regcomp.c: Make comment more accurate

[perl5.git] / lib / version.pod

=head1 NAME

version - Perl extension for Version Objects

=head1 SYNOPSIS

  # Parsing version strings (decimal or dotted-decimal)

  use version 0.77; # get latest bug-fixes and API
  $ver = version->parse($string)

  # Declaring a dotted-decimal $VERSION (keep on one line!)

  use version; our $VERSION = version->declare("v1.2.3"); # formal
  use version; our $VERSION = qv("v1.2.3");               # shorthand
  use version; our $VERSION = qv("v1.2_3");               # alpha

  # Declaring an old-style decimal $VERSION (use quotes!)

  our $VERSION = "1.0203";                                     # recommended
  use version; our $VERSION = version->parse("1.0203");   # formal
  use version; our $VERSION = version->parse("1.02_03");  # alpha

  # Comparing mixed version styles (decimals, dotted-decimals, objects)

  if ( version->parse($v1) == version->parse($v2) ) {
    # do stuff
  }

  # Sorting mixed version styles

  @ordered = sort { version->parse($a) <=> version->parse($b) } @list;

=head1 DESCRIPTION

Version objects were added to Perl in 5.10.  This module implements version
objects for older version of Perl and provides the version object API for all
versions of Perl.  All previous releases before 0.74 are deprecated and should
not be used due to incompatible API changes.  Version 0.77 introduces the new
'parse' and 'declare' methods to standardize usage.  You are strongly urged to
set 0.77 as a minimum in your code, e.g.

  use version 0.77; # even for Perl v.5.10.0

=head1 TYPES OF VERSION OBJECTS

There are two different types of version objects, corresponding to the two
different styles of versions in use:

=over 2

=item Decimal Versions

The classic floating-point number $VERSION.  The advantage to this style is
that you don't need to do anything special, just type a number into your
source file.  Quoting is recommended, as it ensures that trailing zeroes
("1.50") are preserved in any warnings or other output.

=item Dotted Decimal Versions

The more modern form of version assignment, with 3 (or potentially more)
integers separated by decimal points (e.g. v1.2.3).  This is the form that
Perl itself has used since 5.6.0 was released.  The leading 'v' is now
strongly recommended for clarity, and will throw a warning in a future
release if omitted.  A leading 'v' character is required to pass the
L</is_strict()> test.

=back

=head1 DECLARING VERSIONS

If you have a module that uses a decimal $VERSION (floating point), and you
do not intend to ever change that, this module is not for you.  There is
nothing that version.pm gains you over a simple $VERSION assignment:

  our $VERSION = "1.02";

Since Perl v5.10.0 includes the version.pm comparison logic anyways,
you don't need to do anything at all.

=head2 How to convert a module from decimal to dotted-decimal

If you have used a decimal $VERSION in the past and wish to switch to a
dotted-decimal $VERSION, then you need to make a one-time conversion to
the new format.

B<Important Note>: you must ensure that your new $VERSION is numerically
greater than your current decimal $VERSION; this is not always obvious. First,
convert your old decimal version (e.g. 1.02) to a normalized dotted-decimal
form:

  $ perl -Mversion -e 'print version->parse("1.02")->normal'
  v1.20.0

Then increment any of the dotted-decimal components (v1.20.1 or v1.21.0).

=head2 How to C<declare()> a dotted-decimal version

  use version; our $VERSION = version->declare("v1.2.3");

The C<declare()> method always creates dotted-decimal version objects.  When
used in a module, you B<must> put it on the same line as "use version" to
ensure that $VERSION is read correctly by PAUSE and installer tools.  You
should also add 'version' to the 'configure_requires' section of your
module metadata file.  See instructions in L<ExtUtils::MakeMaker> or
L<Module::Build> for details.

B<Important Note>: Even if you pass in what looks like a decimal number
("1.2"), a dotted-decimal will be created ("v1.200.0"). To avoid confusion
or unintentional errors on older Perls, follow these guidelines:

=over 2

=item *

Always use a dotted-decimal with (at least) three components

=item *

Always use a leading-v

=item *

Always quote the version

=back

If you really insist on using version.pm with an ordinary decimal version,
use C<parse()> instead of declare.  See the L<PARSING AND COMPARING VERSIONS>
for details.

See also L<version::Internals> for more on version number conversion,
quoting, calculated version numbers and declaring developer or "alpha" version
numbers.

=head1 PARSING AND COMPARING VERSIONS

If you need to compare version numbers, but can't be sure whether they are
expressed as numbers, strings, v-strings or version objects,  then you should
use version.pm to parse them all into objects for comparison.

=head2 How to C<parse()> a version

The C<parse()> method takes in anything that might be a version and returns
a corresponding version object, doing any necessary conversion along the way.

=over 2

=item *

Dotted-decimal: bare v-strings (v1.2.3) and strings with more than one
decimal point and a leading 'v' ("v1.2.3"); NOTE you can technically use a
v-string or strings with a leading-v and only one decimal point (v1.2 or
"v1.2"), but you will confuse both yourself and others.

=item *

Decimal: regular decimal numbers (literal or in a string)

=back

Some examples:

  $variable   version->parse($variable)
  ---------   -------------------------
  1.23        v1.230.0
  "1.23"      v1.230.0
  v1.23       v1.23.0
  "v1.23"     v1.23.0
  "1.2.3"     v1.2.3
  "v1.2.3"    v1.2.3

See L<version::Internals> for more on version number conversion.

=head2 How to check for a legal version string

If you do not want to actually create a full blown version object, but
would still like to verify that a given string meets the criteria to
be parsed as a version, there are two helper functions that can be
employed directly:

=over 4

=item C<is_lax()>

The lax criteria corresponds to what is currently allowed by the
version parser.  All of the following formats are acceptable
for dotted-decimal formats strings:

    v1.2
    1.2345.6
    v1.23_4
    1.2345
    1.2345_01

=item C<is_strict()>

If you want to limit yourself to a much more narrow definition of what
a version string constitutes, C<is_strict()> is limited to version
strings like the following list:

    v1.234.5
    2.3456

=back

See L<version::Internals> for details of the regular expressions
that define the legal version string forms, as well as how to use
those regular expressions in your own code if C<is_lax()> and
C<is_strict()> are not sufficient for your needs.

=head2 How to compare version objects

Version objects overload the C<cmp> and C<< <=> >> operators.  Perl
automatically generates all of the other comparison operators based on those
two so all the normal logical comparisons will work.

  if ( version->parse($v1) == version->parse($v2) ) {
    # do stuff
  }

If a version object is compared against a non-version object, the non-object
term will be converted to a version object using C<parse()>.  This may give
surprising results:

  $v1 = version->parse("v0.95.0");
  $bool = $v1 < 0.96; # FALSE since 0.96 is v0.960.0

Always comparing to a version object will help avoid surprises:

  $bool = $v1 < version->parse("v0.96.0"); # TRUE

Note that "alpha" version objects (where the version string contains
a trailing underscore segment) compare as less than the equivalent
version without an underscore:

  $bool = version->parse("1.23_45") < version->parse("1.2345"); # TRUE

See L<version::Internals> for more details on "alpha" versions.

=head1 OBJECT METHODS

=head2 is_alpha()

True if and only if the version object was created with a underscore, e.g.

  version->parse('1.002_03')->is_alpha;  # TRUE
  version->declare('1.2.3_4')->is_alpha; # TRUE

=head2 is_qv()

True only if the version object is a dotted-decimal version, e.g.

  version->parse('v1.2.0')->is_qv;        # TRUE
  version->declare('v1.2')->is_qv;       # TRUE
  qv('1.2')->is_qv;                      # TRUE
  version->parse('1.2')->is_qv;          # FALSE

=head2 normal()

Returns a string with a standard 'normalized' dotted-decimal form with a
leading-v and at least 3 components.

 version->declare('v1.2')->normal;  # v1.2.0
 version->parse('1.2')->normal;     # v1.200.0

=head2 numify()

Returns a value representing the object in a pure decimal form without
trailing zeroes.

 version->declare('v1.2')->numify;  # 1.002
 version->parse('1.2')->numify;     # 1.2

=head2 stringify()

Returns a string that is as close to the original representation as possible.
If the original representation was a numeric literal, it will be returned the
way perl would normally represent it in a string.  This method is used whenever
a version object is interpolated into a string.

 version->declare('v1.2')->stringify;    # v1.2
 version->parse('1.200')->stringify;     # 1.200
 version->parse(1.02_30)->stringify;     # 1.023

=head1 EXPORTED FUNCTIONS

=head2 qv()

This function is no longer recommended for use, but is maintained for
compatibility with existing code.  If you do not want to have it exported
to your namespace, use this form:

  use version 0.77 ();

=head2 is_lax()

(Not exported by default)

This function takes a scalar argument and returns a boolean value indicating
whether the argument meets the "lax" rules for a version number.  Leading and
trailing spaces are not allowed.

=head2 is_strict()

(Not exported by default)

This function takes a scalar argument and returns a boolean value indicating
whether the argument meets the "strict" rules for a version number.  Leading
and trailing spaces are not allowed.

=head1 AUTHOR

John Peacock E<lt>jpeacock@cpan.orgE<gt>

=head1 SEE ALSO

L<version::Internals>.

L<perl>.

=cut