version::Internals(3pm)Perl Programmers Reference Guideversion::Internals(3pm)NAME
version::Internal - Perl extension for Version Objects
DESCRIPTION
Overloaded version objects for all modern versions of Perl. This
documents the internal data representation and underlying code for
version.pm. See version.pod for daily usage. This document is only
useful for users writing a subclass of version.pm or interested in the
gory details.
What IS a version
For the purposes of this module, a version "number" is a sequence of
positive integer values separated by one or more decimal points and
optionally a single underscore. This corresponds to what Perl itself
uses for a version, as well as extending the "version as number" that
is discussed in the various editions of the Camel book.
There are actually two distinct kinds of version objects:
· Decimal Versions
Any version which "looks like a number", see "Decimal Versions".
This also includes versions with a single decimal point and a
single embedded underscore, see "Decimal Alpha Versions", even
though these must be quoted to preserve the underscore formatting.
· Dotted-Decimal Versions
Also referred to as "Dotted-Integer", these contains more than one
decimal point and may have an optional embedded underscore, see
Dotted-Decimal Versions. This is what is commonly used in most
open source software as the "external" version (the one used as
part of the tag or tarfile name). A leading 'v' character is now
required and will warn if it missing.
Both of these methods will produce similar version objects, in that the
default stringification will yield the version "Normal Form" only if
required:
$v = version->new(1.002); # 1.002, but compares like 1.2.0
$v = version->new(1.002003); # 1.002003
$v2 = version->new("v1.2.3"); # v1.2.3
In specific, version numbers initialized as "Decimal Versions" will
stringify as they were originally created (i.e. the same string that
was passed to "new()". Version numbers initialized as "Dotted-Decimal
Versions" will be stringified as "Normal Form".
Decimal Versions
These correspond to historical versions of Perl itself prior to 5.6.0,
as well as all other modules which follow the Camel rules for the
$VERSION scalar. A Decimal version is initialized with what looks like
a floating point number. Leading zeros are significant and trailing
zeros are implied so that a minimum of three places is maintained
between subversions. What this means is that any subversion (digits to
the right of the decimal place) that contains less than three digits
will have trailing zeros added to make up the difference, but only for
purposes of comparison with other version objects. For example:
# Prints Equivalent to
$v = version->new( 1.2); # 1.2 v1.200.0
$v = version->new( 1.02); # 1.02 v1.20.0
$v = version->new( 1.002); # 1.002 v1.2.0
$v = version->new( 1.0023); # 1.0023 v1.2.300
$v = version->new( 1.00203); # 1.00203 v1.2.30
$v = version->new( 1.002003); # 1.002003 v1.2.3
All of the preceding examples are true whether or not the input value
is quoted. The important feature is that the input value contains only
a single decimal. See also "Alpha Versions" for how to handle
IMPORTANT NOTE: As shown above, if your Decimal version contains more
than 3 significant digits after the decimal place, it will be split on
each multiple of 3, so 1.0003 is equivalent to v1.0.300, due to the
need to remain compatible with Perl's own 5.005_03 == 5.5.30
interpretation. Any trailing zeros are ignored for mathematical
comparison purposes.
Dotted-Decimal Versions
These are the newest form of versions, and correspond to Perl's own
version style beginning with 5.6.0. Starting with Perl 5.10.0, and
most likely Perl 6, this is likely to be the preferred form. This
method normally requires that the input parameter be quoted, although
Perl's after 5.8.1 can use v-strings as a special form of quoting, but
this is highly discouraged.
Unlike "Decimal Versions", Dotted-Decimal Versions have more than a
single decimal point, e.g.:
# Prints
$v = version->new( "v1.200"); # v1.200.0
$v = version->new("v1.20.0"); # v1.20.0
$v = qv("v1.2.3"); # v1.2.3
$v = qv("1.2.3"); # v1.2.3
$v = qv("1.20"); # v1.20.0
In general, Dotted-Decimal Versions permit the greatest amount of
freedom to specify a version, whereas Decimal Versions enforce a
certain uniformity. See also "New Operator" for an additional method
of initializing version objects.
Just like "Decimal Versions", Dotted-Decimal Versions can be used as
"Alpha Versions".
Decimal Alpha Versions
The one time that a Decimal version must be quoted is when a alpha form
is used with an otherwise Decimal version (i.e. a single decimal
point). This is commonly used for CPAN releases, where CPAN or
CPANPLUS will ignore alpha versions for automatic updating purposes.
Since some developers have used only two significant decimal places for
their non-alpha releases, the version object will automatically take
that into account if the initializer is quoted. For example
Module::Example was released to CPAN with the following sequence of
$VERSION's:
# $VERSION Stringified
0.01 0.01
0.02 0.02
0.02_01 0.02_01
0.02_02 0.02_02
0.03 0.03
etc.
The stringified form of Decimal versions will always be the same string
that was used to initialize the version object.
High level design
version objects
version.pm provides an overloaded version object that is designed to
both encapsulate the author's intended $VERSION assignment as well as
make it completely natural to use those objects as if they were numbers
(e.g. for comparisons). To do this, a version object contains both the
original representation as typed by the author, as well as a parsed
representation to ease comparisons. Version objects employ overload
methods to simplify code that needs to compare, print, etc the objects.
The internal structure of version objects is a blessed hash with
several components:
bless( {
'original' => 'v1.2.3_4',
'alpha' => 1,
'qv' => 1,
'version' => [
1,
2,
3,
4
]
}, 'version' );
original
A faithful representation of the value used to initialize this
version object. The only time this will not be precisely the same
characters that exist in the source file is if a short dotted-
decimal version like v1.2 was used (in which case it will contain
'v1.2'). This form is STRONGLY discouraged, in that it will
confuse you and your users.
qv A boolean that denotes whether this is a decimal or dotted-decimal
version. See is_qv.
alpha
A boolean that denotes whether this is an alpha version. NOTE:
that the underscore can can only appear in the last position. See
is_alpha.
version
An array of non-negative integers that is used for comparison
purposes with other version objects.
Replacement UNIVERSAL::VERSION
In addition to the version objects, this modules also replaces the core
UNIVERSAL::VERSION function with one that uses version objects for its
comparisons. The return from this operator is always the stringified
form as a simple scalar (i.e. not an object), but the warning message
generated includes either the stringified form or the normal form,
depending on how it was called.
For example:
package Foo;
$VERSION = 1.2;
package Bar;
$VERSION = "v1.3.5"; # works with all Perl's (since it is quoted)
package main;
use version;
print $Foo::VERSION; # prints 1.2
print $Bar::VERSION; # prints 1.003005
eval "use foo 10";
print $@; # prints "foo version 10 required..."
eval "use foo 1.3.5; # work in Perl 5.6.1 or better
print $@; # prints "foo version 1.3.5 required..."
eval "use bar 1.3.6";
print $@; # prints "bar version 1.3.6 required..."
eval "use bar 1.004"; # note Decimal version
print $@; # prints "bar version 1.004 required..."
IMPORTANT NOTE: This may mean that code which searches for a specific
string (to determine whether a given module is available) may need to
be changed. It is always better to use the built-in comparison
implicit in "use" or "require", rather than manually poking at
"class-"VERSION> and then doing a comparison yourself.
The replacement UNIVERSAL::VERSION, when used as a function, like this:
print $module->VERSION;
will also exclusively return the stringified form. See Stringification
for more details.
Usage question
Using modules that use version.pm
As much as possible, the version.pm module remains compatible with all
current code. However, if your module is using a module that has
defined $VERSION using the version class, there are a couple of things
to be aware of. For purposes of discussion, we will assume that we
have the following module installed:
package Example;
use version; $VERSION = qv('1.2.2');
...module code here...
1;
Decimal versions always work
Code of the form:
use Example 1.002003;
will always work correctly. The "use" will perform an automatic
$VERSION comparison using the floating point number given as the
first term after the module name (e.g. above 1.002.003). In this
case, the installed module is too old for the requested line, so
you would see an error like:
Example version 1.002003 (v1.2.3) required--this is only version 1.002002 (v1.2.2)...
Dotted-Decimal version work sometimes
With Perl >= 5.6.2, you can also use a line like this:
use Example 1.2.3;
and it will again work (i.e. give the error message as above), even
with releases of Perl which do not normally support v-strings (see
"What about v-strings" below). This has to do with that fact that
"use" only checks to see if the second term looks like a number and
passes that to the replacement UNIVERSAL::VERSION. This is not
true in Perl 5.005_04, however, so you are strongly encouraged to
always use a Decimal version in your code, even for those versions
of Perl which support the Dotted-Decimal version.
Object Methods
Overloading has been used with version objects to provide a natural
interface for their use. All mathematical operations are forbidden,
since they don't make any sense for base version objects.
Consequently, there is no overloaded numification available. If you
want to use a version object in a Decimal context for some reason, see
the numify object method.
· 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 "Dotted-Decimal Version".
A new version object can be created as a copy of an existing
version object, either as a class method:
$v1 = version->new(12.3);
$v2 = version->new($v1);
or as an object method:
$v1 = version->new(12.3);
$v2 = $v1->new(12.3);
and in each case, $v1 and $v2 will be identical. NOTE: if you
create a new object using an existing object like this:
$v2 = $v1->new();
the new object will not be a clone of the existing object. In the
example case, $v2 will be an empty object of the same type as $v1.
· qv()
An alternate way to create a new version object is through the
exported qv() sub. This is not strictly like other q? operators
(like qq, qw), in that the only delimiters supported are
parentheses (or spaces). It is the best way to initialize a short
version without triggering the floating point interpretation. For
example:
$v1 = qv(1.2); # v1.2.0
$v2 = qv("1.2"); # also v1.2.0
As you can see, either a bare number or a quoted string can usually
be used 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 "Decimal 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.
IMPORTANT NOTE: There is one exceptional cases shown in the above
table where the "initializer" is not stringwise equivalent to the
stringified representation. If you use the "qv()" operator on a
version without a leading 'v' and with only a single decimal place,
the stringified output will have a leading 'v', to preserve the
sense. See the qv() operator for more details.
IMPORTANT NOTE 2: Attempting to bypass the normal stringification
rules by manually applying numify() and normal() will sometimes
yield surprising results:
print version->new(version->new("v1.0")->numify)->normal; # v1.0.0
The reason for this is that the numify() operator will turn "v1.0"
into the equivalent string "1.000000". Forcing the outer version
object to normal() form will display the mathematically equivalent
"v1.0.0".
As the example in new() shows, you can always create a copy of an
existing version object with the same value by the very compact:
$v2 = $v1->new($v1);
and be assured that both $v1 and $v2 will be completely equivalent,
down to the same internal representation as well as
stringification.
· Comparison operators
Both "cmp" and "<=>" operators perform the same comparison between
terms (upgrading to a version object automatically). Perl
automatically generates all of the other comparison operators based
on those two. In addition to the obvious equalities listed below,
appending a single trailing 0 term does not change the value of a
version for comparison purposes. In other words "v1.2" and "1.2.0"
will compare as identical.
For example, the following relations hold:
As Number As String Truth Value
----------------------------------------
$ver > 1.0 $ver gt "1.0" true
$ver < 2.5 $ver lt true
$ver != 1.3 $ver ne "1.3" true
$ver == 1.2 $ver eq "1.2" false
$ver == 1.2.3.4 $ver eq "1.2.3.4" see discussion below
It is probably best to chose either the Decimal notation or the
string notation and stick with it, to reduce confusion. Perl6
version objects may only support Decimal comparisons. See also
Quoting.
WARNING: Comparing version with unequal numbers of decimal points
(whether explicitly or implicitly initialized), may yield
unexpected results at first glance. For example, the following
inequalities hold:
version->new(0.96) > version->new(0.95); # 0.960.0 > 0.950.0
version->new("0.96.1") < version->new(0.95); # 0.096.1 < 0.950.0
For this reason, it is best to use either exclusively "Decimal
Versions" or "Dotted-Decimal Versions" with multiple decimal
points.
· 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 Decimal character and is automatically stripped
by the Perl tokenizer before the version code is called. However, if a
number containing one or more decimals and an underscore is quoted,
i.e. not bare, that is considered a "Alpha Version" and the underscore
is significant.
If you use a mathematic formula that resolves to a floating point
number, you are dependent on Perl's conversion routines to yield the
version you expect. You are pretty safe by dividing by a power of 10,
for example, but other operations are not likely to be what you intend.
For example:
$VERSION = version->new((qw$Revision: 1.4)[1]/10);
print $VERSION; # yields 0.14
$V2 = version->new(100/9); # Integer overflow in decimal number
print $V2; # yields something like 11.111.111.100
Perl 5.8.1 and beyond will be able to automatically quote v-strings but
that is not possible in earlier versions of Perl. In other words:
$version = version->new("v2.5.4"); # legal in all versions of Perl
$newvers = version->new(v2.5.4); # legal only in Perl >= 5.8.1
SUBCLASSING
This module is specifically designed and tested to be easily
subclassed. In practice, you only need to override the methods you
want to change, but you have to take some care when overriding new()
(since that is where all of the parsing takes place). For example,
this is a perfect acceptable derived class:
package myversion;
use base version;
sub new {
my($self,$n)=@_;
my $obj;
# perform any special input handling here
$obj = $self->SUPER::new($n);
# and/or add additional hash elements here
return $obj;
}
See also version::AlphaBeta on CPAN for an alternate representation of
version strings.
NOTE: Although the qv operator is not a true class method, but rather a
function exported into the caller's namespace, a subclass of version
will inherit an import() function which will perform the correct magic
on behalf of the subclass.
EXPORT
qv - Dotted-Decimal Version initialization operator
AUTHOR
John Peacock <jpeacock@cpan.org>
SEE ALSO
perl.
perl v5.10.1 2009-07-27 version::Internals(3pm)
