5 # (feature name) => (internal name, used in %^H)
7 switch => 'feature_switch',
13 my %feature_bundle = (
14 "5.10" => [qw(switch ~~ say err)],
18 # Here are some notes that probably shouldn't be in the public
19 # documentation, but which it's useful to have somewhere.
21 # One side-effect of the change is that C<prototype("CORE::continue")>
22 # no longer throws the error C<Can't find an opnumber for "continue">.
23 # One of the tests in t/op/cproto.t had to be changed to accommodate
24 # this, but it really shouldn't affect real-world code.
27 # - sort out the smartmatch semantics
28 # - think about versioned features (use switch => 2)
34 feature - Perl pragma to enable new syntactic features
38 use feature qw(switch say);
40 when (1) { say "\$foo == 1" }
41 when ([2,3]) { say "\$foo == 2 || \$foo == 3" }
42 when (/^a[bc]d$/) { say "\$foo eq 'abd' || \$foo eq 'acd'" }
43 when ($_ > 100) { say "\$foo > 100" }
44 default { say "None of the above" }
49 It is usually impossible to add new syntax to Perl without breaking
50 some existing programs. This pragma provides a way to minimize that
51 risk. New syntactic constructs can be enabled by C<use feature 'foo'>,
52 and will be parsed only when the appropriate feature pragma is in
55 =head2 The 'switch' feature
57 C<use feature 'switch'> tells the compiler to enable the Perl 6
58 given/when construct from here to the end of the enclosing BLOCK.
60 See L<perlsyn/"Switch statements"> for details.
62 =head2 The '~~' feature
64 C<use feature '~~'> tells the compiler to enable the Perl 6
65 smart match C<~~> operator from here to the end of the enclosing BLOCK.
67 See L<perlsyn/"Smart Matching in Detail"> for details.
69 =head2 The 'say' feature
71 C<use feature 'say'> tells the compiler to enable the Perl 6
72 C<say> function from here to the end of the enclosing BLOCK.
74 See L<perlfunc/say> for details.
76 =head2 the 'err' feature
78 C<use feature 'err'> tells the compiler to enable the C<err>
79 operator from here to the end of the enclosing BLOCK.
81 C<err> is a low-precedence variant of the C<//> operator:
82 see C<perlop> for details.
84 =head1 FEATURE BUNDLES
86 It's possible to load a whole slew of features in one go, using
87 a I<feature bundle>. The name of a feature bundle is prefixed with
88 a colon, to distinguish it from an actual feature. At present, the
89 only feature bundle is C<use feature ":5.10">, which is equivalent
90 to C<use feature qw(switch ~~ say err)>.
98 Carp->import("croak");
99 croak("No features specified");
102 my $name = shift(@_);
103 if ($name =~ /^:(.*)/) {
104 if (!exists $feature_bundle{$1}) {
106 Carp->import("croak");
107 croak(sprintf('Feature bundle "%s" is not supported by Perl %vd',
110 unshift @_, @{$feature_bundle{$1}};
113 if (!exists $feature{$name}) {
115 Carp->import("croak");
116 croak(sprintf('Feature "%s" is not supported by Perl %vd',
119 $^H{$feature{$name}} = 1;
126 # A bare C<no feature> should disable *all* features
128 delete @^H{ values(%feature) };
134 if ($name =~ /^:(.*)/) {
135 if (!exists $feature_bundle{$1}) {
137 Carp->import("croak");
138 croak(sprintf('Feature bundle "%s" is not supported by Perl %vd',
141 unshift @_, @{$feature_bundle{$1}};
144 if (!exists($feature{$name})) {
146 Carp->import("croak");
147 croak(sprintf('Feature "%s" is not supported by Perl %vd',
151 delete $^H{$feature{$name}};