=head1 SYNOPSIS
- use version;
- $version = version->new("12.2.1"); # must be quoted for Perl < 5.8.1
- print $version; # v12.2.1
- print $version->numify; # 12.002001
- if ( $version gt "12.2" ) # true
+ # Parsing version strings (decimal or dotted-decimal)
- $alphaver = version->new("1.02_03"); # must be quoted!
- print $alphaver; # 1.02_0300
- print $alphaver->is_alpha(); # true
-
- $ver = qv("1.2.0"); # v1.2.0
+ use version 0.77; # get latest bug-fixes and API
+ $ver = version->parse($string)
- $perlver = version->new(5.005_03); # must not be quoted!
- print $perlver; # 5.005030
+ # Declaring a dotted-decimal $VERSION (keep on one line!)
-=head1 DESCRIPTION
-
-Overloaded version objects for all modern versions of Perl. This module
-implements all of the features of version objects which are part
-of Perl 5.10.0. All previous releases (i.e. before 0.74) are deprecated
-and should not be used due to incompatible API changes. If you 'use
-version' in your code, you are strongly urged to set a minimum, e.g.
-
- use version 0.74; # to remain compatible with Perl v5.10.0
-
-=head2 BEST PRACTICES
-
-If you intend for your module to be used by different releases of Perl,
-and/or for your $VERSION scalar to mean what you think it means, there
-are a few simple rules to follow:
-
-=over 4
-
-=item * Be consistent
-
-Whichever of the two types of version objects that you choose to employ,
-you should stick to either L<Numeric Versions> or L<Extended Versions>
-and not mix them together. While this is I<possible>, it is very
-confusing to the average user.
-
-If you intend to use L<Extended Versions>, you are strongly encouraged
-to use the L<qv()> operator with a quoted term, e.g.:
-
- use version; our $VERSION = qv("1.2.3");
-
-on a single line as above.
-
-At the very least, decide on which of the several ways to initialize
-your version objects you prefer and stick with it. It is also best to
-be explicit about what value you intend to assign your version object
-and to not rely on hidden behavior of the parser.
-
-=item * Be careful
-
-If you are using Module::Build or ExtUtils::MakeMaker, so that you can
-release your module to CPAN, you have to recognize that neither of those
-programs completely handles version objects natively (yet). If you use
-version objects with Module::Build, you should add an explicit dependency
-to the release of version.pm in your Build.PL:
-
- my $builder = Module::Build->new(
- ...
- requires => {
- ... ,
- 'version' => 0.50,
- ...,
- },
- ...
- );
-
-and it should Just Work(TM). Module::Build will [hopefully soon]
-include full support for version objects; there are no current plans
-to patch ExtUtils::MakeMaker to support version objects.
-
-=back
-
-=head2 Using modules that use version.pm
-
-As much as possible, the version.pm module remains compatible with all
-current code. However, if your module is using a module that has defined
-C<$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;
+ use version 0.77; our $VERSION = version->declare("v1.2.3"); # formal
+ use version 0.77; our $VERSION = qv("v1.2.3"); # shorthand
+ use version 0.77; our $VERSION = qv("v1.2_3"); # alpha
-=over 4
+ # Declaring an old-style decimal $VERSION (use quotes!)
-=item Numeric versions always work
+ use version 0.77; our $VERSION = version->parse("1.0203"); # formal
+ use version 0.77; our $VERSION = version->parse("1.02_03"); # alpha
-Code of the form:
+ # Comparing mixed version styles (decimals, dotted-decimals, objects)
- use Example 1.002003;
-
-will always work correctly. The C<use> will perform an automatic
-C<$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)...
-
-=item Extended version work sometimes
+ if ( version->parse($v1) == version->parse($v2) ) {
+ # do stuff
+ }
-With Perl >= 5.6.2, you can also use a line like this:
+ # Sorting mixed version styles
- use Example 1.2.3;
+ @ordered = sort { version->parse($a) <=> version->parse($b) } @list;
-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 L<What about
-v-strings> below). This has to do with that fact that C<use> only checks
-to see if the second term I<looks like a number> and passes that to the
-replacement L<UNIVERSAL::VERSION>. This is not true in Perl 5.005_04,
-however, so you are B<strongly encouraged> to always use a numeric version
-in your code, even for those versions of Perl which support the extended
-version.
+=head1 DESCRIPTION
-=back
+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.
-=head2 What IS a version
+ use version 0.77; # even for Perl v.5.10.0
-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.
+=head1 TYPES OF VERSION OBJECTS
-There are actually two distinct kinds of version objects:
+There are two different types of version objects, corresponding to the two
+different styles of versions in use:
-=over 4
+=over 2
-=item * Numeric Versions
+=item Decimal Versions
-Any initial parameter which "looks like a number", see L<Numeric
-Versions>. This also covers versions with a single decimal point and
-a single embedded underscore, see L<Numeric Alpha Versions>, even though
-these must be quoted to preserve the underscore formatting.
+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 (without
+quotes) into your source file.
-=item * Extended Versions
+=item Dotted Decimal Versions
-Any initial parameter which contains more than one decimal point
-and an optional embedded underscore, see L<Extended 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). The use
-of the exported L<qv()> function also produces this kind of version
-object.
+The more modern form of version assignment, with 3 (or potentially more)
+integers seperated 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.
=back
-Both of these methods will produce similar version objects, in that
-the default stringification will yield the version L<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
- $v2 = version->new("1.2.3"); # v1.2.3
-
-In specific, version numbers initialized as L<Numeric Versions> will
-stringify as they were originally created (i.e. the same string that was
-passed to C<new()>. Version numbers initialized as L<Extended Versions>
-will be stringified as L<Normal Form>.
-
-=head2 Numeric Versions
-
-These correspond to historical versions of Perl itself prior to 5.6.0,
-as well as all other modules which follow the Camel rules for the
-$VERSION scalar. A numeric version is initialized with what looks like
-a floating point number. Leading zeros B<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 L<Alpha Versions> for how to handle
-
-IMPORTANT NOTE: As shown above, if your numeric 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 Extended 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<Numeric Versions>, Extended 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, Extended Versions permit the greatest amount of freedom
-to specify a version, whereas Numeric Versions enforce a certain
-uniformity. See also L<New Operator> for an additional method of
-initializing version objects.
+See L<VERSION OBJECT DETAILS> for further information.
-Just like L<Numeric Versions>, Extended Versions can be used as
-L<Alpha Versions>.
+=head1 DECLARING VERSIONS
-=head2 Numeric Alpha 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:
-The one time that a numeric version must be quoted is when a alpha form is
-used with an otherwise numeric 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:
+ our $VERSION = 1.02;
- # $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.
+Since Perl v5.10.0 includes the version.pm comparison logic anyways,
+you don't need to do anything at all.
-The stringified form of numeric versions will always be the same string
-that was used to initialize the version object.
+=head2 How to convert a module from decimal to dotted-decimal
-=head2 Object Methods
+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.
-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 numeric context for some reason, see the L<numify>
-object method.
-
-=over 4
+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:
-=item * 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:
+ $ perl -Mversion -e 'print version->parse("1.02")->normal'
+ v1.20.0
- $VERSION = version->new(qw$Revision: 2.7 $);
+Then increment any of the dotted-decimal components (v1.20.1 or v1.21.0).
-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
-numeric versions (i.e. 1.10 follows 1.9), so it must be handled as if
-it were a L<Extended 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 B<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.
-
-=back
+=head2 How to C<declare()> a dotted-decimal version
-=over 4
+ use version 0.77; our $VERSION = version->declare("v1.2.3");
-=item * qv()
+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.
-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:
+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:
- $v1 = qv(1.2); # 1.2.0
- $v2 = qv("1.2"); # also 1.2.0
+=over 2
-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.
+=item *
-To prevent the C<qv()> function from being exported to the caller's namespace,
-either use version with a null parameter:
+Always use a dotted-decimal with (at least) three components
- use version ();
+=item *
-or just require version, like this:
+Always use a leading-v
- require version;
+=item *
-Both methods will prevent the import() method from firing and exporting the
-C<qv()> sub. This is true of subclasses of version as well, see
-L<SUBCLASSING> for details.
+Always quote the version
=back
-For the subsequent examples, the following three objects will be used:
+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.
- $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 "Numeric Versions" above
+See also L<VERSION OBJECT DETAILS> for more on version number conversion,
+quoting, calculated version numbers and declaring developer or "alpha" version
+numbers.
-=over 4
+=head1 PARSING AND COMPARING VERSIONS
-=item * Normal Form
+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 can
+use version.pm to parse them all into objects for comparison.
-For any version object which is initialized with multiple decimal
-places (either quoted or if possible v-string), or initialized using
-the L<qv()> operator, the stringified representation is returned in
-a normalized or reduced form (no extraneous zeros), and with a leading 'v':
+=head2 How to C<parse()> a version
- 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"
+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.
-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:
+=over 2
- my $newver = version->new($ver->stringify);
- if ($newver eq $ver ) # always true
- {...}
+=item *
-=back
-
-=over 4
-
-=item * Numification
+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.
-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:
+=item *
- 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.
+Decimal: regular decimal numbers (literal or in a string)
=back
-=over 4
-
-=item * Stringification
+Some examples:
-The default stringification for version objects returns exactly the same
-string as was used to create it, whether you used C<new()> or C<qv()>,
-with one exception. The sole exception is if the object was created using
-C<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.
+ $variable version->parse($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
-For example:
+See L<VERSION OBJECT DETAILS> for more on version number conversion.
- 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
+=head2 How to compare version objects
-See also L<UNIVERSAL::VERSION>, as this also returns the stringified form
-when used as a class method.
+Version objects overload the C<cmp> and C<< E<lt>=E<gt> >> operators. Perl
+automatically generates all of the other comparison operators based on those
+two so all the normal logical comparisons will work.
-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 C<qv()> operator on a version without a
-leading 'v' B<and> with only a single decimal place, the stringified output
-will have a leading 'v', to preserve the sense. See the L<qv()> operator
-for more details.
+ if ( version->parse($v1) == version->parse($v2) ) {
+ # do stuff
+ }
-IMPORTANT NOTE 2: Attempting to bypass the normal stringification rules by
-manually applying L<numify()> and L<normal()> will sometimes yield
+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:
- print version->new(version->new("v1.0")->numify)->normal; # v1.0.0
+ $v1 = version->parse("v0.95.0");
+ $bool = $v1 < 0.96; # FALSE since 0.96 is v0.960.0
-The reason for this is that the L<numify()> operator will turn "v1.0"
-into the equivalent string "1.000000". Forcing the outer version object
-to L<normal()> form will display the mathematically equivalent "v1.0.0".
-
-As the example in L<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 C<$v1> and C<$v2> will be completely equivalent,
-down to the same internal representation as well as stringification.
-
-=back
+Always comparing to a version object will help avoid surprises:
-=over 4
+ $bool = $v1 < version->parse("v0.96.0"); # TRUE
-=item * Comparison operators
+=head1 VERSION OBJECT DETAILS
-Both C<cmp> and C<E<lt>=E<gt>> 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.
+=head2 Equivalence between Decimal and Dotted-Decimal Versions
-For example, the following relations hold:
+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:
- 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
+ 5.6.0 == 5.006000
+ 5.005_04 == 5.5.40
-It is probably best to chose either the numeric notation or the string
-notation and stick with it, to reduce confusion. Perl6 version objects
-B<may> only support numeric comparisons. See also L<Quoting>.
+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,
+B<plus> enough trailing zeros to reach the next multiple of three.
-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:
+This was the method that version.pm adopted as well. Some examples may be
+helpful:
- 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
+ equivalent
+ decimal zero-padded dotted-decimal
+ ------- ----------- --------------
+ 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
-For this reason, it is best to use either exclusively L<Numeric Versions> or
-L<Extended Versions> with multiple decimal points.
-
-=back
-
-=over 4
-
-=item * 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 L<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
-
-=back
-
-=head2 Quoting
+=head2 Quoting rules
Because of the nature of the Perl parsing and tokenizing routines,
certain initialization values B<must> be quoted in order to correctly
-parse as the intended version, especially when using the L<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 L<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 numeric 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 L<Alpha Version> and the underscore is
-significant.
+parse as the intended version, especially when using the L<declare> or
+L<qv> methods. While you do not have to quote decimal numbers when
+creating version objects, it is always safe to quote B<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
+B<in> will be be exactly what comes B<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
$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
+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
=head2 What about v-strings?
-Beginning with Perl 5.6.0, an alternate method to code arbitrary strings
-of bytes was introduced, called v-strings. They were intended to be an
-easy way to enter, for example, Unicode strings (which contain two bytes
-per character). Some programs have used them to encode printer control
-characters (e.g. CRLF). They were also intended to be used for $VERSION,
-but their use as such has been problematic from the start.
-
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:
$vs2 = v1.2; # encoded as \1\2
However, the use of bare v-strings to initialize version objects is
-B<strongly> discouraged in all circumstances (especially the leading
-'v' style), since the meaning will change depending on which Perl you
-are running. It is better to directly use L<"Extended Versions"> to
-ensure the proper interpretation.
+B<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:
form that has a leading 'v' character, for the simple reason that sometimes
it is impossible to tell whether one was present initially.
-=head2 Types of Versions Objects
-
-There are two types of Version Objects:
-
-=over 4
-
-=item * Ordinary versions
-
-These are the versions that normal modules will use. Can contain as
-many subversions as required. In particular, those using RCS/CVS can
-use the following:
-
- $VERSION = version->new(qw$Revision: 2.7 $);
-
-and the current RCS Revision for that file will be inserted
-automatically. If the file has been moved to a branch, the Revision
-will have three or more elements; otherwise, it will have only two.
-This allows you to automatically increment your module version by
-using the Revision number from the primary file in a distribution, see
-L<ExtUtils::MakeMaker/"VERSION_FROM">.
-
-=item * Alpha Versions
+=head2 Alpha versions
-For module authors using CPAN, the convention has been to note
-unstable releases with an underscore in the version string, see
-L<CPAN>. Alpha releases will test as being newer than the more recent
-stable release, and less than the next stable release. For example:
+For module authors using CPAN, the convention has been to note unstable
+releases with an underscore in the version string. (See L<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. For
+dotted-decimal versions, only the last element may be separated by an
+underscore:
- $alphaver = version->new("12.03_01"); # must be quoted
+ # Declaring
+ use version 0.77; our $VERSION = version->declare("v1.2_3");
-obeys the relationship
+ # Parsing
+ $v1 = version->parse("v1.2_3");
+ $v1 = version->parse("1.002_003");
- 12.03 < $alphaver < 12.04
+=head1 OBJECT METHODS
-Alpha versions with a single decimal point will be treated exactly as if
-they were L<Numeric Versions>, for parsing and output purposes. The
-underscore will be output when an alpha version is stringified, in the same
-place as it was when input.
+=head2 is_alpha()
-Alpha versions with more than a single decimal point will be treated
-exactly as if they were L<Extended Versions>, and will display without any
-trailing (or leading) zeros, in the L<Version Normal> form. For example,
+True if and only if the version object was created with a underscore, e.g.
- $newver = version->new("12.3.1_1");
- print $newver; # v12.3.1_1
+ version->parse('1.002_03')->is_alpha; # TRUE
+ version->declare('1.2.3_4')->is_alpha; # TRUE
-=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,
-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;
+=head2 is_qv()
- package Bar;
- $VERSION = "1.3.5"; # works with all Perl's (since it is quoted)
+True only if the version object is a dotted-decimal version, e.g.
- package main;
- use version;
+ 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
- print $Foo::VERSION; # prints 1.2
+=head2 normal()
- print $Bar::VERSION; # prints 1.003005
+Returns a string with a standard 'normalized' dotted-decimal form with a
+leading-v and at least 3 components.
- 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..."
+ version->declare('v1.2')->normal; # v1.2.0
+ version->parse('1.2')->normal; # v1.200.0
- eval "use bar 1.3.6";
- print $@; # prints "bar version 1.3.6 required..."
- eval "use bar 1.004"; # note numeric version
- print $@; # prints "bar version 1.004 required..."
+=head2 numify()
+Returns a value representing the object in a pure decimal form without
+trailing zeroes.
-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<use> or C<require>, rather than manually poking at C<class->VERSION>
-and then doing a comparison yourself.
+ version->declare('v1.2')->numify; # 1.002
+ version->parse('1.2')->numify; # 1.2
-The replacement UNIVERSAL::VERSION, when used as a function, like this:
+=head2 stringify()
- print $module->VERSION;
+Returns a string that is as close to the original representation as possible.
+If the original representation was a numeric literal, it will be returned the
+way perl would normally represent it in a string. This method is used whenever
+a version object is interpolated into a string.
-will also exclusively return the stringified form. See L<Stringification>
-for more details.
+ version->declare('v1.2')->stringify; # v1.2
+ version->parse('1.200')->stringify; # 1.200
+ version->parse(1.02_30)->stringify; # 1.023
-=head1 SUBCLASSING
+=head1 EXPORTED FUNCTIONS
-This module is specifically designed and tested to be easily subclassed.
-In practice, you only need to override the methods you want to change, but
-you have to take some care when overriding new() (since that is where all
-of the parsing takes place). For example, this is a perfect acceptable
-derived class:
+=head2 qv()
- package myversion;
- use base version;
- sub new {
- my($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 L<version::AlphaBeta> on CPAN for an alternate representation of
-version strings.
-
-B<NOTE:> Although the L<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.
+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:
-=head1 EXPORT
-
-qv - Extended Version initialization operator
+ use version 0.77 ();
=head1 AUTHOR
=head1 SEE ALSO
+L<version::Internal>.
+
L<perl>.
=cut
--- /dev/null
+=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<version.pod> 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<Decimal Versions>. This
+also includes versions with a single decimal point and a single embedded
+underscore, see L<Decimal Alpha Versions>, 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<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.
+
+=back
+
+Both of these methods will produce similar version objects, in that
+the default stringification will yield the version L<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
+ $v2 = version->new("v1.2.3"); # v1.2.3
+
+In specific, version numbers initialized as L<Decimal Versions> will
+stringify as they were originally created (i.e. the same string that was
+passed to C<new()>. Version numbers initialized as L<Dotted-Decimal Versions>
+will be stringified as L<Normal Form>.
+
+=head2 Decimal Versions
+
+These correspond to historical versions of Perl itself prior to 5.6.0,
+as well as all other modules which follow the Camel rules for the
+$VERSION scalar. A Decimal version is initialized with what looks like
+a floating point number. Leading zeros B<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 L<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.
+
+=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<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 L<New Operator> for an additional method of
+initializing version objects.
+
+Just like L<Decimal Versions>, Dotted-Decimal Versions can be used as
+L<Alpha Versions>.
+
+=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<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' );
+
+=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<STRONGLY> 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<is_qv>.
+
+=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<is_alpha>.
+
+=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<use> or C<require>, rather than manually poking at C<class->VERSION>
+and then doing a comparison yourself.
+
+The replacement UNIVERSAL::VERSION, when used as a function, like this:
+
+ print $module->VERSION;
+
+will also exclusively return the stringified form. See L<Stringification>
+for more details.
+
+=head1 Usage question
+
+=head2 Using modules that use version.pm
+
+As much as possible, the version.pm module remains compatible with all
+current code. However, if your module is using a module that has defined
+C<$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; $VERSION = qv('1.2.2');
+ ...module code here...
+ 1;
+
+=over 4
+
+=item Decimal versions always work
+
+Code of the form:
+
+ use Example 1.002003;
+
+will always work correctly. The C<use> will perform an automatic
+C<$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)...
+
+=item 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 L<What about
+v-strings> below). This has to do with that fact that C<use> only checks
+to see if the second term I<looks like a number> and passes that to the
+replacement L<UNIVERSAL::VERSION>. This is not true in Perl 5.005_04,
+however, so you are B<strongly encouraged> to always use a Decimal version
+in your code, even for those versions of Perl which support the Dotted-Decimal
+version.
+
+=back
+
+=head2 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 L<numify>
+object method.
+
+=over 4
+
+=item * 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 L<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 B<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.
+
+=back
+
+=over 4
+
+=item * 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 C<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
+C<qv()> sub. This is true of subclasses of version as well, see
+L<SUBCLASSING> for details.
+
+=back
+
+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
+
+=over 4
+
+=item * Normal Form
+
+For any version object which is initialized with multiple decimal
+places (either quoted or if possible v-string), or initialized using
+the L<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
+ {...}
+
+=back
+
+=over 4
+
+=item * 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.
+
+=back
+
+=over 4
+
+=item * Stringification
+
+The default stringification for version objects returns exactly the same
+string as was used to create it, whether you used C<new()> or C<qv()>,
+with one exception. The sole exception is if the object was created using
+C<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 L<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 C<qv()> operator on a version without a
+leading 'v' B<and> with only a single decimal place, the stringified output
+will have a leading 'v', to preserve the sense. See the L<qv()> operator
+for more details.
+
+IMPORTANT NOTE 2: Attempting to bypass the normal stringification rules by
+manually applying L<numify()> and L<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 L<numify()> operator will turn "v1.0"
+into the equivalent string "1.000000". Forcing the outer version object
+to L<normal()> form will display the mathematically equivalent "v1.0.0".
+
+As the example in L<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 C<$v1> and C<$v2> will be completely equivalent,
+down to the same internal representation as well as stringification.
+
+=back
+
+=over 4
+
+=item * Comparison operators
+
+Both C<cmp> and C<E<lt>=E<gt>> 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
+B<may> only support Decimal comparisons. See also L<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 L<Decimal Versions> or
+L<Dotted-Decimal Versions> with multiple decimal points.
+
+=back
+
+=over 4
+
+=item * 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 L<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
+
+=back
+
+=head2 Quoting
+
+Because of the nature of the Perl parsing and tokenizing routines,
+certain initialization values B<must> be quoted in order to correctly
+parse as the intended version, especially when using the L<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 L<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 L<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
+ $newvers = version->new(v2.5.4); # legal only in Perl >= 5.8.1
+
+=head1 SUBCLASSING
+
+This module is specifically designed and tested to be easily subclassed.
+In practice, you only need to override the methods you want to change, but
+you have to take some care when overriding new() (since that is where all
+of the parsing takes place). For example, this is a perfect acceptable
+derived class:
+
+ package myversion;
+ use base version;
+ sub new {
+ my($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 L<version::AlphaBeta> on CPAN for an alternate representation of
+version strings.
+
+B<NOTE:> Although the L<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.
+
+=head1 EXPORT
+
+qv - Dotted-Decimal Version initialization operator
+
+=head1 AUTHOR
+
+John Peacock E<lt>jpeacock@cpan.orgE<gt>
+
+=head1 SEE ALSO
+
+L<perl>.
+
+=cut
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