version(3) Perl Programmers Reference Guide version(3)NAMEversion - 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 as they were originally created (i.e. the same string that
was passed to "new()". 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); # 1.2 v1.200.0
$v = version->new( 1.02); # 1.02 v1.20.0
$v = version->new( 1.002); # 1.002 v1.2.0
$v = version->new( 1.0023); # 1.0023 v1.2.300
$v = version->new( 1.00203); # 1.00203 v1.2.30
$v = version->new( 1.002003); # 1.002003 v1.2.3
All of the preceding examples are true whether or not the input value
is quoted. The important feature is that the input value contains only
a single decimal. See also "Alpha Versions" for how to handle
IMPORTANT NOTE: As shown above, if your 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 0.01
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 numeric versions will always be the same string
that was used to initialize the version object.
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
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.
· Comparison operators
Both "cmp" and "<=>" operators perform the same comparison between
terms (upgrading to a version object automatically). Perl
automatically generates all of the other comparison operators based
on those two. In addition to the obvious equalities listed below,
appending a single trailing 0 term does not change the value of a
version for comparison purposes. In other words "v1.2" and "1.2.0"
will compare as identical.
For example, the following relations hold:
As Number As String Truth Value
----------------------------------------
$ver > 1.0 $ver gt "1.0" true
$ver < 2.5 $ver lt true
$ver != 1.3 $ver ne "1.3" true
$ver == 1.2 $ver eq "1.2" false
$ver == 1.2.3.4 $ver eq "1.2.3.4" see discussion below
It is probably best to chose either the 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.
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.
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 and output
purposes. The underscore will be output when an alpha version is
stringified, in the same place as it was when input.
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 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;
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 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 numeric 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 $module->VERSION;
will also exclusively return the stringified form. See Stringification
for more details.
SUBCLASSING
This module is specifically designed and tested to be easily
subclassed. In practice, you only need to override the methods you
want to change, but you have to take some care when overriding new()
(since that is where all of the parsing takes place). For example,
this is a perfect acceptable derived class:
package myversion;
use base version;
sub new {
my($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 v5.10.0 2007-12-18 version(3)
