version::Internals(3) User Contributed Perl Documentationversion::Internals(3)
NAME
version::Internals - Perl extension for Version Objects
DESCRIPTION
Overloaded version objects for all modern versions of Perl. This
documents the internal data representation and underlying code for
version.pm. See version.pod for daily usage. This document is only
useful for users interested in the gory details.
WHAT IS A VERSION?
For the purposes of this module, a version "number" is a sequence of
positive integer values separated by one or more decimal points and
optionally a single underscore. This corresponds to what Perl itself
uses for a version, as well as extending the "version as number" that
is discussed in the various editions of the Camel book.
There are actually two distinct kinds of version objects:
Decimal Versions
Any version which "looks like a number", see "Decimal Versions".
This also includes versions with a single decimal point and a
single embedded underscore, see "Alpha Versions", even though these
must be quoted to preserve the underscore formatting.
Dotted-Decimal Versions
Also referred to as "Dotted-Integer", these contains more than one
decimal point and may have an optional embedded underscore, see
Dotted-Decimal Versions. This is what is commonly used in most
open source software as the "external" version (the one used as
part of the tag or tarfile name). A leading 'v' character is now
required and will warn if it missing.
Both of these methods will produce similar version objects, in that the
default stringification will yield the version "Normal Form" only if
required:
$v = version->new(1.002); # 1.002, but compares like 1.2.0
$v = version->new(1.002003); # 1.002003
$v2 = version->new("v1.2.3"); # v1.2.3
In specific, version numbers initialized as "Decimal Versions" will
stringify as they were originally created (i.e. the same string that
was passed to "new()". Version numbers initialized as "Dotted-Decimal
Versions" will be stringified as "Normal Form".
Decimal Versions
These correspond to historical versions of Perl itself prior to 5.6.0,
as well as all other modules which follow the Camel rules for the
$VERSION scalar. A Decimal version is initialized with what looks like
a floating point number. Leading zeros are significant and trailing
zeros are implied so that a minimum of three places is maintained
between subversions. What this means is that any subversion (digits to
the right of the decimal place) that contains less than three digits
will have trailing zeros added to make up the difference, but only for
purposes of comparison with other version objects. For example:
# Prints Equivalent to
$v = version->new( 1.2); # 1.2 v1.200.0
$v = version->new( 1.02); # 1.02 v1.20.0
$v = version->new( 1.002); # 1.002 v1.2.0
$v = version->new( 1.0023); # 1.0023 v1.2.300
$v = version->new( 1.00203); # 1.00203 v1.2.30
$v = version->new( 1.002003); # 1.002003 v1.2.3
All of the preceding examples are true whether or not the input value
is quoted. The important feature is that the input value contains only
a single decimal. See also "Alpha Versions".
IMPORTANT NOTE: As shown above, if your Decimal version contains more
than 3 significant digits after the decimal place, it will be split on
each multiple of 3, so 1.0003 is equivalent to v1.0.300, due to the
need to remain compatible with Perl's own 5.005_03 == 5.5.30
interpretation. Any trailing zeros are ignored for mathematical
comparison purposes.
Dotted-Decimal Versions
These are the newest form of versions, and correspond to Perl's own
version style beginning with 5.6.0. Starting with Perl 5.10.0, and
most likely Perl 6, this is likely to be the preferred form. This
method normally requires that the input parameter be quoted, although
Perl's after 5.8.1 can use v-strings as a special form of quoting, but
this is highly discouraged.
Unlike "Decimal Versions", Dotted-Decimal Versions have more than a
single decimal point, e.g.:
# Prints
$v = version->new( "v1.200"); # v1.200.0
$v = version->new("v1.20.0"); # v1.20.0
$v = qv("v1.2.3"); # v1.2.3
$v = qv("1.2.3"); # v1.2.3
$v = qv("1.20"); # v1.20.0
In general, Dotted-Decimal Versions permit the greatest amount of
freedom to specify a version, whereas Decimal Versions enforce a
certain uniformity.
Just like "Decimal Versions", Dotted-Decimal Versions can be used as
"Alpha Versions".
Alpha Versions
For module authors using CPAN, the convention has been to note unstable
releases with an underscore in the version string. (See CPAN.)
version.pm follows this convention and alpha releases will test as
being newer than the more recent stable release, and less than the next
stable release. Only the last element may be separated by an
underscore:
# Declaring
use version 0.77; our $VERSION = version->declare("v1.2_3");
# Parsing
$v1 = version->parse("v1.2_3");
$v1 = version->parse("1.002_003");
Note that you must quote the version when writing an alpha Decimal
version. The stringified form of Decimal versions will always be the
same string that was used to initialize the version object.
Regular Expressions for Version Parsing
A formalized definition of the legal forms for version strings is
included in the "version::regex" class. Primitives are included for
common elements, although they are scoped to the file so they are
useful for reference purposes only. There are two publicly accessible
scalars that can be used in other code (not exported):
$version::LAX
This regexp covers all of the legal forms allowed under the current
version string parser. This is not to say that all of these forms
are recommended, and some of them can only be used when quoted.
For dotted decimals:
v1.2
1.2345.6
v1.23_4
The leading 'v' is optional if two or more decimals appear. If
only a single decimal is included, then the leading 'v' is required
to trigger the dotted-decimal parsing. A leading zero is
permitted, though not recommended except when quoted, because of
the risk that Perl will treat the number as octal. A trailing
underscore plus one or more digits denotes an alpha or development
release (and must be quoted to be parsed properly).
For decimal versions:
1
1.2345
1.2345_01
an integer portion, an optional decimal point, and optionally one
or more digits to the right of the decimal are all required. A
trailing underscore is permitted and a leading zero is permitted.
Just like the lax dotted-decimal version, quoting the values is
required for alpha/development forms to be parsed correctly.
$version::STRICT
This regexp covers a much more limited set of formats and
constitutes the best practices for initializing version objects.
Whether you choose to employ decimal or dotted-decimal for is a
personal preference however.
v1.234.5
For dotted-decimal versions, a leading 'v' is required, with
three or more sub-versions of no more than three digits. A
leading 0 (zero) before the first sub-version (in the above
example, '1') is also prohibited.
2.3456
For decimal versions, an integer portion (no leading 0), a
decimal point, and one or more digits to the right of the
decimal are all required.
Both of the provided scalars are already compiled as regular
expressions and do not contain either anchors or implicit groupings, so
they can be included in your own regular expressions freely. For
example, consider the following code:
($pkg, $ver) =~ /
^[ \t]*
use [ \t]+($PKGNAME)
(?:[ \t]+($version::STRICT))?
[ \t]*;
/x;
This would match a line of the form:
use Foo::Bar::Baz v1.2.3; # legal only in Perl 5.8.1+
where $PKGNAME is another regular expression that defines the legal
forms for package names.
IMPLEMENTATION DETAILS
Equivalence between Decimal and Dotted-Decimal Versions
When Perl 5.6.0 was released, the decision was made to provide a
transformation between the old-style decimal versions and new-style
dotted-decimal versions:
5.6.0 == 5.006000
5.005_04 == 5.5.40
The floating point number is taken and split first on the single
decimal place, then each group of three digits to the right of the
decimal makes up the next digit, and so on until the number of
significant digits is exhausted, plus enough trailing zeros to reach
the next multiple of three.
This was the method that version.pm adopted as well. Some examples may
be helpful:
equivalent
decimal zero-padded dotted-decimal
------- ----------- --------------
1.2 1.200 v1.200.0
1.02 1.020 v1.20.0
1.002 1.002 v1.2.0
1.0023 1.002300 v1.2.300
1.00203 1.002030 v1.2.30
1.002003 1.002003 v1.2.3
Quoting Rules
Because of the nature of the Perl parsing and tokenizing routines,
certain initialization values must be quoted in order to correctly
parse as the intended version, especially when using the "declare" or
"qv()" methods. While you do not have to quote decimal numbers when
creating version objects, it is always safe to quote all initial values
when using version.pm methods, as this will ensure that what you type
is what is used.
Additionally, if you quote your initializer, then the quoted value that
goes in will be exactly what comes out when your $VERSION is printed
(stringified). If you do not quote your value, Perl's normal numeric
handling comes into play and you may not get back what you were
expecting.
If you use a mathematic formula that resolves to a floating point
number, you are dependent on Perl's conversion routines to yield the
version you expect. You are pretty safe by dividing by a power of 10,
for example, but other operations are not likely to be what you intend.
For example:
$VERSION = version->new((qw$Revision: 1.4)[1]/10);
print $VERSION; # yields 0.14
$V2 = version->new(100/9); # Integer overflow in decimal number
print $V2; # yields something like 11.111.111.100
Perl 5.8.1 and beyond are able to automatically quote v-strings but
that is not possible in earlier versions of Perl. In other words:
$version = version->new("v2.5.4"); # legal in all versions of Perl
$newvers = version->new(v2.5.4); # legal only in Perl >= 5.8.1
What about v-strings?
There are two ways to enter v-strings: a bare number with two or more
decimal points, or a bare number with one or more decimal points and a
leading 'v' character (also bare). For example:
$vs1 = 1.2.3; # encoded as \1\2\3
$vs2 = v1.2; # encoded as \1\2
However, the use of bare v-strings to initialize version objects is
strongly discouraged in all circumstances. Also, bare v-strings are
not completely supported in any version of Perl prior to 5.8.1.
If you insist on using bare v-strings with Perl > 5.6.0, be aware of
the following limitations:
1) For Perl releases 5.6.0 through 5.8.0, the v-string code merely
guesses, based on some characteristics of v-strings. You must use a
three part version, e.g. 1.2.3 or v1.2.3 in order for this heuristic to
be successful.
2) For Perl releases 5.8.1 and later, v-strings have changed in the
Perl core to be magical, which means that the version.pm code can
automatically determine whether the v-string encoding was used.
3) In all cases, a version created using v-strings will have a
stringified form that has a leading 'v' character, for the simple
reason that sometimes it is impossible to tell whether one was present
initially.
Version Object Internals
version.pm provides an overloaded version object that is designed to
both encapsulate the author's intended $VERSION assignment as well as
make it completely natural to use those objects as if they were numbers
(e.g. for comparisons). To do this, a version object contains both the
original representation as typed by the author, as well as a parsed
representation to ease comparisons. Version objects employ overload
methods to simplify code that needs to compare, print, etc the objects.
The internal structure of version objects is a blessed hash with
several components:
bless( {
'original' => 'v1.2.3_4',
'alpha' => 1,
'qv' => 1,
'version' => [
1,
2,
3,
4
]
}, 'version' );
original
A faithful representation of the value used to initialize this
version object. The only time this will not be precisely the same
characters that exist in the source file is if a short dotted-
decimal version like v1.2 was used (in which case it will contain
'v1.2'). This form is STRONGLY discouraged, in that it will
confuse you and your users.
qv A boolean that denotes whether this is a decimal or dotted-decimal
version. See "is_qv()" in version.
alpha
A boolean that denotes whether this is an alpha version. NOTE:
that the underscore can only appear in the last position. See
"is_alpha()" in version.
version
An array of non-negative integers that is used for comparison
purposes with other version objects.
Replacement UNIVERSAL::VERSION
In addition to the version objects, this modules also replaces the core
UNIVERSAL::VERSION function with one that uses version objects for its
comparisons. The return from this operator is always the stringified
form as a simple scalar (i.e. not an object), but the warning message
generated includes either the stringified form or the normal form,
depending on how it was called.
For example:
package Foo;
$VERSION = 1.2;
package Bar;
$VERSION = "v1.3.5"; # works with all Perl's (since it is quoted)
package main;
use version;
print $Foo::VERSION; # prints 1.2
print $Bar::VERSION; # prints 1.003005
eval "use foo 10";
print $@; # prints "foo version 10 required..."
eval "use foo 1.3.5; # work in Perl 5.6.1 or better
print $@; # prints "foo version 1.3.5 required..."
eval "use bar 1.3.6";
print $@; # prints "bar version 1.3.6 required..."
eval "use bar 1.004"; # note Decimal version
print $@; # prints "bar version 1.004 required..."
IMPORTANT NOTE: This may mean that code which searches for a specific
string (to determine whether a given module is available) may need to
be changed. It is always better to use the built-in comparison
implicit in "use" or "require", rather than manually poking at
"class->VERSION" and then doing a comparison yourself.
The replacement UNIVERSAL::VERSION, when used as a function, like this:
print $module->VERSION;
will also exclusively return the stringified form. See
"Stringification" for more details.
USAGE DETAILS
Using modules that use version.pm
As much as possible, the version.pm module remains compatible with all
current code. However, if your module is using a module that has
defined $VERSION using the version class, there are a couple of things
to be aware of. For purposes of discussion, we will assume that we
have the following module installed:
package Example;
use version; $VERSION = qv('1.2.2');
...module code here...
1;
Decimal versions always work
Code of the form:
use Example 1.002003;
will always work correctly. The "use" will perform an automatic
$VERSION comparison using the floating point number given as the
first term after the module name (e.g. above 1.002.003). In this
case, the installed module is too old for the requested line, so
you would see an error like:
Example version 1.002003 (v1.2.3) required--this is only version 1.002002 (v1.2.2)...
Dotted-Decimal version work sometimes
With Perl >= 5.6.2, you can also use a line like this:
use Example 1.2.3;
and it will again work (i.e. give the error message as above), even
with releases of Perl which do not normally support v-strings (see
"What about v-strings?" above). This has to do with that fact that
"use" only checks to see if the second term looks like a number and
passes that to the replacement UNIVERSAL::VERSION. This is not
true in Perl 5.005_04, however, so you are strongly encouraged to
always use a Decimal version in your code, even for those versions
of Perl which support the Dotted-Decimal version.
Object Methods
new()
Like many OO interfaces, the new() method is used to initialize
version objects. If two arguments are passed to "new()", the
second one will be used as if it were prefixed with "v". This is
to support historical use of the "qw" operator with the CVS
variable $Revision, which is automatically incremented by CVS every
time the file is committed to the repository.
In order to facilitate this feature, the following code can be
employed:
$VERSION = version->new(qw$Revision: 2.7 $);
and the version object will be created as if the following code
were used:
$VERSION = version->new("v2.7");
In other words, the version will be automatically parsed out of the
string, and it will be quoted to preserve the meaning CVS normally
carries for versions. The CVS $Revision$ increments differently
from Decimal versions (i.e. 1.10 follows 1.9), so it must be
handled as if it were a Dotted-Decimal Version.
A new version object can be created as a copy of an existing
version object, either as a class method:
$v1 = version->new(12.3);
$v2 = version->new($v1);
or as an object method:
$v1 = version->new(12.3);
$v2 = $v1->new(12.3);
and in each case, $v1 and $v2 will be identical. NOTE: if you
create a new object using an existing object like this:
$v2 = $v1->new();
the new object will not be a clone of the existing object. In the
example case, $v2 will be an empty object of the same type as $v1.
qv()
An alternate way to create a new version object is through the
exported qv() sub. This is not strictly like other q? operators
(like qq, qw), in that the only delimiters supported are
parentheses (or spaces). It is the best way to initialize a short
version without triggering the floating point interpretation. For
example:
$v1 = qv(1.2); # v1.2.0
$v2 = qv("1.2"); # also v1.2.0
As you can see, either a bare number or a quoted string can usually
be used interchangeably, except in the case of a trailing zero,
which must be quoted to be converted properly. For this reason, it
is strongly recommended that all initializers to qv() be quoted
strings instead of bare numbers.
To prevent the "qv()" function from being exported to the caller's
namespace, either use version with a null parameter:
use version ();
or just require version, like this:
require version;
Both methods will prevent the import() method from firing and
exporting the "qv()" sub.
For the subsequent examples, the following three objects will be used:
$ver = version->new("1.2.3.4"); # see "Quoting Rules"
$alpha = version->new("1.2.3_4"); # see "Alpha Versions"
$nver = version->new(1.002); # see "Decimal Versions"
Normal Form
For any version object which is initialized with multiple decimal
places (either quoted or if possible v-string), or initialized
using the qv() operator, the stringified representation is returned
in a normalized or reduced form (no extraneous zeros), and with a
leading 'v':
print $ver->normal; # prints as v1.2.3.4
print $ver->stringify; # ditto
print $ver; # ditto
print $nver->normal; # prints as v1.2.0
print $nver->stringify; # prints as 1.002,
# see "Stringification"
In order to preserve the meaning of the processed version, the
normalized representation will always contain at least three sub
terms. In other words, the following is guaranteed to always be
true:
my $newver = version->new($ver->stringify);
if ($newver eq $ver ) # always true
{...}
Numification
Although all mathematical operations on version objects are
forbidden by default, it is possible to retrieve a number which
corresponds to the version object through the use of the
$obj->numify method. For formatting purposes, when displaying a
number which corresponds a version object, all sub versions are
assumed to have three decimal places. So for example:
print $ver->numify; # prints 1.002003004
print $nver->numify; # prints 1.002
Unlike the stringification operator, there is never any need to
append trailing zeros to preserve the correct version value.
Stringification
The default stringification for version objects returns exactly the
same string as was used to create it, whether you used "new()" or
"qv()", with one exception. The sole exception is if the object
was created using "qv()" and the initializer did not have two
decimal places or a leading 'v' (both optional), then the
stringified form will have a leading 'v' prepended, in order to
support round-trip processing.
For example:
Initialized as Stringifies to
============== ==============
version->new("1.2") 1.2
version->new("v1.2") v1.2
qv("1.2.3") 1.2.3
qv("v1.3.5") v1.3.5
qv("1.2") v1.2 ### exceptional case
See also UNIVERSAL::VERSION, as this also returns the stringified
form when used as a class method.
IMPORTANT NOTE: There is one exceptional cases shown in the above
table where the "initializer" is not stringwise equivalent to the
stringified representation. If you use the "qv"() operator on a
version without a leading 'v' and with only a single decimal place,
the stringified output will have a leading 'v', to preserve the
sense. See the "qv()" operator for more details.
IMPORTANT NOTE 2: Attempting to bypass the normal stringification
rules by manually applying numify() and normal() will sometimes
yield surprising results:
print version->new(version->new("v1.0")->numify)->normal; # v1.0.0
The reason for this is that the numify() operator will turn "v1.0"
into the equivalent string "1.000000". Forcing the outer version
object to normal() form will display the mathematically equivalent
"v1.0.0".
As the example in "new()" shows, you can always create a copy of an
existing version object with the same value by the very compact:
$v2 = $v1->new($v1);
and be assured that both $v1 and $v2 will be completely equivalent,
down to the same internal representation as well as
stringification.
Comparison operators
Both "cmp" and "<=>" operators perform the same comparison between
terms (upgrading to a version object automatically). Perl
automatically generates all of the other comparison operators based
on those two. In addition to the obvious equalities listed below,
appending a single trailing 0 term does not change the value of a
version for comparison purposes. In other words "v1.2" and "1.2.0"
will compare as identical.
For example, the following relations hold:
As Number As String Truth Value
------------- ---------------- -----------
$ver > 1.0 $ver gt "1.0" true
$ver < 2.5 $ver lt true
$ver != 1.3 $ver ne "1.3" true
$ver == 1.2 $ver eq "1.2" false
$ver == 1.2.3.4 $ver eq "1.2.3.4" see discussion below
It is probably best to chose either the Decimal notation or the
string notation and stick with it, to reduce confusion. Perl6
version objects may only support Decimal comparisons. See also
"Quoting Rules".
WARNING: Comparing version with unequal numbers of decimal points
(whether explicitly or implicitly initialized), may yield
unexpected results at first glance. For example, the following
inequalities hold:
version->new(0.96) > version->new(0.95); # 0.960.0 > 0.950.0
version->new("0.96.1") < version->new(0.95); # 0.096.1 < 0.950.0
For this reason, it is best to use either exclusively "Decimal
Versions" or "Dotted-Decimal Versions" with multiple decimal
points.
Logical Operators
If you need to test whether a version object has been initialized,
you can simply test it directly:
$vobj = version->new($something);
if ( $vobj ) # true only if $something was non-blank
You can also test whether a version object is an alpha version, for
example to prevent the use of some feature not present in the main
release:
$vobj = version->new("1.2_3"); # MUST QUOTE
...later...
if ( $vobj->is_alpha ) # True
AUTHOR
John Peacock <jpeacock AT cpan.org>
SEE ALSO
perl.
perl v5.16.3 2014-01-15 version::Internals(3)
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