5 # (feature name) => (internal name, used in %^H)
7 switch => 'feature_switch',
12 state => "feature_state",
15 my %feature_bundle = (
16 "5.10" => [qw(switch ~~ say err state)],
21 # - think about versioned features (use feature switch => 2)
25 feature - Perl pragma to enable new syntactic features
29 use feature qw(switch say);
31 when (1) { say "\$foo == 1" }
32 when ([2,3]) { say "\$foo == 2 || \$foo == 3" }
33 when (/^a[bc]d$/) { say "\$foo eq 'abd' || \$foo eq 'acd'" }
34 when ($_ > 100) { say "\$foo > 100" }
35 default { say "None of the above" }
40 It is usually impossible to add new syntax to Perl without breaking
41 some existing programs. This pragma provides a way to minimize that
42 risk. New syntactic constructs can be enabled by C<use feature 'foo'>,
43 and will be parsed only when the appropriate feature pragma is in
48 Like other pragmas (C<use strict>, for example), features have a lexical
49 effect. C<use feature qw(foo)> will only make the feature "foo" available
50 from that point to the end of the enclosing block.
54 say "say is available here";
56 print "But not here.\n";
60 Features can also be turned off by using C<no feature "foo">. This too
64 say "say is available here";
67 print "But not here.\n";
69 say "Yet it is here.";
71 C<no feature> with no features specified will turn off all features.
73 =head2 The 'switch' feature
75 C<use feature 'switch'> tells the compiler to enable the Perl 6
78 See L<perlsyn/"Switch statements"> for details.
80 =head2 The '~~' feature
82 C<use feature '~~'> tells the compiler to enable the Perl 6
83 smart match C<~~> operator.
85 See L<perlsyn/"Smart Matching in Detail"> for details.
87 =head2 The 'say' feature
89 C<use feature 'say'> tells the compiler to enable the Perl 6
92 See L<perlfunc/say> for details.
94 =head2 the 'err' feature
96 C<use feature 'err'> tells the compiler to enable the C<err>
99 C<err> is a low-precedence variant of the C<//> operator:
100 see C<perlop> for details.
102 =head2 the 'dor' feature
104 The 'dor' feature is an alias for the 'err' feature.
106 =head2 the 'state' feature
108 C<use feature 'state'> tells the compiler to enable C<state>
111 See L<perlsub/"Persistent Private Variables"> for details.
113 =head1 FEATURE BUNDLES
115 It's possible to load a whole slew of features in one go, using
116 a I<feature bundle>. The name of a feature bundle is prefixed with
117 a colon, to distinguish it from an actual feature. At present, the
118 only feature bundle is C<use feature ":5.10">, which is equivalent
119 to C<use feature qw(switch ~~ say err state)>.
126 croak("No features specified");
129 my $name = shift(@_);
130 if ($name =~ /^:(.*)/) {
131 if (!exists $feature_bundle{$1}) {
132 unknown_feature_bundle($1);
134 unshift @_, @{$feature_bundle{$1}};
137 if (!exists $feature{$name}) {
138 unknown_feature($name);
140 $^H{$feature{$name}} = 1;
147 # A bare C<no feature> should disable *all* features
149 delete @^H{ values(%feature) };
155 if ($name =~ /^:(.*)/) {
156 if (!exists $feature_bundle{$1}) {
157 unknown_feature_bundle($1);
159 unshift @_, @{$feature_bundle{$1}};
162 if (!exists($feature{$name})) {
163 unknown_feature($name);
166 delete $^H{$feature{$name}};
171 sub unknown_feature {
173 croak(sprintf('Feature "%s" is not supported by Perl %vd',
177 sub unknown_feature_bundle {
179 croak(sprintf('Feature bundle "%s" is not supported by Perl %vd',