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
46 =head2 The 'switch' feature
48 C<use feature 'switch'> tells the compiler to enable the Perl 6
49 given/when construct from here to the end of the enclosing BLOCK.
51 See L<perlsyn/"Switch statements"> for details.
53 =head2 The '~~' feature
55 C<use feature '~~'> tells the compiler to enable the Perl 6
56 smart match C<~~> operator from here to the end of the enclosing BLOCK.
58 See L<perlsyn/"Smart Matching in Detail"> for details.
60 =head2 The 'say' feature
62 C<use feature 'say'> tells the compiler to enable the Perl 6
63 C<say> function from here to the end of the enclosing BLOCK.
65 See L<perlfunc/say> for details.
67 =head2 the 'err' feature
69 C<use feature 'err'> tells the compiler to enable the C<err>
70 operator from here to the end of the enclosing BLOCK.
72 C<err> is a low-precedence variant of the C<//> operator:
73 see C<perlop> for details.
75 =head2 the 'dor' feature
77 The 'dor' feature is an alias for the 'err' feature.
79 =head2 the 'state' feature
81 C<use feature 'state'> tells the compiler to enable C<state>
82 variables from here to the end of the enclosing BLOCK.
84 See L<perlsub/"Persistent Private Variables"> for details.
86 =head1 FEATURE BUNDLES
88 It's possible to load a whole slew of features in one go, using
89 a I<feature bundle>. The name of a feature bundle is prefixed with
90 a colon, to distinguish it from an actual feature. At present, the
91 only feature bundle is C<use feature ":5.10">, which is equivalent
92 to C<use feature qw(switch ~~ say err state)>.
99 croak("No features specified");
102 my $name = shift(@_);
103 if ($name =~ /^:(.*)/) {
104 if (!exists $feature_bundle{$1}) {
105 unknown_feature_bundle($1);
107 unshift @_, @{$feature_bundle{$1}};
110 if (!exists $feature{$name}) {
111 unknown_feature($name);
113 $^H{$feature{$name}} = 1;
120 # A bare C<no feature> should disable *all* features
122 delete @^H{ values(%feature) };
128 if ($name =~ /^:(.*)/) {
129 if (!exists $feature_bundle{$1}) {
130 unknown_feature_bundle($1);
132 unshift @_, @{$feature_bundle{$1}};
135 if (!exists($feature{$name})) {
136 unknown_feature($name);
139 delete $^H{$feature{$name}};
144 sub unknown_feature {
146 croak(sprintf('Feature "%s" is not supported by Perl %vd',
150 sub unknown_feature_bundle {
152 croak(sprintf('Feature bundle "%s" is not supported by Perl %vd',