Rafaël Garcia-Suarez > perl-5.9.3 > version

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Module Version: 0.53   Source   Latest Release: perl-5.9.4

NAME ^

version - Perl extension for Version Objects

SYNOPSIS ^

  use version;
  $version = version->new("12.2.1"); # must be quoted for Perl < 5.8.1
  print $version;               # v12.2.1
  print $version->numify;       # 12.002001
  if ( $version gt "12.2" )     # true

  $alphaver = version->new("1.02_03"); # must be quoted!
  print $alphaver;              # 1.02_0300
  print $alphaver->is_alpha();  # true
  
  $ver = qv("1.2.0");           # v1.2.0

  $perlver = version->new(5.005_03); # must not be quoted!
  print $perlver;               # 5.005030

DESCRIPTION ^

Overloaded version objects for all versions of Perl. This module implements all of the features of version objects which will be part of Perl 5.10.0.

BEST PRACTICES

If you intend for your module to be used by different releases of Perl, and/or for your $VERSION scalar to mean what you think it means, there are a few simple rules to follow:

What IS a version

For the purposes of this module, a version "number" is a sequence of positive integer values separated by one or more decimal points and optionally a single underscore. This corresponds to what Perl itself uses for a version, as well as extending the "version as number" that is discussed in the various editions of the Camel book.

There are actually two distinct kinds of version objects:

Both of these methods will produce similar version objects, in that the default stringification will yield the version "Normal Form" only if required:

  $v  = version->new(1.002);     # 1.002, but compares like 1.2.0
  $v  = version->new(1.002003);  # 1.002003
  $v2 = version->new( "1.2.3");  # v1.2.3

In specific, version numbers initialized as "Numeric Versions" will stringify in Numeric form. Version numbers initialized as "Extended Versions" will be stringified as "Normal Form".

Numeric Versions

These correspond to historical versions of Perl itself prior to 5.6.0, as well as all other modules which follow the Camel rules for the $VERSION scalar. A numeric version is initialized with what looks like a floating point number. Leading zeros are significant and trailing zeros are implied so that a minimum of three places is maintained between subversions. What this means is that any subversion (digits to the right of the decimal place) that contains less than three digits will have trailing zeros added to make up the difference, but only for purposes of comparison with other version objects. For example:

                                   # Prints     Equivalent to  
  $v = version->new(      1.2);    # 1.200      v1.200.0
  $v = version->new(     1.02);    # 1.020      v1.20.0
  $v = version->new(    1.002);    # 1.002      v1.2.0
  $v = version->new(   1.0023);    # 1.002300   v1.2.300
  $v = version->new(  1.00203);    # 1.002030   v1.2.30
  $v = version->new( 1.002003);    # 1.002003   v1.2.3

All of the preceding examples are true whether or not the input value is quoted. The important feature is that the input value contains only a single decimal. See also "Alpha Versions" for how to handle

IMPORTANT NOTE: As shown above, if your numeric version contains more than 3 significant digits after the decimal place, it will be split on each multiple of 3, so 1.0003 is equivalent to v1.0.300, due to the need to remain compatible with Perl's own 5.005_03 == 5.5.30 interpretation. Any trailing zeros are ignored for mathematical comparison purposes.

Extended Versions

These are the newest form of versions, and correspond to Perl's own version style beginning with 5.6.0. Starting with Perl 5.10.0, and most likely Perl 6, this is likely to be the preferred form. This method normally requires that the input parameter be quoted, although Perl's after 5.8.1 can use v-strings as a special form of quoting, but this is highly discouraged.

Unlike "Numeric Versions", Extended Versions have more than a single decimal point, e.g.:

                                   # Prints
  $v = version->new( "v1.200");    # v1.200.0
  $v = version->new("v1.20.0");    # v1.20.0
  $v = qv("v1.2.3);                # v1.2.3
  $v = qv("1.2.3");                # v1.2.3
  $v = qv("1.20");                 # v1.20.0

In general, Extended Versions permit the greatest amount of freedom to specify a version, whereas Numeric Versions enforce a certain uniformity. See also "New Operator" for an additional method of initializing version objects.

Just like "Numeric Versions", Extended Versions can be used as "Alpha Versions".

Numeric Alpha Versions

The one time that a numeric version must be quoted is when a alpha form is used with an otherwise numeric version (i.e. a single decimal point). This is commonly used for CPAN releases, where CPAN or CPANPLUS will ignore alpha versions for automatic updating purposes. Since some developers have used only two significant decimal places for their non-alpha releases, the version object will automatically take that into account if the initializer is quoted. For example Module::Example was released to CPAN with the following sequence of $VERSION's:

  # $VERSION    Stringified
  0.01          0.010
  0.02          0.020
  0.02_01       0.02_0100
  0.02_02       0.02_0200
  0.03          0.030
  etc.

As you can see, the version object created from the values in the first column may contain a trailing 0, but will otherwise be both mathematically equivalent and sorts alpha-numerically as would be expected.

Object Methods

Overloading has been used with version objects to provide a natural interface for their use. All mathematical operations are forbidden, since they don't make any sense for base version objects.

For the subsequent examples, the following three objects will be used:

  $ver   = version->new("1.2.3.4"); # see "Quoting" below
  $alpha = version->new("1.2.3_4"); # see "Alpha versions" below
  $nver  = version->new(1.002);     # see "Numeric Versions" above

Quoting

Because of the nature of the Perl parsing and tokenizing routines, certain initialization values must be quoted in order to correctly parse as the intended version, especially when using the qv() operator. In all cases, a floating point number passed to version->new() will be identically converted whether or not the value itself is quoted. This is not true for qv(), however, when trailing zeros would be stripped on an unquoted input, which would result in a very different version object.

In addition, in order to be compatible with earlier Perl version styles, any use of versions of the form 5.006001 will be translated as v5.6.1. In other words, a version with a single decimal point will be parsed as implicitly having three digits between subversions, but only for internal comparison purposes.

The complicating factor is that in bare numbers (i.e. unquoted), the underscore is a legal numeric character and is automatically stripped by the Perl tokenizer before the version code is called. However, if a number containing one or more decimals and an underscore is quoted, i.e. not bare, that is considered a "Alpha Version" and the underscore is significant.

If you use a mathematic formula that resolves to a floating point number, you are dependent on Perl's conversion routines to yield the version you expect. You are pretty safe by dividing by a power of 10, for example, but other operations are not likely to be what you intend. For example:

  $VERSION = version->new((qw$Revision: 1.4)[1]/10);
  print $VERSION;          # yields 0.14
  $V2 = version->new(100/9); # Integer overflow in decimal number
  print $V2;               # yields something like 11.111.111.100

Perl 5.8.1 and beyond will be able to automatically quote v-strings but that is not possible in earlier versions of Perl. In other words:

  $version = version->new("v2.5.4");  # legal in all versions of Perl
  $newvers = version->new(v2.5.4);    # legal only in Perl >= 5.8.1

What about v-strings?

Beginning with Perl 5.6.0, an alternate method to code arbitrary strings of bytes was introduced, called v-strings. They were intended to be an easy way to enter, for example, Unicode strings (which contain two bytes per character). Some programs have used them to encode printer control characters (e.g. CRLF). They were also intended to be used for $VERSION, but their use as such has been problematic from the start.

There are two ways to enter v-strings: a bare number with two or more decimal points, or a bare number with one or more decimal points and a leading 'v' character (also bare). For example:

  $vs1 = 1.2.3; # encoded as \1\2\3
  $vs2 = v1.2;  # encoded as \1\2 

However, the use of v-strings to initialize version objects with this module is only possible with Perl 5.8.1 or better (which contain special code to enable it). Their use is strongly discouraged in all circumstances (especially the leading 'v' style), since the meaning will change depending on which Perl you are running. It is better to directly use "Extended Versions" to ensure the proper interpretation.

Types of Versions Objects

There are two types of Version Objects:

Replacement UNIVERSAL::VERSION

In addition to the version objects, this modules also replaces the core UNIVERSAL::VERSION function with one that uses version objects for its comparisons. The return from this operator is always the numified form, and the warning message generated includes both the numified and normal forms (for clarity).

For example:

  package Foo;
  $VERSION = 1.2;

  package Bar;
  $VERSION = "1.3.5"; # works with all Perl's (since it is quoted)

  package main;
  use version;

  print $Foo::VERSION; # prints 1.2

  print $Bar::VERSION; # prints 1.003005

  eval "use CGI 10"; # some far future release
  print $@; # prints "CGI version 10 (10.0.0) required..."

IMPORTANT NOTE: This may mean that code which searches for a specific string (to determine whether a given module is available) may need to be changed.

The replacement UNIVERSAL::VERSION, when used as a function, like this:

  print $module->VERSION;

will also exclusively return the numified form. Technically, the $module->VERSION function returns a string (PV) that can be converted to a number following the normal Perl rules, when used in a numeric context.

SUBCLASSING ^

This module is specifically designed and tested to be easily subclassed. In practice, you only need to override the methods you want to change, but you have to take some care when overriding new() (since that is where all of the parsing takes place). For example, this is a perfect acceptable derived class:

  package myversion;
  use base version;
  sub new { 
      my($self,$n)=@_;
      my $obj;
      # perform any special input handling here
      $obj = $self->SUPER::new($n);
      # and/or add additional hash elements here
      return $obj;
  }

See also version::AlphaBeta on CPAN for an alternate representation of version strings.

NOTE: the qv operator is not a class method and will not be inherited in the same way as the other methods. qv will always return an object of type version and not an object in the derived class. If you need to have qv return an object in your derived class, add something like this:

  *::qv = sub { return bless version::qv(shift), __PACKAGE__ };

as seen in the test file t/02derived.t.

EXPORT ^

qv - Extended Version initialization operator

AUTHOR ^

John Peacock <jpeacock@cpan.org>

SEE ALSO ^

perl.

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