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.

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

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

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 bundle is "use feature ":5.10"" which is equivalent to "use feature qw(switch say state)".

Specifying sub-versions such as the 0 in 5.10.0 in feature bundles has no effect: feature bundles are guaranteed to be the same for all sub-versions.

IMPLICIT LOADING¶

There are two ways to load the "feature" pragma implicitly :

• By using the "-E" switch on the command-line instead of "-e". It enables all available features in the main compilation unit (that is, the one-liner.)
• By requiring explicitly a minimal Perl version number for your program, with the "use VERSION" construct, and when the version is higher than or equal to 5.10.0. That is,

      use 5.10.0;
      

  will do an implicit

      use feature ':5.10';
      

  and so on. Note how the trailing sub-version is automatically stripped from the version.

  But to avoid portability warnings (see "use" in perlfunc), you may prefer:

      use 5.010;
      

  with the same effect.