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0d863452 RH |
1 | package feature; |
2 | ||
82cfb3a2 | 3 | our $VERSION = '1.13'; |
0d863452 RH |
4 | |
5 | # (feature name) => (internal name, used in %^H) | |
6 | my %feature = ( | |
7b9ef140 | 7 | switch => 'feature_switch', |
7b9ef140 | 8 | say => "feature_say", |
712d05cf | 9 | state => "feature_state", |
bc9b29db RH |
10 | ); |
11 | ||
13a7998c RGS |
12 | # NB. the latest bundle must be loaded by the -E switch (see toke.c) |
13 | ||
bc9b29db | 14 | my %feature_bundle = ( |
82cfb3a2 S |
15 | "5.10" => [qw(switch say state)], |
16 | "5.11" => [qw(switch say state)], | |
0d863452 | 17 | ); |
d052521a | 18 | |
82cfb3a2 S |
19 | # special case |
20 | $feature_bundle{"5.9.5"} = $feature_bundle{"5.10"}; | |
7dfde25d | 21 | |
0d863452 | 22 | # TODO: |
1c321dc6 | 23 | # - think about versioned features (use feature switch => 2) |
0d863452 RH |
24 | |
25 | =head1 NAME | |
26 | ||
27 | feature - Perl pragma to enable new syntactic features | |
28 | ||
29 | =head1 SYNOPSIS | |
30 | ||
bc9b29db | 31 | use feature qw(switch say); |
0d863452 | 32 | given ($foo) { |
bc9b29db RH |
33 | when (1) { say "\$foo == 1" } |
34 | when ([2,3]) { say "\$foo == 2 || \$foo == 3" } | |
35 | when (/^a[bc]d$/) { say "\$foo eq 'abd' || \$foo eq 'acd'" } | |
36 | when ($_ > 100) { say "\$foo > 100" } | |
37 | default { say "None of the above" } | |
0d863452 RH |
38 | } |
39 | ||
ec488c7f RGS |
40 | use feature ':5.10'; # loads all features available in perl 5.10 |
41 | ||
0d863452 RH |
42 | =head1 DESCRIPTION |
43 | ||
44 | It is usually impossible to add new syntax to Perl without breaking | |
45 | some existing programs. This pragma provides a way to minimize that | |
46 | risk. New syntactic constructs can be enabled by C<use feature 'foo'>, | |
47 | and will be parsed only when the appropriate feature pragma is in | |
48 | scope. | |
49 | ||
9eb27be9 RGS |
50 | =head2 Lexical effect |
51 | ||
52 | Like other pragmas (C<use strict>, for example), features have a lexical | |
5e36ed56 | 53 | effect. C<use feature qw(foo)> will only make the feature "foo" available |
9eb27be9 RGS |
54 | from that point to the end of the enclosing block. |
55 | ||
56 | { | |
57 | use feature 'say'; | |
58 | say "say is available here"; | |
59 | } | |
60 | print "But not here.\n"; | |
61 | ||
5e36ed56 RGS |
62 | =head2 C<no feature> |
63 | ||
64 | Features can also be turned off by using C<no feature "foo">. This too | |
65 | has lexical effect. | |
66 | ||
67 | use feature 'say'; | |
68 | say "say is available here"; | |
69 | { | |
70 | no feature 'say'; | |
71 | print "But not here.\n"; | |
72 | } | |
73 | say "Yet it is here."; | |
74 | ||
75 | C<no feature> with no features specified will turn off all features. | |
76 | ||
0d863452 RH |
77 | =head2 The 'switch' feature |
78 | ||
79 | C<use feature 'switch'> tells the compiler to enable the Perl 6 | |
9eb27be9 | 80 | given/when construct. |
0d863452 RH |
81 | |
82 | See L<perlsyn/"Switch statements"> for details. | |
83 | ||
0d863452 RH |
84 | =head2 The 'say' feature |
85 | ||
86 | C<use feature 'say'> tells the compiler to enable the Perl 6 | |
9eb27be9 | 87 | C<say> function. |
0d863452 RH |
88 | |
89 | See L<perlfunc/say> for details. | |
90 | ||
712d05cf RGS |
91 | =head2 the 'state' feature |
92 | ||
93 | C<use feature 'state'> tells the compiler to enable C<state> | |
9eb27be9 | 94 | variables. |
712d05cf | 95 | |
e60bcc8b RGS |
96 | See L<perlsub/"Persistent Private Variables"> for details. |
97 | ||
bc9b29db RH |
98 | =head1 FEATURE BUNDLES |
99 | ||
100 | It's possible to load a whole slew of features in one go, using | |
101 | a I<feature bundle>. The name of a feature bundle is prefixed with | |
102 | a colon, to distinguish it from an actual feature. At present, the | |
82cfb3a2 S |
103 | only feature bundle is C<use feature ":5.10"> which is equivalent |
104 | to C<use feature qw(switch say state)>. | |
8fd870d9 | 105 | |
82cfb3a2 S |
106 | Specifying sub-versions such as the C<0> in C<5.10.0> in feature bundles has |
107 | no effect: feature bundles are guaranteed to be the same for all sub-versions. | |
bc9b29db | 108 | |
7dfde25d RGS |
109 | =head1 IMPLICIT LOADING |
110 | ||
111 | There are two ways to load the C<feature> pragma implicitly : | |
112 | ||
113 | =over 4 | |
114 | ||
115 | =item * | |
116 | ||
117 | By using the C<-E> switch on the command-line instead of C<-e>. It enables | |
118 | all available features in the main compilation unit (that is, the one-liner.) | |
119 | ||
120 | =item * | |
121 | ||
122 | By requiring explicitly a minimal Perl version number for your program, with | |
123 | the C<use VERSION> construct, and when the version is higher than or equal to | |
8d115822 | 124 | 5.10.0. That is, |
7dfde25d | 125 | |
8d115822 | 126 | use 5.10.0; |
7dfde25d RGS |
127 | |
128 | will do an implicit | |
129 | ||
82cfb3a2 | 130 | use feature ':5.10'; |
7dfde25d | 131 | |
82cfb3a2 S |
132 | and so on. Note how the trailing sub-version is automatically stripped from the |
133 | version. | |
7dfde25d | 134 | |
8d115822 RB |
135 | But to avoid portability warnings (see L<perlfunc/use>), you may prefer: |
136 | ||
137 | use 5.010; | |
138 | ||
139 | with the same effect. | |
140 | ||
7dfde25d RGS |
141 | =back |
142 | ||
0d863452 RH |
143 | =cut |
144 | ||
145 | sub import { | |
0d863452 RH |
146 | my $class = shift; |
147 | if (@_ == 0) { | |
0d863452 RH |
148 | croak("No features specified"); |
149 | } | |
150 | while (@_) { | |
151 | my $name = shift(@_); | |
89c3975a RGS |
152 | if (substr($name, 0, 1) eq ":") { |
153 | my $v = substr($name, 1); | |
7be54ea7 | 154 | if (!exists $feature_bundle{$v}) { |
82cfb3a2 S |
155 | $v =~ s/^([0-9]+)\.([0-9]+).[0-9]+$/$1.$2/; |
156 | if (!exists $feature_bundle{$v}) { | |
157 | unknown_feature_bundle(substr($name, 1)); | |
158 | } | |
bc9b29db | 159 | } |
7be54ea7 | 160 | unshift @_, @{$feature_bundle{$v}}; |
bc9b29db RH |
161 | next; |
162 | } | |
0d863452 | 163 | if (!exists $feature{$name}) { |
b42943c4 | 164 | unknown_feature($name); |
0d863452 RH |
165 | } |
166 | $^H{$feature{$name}} = 1; | |
167 | } | |
168 | } | |
169 | ||
170 | sub unimport { | |
171 | my $class = shift; | |
172 | ||
173 | # A bare C<no feature> should disable *all* features | |
bc9b29db RH |
174 | if (!@_) { |
175 | delete @^H{ values(%feature) }; | |
176 | return; | |
177 | } | |
178 | ||
179 | while (@_) { | |
180 | my $name = shift; | |
89c3975a RGS |
181 | if (substr($name, 0, 1) eq ":") { |
182 | my $v = substr($name, 1); | |
7be54ea7 | 183 | if (!exists $feature_bundle{$v}) { |
82cfb3a2 S |
184 | $v =~ s/^([0-9]+)\.([0-9]+).[0-9]+$/$1.$2/; |
185 | if (!exists $feature_bundle{$v}) { | |
186 | unknown_feature_bundle(substr($name, 1)); | |
187 | } | |
bc9b29db | 188 | } |
7be54ea7 | 189 | unshift @_, @{$feature_bundle{$v}}; |
bc9b29db RH |
190 | next; |
191 | } | |
0d863452 | 192 | if (!exists($feature{$name})) { |
b42943c4 | 193 | unknown_feature($name); |
0d863452 RH |
194 | } |
195 | else { | |
196 | delete $^H{$feature{$name}}; | |
197 | } | |
198 | } | |
0d863452 RH |
199 | } |
200 | ||
b42943c4 RGS |
201 | sub unknown_feature { |
202 | my $feature = shift; | |
203 | croak(sprintf('Feature "%s" is not supported by Perl %vd', | |
204 | $feature, $^V)); | |
205 | } | |
206 | ||
207 | sub unknown_feature_bundle { | |
208 | my $feature = shift; | |
209 | croak(sprintf('Feature bundle "%s" is not supported by Perl %vd', | |
210 | $feature, $^V)); | |
211 | } | |
212 | ||
213 | sub croak { | |
214 | require Carp; | |
215 | Carp::croak(@_); | |
216 | } | |
217 | ||
0d863452 | 218 | 1; |