There are actually two distinct kinds of version objects:
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''.
# 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.
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''.
# Declaring
use version 0.77; our $VERSION = version->declare("v1.2_3");
# Parsing
$v1 = version->parse("v1.2_3");
$v1 = version->parse("1.002_003");
Note that you must quote the version when writing an alpha Decimal version. The stringified form of Decimal versions will always be the same string that was used to initialize the version object.
For dotted decimals:
v1.2
1.2345.6
v1.23_4
The leading 'v' is optional if two or more decimals appear. If only a single decimal is included, then the leading 'v' is required to trigger the dotted-decimal parsing. A leading zero is permitted, though not recommended except when quoted, because of the risk that Perl will treat the number as octal. A trailing underscore plus one or more digits denotes an alpha or development release (and must be quoted to be parsed properly).
For decimal versions:
1
1.2345
1.2345_01
an integer portion, an optional decimal point, and optionally one or more digits to the right of the decimal are all required. A trailing underscore is permitted and a leading zero is permitted. Just like the lax dotted-decimal version, quoting the values is required for alpha/development forms to be parsed correctly.
Both of the provided scalars are already compiled as regular expressions and do not contain either anchors or implicit groupings, so they can be included in your own regular expressions freely. For example, consider the following code:
($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.
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
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
$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.
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' );
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.
package Example;
use version; $VERSION = qv('1.2.2');
...module code here...
1;
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)...
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.
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.
$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"
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
{...}
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.
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.
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.
$vobj = version->new($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