version(3) User Contributed Perl Documentation version(3)
NAME
version - Perl extension for Version Objects
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
$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
$perlver = version->new(5.005_03); # must not be quoted!
print $perlver; # 5.005030
DESCRIPTION
Overloaded version objects for all modern versions of Perl. This module implements all of the
features of version objects which will be part of Perl 5.10.0.
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:
Be consistent
Whichever of the two types of version objects that you choose to employ, you should stick to
either "Numeric Versions" or "Extended Versions" and not mix them together. While this is
possible, it is very confusing to the average user.
If you intend to use "Extended Versions", you are strongly encouraged to use the 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.
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.
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;
Numeric 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)...
Extended 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 numeric version in your code, even for those versions of Perl which
support the extended version.
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:
Numeric Versions
Any initial parameter which "looks like a number", see Numeric Versions. This also covers
versions with a single decimal point and a single embedded underscore, see "Numeric Alpha
Versions", even though these must be quoted to preserve the underscore formatting.
Extended Versions
Any initial parameter which contains more than one decimal point and an optional embedded
underscore, see "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 qv() function also produces this kind of version object.
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("1.2.3"); # v1.2.3
In specific, version numbers initialized as "Numeric Versions" will stringify in Numeric form.
Version numbers initialized as "Extended Versions" will be stringified as "Normal Form".
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 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); # 1.200 v1.200.0
$v = version->new( 1.02); # 1.020 v1.20.0
$v = version->new( 1.002); # 1.002 v1.2.0
$v = version->new( 1.0023); # 1.002300 v1.2.300
$v = version->new( 1.00203); # 1.002030 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 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.
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 "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 "New Operator" for an additional method of
initializing version objects.
Just like "Numeric Versions", Extended Versions can be used as "Alpha Versions".
Numeric Alpha Versions
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:
# $VERSION Stringified
0.01 0.010
0.02 0.020
0.02_01 0.02_0100
0.02_02 0.02_0200
0.03 0.030
etc.
As you can see, the version object created from the values in the first column may contain a trailing
0, but will otherwise be both mathematically equivalent and sorts alpha-numerically as would be
expected.
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 numeric context for some reason, see the numify object method.
New Operator
Like all OO interfaces, the new() operator is used to initialize version objects. One way to
increment versions when programming is to use the CVS variable $Revision, which is automatically
incremented by CVS every time the file is committed to the repository.
In order to facilitate this feature, the following code can be employed:
$VERSION = version->new(qw$Revision: 2.7 $);
and the version object will be created as if the following code were used:
$VERSION = version->new("v2.7");
In other words, the version will be automatically parsed out of the string, and it will be quoted
to preserve the meaning CVS normally carries for versions. The CVS $Revision$ increments
differently from numeric versions (i.e. 1.10 follows 1.9), so it must be handled as if it were a
"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 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); # 1.2.0
$v2 = qv("1.2"); # also 1.2.0
As you can see, either a bare number or a quoted string can usually be used interchangably,
except in the case of a trailing zero, which must be quoted to be converted properly. For this
reason, it is strongly recommended that all initializers to qv() be quoted strings instead of
bare numbers.
To prevent the "qv()" function from being exported to the caller's namespace, either use version
with a null parameter:
use version ();
or just require version, like this:
require version;
Both methods will prevent the import() method from firing and exporting the "qv()" sub. This is
true of subclasses of version as well, see SUBCLASSING for details.
For the subsequent examples, the following three objects will be used:
$ver = version->new("1.2.3.4"); # see "Quoting" below
$alpha = version->new("1.2.3_4"); # see "Alpha versions" below
$nver = version->new(1.002); # see "Numeric Versions" above
Normal Form
For any version object which is initialized with multiple decimal places (either quoted or if
possible v-string), or initialized using the qv() operator, the stringified representation is
returned in a normalized or reduced form (no extraneous zeros), and with a leading 'v':
print $ver->normal; # prints as v1.2.3.4
print $ver->stringify; # ditto
print $ver; # ditto
print $nver->normal; # prints as v1.2.0
print $nver->stringify; # prints as 1.002, see "Stringification"
In order to preserve the meaning of the processed version, the normalized representation will
always contain at least three sub terms. In other words, the following is guaranteed to always
be true:
my $newver = version->new($ver->stringify);
if ($newver eq $ver ) # always true
{...}
Numification
Although all mathematical operations on version objects are forbidden by default, it is possible
to retrieve a number which corresponds to the version object through the use of the $obj->numify
method. For formatting purposes, when displaying a number which corresponds a version object,
all sub versions are assumed to have three decimal places. So for example:
print $ver->numify; # prints 1.002003004
print $nver->numify; # prints 1.002
Unlike the stringification operator, there is never any need to append trailing zeros to preserve
the correct version value.
Stringification
In order to mirror as much as possible the existing behavior of ordinary $VERSION scalars, the
stringification operation will display differently, depending on whether the version was
initialized as a "Numeric Version" or "Extended Version".
What this means in practice is that if the normal CPAN and Camel rules are followed ($VERSION is
a floating point number with no more than 3 decimal points), the stringified output will be
exactly the same as the numified output. There will be no visible difference, although the
internal representation will be different, and the "Comparison operators" will function using the
internal coding.
If a version object is initialized using a "Extended Version" form, then the stringified form
will be the "Normal Form". The $obj->normal operation can always be used to produce the "Normal
Form", even if the version was originally a "Numeric Version".
print $ver->stringify; # prints v1.2.3.4
print $nver->stringify; # prints 1.002
Comparison operators
Both "cmp" and "<=>" operators perform the same comparison between terms (upgrading to a version
object automatically). Perl automatically generates all of the other comparison operators based
on those two. In addition to the obvious equalities listed below, appending a single trailing 0
term does not change the value of a version for comparison purposes. In other words "v1.2" and
"1.2.0" will compare as identical.
For example, the following relations hold:
As Number As String Truth Value
------------- ---------------- -----------$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 numeric notation or the string notation and stick with
it, to reduce confusion. Perl6 version objects may only support numeric 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 "Numeric Versions" or "Extended Versions"
with multiple decimal points.
Logical Operators
If you need to test whether a version object has been initialized, you can simply test it
directly:
$vobj = version->new($something);
if ( $vobj ) # true only if $something was non-blank
You can also test whether a version object is an "Alpha version", for example to prevent the use
of some feature not present in the main release:
$vobj = version->new("1.2_3"); # MUST QUOTE
...later...
if ( $vobj->is_alpha ) # True
Quoting
Because of the nature of the Perl parsing and tokenizing routines, certain initialization values must
be quoted in order to correctly parse as the intended version, especially when using the qv()
operator. In all cases, a floating point number passed to version->new() will be identically
converted whether or not the value itself is quoted. This is not true for qv(), however, when
trailing zeros would be stripped on an unquoted input, which would result in a very different version
object.
In addition, in order to be compatible with earlier Perl version styles, any use of versions of the
form 5.006001 will be translated as v5.6.1. In other words, a version with a single decimal point
will be parsed as implicitly having three digits between subversions, but only for internal
comparison purposes.
The complicating factor is that in bare numbers (i.e. unquoted), the underscore is a legal 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 "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
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:
$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 (especially the leading 'v' style), since the meaning will change depending on which
Perl you are running. It is better to directly use "Extended Versions" to ensure the proper
interpretation.
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.
Types of Versions Objects
There are two types of Version Objects:
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 "VERSION_FROM" in ExtUtils::MakeMaker.
Alpha Versions
For module authors using CPAN, the convention has been to note unstable releases with an
underscore in the version string, see CPAN. Alpha releases will test as being newer than the
more recent stable release, and less than the next stable release. For example:
$alphaver = version->new("12.03_01"); # must be quoted
obeys the relationship
12.03 < $alphaver < 12.04
Alpha versions with a single decimal point will be treated exactly as if they were "Numeric
Versions", for parsing purposes. The stringification for alpha versions with a single decimal
point may seem surprising, since any trailing zeros will visible. For example, the above
$alphaver will print as
12.03_0100
which is mathematically equivalent and ASCII sorts exactly the same as without the trailing
zeros.
Alpha versions with more than a single decimal point will be treated exactly as if they were
"Extended Versions", and will display without any trailing (or leading) zeros, in the "Version
Normal" form. For example,
$newver = version->new("12.3.1_1");
print $newver; # v12.3.1_1
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
numified form, and the warning message generated includes both the numified and normal forms (for
clarity).
For example:
package Foo;
$VERSION = 1.2;
package Bar;
$VERSION = "1.3.5"; # 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 CGI 10"; # some far future release
print $@; # prints "CGI version 10 (10.0.0) 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.
The replacement UNIVERSAL::VERSION, when used as a function, like this:
print $module->VERSION;
will also exclusively return the numified form. Technically, the $module->VERSION function returns a
string (PV) that can be converted to a number following the normal Perl rules, when used in a numeric
context.
SUBCLASSING
This module is specifically designed and tested to be easily subclassed. In practice, you only need
to override the methods you want to change, but you have to take some care when overriding new()
(since that is where all of the parsing takes place). For example, this is a perfect acceptable
derived class:
package myversion;
use base version;
sub new {
my($self,$n)=@_;
my $obj;
# perform any special input handling here
$obj = $self->SUPER::new($n);
# and/or add additional hash elements here
return $obj;
}
See also version::AlphaBeta on CPAN for an alternate representation of version strings.
NOTE: Although the qv operator is not a true class method, but rather a function exported into the
caller's namespace, a subclass of version will inherit an import() function which will perform the
correct magic on behalf of the subclass.
EXPORT
qv - Extended Version initialization operator
AUTHOR
John Peacock <jpeacock@cpan.org>
SEE ALSO
perl.
perl v5.8.8 2007-02-12 version(3)
|