5 # (feature name) => (internal name, used in %^H)
7 switch => 'feature_switch',
10 state => "feature_state",
13 my %feature_bundle = (
14 "5.10.0" => [qw(switch say err state)],
17 # keep it harcoded until we actually bump the version number to 5.10
18 $feature_bundle{"5.10"} = $feature_bundle{"5.10.0"};
19 #$feature_bundle{"5.10"} = $feature_bundle{sprintf("%vd",$^V)};
22 # - think about versioned features (use feature switch => 2)
26 feature - Perl pragma to enable new syntactic features
30 use feature qw(switch say);
32 when (1) { say "\$foo == 1" }
33 when ([2,3]) { say "\$foo == 2 || \$foo == 3" }
34 when (/^a[bc]d$/) { say "\$foo eq 'abd' || \$foo eq 'acd'" }
35 when ($_ > 100) { say "\$foo > 100" }
36 default { say "None of the above" }
41 It is usually impossible to add new syntax to Perl without breaking
42 some existing programs. This pragma provides a way to minimize that
43 risk. New syntactic constructs can be enabled by C<use feature 'foo'>,
44 and will be parsed only when the appropriate feature pragma is in
49 Like other pragmas (C<use strict>, for example), features have a lexical
50 effect. C<use feature qw(foo)> will only make the feature "foo" available
51 from that point to the end of the enclosing block.
55 say "say is available here";
57 print "But not here.\n";
61 Features can also be turned off by using C<no feature "foo">. This too
65 say "say is available here";
68 print "But not here.\n";
70 say "Yet it is here.";
72 C<no feature> with no features specified will turn off all features.
74 =head2 The 'switch' feature
76 C<use feature 'switch'> tells the compiler to enable the Perl 6
79 See L<perlsyn/"Switch statements"> for details.
81 =head2 The 'say' feature
83 C<use feature 'say'> tells the compiler to enable the Perl 6
86 See L<perlfunc/say> for details.
88 =head2 the 'err' feature
90 C<use feature 'err'> tells the compiler to enable the C<err>
93 C<err> is a low-precedence variant of the C<//> operator:
94 see C<perlop> for details.
96 =head2 the 'state' feature
98 C<use feature 'state'> tells the compiler to enable C<state>
101 See L<perlsub/"Persistent Private Variables"> for details.
103 =head1 FEATURE BUNDLES
105 It's possible to load a whole slew of features in one go, using
106 a I<feature bundle>. The name of a feature bundle is prefixed with
107 a colon, to distinguish it from an actual feature. At present, the
108 only feature bundles are C<use feature ":5.10"> and C<use feature ":5.10.0">,
109 which both are equivalent to C<use feature qw(switch say err state)>.
111 In the forthcoming 5.10.X perl releases, C<use feature ":5.10"> will be
112 equivalent to the latest C<use feature ":5.10.X">.
119 croak("No features specified");
122 my $name = shift(@_);
123 if ($name =~ /^:(.*)/) {
124 if (!exists $feature_bundle{$1}) {
125 unknown_feature_bundle($1);
127 unshift @_, @{$feature_bundle{$1}};
130 if (!exists $feature{$name}) {
131 unknown_feature($name);
133 $^H{$feature{$name}} = 1;
140 # A bare C<no feature> should disable *all* features
142 delete @^H{ values(%feature) };
148 if ($name =~ /^:(.*)/) {
149 if (!exists $feature_bundle{$1}) {
150 unknown_feature_bundle($1);
152 unshift @_, @{$feature_bundle{$1}};
155 if (!exists($feature{$name})) {
156 unknown_feature($name);
159 delete $^H{$feature{$name}};
164 sub unknown_feature {
166 croak(sprintf('Feature "%s" is not supported by Perl %vd',
170 sub unknown_feature_bundle {
172 croak(sprintf('Feature bundle "%s" is not supported by Perl %vd',