5 # (feature name) => (internal name, used in %^H)
7 switch => 'feature_switch',
11 state => "feature_state",
14 my %feature_bundle = (
15 "5.10" => [qw(switch ~~ say err state)],
20 # - think about versioned features (use feature switch => 2)
24 feature - Perl pragma to enable new syntactic features
28 use feature qw(switch say);
30 when (1) { say "\$foo == 1" }
31 when ([2,3]) { say "\$foo == 2 || \$foo == 3" }
32 when (/^a[bc]d$/) { say "\$foo eq 'abd' || \$foo eq 'acd'" }
33 when ($_ > 100) { say "\$foo > 100" }
34 default { say "None of the above" }
39 It is usually impossible to add new syntax to Perl without breaking
40 some existing programs. This pragma provides a way to minimize that
41 risk. New syntactic constructs can be enabled by C<use feature 'foo'>,
42 and will be parsed only when the appropriate feature pragma is in
47 Like other pragmas (C<use strict>, for example), features have a lexical
48 effect. C<use feature qw(foo)> will only make the feature "foo" available
49 from that point to the end of the enclosing block.
53 say "say is available here";
55 print "But not here.\n";
59 Features can also be turned off by using C<no feature "foo">. This too
63 say "say is available here";
66 print "But not here.\n";
68 say "Yet it is here.";
70 C<no feature> with no features specified will turn off all features.
72 =head2 The 'switch' feature
74 C<use feature 'switch'> tells the compiler to enable the Perl 6
77 See L<perlsyn/"Switch statements"> for details.
79 =head2 The '~~' feature
81 C<use feature '~~'> tells the compiler to enable the Perl 6
82 smart match C<~~> operator.
84 See L<perlsyn/"Smart matching in detail"> for details.
86 =head2 The 'say' feature
88 C<use feature 'say'> tells the compiler to enable the Perl 6
91 See L<perlfunc/say> for details.
93 =head2 the 'err' feature
95 C<use feature 'err'> tells the compiler to enable the C<err>
98 C<err> is a low-precedence variant of the C<//> operator:
99 see C<perlop> for details.
101 =head2 the 'state' feature
103 C<use feature 'state'> tells the compiler to enable C<state>
106 See L<perlsub/"Persistent Private Variables"> for details.
108 =head1 FEATURE BUNDLES
110 It's possible to load a whole slew of features in one go, using
111 a I<feature bundle>. The name of a feature bundle is prefixed with
112 a colon, to distinguish it from an actual feature. At present, the
113 only feature bundle is C<use feature ":5.10">, which is equivalent
114 to C<use feature qw(switch ~~ say err state)>.
121 croak("No features specified");
124 my $name = shift(@_);
125 if ($name =~ /^:(.*)/) {
126 if (!exists $feature_bundle{$1}) {
127 unknown_feature_bundle($1);
129 unshift @_, @{$feature_bundle{$1}};
132 if (!exists $feature{$name}) {
133 unknown_feature($name);
135 $^H{$feature{$name}} = 1;
142 # A bare C<no feature> should disable *all* features
144 delete @^H{ values(%feature) };
150 if ($name =~ /^:(.*)/) {
151 if (!exists $feature_bundle{$1}) {
152 unknown_feature_bundle($1);
154 unshift @_, @{$feature_bundle{$1}};
157 if (!exists($feature{$name})) {
158 unknown_feature($name);
161 delete $^H{$feature{$name}};
166 sub unknown_feature {
168 croak(sprintf('Feature "%s" is not supported by Perl %vd',
172 sub unknown_feature_bundle {
174 croak(sprintf('Feature bundle "%s" is not supported by Perl %vd',