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0d863452 RH |
1 | package feature; |
2 | ||
d052521a | 3 | our $VERSION = '1.11'; |
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 | ||
12 | my %feature_bundle = ( | |
f23102e2 | 13 | "5.10.0" => [qw(switch say state)], |
0d863452 | 14 | ); |
d052521a | 15 | |
8fd870d9 | 16 | # latest version here |
d052521a | 17 | $feature_bundle{"5.10"} = $feature_bundle{sprintf("%vd",$^V)}; |
0d863452 | 18 | |
7dfde25d RGS |
19 | $feature_bundle{"5.9.5"} = $feature_bundle{"5.10.0"}; |
20 | ||
0d863452 | 21 | # TODO: |
1c321dc6 | 22 | # - think about versioned features (use feature switch => 2) |
0d863452 RH |
23 | |
24 | =head1 NAME | |
25 | ||
26 | feature - Perl pragma to enable new syntactic features | |
27 | ||
28 | =head1 SYNOPSIS | |
29 | ||
bc9b29db | 30 | use feature qw(switch say); |
0d863452 | 31 | given ($foo) { |
bc9b29db RH |
32 | when (1) { say "\$foo == 1" } |
33 | when ([2,3]) { say "\$foo == 2 || \$foo == 3" } | |
34 | when (/^a[bc]d$/) { say "\$foo eq 'abd' || \$foo eq 'acd'" } | |
35 | when ($_ > 100) { say "\$foo > 100" } | |
36 | default { say "None of the above" } | |
0d863452 RH |
37 | } |
38 | ||
ec488c7f RGS |
39 | use feature ':5.10'; # loads all features available in perl 5.10 |
40 | ||
0d863452 RH |
41 | =head1 DESCRIPTION |
42 | ||
43 | It is usually impossible to add new syntax to Perl without breaking | |
44 | some existing programs. This pragma provides a way to minimize that | |
45 | risk. New syntactic constructs can be enabled by C<use feature 'foo'>, | |
46 | and will be parsed only when the appropriate feature pragma is in | |
47 | scope. | |
48 | ||
9eb27be9 RGS |
49 | =head2 Lexical effect |
50 | ||
51 | Like other pragmas (C<use strict>, for example), features have a lexical | |
5e36ed56 | 52 | effect. C<use feature qw(foo)> will only make the feature "foo" available |
9eb27be9 RGS |
53 | from that point to the end of the enclosing block. |
54 | ||
55 | { | |
56 | use feature 'say'; | |
57 | say "say is available here"; | |
58 | } | |
59 | print "But not here.\n"; | |
60 | ||
5e36ed56 RGS |
61 | =head2 C<no feature> |
62 | ||
63 | Features can also be turned off by using C<no feature "foo">. This too | |
64 | has lexical effect. | |
65 | ||
66 | use feature 'say'; | |
67 | say "say is available here"; | |
68 | { | |
69 | no feature 'say'; | |
70 | print "But not here.\n"; | |
71 | } | |
72 | say "Yet it is here."; | |
73 | ||
74 | C<no feature> with no features specified will turn off all features. | |
75 | ||
0d863452 RH |
76 | =head2 The 'switch' feature |
77 | ||
78 | C<use feature 'switch'> tells the compiler to enable the Perl 6 | |
9eb27be9 | 79 | given/when construct. |
0d863452 RH |
80 | |
81 | See L<perlsyn/"Switch statements"> for details. | |
82 | ||
0d863452 RH |
83 | =head2 The 'say' feature |
84 | ||
85 | C<use feature 'say'> tells the compiler to enable the Perl 6 | |
9eb27be9 | 86 | C<say> function. |
0d863452 RH |
87 | |
88 | See L<perlfunc/say> for details. | |
89 | ||
712d05cf RGS |
90 | =head2 the 'state' feature |
91 | ||
92 | C<use feature 'state'> tells the compiler to enable C<state> | |
9eb27be9 | 93 | variables. |
712d05cf | 94 | |
e60bcc8b RGS |
95 | See L<perlsub/"Persistent Private Variables"> for details. |
96 | ||
bc9b29db RH |
97 | =head1 FEATURE BUNDLES |
98 | ||
99 | It's possible to load a whole slew of features in one go, using | |
100 | a I<feature bundle>. The name of a feature bundle is prefixed with | |
101 | a colon, to distinguish it from an actual feature. At present, the | |
8fd870d9 | 102 | only feature bundles are C<use feature ":5.10"> and C<use feature ":5.10.0">, |
f23102e2 | 103 | which both are equivalent to C<use feature qw(switch say state)>. |
8fd870d9 RGS |
104 | |
105 | In the forthcoming 5.10.X perl releases, C<use feature ":5.10"> will be | |
106 | equivalent to the latest C<use feature ":5.10.X">. | |
bc9b29db | 107 | |
7dfde25d RGS |
108 | =head1 IMPLICIT LOADING |
109 | ||
110 | There are two ways to load the C<feature> pragma implicitly : | |
111 | ||
112 | =over 4 | |
113 | ||
114 | =item * | |
115 | ||
116 | By using the C<-E> switch on the command-line instead of C<-e>. It enables | |
117 | all available features in the main compilation unit (that is, the one-liner.) | |
118 | ||
119 | =item * | |
120 | ||
121 | By requiring explicitly a minimal Perl version number for your program, with | |
122 | the C<use VERSION> construct, and when the version is higher than or equal to | |
8d115822 | 123 | 5.10.0. That is, |
7dfde25d | 124 | |
8d115822 | 125 | use 5.10.0; |
7dfde25d RGS |
126 | |
127 | will do an implicit | |
128 | ||
8d115822 | 129 | use feature ':5.10.0'; |
7dfde25d RGS |
130 | |
131 | and so on. | |
132 | ||
8d115822 RB |
133 | But to avoid portability warnings (see L<perlfunc/use>), you may prefer: |
134 | ||
135 | use 5.010; | |
136 | ||
137 | with the same effect. | |
138 | ||
7dfde25d RGS |
139 | =back |
140 | ||
0d863452 RH |
141 | =cut |
142 | ||
143 | sub import { | |
0d863452 RH |
144 | my $class = shift; |
145 | if (@_ == 0) { | |
0d863452 RH |
146 | croak("No features specified"); |
147 | } | |
148 | while (@_) { | |
149 | my $name = shift(@_); | |
89c3975a RGS |
150 | if (substr($name, 0, 1) eq ":") { |
151 | my $v = substr($name, 1); | |
7be54ea7 AB |
152 | if (!exists $feature_bundle{$v}) { |
153 | unknown_feature_bundle($v); | |
bc9b29db | 154 | } |
7be54ea7 | 155 | unshift @_, @{$feature_bundle{$v}}; |
bc9b29db RH |
156 | next; |
157 | } | |
0d863452 | 158 | if (!exists $feature{$name}) { |
b42943c4 | 159 | unknown_feature($name); |
0d863452 RH |
160 | } |
161 | $^H{$feature{$name}} = 1; | |
162 | } | |
163 | } | |
164 | ||
165 | sub unimport { | |
166 | my $class = shift; | |
167 | ||
168 | # A bare C<no feature> should disable *all* features | |
bc9b29db RH |
169 | if (!@_) { |
170 | delete @^H{ values(%feature) }; | |
171 | return; | |
172 | } | |
173 | ||
174 | while (@_) { | |
175 | my $name = shift; | |
89c3975a RGS |
176 | if (substr($name, 0, 1) eq ":") { |
177 | my $v = substr($name, 1); | |
7be54ea7 AB |
178 | if (!exists $feature_bundle{$v}) { |
179 | unknown_feature_bundle($v); | |
bc9b29db | 180 | } |
7be54ea7 | 181 | unshift @_, @{$feature_bundle{$v}}; |
bc9b29db RH |
182 | next; |
183 | } | |
0d863452 | 184 | if (!exists($feature{$name})) { |
b42943c4 | 185 | unknown_feature($name); |
0d863452 RH |
186 | } |
187 | else { | |
188 | delete $^H{$feature{$name}}; | |
189 | } | |
190 | } | |
0d863452 RH |
191 | } |
192 | ||
b42943c4 RGS |
193 | sub unknown_feature { |
194 | my $feature = shift; | |
195 | croak(sprintf('Feature "%s" is not supported by Perl %vd', | |
196 | $feature, $^V)); | |
197 | } | |
198 | ||
199 | sub unknown_feature_bundle { | |
200 | my $feature = shift; | |
201 | croak(sprintf('Feature bundle "%s" is not supported by Perl %vd', | |
202 | $feature, $^V)); | |
203 | } | |
204 | ||
205 | sub croak { | |
206 | require Carp; | |
207 | Carp::croak(@_); | |
208 | } | |
209 | ||
0d863452 | 210 | 1; |