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version::Internals(3pm)               Perl Programmers Reference Guide               version::Internals(3pm)



NAME
       version::Internals - 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 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 "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 "DottedDecimal
       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".

       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.

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

   Alpha Versions
       For module authors using CPAN, the convention has been to note unstable releases with an underscore
       in the version string. (See CPAN.)  version.pm follows this convention and alpha releases will test
       as being newer than the more recent stable release, and less than the next stable release.  Only the
       last element may be separated by an underscore:

         # Declaring
         use version 0.77; our $VERSION = version->declare("v1.2_3");

         # Parsing
         $v1 = version->parse("v1.2_3");
         $v1 = version->parse("1.002_003");

       Note that you must quote the version when writing an alpha Decimal version.  The stringified form of
       Decimal versions will always be the same string that was used to initialize the version object.

   Regular Expressions for Version Parsing
       A formalized definition of the legal forms for version strings is included in the main version.pm
       file.  Primitives are included for common elements, although they are scoped to the file so they are
       useful for reference purposes only.  There are two publicly accessible scalars that can be used in
       other code (not exported):

       $version::LAX
           This regexp covers all of the legal forms allowed under the current version string parser.  This
           is not to say that all of these forms are recommended, and some of them can only be used when
           quoted.

           For dotted decimals:

               v1.2
               1.2345.6
               v1.23_4

           The leading 'v' is optional if two or more decimals appear.  If only a single decimal is
           included, then the leading 'v' is required to trigger the dotted-decimal parsing.  A leading zero
           is permitted, though not recommended except when quoted, because of the risk that Perl will treat
           the number as octal.  A trailing underscore plus one or more digits denotes an alpha or
           development release (and must be quoted to be parsed properly).

           For decimal versions:

               1
               1.2345
               1.2345_01

           an integer portion, an optional decimal point, and optionally one or more digits to the right of
           the decimal are all required.  A trailing underscore is permitted and a leading zero is
           permitted.  Just like the lax dotted-decimal version, quoting the values is required for
           alpha/development forms to be parsed correctly.

       $version::STRICT
           This regexp covers a much more limited set of formats and constitutes the best practices for
           initializing version objects.  Whether you choose to employ decimal or dotted-decimal for is a
           personal preference however.

           v1.234.5
               For dotted-decimal versions, a leading 'v' is required, with three or more sub-versions of no
               more than three digits.  A leading 0 (zero) before the first sub-version (in the above
               example, '1') is also prohibited.

           2.3456
               For decimal versions, an integer portion (no leading 0), a decimal point, and one or more
               digits to the right of the decimal are all required.

       Both of the provided scalars are already compiled as regular expressions and do not contain either
       anchors or implicit groupings, so they can be included in your own regular expressions freely.  For
       example, consider the following code:

               ($pkg, $ver) =~ /
                       ^[ \t]*
                       use [ \t]+($PKGNAME)
                       (?:[ \t]+($version::STRICT))?
                       [ \t]*;
               /x;

       This would match a line of the form:

               use Foo::Bar::Baz v1.2.3;       # legal only in Perl 5.8.1+

       where $PKGNAME is another regular expression that defines the legal forms for package names.

IMPLEMENTATION DETAILS
   Equivalence between Decimal and Dotted-Decimal Versions
       When Perl 5.6.0 was released, the decision was made to provide a transformation between the old-style
       decimal versions and new-style dotted-decimal versions:

         5.6.0    == 5.006000
         5.005_04 == 5.5.40

       The floating point number is taken and split first on the single decimal place, then each group of
       three digits to the right of the decimal makes up the next digit, and so on until the number of
       significant digits is exhausted, plus enough trailing zeros to reach the next multiple of three.

       This was the method that version.pm adopted as well.  Some examples may be helpful:

                                   equivalent
         decimal    zero-padded    dotted-decimal
         -------    -----------    --------------1.2 -------------1.2
         1.2        1.200          v1.200.0
         1.02       1.020          v1.20.0
         1.002      1.002          v1.2.0
         1.0023     1.002300       v1.2.300
         1.00203    1.002030       v1.2.30
         1.002003   1.002003       v1.2.3

   Quoting Rules
       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 "declare" or
       "qv()" methods.  While you do not have to quote decimal numbers when creating version objects, it is
       always safe to quote all initial values when using version.pm methods, as this will ensure that what
       you type is what is used.

       Additionally, if you quote your initializer, then the quoted value that goes in will be be exactly
       what comes out when your $VERSION is printed (stringified).  If you do not quote your value, Perl's
       normal numeric handling comes into play and you may not get back what you were expecting.

       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 are 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?
       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 bare v-strings to initialize version objects is strongly discouraged in all
       circumstances.  Also, bare v-strings are not completely supported in any version of Perl prior to
       5.8.1.

       If you insist on using bare v-strings with Perl > 5.6.0, be aware of the following limitations:

       1) For Perl releases 5.6.0 through 5.8.0, the v-string code merely guesses, based on some
       characteristics of v-strings.  You must use a three part version, e.g. 1.2.3 or v1.2.3 in order for
       this heuristic to be successful.

       2) For Perl releases 5.8.1 and later, v-strings have changed in the Perl core to be magical, which
       means that the version.pm code can automatically determine whether the v-string encoding was used.

       3) In all cases, a version created using v-strings will have a stringified form that has a leading
       'v' character, for the simple reason that sometimes it is impossible to tell whether one was present
       initially.

   Version Object Internals
       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()" in
           version.

       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()" in version.

       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 DETAILS
   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?" above).  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
       new()
           Like many OO interfaces, the new() method is used to initialize version objects.  If two
           arguments are passed to "new()", the second one will be used as if it were prefixed with "v".
           This is to support historical use of the "qw" operator with 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 interchangeably,
           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.

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

         $ver   = version->new("1.2.3.4"); # see "Quoting Rules"
         $alpha = version->new("1.2.3_4"); # see "Alpha Versions"
         $nver  = version->new(1.002);     # see "Decimal Versions"

       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
             -------------    ----------------    -----------$ver ----------$ver
             $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 Rules".

           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

AUTHOR
       John Peacock <jpeacock@cpan.org>

SEE ALSO
       perl.



perl v5.16.2                                     2012-10-11                          version::Internals(3pm)