versio...ernals(3perl)

📦
version 5.44.0 · 14 versions
, in arch rolling

💖 version::Internals — the Perl version-object lore, explained by your favorite Unix bestie 🫶

okay so you found version::Internals, the deep lore doc for version::Internals - Perl extension for Version Objects. 💅

✨ DESCRIPTION ✨

so basically: Overloaded version objects for all modern versions of Perl. like, all of them. every era. iconic behavior honestly.

this page is the backstage tour 👑 — it documents the internal data representation and underlying code for version.pm. if you just wanna know how to use it day-to-day, go read version.pod instead, bestie. this one is literally only useful for the users who are obsessed with the gory details. and if that's you? welcome, you're home. 🎀

🌸 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. that's the whole vibe. it lines up with what Perl itself uses for a version, and it extends the whole "version as number" thing discussed in the various editions of the Camel book. 📚

there are actually two distinct kinds of version objects, and you gotta know the difference:

  • 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 contain more than one decimal point and may have an optional embedded underscore, see Dotted-Decimal Versions. this is what's 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

and to be 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, plus all the 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 that means: 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. sneaky but valid. 🙈

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 — because of 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. no cap. 💀

🦋 Dotted-Decimal Versions

these are the newest form of versions, and they 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: 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 ✨

Okay so when Perl 5.6.0 dropped, the decision was made to give us a transformation between the old-style decimal versions and the new-style dotted-decimal versions. It's giving bridge energy:

5.6.0    == 5.006000
5.005_04 == 5.5.40

The way it works: take that floating point number and split it first on the single decimal place. Then every group of three digits to the right of the decimal makes up the next digit, and you keep going until the number of significant digits is exhausted, plus enough trailing zeros to reach the next multiple of three. Iconic math behavior.

This was the method that version.pm adopted too. Some examples may be helpful, bestie:

                                   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 Perl's parsing and tokenizing routines are kind of extra, certain initialization values must be quoted to correctly parse as the intended version. Especially when you're using the declare or qv() methods. You don't have to quote decimal numbers when creating version objects, but it's always safe to quote all initial values when using version.pm methods. That way, what you type is what is used. Periodt.

Also, 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 don't quote your value, Perl's normal numeric handling comes into play, and you may not get back what you were expecting. It's giving unpredictable.

If you use a mathematic formula that resolves to a floating point number, you're dependent on Perl's conversion routines to yield the version you expect. Dividing by a power of 10? Pretty safe, 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, using 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 these 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.

👑 Replacement UNIVERSAL::VERSION 👑

In addition to the version objects, this module 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.

💖 Using modules that use version.pm 💖

Bestie, version.pm stays compatible with basically all the code you already have, as much as it possibly can. But if your module is using a module that set $VERSION with the version class, there's a couple things you gotta know. For the sake of us chatting about it, let's pretend you've got this module installed:

package Example;
use version;  $VERSION = qv('1.2.2');
...module code here...
1;

✨ Decimal versions always work ✨

Code that looks like this:

use Example 1.002003;

is always gonna work correctly. The use will do an automatic $VERSION comparison using that floating point number you gave 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 line you requested, so you'd get 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'll again work (i.e. throw that same error message as above), even on releases of Perl that don't normally support v-strings (peep "What about v-strings?" above). This happens because use only bothers to check whether the second term looks like a number, and passes that along to the replacement UNIVERSAL::VERSION. That is not true in Perl 5.005_04 though, so you are strongly encouraged to always use a Decimal version in your code, even for those versions of Perl that do support the Dotted-Decimal version. Fr fr, just use Decimal.

👑 Object Methods 👑

new()

Like a whole bunch of OO interfaces, the new() method is what you use to initialize version objects. If you pass two arguments to new(), that second one gets used as if it were prefixed with "v". This is to support the historical use of the qw operator with the CVS variable $Revision, which CVS auto-increments every time the file gets committed to the repository.

To make that feature happen, you can employ this code:

$VERSION = version->new(qw$Revision: 2.7 $);

and the version object gets created as if you'd written this:

$VERSION = version->new("v2.7");

In other words: the version is automatically parsed out of the string, and it gets 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 has to be handled as if it were a Dotted-Decimal Version.

A new version object can also 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();

then the new object will not be a clone of the existing object. In that example case, $v2 will be an empty object of the same type as $v1. Not a copy, just vibes of a copy. 💀

qv()

Another way to create a new version object is through the exported qv() sub. Heads up: this is not strictly like other q? operators (like qq, qw), because the only delimiters supported are parentheses (or spaces). It's the best way to initialize a short version without triggering the floating point interpretation. Like so:

$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. Quote it, bestie. 🎀

To stop the qv() function from being exported into 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 initialized with multiple decimal places (quoted, or a v-string if possible), or initialized using the qv() operator, the stringified representation is returned in a normalized or reduced form (no extraneous zeros), 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"

And to preserve the meaning of the processed version, the normalized representation will always contain at least three sub terms. In other words, this here is guaranteed to always be true:

my $newver = version->new($ver->stringify);
if ($newver eq $ver ) # always true
  {...}

🔥 Numification 🔥

Even though all mathematical operations on version objects are forbidden by default, you can still retrieve a number corresponding to the version object with the $obj->numify method. For formatting purposes, when displaying a number corresponding to 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

And unlike the stringification operator, you never need to append trailing zeros to preserve the correct version value. Periodt.

🦋 Stringification 🦋

The default stringification for version objects returns exactly the same string you 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 are optional), because then the stringified form gets 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, since that also returns the stringified form when used as a class method.

IMPORTANT NOTE: There is one exceptional case 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 into normal() form will display the mathematically equivalent "v1.0.0". It's giving math, not vibes. 😭

As the example in "new()" shows, you can always create a copy of an existing version object with the same value using this very compact form:

$v2 = $v1->new($v1);

and be assured that both $v1 and $v2 will be completely equivalent — down to the same internal representation and the same stringification. Iconic behavior honestly. 💅

⭐ Comparison operators ⭐

Both "cmp" and "<=>" operators perform the same comparison between terms (upgrading to a version object automatically), and Perl automatically generates all of the other comparison operators based on those two. On top of 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's probably best to choose 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 versions 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. Pick a lane, babe. 🚗

💜 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 that isn't present in the main release:

$vobj = version->new("1.2_3"); # MUST QUOTE
...later...
if ( $vobj->is_alpha )       # True

🌸 AUTHOR 🌸

John Peacock <jpeacock@cpan.org>

🌟 SEE ALSO 🌟

perl.

And that's a wrap on this page, bestie! 💖 This was taken from Perl v5.44.0, dated 2026-10-17 — yes, the versio...ernals(3perl) page, all three parts, complete. Go forth and version responsibly. 🫶✨

📦 where this page comes from