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 to pass the is_strict() test.
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 main
version.pm file. 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 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.
- 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 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" in version 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¶
- 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
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.
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@cpan.org>
SEE ALSO¶
perl.