CONTENTS

• NAME
• DESCRIPTION
• What IS a version
  • Decimal Versions
  • Dotted-Decimal Versions
  • Decimal Alpha Versions
• High level design
  • version objects
  • Replacement UNIVERSAL::VERSION
• Usage question
  • Using modules that use version.pm
  • Object Methods
  • Quoting
• SUBCLASSING
• EXPORT
• AUTHOR
• SEE ALSO

#NAME

version::Internal - Perl extension for Version Objects

#DESCRIPTION

Overloaded version objects for all modern versions of Perl. This documents the internal data representation and underlying code for version.pm. See version.pod for daily usage. This document is only useful for users writing a subclass of version.pm or interested in the gory details.

#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:

• Decimal Versions

  Any version which "looks like a number", see "Decimal Versions". This also includes versions with a single decimal point and a single embedded underscore, see "Decimal Alpha Versions", even though these must be quoted to preserve the underscore formatting.

• Dotted-Decimal Versions

  Also referred to as "Dotted-Integer", these contains more than one decimal point and may have an optional embedded underscore, see "Dotted-Decimal Versions". 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.

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("v1.2.3");  # v1.2.3

In specific, version numbers initialized as "Decimal Versions" will stringify as they were originally created (i.e. the same string that was passed to new(). Version numbers initialized as "Dotted-Decimal Versions" will be stringified as "Normal Form".

#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 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);    # 1.2        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 "Alpha Versions" 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.

#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 "Decimal Versions", 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 "New Operator" for an additional method of initializing version objects.

Just like "Decimal Versions", Dotted-Decimal Versions can be used as "Alpha Versions".

#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.

#High level design

#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 overload 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' );

#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 STRONGLY discouraged, in that it will confuse you and your users.

#qv

A boolean that denotes whether this is a decimal or dotted-decimal version. See is_qv.

#alpha

A boolean that denotes whether this is an alpha version. NOTE: that the underscore can can only appear in the last position. See is_alpha.

#version

An array of non-negative integers that is used for comparison purposes with other 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 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 use or require, rather than manually poking at class-VERSION> and then doing a comparison yourself.

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

print $module->VERSION;

will also exclusively return the stringified form. See Stringification for more details.

#Usage question

#Using modules that use version.pm

As much as possible, the version.pm module remains compatible with all current code. However, if your module is using a module that has defined $VERSION using the version class, there are a couple of things to be aware of. For purposes of discussion, we will assume that we have the following module installed:

package Example;
use version;  $VERSION = qv('1.2.2');
...module code here...
1;

#Decimal versions always work

Code of the form:

use Example 1.002003;

will always work correctly. The use will perform an automatic $VERSION comparison using the floating point number given as the first term after the module name (e.g. above 1.002.003). In this case, the installed module is too old for the requested line, so you would see an error like:

Example version 1.002003 (v1.2.3) required--this is only version 1.002002 (v1.2.2)...

#Dotted-Decimal version work sometimes

With Perl >= 5.6.2, you can also use a line like this:

use Example 1.2.3;

and it will again work (i.e. give the error message as above), even with releases of Perl which do not normally support v-strings (see "What about v-strings" below). This has to do with that fact that use only checks to see if the second term looks like a number and passes that to the replacement UNIVERSAL::VERSION. This is not true in Perl 5.005_04, however, so you are strongly encouraged to always use a Decimal version in your code, even for those versions of Perl which support the Dotted-Decimal version.

#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. Consequently, there is no overloaded numification available. If you want to use a version object in a Decimal context for some reason, see the numify object method.

• New Operator

  Like all OO interfaces, the new() operator is used to initialize version objects. One way to increment versions when programming is to use the CVS variable $Revision, which is automatically incremented by CVS every time the file is committed to the repository.

  In order to facilitate this feature, the following code can be employed:

  $VERSION = version->new(qw$Revision: 2.7 $);

  and the version object will be created as if the following code were used:

  $VERSION = version->new("v2.7");

  In other words, the version will be automatically parsed out of the string, and it will be quoted to preserve the meaning CVS normally carries for versions. The CVS $Revision$ increments differently from Decimal versions (i.e. 1.10 follows 1.9), so it must be handled as if it were a "Dotted-Decimal Version".

  A new version object can be created as a copy of an existing version object, either as a class method:

  $v1 = version->new(12.3);
  $v2 = version->new($v1);

  or as an object method:

  $v1 = version->new(12.3);
  $v2 = $v1->new(12.3);

  and in each case, $v1 and $v2 will be identical. NOTE: if you create a new object using an existing object like this:

  $v2 = $v1->new();

  the new object will not be a clone of the existing object. In the example case, $v2 will be an empty object of the same type as $v1.

• qv()

  An alternate way to create a new version object is through the exported qv() sub. This is not strictly like other q? operators (like qq, qw), in that the only delimiters supported are parentheses (or spaces). It is the best way to initialize a short version without triggering the floating point interpretation. For example:

  $v1 = qv(1.2);         # v1.2.0
  $v2 = qv("1.2");       # also v1.2.0

  As you can see, either a bare number or a quoted string can usually be used interchangably, except in the case of a trailing zero, which must be quoted to be converted properly. For this reason, it is strongly recommended that all initializers to qv() be quoted strings instead of bare numbers.

  To prevent the qv() function from being exported to the caller's namespace, either use version with a null parameter:

  use version ();

  or just require version, like this:

  require version;

  Both methods will prevent the import() method from firing and exporting the qv() sub. This is true of subclasses of version as well, see SUBCLASSING for details.

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 "Decimal Versions" above

• Normal Form

  For any version object which is initialized with multiple decimal places (either quoted or if possible v-string), or initialized using the qv() operator, the stringified representation is returned in a normalized or reduced form (no extraneous zeros), and with a leading 'v':

  print $ver->normal;         # prints as v1.2.3.4
  print $ver->stringify;      # ditto
  print $ver;                 # ditto
  print $nver->normal;        # prints as v1.2.0
  print $nver->stringify;     # prints as 1.002, see "Stringification" 

  In order to preserve the meaning of the processed version, the normalized representation will always contain at least three sub terms. In other words, the following is guaranteed to always be true:

  my $newver = version->new($ver->stringify);
  if ($newver eq $ver ) # always true
    {...}

• Numification

  Although all mathematical operations on version objects are forbidden by default, it is possible to retrieve a number which corresponds to the version object through the use of the $obj->numify method. For formatting purposes, when displaying a number which corresponds a version object, all sub versions are assumed to have three decimal places. So for example:

  print $ver->numify;         # prints 1.002003004
  print $nver->numify;        # prints 1.002

  Unlike the stringification operator, there is never any need to append trailing zeros to preserve the correct version value.

• Stringification

  The default stringification for version objects returns exactly the same string as was used to create it, whether you used new() or qv(), with one exception. The sole exception is if the object was created using qv() and the initializer did not have two decimal places or a leading 'v' (both optional), then the stringified form will have a leading 'v' prepended, in order to support round-trip processing.

  For example:

  Initialized as          Stringifies to
  ==============          ==============
  version->new("1.2")       1.2
  version->new("v1.2")     v1.2
  qv("1.2.3")               1.2.3
  qv("v1.3.5")             v1.3.5
  qv("1.2")                v1.2   ### exceptional case 

  See also UNIVERSAL::VERSION, as this also returns the stringified form when used as a class method.

  IMPORTANT NOTE: There is one exceptional cases shown in the above table where the "initializer" is not stringwise equivalent to the stringified representation. If you use the qv() operator on a version without a leading 'v' and with only a single decimal place, the stringified output will have a leading 'v', to preserve the sense. See the qv() operator for more details.

  IMPORTANT NOTE 2: Attempting to bypass the normal stringification rules by manually applying numify() and normal() will sometimes yield surprising results:

  print version->new(version->new("v1.0")->numify)->normal; # v1.0.0

  The reason for this is that the numify() operator will turn "v1.0" into the equivalent string "1.000000". Forcing the outer version object to normal() form will display the mathematically equivalent "v1.0.0".

  As the example in new() shows, you can always create a copy of an existing version object with the same value by the very compact:

  $v2 = $v1->new($v1);

  and be assured that both $v1 and $v2 will be completely equivalent, down to the same internal representation as well as stringification.

• Comparison operators

  Both cmp and <=> operators perform the same comparison between terms (upgrading to a version object automatically). Perl automatically generates all of the other comparison operators based on those two. In addition to the obvious equalities listed below, appending a single trailing 0 term does not change the value of a version for comparison purposes. In other words "v1.2" and "1.2.0" will compare as identical.

  For example, the following relations hold:

  As Number        As String           Truth Value
  -------------    ----------------    -----------
  $ver >  1.0      $ver gt "1.0"       true
  $ver <  2.5      $ver lt             true
  $ver != 1.3      $ver ne "1.3"       true
  $ver == 1.2      $ver eq "1.2"       false
  $ver == 1.2.3.4  $ver eq "1.2.3.4"   see discussion below

  It is probably best to chose either the Decimal notation or the string notation and stick with it, to reduce confusion. Perl6 version objects may only support Decimal comparisons. See also Quoting.

  WARNING: Comparing version with unequal numbers of decimal points (whether explicitly or implicitly initialized), may yield unexpected results at first glance. For example, the following inequalities hold:

  version->new(0.96)     > version->new(0.95); # 0.960.0 > 0.950.0
  version->new("0.96.1") < version->new(0.95); # 0.096.1 < 0.950.0

  For this reason, it is best to use either exclusively "Decimal Versions" or "Dotted-Decimal Versions" with multiple decimal points.

• Logical Operators

  If you need to test whether a version object has been initialized, you can simply test it directly:

  $vobj = version->new($something);
  if ( $vobj )   # true only if $something was non-blank

  You can also test whether a version object is an "Alpha version", for example to prevent the use of some feature not present in the main release:

  $vobj = version->new("1.2_3"); # MUST QUOTE
  ...later...
  if ( $vobj->is_alpha )       # True

#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 Decimal 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

#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: Although the qv operator is not a true class method, but rather a function exported into the caller's namespace, a subclass of version will inherit an import() function which will perform the correct magic on behalf of the subclass.

#EXPORT

qv - Dotted-Decimal Version initialization operator

#AUTHOR

John Peacock <jpeacock@cpan.org>

#SEE ALSO

perl.

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