=head1 NAME
version::Internal - Perl extension for Version Objects
=head1 DESCRIPTION
Overloaded version objects for all modern versions of Perl. This documents
the internal data representation and underlying code for version.pm. See
L for daily usage. This document is only useful for users
writing a subclass of version.pm or interested in the gory details.
=head1 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:
=over 4
=item * Decimal Versions
Any version which "looks like a number", see L. This
also includes versions with a single decimal point and a single embedded
underscore, see L, even though these must be quoted
to preserve the underscore formatting.
=item * Dotted-Decimal Versions
Also referred to as "Dotted-Integer", these contains more than one decimal
point and may have an optional embedded underscore, see L. This is what is commonly used in most open source software as
the "external" version (the one used as part of the tag or tarfile name).
A leading 'v' character is now required and will warn if it missing.
=back
Both of these methods will produce similar version objects, in that
the default stringification will yield the version L 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("v1.2.3"); # v1.2.3
In specific, version numbers initialized as L will
stringify as they were originally created (i.e. the same string that was
passed to C. Version numbers initialized as L
will be stringified as L.
=head2 Decimal 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 Decimal version is initialized with what looks like
a floating point number. Leading zeros B 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); # 1.2 v1.200.0
$v = version->new( 1.02); # 1.02 v1.20.0
$v = version->new( 1.002); # 1.002 v1.2.0
$v = version->new( 1.0023); # 1.0023 v1.2.300
$v = version->new( 1.00203); # 1.00203 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 L for how to handle
IMPORTANT NOTE: As shown above, if your Decimal 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.
=head2 Dotted-Decimal 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 L, Dotted-Decimal 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, Dotted-Decimal Versions permit the greatest amount of freedom
to specify a version, whereas Decimal Versions enforce a certain
uniformity. See also L for an additional method of
initializing version objects.
Just like L, Dotted-Decimal Versions can be used as
L.
=head2 Decimal Alpha Versions
The one time that a Decimal version must be quoted is when a alpha form is
used with an otherwise Decimal 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 0.01
0.02 0.02
0.02_01 0.02_01
0.02_02 0.02_02
0.03 0.03
etc.
The stringified form of Decimal versions will always be the same string
that was used to initialize the version object.
=head1 High level design
=head2 version objects
version.pm provides an overloaded version object that is designed to both
encapsulate the author's intended $VERSION assignment as well as make it
completely natural to use those objects as if they were numbers (e.g. for
comparisons). To do this, a version object contains both the original
representation as typed by the author, as well as a parsed representation
to ease comparisons. Version objects employ L methods to
simplify code that needs to compare, print, etc the objects.
The internal structure of version objects is a blessed hash with several
components:
bless( {
'original' => 'v1.2.3_4',
'alpha' => 1,
'qv' => 1,
'version' => [
1,
2,
3,
4
]
}, 'version' );
=over 4
=item original
A faithful representation of the value used to initialize this version
object. The only time this will not be precisely the same characters
that exist in the source file is if a short dotted-decimal version like
v1.2 was used (in which case it will contain 'v1.2'). This form is
B discouraged, in that it will confuse you and your users.
=item qv
A boolean that denotes whether this is a decimal or dotted-decimal version.
See L.
=item alpha
A boolean that denotes whether this is an alpha version. NOTE: that the
underscore can can only appear in the last position. See L.
=item version
An array of non-negative integers that is used for comparison purposes with
other version objects.
=back
=head2 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 stringified form
as a simple scalar (i.e. not an object), but the warning message generated
includes either the stringified form or the normal form, depending on how
it was called.
For example:
package Foo;
$VERSION = 1.2;
package Bar;
$VERSION = "v1.3.5"; # 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 foo 10";
print $@; # prints "foo version 10 required..."
eval "use foo 1.3.5; # work in Perl 5.6.1 or better
print $@; # prints "foo version 1.3.5 required..."
eval "use bar 1.3.6";
print $@; # prints "bar version 1.3.6 required..."
eval "use bar 1.004"; # note Decimal version
print $@; # prints "bar version 1.004 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. It is always better to use the built-in comparison implicit in
C