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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:

       o   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.

       o   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



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       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



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       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:












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           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



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         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:




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             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.

       o   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: 1.2 $);

           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: 1.2 $ 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



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           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.

       o   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.



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       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

       o   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
               {...}

       o   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.

       o   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



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           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.

       o   Comparison operators

           Both "cmp" and "<=>" operators perform the same
           comparison between terms (upgrading to a version
           object automatically).  Perl automatically generates



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           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.

       o   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,



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       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:









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         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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