Rafaël Garcia-Suarez > perl-5.10.0 > feature

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Module Version: 1.11   Source   Latest Release: perl-5.21.4

NAME ^

feature - Perl pragma to enable new syntactic features

SYNOPSIS ^

    use feature qw(switch say);
    given ($foo) {
        when (1)          { say "\$foo == 1" }
        when ([2,3])      { say "\$foo == 2 || \$foo == 3" }
        when (/^a[bc]d$/) { say "\$foo eq 'abd' || \$foo eq 'acd'" }
        when ($_ > 100)   { say "\$foo > 100" }
        default           { say "None of the above" }
    }

    use feature ':5.10'; # loads all features available in perl 5.10

DESCRIPTION ^

It is usually impossible to add new syntax to Perl without breaking some existing programs. This pragma provides a way to minimize that risk. New syntactic constructs can be enabled by use feature 'foo', and will be parsed only when the appropriate feature pragma is in scope.

Lexical effect

Like other pragmas (use strict, for example), features have a lexical effect. use feature qw(foo) will only make the feature "foo" available from that point to the end of the enclosing block.

    {
        use feature 'say';
        say "say is available here";
    }
    print "But not here.\n";

no feature

Features can also be turned off by using no feature "foo". This too has lexical effect.

    use feature 'say';
    say "say is available here";
    {
        no feature 'say';
        print "But not here.\n";
    }
    say "Yet it is here.";

no feature with no features specified will turn off all features.

The 'switch' feature

use feature 'switch' tells the compiler to enable the Perl 6 given/when construct.

See "Switch statements" in perlsyn for details.

The 'say' feature

use feature 'say' tells the compiler to enable the Perl 6 say function.

See "say" in perlfunc for details.

the 'state' feature

use feature 'state' tells the compiler to enable state variables.

See "Persistent Private Variables" in perlsub for details.

FEATURE BUNDLES ^

It's possible to load a whole slew of features in one go, using a feature bundle. The name of a feature bundle is prefixed with a colon, to distinguish it from an actual feature. At present, the only feature bundles are use feature ":5.10" and use feature ":5.10.0", which both are equivalent to use feature qw(switch say state).

In the forthcoming 5.10.X perl releases, use feature ":5.10" will be equivalent to the latest use feature ":5.10.X".

IMPLICIT LOADING ^

There are two ways to load the feature pragma implicitly :

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