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0d863452 RH |
1 | package feature; |
2 | ||
712d05cf | 3 | our $VERSION = '1.01'; |
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4 | |
5 | # (feature name) => (internal name, used in %^H) | |
6 | my %feature = ( | |
7b9ef140 RH |
7 | switch => 'feature_switch', |
8 | "~~" => "feature_~~", | |
9 | say => "feature_say", | |
bc9b29db | 10 | err => "feature_err", |
c0cd9745 | 11 | dor => "feature_err", |
712d05cf | 12 | state => "feature_state", |
bc9b29db RH |
13 | ); |
14 | ||
15 | my %feature_bundle = ( | |
712d05cf | 16 | "5.10" => [qw(switch ~~ say err state)], |
0d863452 RH |
17 | ); |
18 | ||
19 | ||
20 | # Here are some notes that probably shouldn't be in the public | |
21 | # documentation, but which it's useful to have somewhere. | |
22 | # | |
23 | # One side-effect of the change is that C<prototype("CORE::continue")> | |
24 | # no longer throws the error C<Can't find an opnumber for "continue">. | |
25 | # One of the tests in t/op/cproto.t had to be changed to accommodate | |
26 | # this, but it really shouldn't affect real-world code. | |
27 | # | |
28 | # TODO: | |
29 | # - sort out the smartmatch semantics | |
30 | # - think about versioned features (use switch => 2) | |
31 | # | |
32 | # -- Robin 2005-12 | |
33 | ||
34 | =head1 NAME | |
35 | ||
36 | feature - Perl pragma to enable new syntactic features | |
37 | ||
38 | =head1 SYNOPSIS | |
39 | ||
bc9b29db | 40 | use feature qw(switch say); |
0d863452 | 41 | given ($foo) { |
bc9b29db RH |
42 | when (1) { say "\$foo == 1" } |
43 | when ([2,3]) { say "\$foo == 2 || \$foo == 3" } | |
44 | when (/^a[bc]d$/) { say "\$foo eq 'abd' || \$foo eq 'acd'" } | |
45 | when ($_ > 100) { say "\$foo > 100" } | |
46 | default { say "None of the above" } | |
0d863452 RH |
47 | } |
48 | ||
49 | =head1 DESCRIPTION | |
50 | ||
51 | It is usually impossible to add new syntax to Perl without breaking | |
52 | some existing programs. This pragma provides a way to minimize that | |
53 | risk. New syntactic constructs can be enabled by C<use feature 'foo'>, | |
54 | and will be parsed only when the appropriate feature pragma is in | |
55 | scope. | |
56 | ||
57 | =head2 The 'switch' feature | |
58 | ||
59 | C<use feature 'switch'> tells the compiler to enable the Perl 6 | |
60 | given/when construct from here to the end of the enclosing BLOCK. | |
61 | ||
62 | See L<perlsyn/"Switch statements"> for details. | |
63 | ||
64 | =head2 The '~~' feature | |
65 | ||
66 | C<use feature '~~'> tells the compiler to enable the Perl 6 | |
67 | smart match C<~~> operator from here to the end of the enclosing BLOCK. | |
68 | ||
69 | See L<perlsyn/"Smart Matching in Detail"> for details. | |
70 | ||
71 | =head2 The 'say' feature | |
72 | ||
73 | C<use feature 'say'> tells the compiler to enable the Perl 6 | |
74 | C<say> function from here to the end of the enclosing BLOCK. | |
75 | ||
76 | See L<perlfunc/say> for details. | |
77 | ||
bc9b29db RH |
78 | =head2 the 'err' feature |
79 | ||
80 | C<use feature 'err'> tells the compiler to enable the C<err> | |
81 | operator from here to the end of the enclosing BLOCK. | |
82 | ||
83 | C<err> is a low-precedence variant of the C<//> operator: | |
84 | see C<perlop> for details. | |
85 | ||
c0cd9745 RGS |
86 | =head2 the 'dor' feature |
87 | ||
88 | The 'dor' feature is an alias for the 'err' feature. | |
89 | ||
712d05cf RGS |
90 | =head2 the 'state' feature |
91 | ||
92 | C<use feature 'state'> tells the compiler to enable C<state> | |
93 | variables from here to the end of the enclosing BLOCK. | |
94 | ||
bc9b29db RH |
95 | =head1 FEATURE BUNDLES |
96 | ||
97 | It's possible to load a whole slew of features in one go, using | |
98 | a I<feature bundle>. The name of a feature bundle is prefixed with | |
99 | a colon, to distinguish it from an actual feature. At present, the | |
100 | only feature bundle is C<use feature ":5.10">, which is equivalent | |
712d05cf | 101 | to C<use feature qw(switch ~~ say err state)>. |
bc9b29db | 102 | |
0d863452 RH |
103 | =cut |
104 | ||
105 | sub import { | |
0d863452 RH |
106 | my $class = shift; |
107 | if (@_ == 0) { | |
108 | require Carp; | |
109 | Carp->import("croak"); | |
110 | croak("No features specified"); | |
111 | } | |
112 | while (@_) { | |
113 | my $name = shift(@_); | |
bc9b29db RH |
114 | if ($name =~ /^:(.*)/) { |
115 | if (!exists $feature_bundle{$1}) { | |
116 | require Carp; | |
117 | Carp->import("croak"); | |
118 | croak(sprintf('Feature bundle "%s" is not supported by Perl %vd', | |
119 | $1, $^V)); | |
120 | } | |
121 | unshift @_, @{$feature_bundle{$1}}; | |
122 | next; | |
123 | } | |
0d863452 RH |
124 | if (!exists $feature{$name}) { |
125 | require Carp; | |
126 | Carp->import("croak"); | |
127 | croak(sprintf('Feature "%s" is not supported by Perl %vd', | |
128 | $name, $^V)); | |
129 | } | |
130 | $^H{$feature{$name}} = 1; | |
131 | } | |
132 | } | |
133 | ||
134 | sub unimport { | |
135 | my $class = shift; | |
136 | ||
137 | # A bare C<no feature> should disable *all* features | |
bc9b29db RH |
138 | if (!@_) { |
139 | delete @^H{ values(%feature) }; | |
140 | return; | |
141 | } | |
142 | ||
143 | while (@_) { | |
144 | my $name = shift; | |
145 | if ($name =~ /^:(.*)/) { | |
146 | if (!exists $feature_bundle{$1}) { | |
147 | require Carp; | |
148 | Carp->import("croak"); | |
149 | croak(sprintf('Feature bundle "%s" is not supported by Perl %vd', | |
150 | $1, $^V)); | |
151 | } | |
152 | unshift @_, @{$feature_bundle{$1}}; | |
153 | next; | |
154 | } | |
0d863452 RH |
155 | if (!exists($feature{$name})) { |
156 | require Carp; | |
157 | Carp->import("croak"); | |
158 | croak(sprintf('Feature "%s" is not supported by Perl %vd', | |
159 | $name, $^V)); | |
160 | } | |
161 | else { | |
162 | delete $^H{$feature{$name}}; | |
163 | } | |
164 | } | |
0d863452 RH |
165 | } |
166 | ||
167 | 1; |