrriiiiddddiiiinnnngggg aaaa ffffuuuunnnnccccttttiiiioooonnnn

         use ex::override
           length => \&mylength,
           open   => \&myopen;

       Overriding a core function happens at compile time.  Argu-
       ments are passed to "ex::override" in a name based, or
       hash style.  The key is the name of the core function to
       override, the value is your subroutine to replace the
       core's.

       UUUUssssiiiinnnngggg aaaannnn oooovvvveeeerrrrrrrriiiiddddeeeennnn ffffuuuunnnnttttiiiioooonnnn

       Nothing changes on the surface.  If you override "stat",
       then you still use "stat" the same way.

       NNNNOOOOTTTTEEEE:::: This is only true if you are keeping the same proto-
       type as the function you've overriden.  To do this, you
       must define your prototype:

         use ex::override values => sub (\%) { values %{+shift} };

       If you don't use this same prototype or force yourself to
       use the function the same, you can extend the functional-
       ity of a core function:

         # length of all arguments passed to length()
         use ex::override length => sub { length join '', @_ };


       OOOOvvvveeeerrrrrrrriiiiddddiiiinnnngggg aaaa ffffuuuunnnnccccttttiiiioooonnnn gggglllloooobbbbaaaallllyyyy

       DDDDoooonnnn''''tttt ddddoooo tttthhhhiiiissss wwwwiiiitttthhhhoooouuuutttt aaaa vvvveeeerrrryyyy ggggoooooooodddd rrrreeeeaaaassssoooonnnn!!!!

       "ex::override" allows you the ability to override core
       functions globaly.  Any packages that inherit from yours
       will use your function override.  There are good reasons
       for doing this, if you think you need to, make sure you
       have a good reason.

         use ex::override
           GLOBAL_length => sub {
                                 # prevent someone from passing a list
                                 croak "Don't do that!" if @_ > 1;
                                 length shift
                                };

       NNNNOOOOTTTTEEEE:::: If you globaly override a function in a package,
       only that package can remove it.

       RRRReeeemmmmoooovvvviiiinnnngggg yyyyoooouuuurrrr oooovvvveeeerrrrrrrriiiiddddeeee

       This works the same way that "no strict" works.

         no ex::override; # remove _all_ overrides

         no ex::override 'values';

         no ex::override 'GLOABL_length';


TTTTIIIIPPPPSSSS
       Get a list of overrideable function
           If you have the Perl source laying around, go to it's
           root dir and try this:

             perl -lne 'print /_(\w+)/ if /return -K/' toke.c

           You'll have to weed out which ones are functions ( vs.
           operators, etc. ).

       Get a functions prototype
             perl -lwe 'print prototype "CORE::length"'

           This prints the prototype, or "Use of uninitialized
           variable..." if there isn't one.

TTTTOOOODDDDOOOO
       Find a way to preserve prototypes so the user doesn't have
       to know them.

AAAAUUUUTTTTHHHHOOOORRRR
       Casey West, <_c_a_s_e_y_@_g_e_e_k_n_e_s_t_._c_o_m>

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       Copyright (c) 2000 Casey West <casey@geeknest.com>.  All
       rights reserved.  This program is free software; you can
       redistribute it and/or modify it under the same terms as
       Perl itself.



2003-03-14                 perl v5.6.1                override(3)