4 $feature::hint_bits = 0x00020000; # HINT_LOCALIZE_HH
6 # (feature name) => (internal name, used in %^H)
8 switch => 'feature_switch',
14 my %feature_bundle = (
15 "5.10" => [qw(switch ~~ say err)],
19 # Here are some notes that probably shouldn't be in the public
20 # documentation, but which it's useful to have somewhere.
22 # One side-effect of the change is that C<prototype("CORE::continue")>
23 # no longer throws the error C<Can't find an opnumber for "continue">.
24 # One of the tests in t/op/cproto.t had to be changed to accommodate
25 # this, but it really shouldn't affect real-world code.
28 # - sort out the smartmatch semantics
29 # - think about versioned features (use switch => 2)
35 feature - Perl pragma to enable new syntactic features
39 use feature qw(switch say);
41 when (1) { say "\$foo == 1" }
42 when ([2,3]) { say "\$foo == 2 || \$foo == 3" }
43 when (/^a[bc]d$/) { say "\$foo eq 'abd' || \$foo eq 'acd'" }
44 when ($_ > 100) { say "\$foo > 100" }
45 default { say "None of the above" }
50 It is usually impossible to add new syntax to Perl without breaking
51 some existing programs. This pragma provides a way to minimize that
52 risk. New syntactic constructs can be enabled by C<use feature 'foo'>,
53 and will be parsed only when the appropriate feature pragma is in
56 =head2 The 'switch' feature
58 C<use feature 'switch'> tells the compiler to enable the Perl 6
59 given/when construct from here to the end of the enclosing BLOCK.
61 See L<perlsyn/"Switch statements"> for details.
63 =head2 The '~~' feature
65 C<use feature '~~'> tells the compiler to enable the Perl 6
66 smart match C<~~> operator from here to the end of the enclosing BLOCK.
68 See L<perlsyn/"Smart Matching in Detail"> for details.
70 =head2 The 'say' feature
72 C<use feature 'say'> tells the compiler to enable the Perl 6
73 C<say> function from here to the end of the enclosing BLOCK.
75 See L<perlfunc/say> for details.
77 =head2 the 'err' feature
79 C<use feature 'err'> tells the compiler to enable the C<err>
80 operator from here to the end of the enclosing BLOCK.
82 C<err> is a low-precedence variant of the C<//> operator:
83 see C<perlop> for details.
85 =head1 FEATURE BUNDLES
87 It's possible to load a whole slew of features in one go, using
88 a I<feature bundle>. The name of a feature bundle is prefixed with
89 a colon, to distinguish it from an actual feature. At present, the
90 only feature bundle is C<use feature ":5.10">, which is equivalent
91 to C<use feature qw(switch ~~ say err)>.
96 $^H |= $feature::hint_bits; # Need this or %^H won't work
101 Carp->import("croak");
102 croak("No features specified");
105 my $name = shift(@_);
106 if ($name =~ /^:(.*)/) {
107 if (!exists $feature_bundle{$1}) {
109 Carp->import("croak");
110 croak(sprintf('Feature bundle "%s" is not supported by Perl %vd',
113 unshift @_, @{$feature_bundle{$1}};
116 if (!exists $feature{$name}) {
118 Carp->import("croak");
119 croak(sprintf('Feature "%s" is not supported by Perl %vd',
122 $^H{$feature{$name}} = 1;
129 # A bare C<no feature> should disable *all* features
131 delete @^H{ values(%feature) };
137 if ($name =~ /^:(.*)/) {
138 if (!exists $feature_bundle{$1}) {
140 Carp->import("croak");
141 croak(sprintf('Feature bundle "%s" is not supported by Perl %vd',
144 unshift @_, @{$feature_bundle{$1}};
147 if (!exists($feature{$name})) {
149 Carp->import("croak");
150 croak(sprintf('Feature "%s" is not supported by Perl %vd',
154 delete $^H{$feature{$name}};