Commit | Line | Data |
---|---|---|
0d863452 RH |
1 | package feature; |
2 | ||
b7569deb | 3 | our $VERSION = '1.16'; |
0d863452 RH |
4 | |
5 | # (feature name) => (internal name, used in %^H) | |
6 | my %feature = ( | |
1863b879 RGS |
7 | switch => 'feature_switch', |
8 | say => "feature_say", | |
9 | state => "feature_state", | |
10 | unicode_strings => "feature_unicode", | |
bc9b29db RH |
11 | ); |
12 | ||
1863b879 RGS |
13 | # This gets set (for now) in $^H as well as in %^H, |
14 | # for runtime speed of the uc/lc/ucfirst/lcfirst functions. | |
b0f41c9d | 15 | # See HINT_UNI_8_BIT in perl.h. |
1863b879 RGS |
16 | our $hint_uni8bit = 0x00000800; |
17 | ||
13a7998c RGS |
18 | # NB. the latest bundle must be loaded by the -E switch (see toke.c) |
19 | ||
bc9b29db | 20 | my %feature_bundle = ( |
82cfb3a2 | 21 | "5.10" => [qw(switch say state)], |
1863b879 | 22 | "5.11" => [qw(switch say state unicode_strings)], |
b7569deb | 23 | "5.12" => [qw(switch say state unicode_strings)], |
0d863452 | 24 | ); |
d052521a | 25 | |
82cfb3a2 S |
26 | # special case |
27 | $feature_bundle{"5.9.5"} = $feature_bundle{"5.10"}; | |
7dfde25d | 28 | |
0d863452 | 29 | # TODO: |
1c321dc6 | 30 | # - think about versioned features (use feature switch => 2) |
0d863452 RH |
31 | |
32 | =head1 NAME | |
33 | ||
e1b711da | 34 | feature - Perl pragma to enable new features |
0d863452 RH |
35 | |
36 | =head1 SYNOPSIS | |
37 | ||
bc9b29db | 38 | use feature qw(switch say); |
0d863452 | 39 | given ($foo) { |
bc9b29db RH |
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" } | |
0d863452 RH |
45 | } |
46 | ||
ec488c7f RGS |
47 | use feature ':5.10'; # loads all features available in perl 5.10 |
48 | ||
0d863452 RH |
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 | |
1863b879 RGS |
53 | risk. New syntactic constructs, or new semantic meanings to older |
54 | constructs, can be enabled by C<use feature 'foo'>, and will be parsed | |
55 | only when the appropriate feature pragma is in scope. | |
0d863452 | 56 | |
9eb27be9 RGS |
57 | =head2 Lexical effect |
58 | ||
59 | Like other pragmas (C<use strict>, for example), features have a lexical | |
5e36ed56 | 60 | effect. C<use feature qw(foo)> will only make the feature "foo" available |
9eb27be9 RGS |
61 | from that point to the end of the enclosing block. |
62 | ||
63 | { | |
64 | use feature 'say'; | |
65 | say "say is available here"; | |
66 | } | |
67 | print "But not here.\n"; | |
68 | ||
5e36ed56 RGS |
69 | =head2 C<no feature> |
70 | ||
71 | Features can also be turned off by using C<no feature "foo">. This too | |
72 | has lexical effect. | |
73 | ||
74 | use feature 'say'; | |
75 | say "say is available here"; | |
76 | { | |
77 | no feature 'say'; | |
78 | print "But not here.\n"; | |
79 | } | |
80 | say "Yet it is here."; | |
81 | ||
82 | C<no feature> with no features specified will turn off all features. | |
83 | ||
0d863452 RH |
84 | =head2 The 'switch' feature |
85 | ||
86 | C<use feature 'switch'> tells the compiler to enable the Perl 6 | |
9eb27be9 | 87 | given/when construct. |
0d863452 RH |
88 | |
89 | See L<perlsyn/"Switch statements"> for details. | |
90 | ||
0d863452 RH |
91 | =head2 The 'say' feature |
92 | ||
93 | C<use feature 'say'> tells the compiler to enable the Perl 6 | |
9eb27be9 | 94 | C<say> function. |
0d863452 RH |
95 | |
96 | See L<perlfunc/say> for details. | |
97 | ||
712d05cf RGS |
98 | =head2 the 'state' feature |
99 | ||
100 | C<use feature 'state'> tells the compiler to enable C<state> | |
9eb27be9 | 101 | variables. |
712d05cf | 102 | |
e60bcc8b RGS |
103 | See L<perlsub/"Persistent Private Variables"> for details. |
104 | ||
1863b879 RGS |
105 | =head2 the 'unicode_strings' feature |
106 | ||
107 | C<use feature 'unicode_strings'> tells the compiler to treat | |
e1b711da KW |
108 | all strings outside of C<use locale> and C<use bytes> as Unicode. It is |
109 | available starting with Perl 5.11.3. | |
1863b879 | 110 | |
e1b711da | 111 | See L<perlunicode/The "Unicode Bug"> for details. |
1863b879 | 112 | |
bc9b29db RH |
113 | =head1 FEATURE BUNDLES |
114 | ||
115 | It's possible to load a whole slew of features in one go, using | |
116 | a I<feature bundle>. The name of a feature bundle is prefixed with | |
117 | a colon, to distinguish it from an actual feature. At present, the | |
82cfb3a2 S |
118 | only feature bundle is C<use feature ":5.10"> which is equivalent |
119 | to C<use feature qw(switch say state)>. | |
8fd870d9 | 120 | |
82cfb3a2 S |
121 | Specifying sub-versions such as the C<0> in C<5.10.0> in feature bundles has |
122 | no effect: feature bundles are guaranteed to be the same for all sub-versions. | |
bc9b29db | 123 | |
7dfde25d RGS |
124 | =head1 IMPLICIT LOADING |
125 | ||
126 | There are two ways to load the C<feature> pragma implicitly : | |
127 | ||
128 | =over 4 | |
129 | ||
130 | =item * | |
131 | ||
132 | By using the C<-E> switch on the command-line instead of C<-e>. It enables | |
133 | all available features in the main compilation unit (that is, the one-liner.) | |
134 | ||
135 | =item * | |
136 | ||
137 | By requiring explicitly a minimal Perl version number for your program, with | |
138 | the C<use VERSION> construct, and when the version is higher than or equal to | |
8d115822 | 139 | 5.10.0. That is, |
7dfde25d | 140 | |
8d115822 | 141 | use 5.10.0; |
7dfde25d RGS |
142 | |
143 | will do an implicit | |
144 | ||
82cfb3a2 | 145 | use feature ':5.10'; |
7dfde25d | 146 | |
82cfb3a2 S |
147 | and so on. Note how the trailing sub-version is automatically stripped from the |
148 | version. | |
7dfde25d | 149 | |
8d115822 RB |
150 | But to avoid portability warnings (see L<perlfunc/use>), you may prefer: |
151 | ||
152 | use 5.010; | |
153 | ||
154 | with the same effect. | |
155 | ||
7dfde25d RGS |
156 | =back |
157 | ||
0d863452 RH |
158 | =cut |
159 | ||
160 | sub import { | |
0d863452 RH |
161 | my $class = shift; |
162 | if (@_ == 0) { | |
0d863452 RH |
163 | croak("No features specified"); |
164 | } | |
165 | while (@_) { | |
166 | my $name = shift(@_); | |
89c3975a RGS |
167 | if (substr($name, 0, 1) eq ":") { |
168 | my $v = substr($name, 1); | |
7be54ea7 | 169 | if (!exists $feature_bundle{$v}) { |
82cfb3a2 S |
170 | $v =~ s/^([0-9]+)\.([0-9]+).[0-9]+$/$1.$2/; |
171 | if (!exists $feature_bundle{$v}) { | |
172 | unknown_feature_bundle(substr($name, 1)); | |
173 | } | |
bc9b29db | 174 | } |
7be54ea7 | 175 | unshift @_, @{$feature_bundle{$v}}; |
bc9b29db RH |
176 | next; |
177 | } | |
0d863452 | 178 | if (!exists $feature{$name}) { |
b42943c4 | 179 | unknown_feature($name); |
0d863452 RH |
180 | } |
181 | $^H{$feature{$name}} = 1; | |
1863b879 | 182 | $^H |= $hint_uni8bit if $name eq 'unicode_strings'; |
0d863452 RH |
183 | } |
184 | } | |
185 | ||
186 | sub unimport { | |
187 | my $class = shift; | |
188 | ||
189 | # A bare C<no feature> should disable *all* features | |
bc9b29db RH |
190 | if (!@_) { |
191 | delete @^H{ values(%feature) }; | |
1863b879 | 192 | $^H &= ~ $hint_uni8bit; |
bc9b29db RH |
193 | return; |
194 | } | |
195 | ||
196 | while (@_) { | |
197 | my $name = shift; | |
89c3975a RGS |
198 | if (substr($name, 0, 1) eq ":") { |
199 | my $v = substr($name, 1); | |
7be54ea7 | 200 | if (!exists $feature_bundle{$v}) { |
82cfb3a2 S |
201 | $v =~ s/^([0-9]+)\.([0-9]+).[0-9]+$/$1.$2/; |
202 | if (!exists $feature_bundle{$v}) { | |
203 | unknown_feature_bundle(substr($name, 1)); | |
204 | } | |
bc9b29db | 205 | } |
7be54ea7 | 206 | unshift @_, @{$feature_bundle{$v}}; |
bc9b29db RH |
207 | next; |
208 | } | |
0d863452 | 209 | if (!exists($feature{$name})) { |
b42943c4 | 210 | unknown_feature($name); |
0d863452 RH |
211 | } |
212 | else { | |
213 | delete $^H{$feature{$name}}; | |
1863b879 | 214 | $^H &= ~ $hint_uni8bit if $name eq 'unicode_strings'; |
0d863452 RH |
215 | } |
216 | } | |
0d863452 RH |
217 | } |
218 | ||
b42943c4 RGS |
219 | sub unknown_feature { |
220 | my $feature = shift; | |
221 | croak(sprintf('Feature "%s" is not supported by Perl %vd', | |
222 | $feature, $^V)); | |
223 | } | |
224 | ||
225 | sub unknown_feature_bundle { | |
226 | my $feature = shift; | |
227 | croak(sprintf('Feature bundle "%s" is not supported by Perl %vd', | |
228 | $feature, $^V)); | |
229 | } | |
230 | ||
231 | sub croak { | |
232 | require Carp; | |
233 | Carp::croak(@_); | |
234 | } | |
235 | ||
0d863452 | 236 | 1; |