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0d863452 RH |
1 | package feature; |
2 | ||
3 | our $VERSION = '1.00'; | |
7168684c | 4 | $feature::hint_bits = 0x00020000; # HINT_LOCALIZE_HH |
0d863452 RH |
5 | |
6 | # (feature name) => (internal name, used in %^H) | |
7 | my %feature = ( | |
7b9ef140 RH |
8 | switch => 'feature_switch', |
9 | "~~" => "feature_~~", | |
10 | say => "feature_say", | |
bc9b29db RH |
11 | err => "feature_err", |
12 | ); | |
13 | ||
14 | my %feature_bundle = ( | |
15 | "5.10" => [qw(switch ~~ say err)], | |
0d863452 RH |
16 | ); |
17 | ||
18 | ||
19 | # Here are some notes that probably shouldn't be in the public | |
20 | # documentation, but which it's useful to have somewhere. | |
21 | # | |
22 | # One side-effect of the change is that C<prototype("CORE::continue")> | |
23 | # no longer throws the error C<Can't find an opnumber for "continue">. | |
24 | # One of the tests in t/op/cproto.t had to be changed to accommodate | |
25 | # this, but it really shouldn't affect real-world code. | |
26 | # | |
27 | # TODO: | |
28 | # - sort out the smartmatch semantics | |
29 | # - think about versioned features (use switch => 2) | |
30 | # | |
31 | # -- Robin 2005-12 | |
32 | ||
33 | =head1 NAME | |
34 | ||
35 | feature - Perl pragma to enable new syntactic features | |
36 | ||
37 | =head1 SYNOPSIS | |
38 | ||
bc9b29db | 39 | use feature qw(switch say); |
0d863452 | 40 | given ($foo) { |
bc9b29db RH |
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" } | |
0d863452 RH |
46 | } |
47 | ||
48 | =head1 DESCRIPTION | |
49 | ||
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 | |
54 | scope. | |
55 | ||
56 | =head2 The 'switch' feature | |
57 | ||
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. | |
60 | ||
61 | See L<perlsyn/"Switch statements"> for details. | |
62 | ||
63 | =head2 The '~~' feature | |
64 | ||
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. | |
67 | ||
68 | See L<perlsyn/"Smart Matching in Detail"> for details. | |
69 | ||
70 | =head2 The 'say' feature | |
71 | ||
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. | |
74 | ||
75 | See L<perlfunc/say> for details. | |
76 | ||
bc9b29db RH |
77 | =head2 the 'err' feature |
78 | ||
79 | C<use feature 'err'> tells the compiler to enable the C<err> | |
80 | operator from here to the end of the enclosing BLOCK. | |
81 | ||
82 | C<err> is a low-precedence variant of the C<//> operator: | |
83 | see C<perlop> for details. | |
84 | ||
85 | =head1 FEATURE BUNDLES | |
86 | ||
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)>. | |
92 | ||
0d863452 RH |
93 | =cut |
94 | ||
95 | sub import { | |
96 | $^H |= $feature::hint_bits; # Need this or %^H won't work | |
97 | ||
98 | my $class = shift; | |
99 | if (@_ == 0) { | |
100 | require Carp; | |
101 | Carp->import("croak"); | |
102 | croak("No features specified"); | |
103 | } | |
104 | while (@_) { | |
105 | my $name = shift(@_); | |
bc9b29db RH |
106 | if ($name =~ /^:(.*)/) { |
107 | if (!exists $feature_bundle{$1}) { | |
108 | require Carp; | |
109 | Carp->import("croak"); | |
110 | croak(sprintf('Feature bundle "%s" is not supported by Perl %vd', | |
111 | $1, $^V)); | |
112 | } | |
113 | unshift @_, @{$feature_bundle{$1}}; | |
114 | next; | |
115 | } | |
0d863452 RH |
116 | if (!exists $feature{$name}) { |
117 | require Carp; | |
118 | Carp->import("croak"); | |
119 | croak(sprintf('Feature "%s" is not supported by Perl %vd', | |
120 | $name, $^V)); | |
121 | } | |
122 | $^H{$feature{$name}} = 1; | |
123 | } | |
124 | } | |
125 | ||
126 | sub unimport { | |
127 | my $class = shift; | |
128 | ||
129 | # A bare C<no feature> should disable *all* features | |
bc9b29db RH |
130 | if (!@_) { |
131 | delete @^H{ values(%feature) }; | |
132 | return; | |
133 | } | |
134 | ||
135 | while (@_) { | |
136 | my $name = shift; | |
137 | if ($name =~ /^:(.*)/) { | |
138 | if (!exists $feature_bundle{$1}) { | |
139 | require Carp; | |
140 | Carp->import("croak"); | |
141 | croak(sprintf('Feature bundle "%s" is not supported by Perl %vd', | |
142 | $1, $^V)); | |
143 | } | |
144 | unshift @_, @{$feature_bundle{$1}}; | |
145 | next; | |
146 | } | |
0d863452 RH |
147 | if (!exists($feature{$name})) { |
148 | require Carp; | |
149 | Carp->import("croak"); | |
150 | croak(sprintf('Feature "%s" is not supported by Perl %vd', | |
151 | $name, $^V)); | |
152 | } | |
153 | else { | |
154 | delete $^H{$feature{$name}}; | |
155 | } | |
156 | } | |
0d863452 RH |
157 | } |
158 | ||
159 | 1; |