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69bcf1d3 FC |
1 | # -*- buffer-read-only: t -*- |
2 | # !!!!!!! DO NOT EDIT THIS FILE !!!!!!! | |
3 | # This file is built by regen/feature.pl. | |
4 | # Any changes made here will be lost! | |
5 | ||
0d863452 RH |
6 | package feature; |
7 | ||
dcdae76b | 8 | our $VERSION = '1.30'; |
0d863452 | 9 | |
0bb01b05 | 10 | our %feature = ( |
2a4315f8 | 11 | fc => 'feature_fc', |
47e9d84a EB |
12 | say => 'feature_say', |
13 | state => 'feature_state', | |
1863b879 | 14 | switch => 'feature_switch', |
7d789282 | 15 | evalbytes => 'feature_evalbytes', |
3fff3427 | 16 | array_base => 'feature_arybase', |
84ed0108 | 17 | current_sub => 'feature___SUB__', |
ebd25686 | 18 | lexical_subs => 'feature_lexsubs', |
cda6b701 | 19 | unicode_eval => 'feature_unieval', |
47e9d84a | 20 | unicode_strings => 'feature_unicode', |
bc9b29db RH |
21 | ); |
22 | ||
0d2bd2aa | 23 | our %feature_bundle = ( |
69bcf1d3 FC |
24 | "5.10" => [qw(array_base say state switch)], |
25 | "5.11" => [qw(array_base say state switch unicode_strings)], | |
2a4315f8 | 26 | "5.15" => [qw(current_sub evalbytes fc say state switch unicode_eval unicode_strings)], |
ebd25686 | 27 | "all" => [qw(array_base current_sub evalbytes fc lexical_subs say state switch unicode_eval unicode_strings)], |
69bcf1d3 | 28 | "default" => [qw(array_base)], |
0d863452 | 29 | ); |
d052521a | 30 | |
88da30d7 FC |
31 | $feature_bundle{"5.12"} = $feature_bundle{"5.11"}; |
32 | $feature_bundle{"5.13"} = $feature_bundle{"5.11"}; | |
33 | $feature_bundle{"5.14"} = $feature_bundle{"5.11"}; | |
34 | $feature_bundle{"5.16"} = $feature_bundle{"5.15"}; | |
d6402ebe | 35 | $feature_bundle{"5.17"} = $feature_bundle{"5.15"}; |
52fc5c56 | 36 | $feature_bundle{"5.18"} = $feature_bundle{"5.15"}; |
88da30d7 | 37 | $feature_bundle{"5.9.5"} = $feature_bundle{"5.10"}; |
ebd25686 FC |
38 | my %experimental = ( |
39 | lexical_subs => 1, | |
40 | ); | |
69bcf1d3 | 41 | |
0bb01b05 FC |
42 | our $hint_shift = 26; |
43 | our $hint_mask = 0x1c000000; | |
44 | our @hint_bundles = qw( default 5.10 5.11 5.15 ); | |
ada44f8c | 45 | |
69bcf1d3 FC |
46 | # This gets set (for now) in $^H as well as in %^H, |
47 | # for runtime speed of the uc/lc/ucfirst/lcfirst functions. | |
48 | # See HINT_UNI_8_BIT in perl.h. | |
49 | our $hint_uni8bit = 0x00000800; | |
7dfde25d | 50 | |
0d863452 | 51 | # TODO: |
1c321dc6 | 52 | # - think about versioned features (use feature switch => 2) |
0d863452 RH |
53 | |
54 | =head1 NAME | |
55 | ||
e1b711da | 56 | feature - Perl pragma to enable new features |
0d863452 RH |
57 | |
58 | =head1 SYNOPSIS | |
59 | ||
47e9d84a | 60 | use feature qw(say switch); |
0d863452 | 61 | given ($foo) { |
0b25e784 DG |
62 | when (1) { say "\$foo == 1" } |
63 | when ([2,3]) { say "\$foo == 2 || \$foo == 3" } | |
64 | when (/^a[bc]d$/) { say "\$foo eq 'abd' || \$foo eq 'acd'" } | |
65 | when ($_ > 100) { say "\$foo > 100" } | |
66 | default { say "None of the above" } | |
0d863452 RH |
67 | } |
68 | ||
ec488c7f RGS |
69 | use feature ':5.10'; # loads all features available in perl 5.10 |
70 | ||
0b25e784 DG |
71 | use v5.10; # implicitly loads :5.10 feature bundle |
72 | ||
0d863452 RH |
73 | =head1 DESCRIPTION |
74 | ||
75 | It is usually impossible to add new syntax to Perl without breaking | |
b22bbcf0 | 76 | some existing programs. This pragma provides a way to minimize that |
1863b879 RGS |
77 | risk. New syntactic constructs, or new semantic meanings to older |
78 | constructs, can be enabled by C<use feature 'foo'>, and will be parsed | |
b22bbcf0 | 79 | only when the appropriate feature pragma is in scope. (Nevertheless, the |
4a904372 FC |
80 | C<CORE::> prefix provides access to all Perl keywords, regardless of this |
81 | pragma.) | |
0d863452 | 82 | |
9eb27be9 RGS |
83 | =head2 Lexical effect |
84 | ||
85 | Like other pragmas (C<use strict>, for example), features have a lexical | |
301381dc | 86 | effect. C<use feature qw(foo)> will only make the feature "foo" available |
9eb27be9 RGS |
87 | from that point to the end of the enclosing block. |
88 | ||
89 | { | |
90 | use feature 'say'; | |
91 | say "say is available here"; | |
92 | } | |
93 | print "But not here.\n"; | |
94 | ||
5e36ed56 RGS |
95 | =head2 C<no feature> |
96 | ||
b22bbcf0 | 97 | Features can also be turned off by using C<no feature "foo">. This too |
5e36ed56 RGS |
98 | has lexical effect. |
99 | ||
100 | use feature 'say'; | |
101 | say "say is available here"; | |
102 | { | |
103 | no feature 'say'; | |
104 | print "But not here.\n"; | |
105 | } | |
106 | say "Yet it is here."; | |
107 | ||
39ec54a5 RS |
108 | C<no feature> with no features specified will reset to the default group. To |
109 | disable I<all> features (an unusual request!) use C<no feature ':all'>. | |
5e36ed56 | 110 | |
0b25e784 DG |
111 | =head1 AVAILABLE FEATURES |
112 | ||
0d863452 RH |
113 | =head2 The 'say' feature |
114 | ||
0b25e784 | 115 | C<use feature 'say'> tells the compiler to enable the Perl 6 style |
9eb27be9 | 116 | C<say> function. |
0d863452 RH |
117 | |
118 | See L<perlfunc/say> for details. | |
119 | ||
0b25e784 DG |
120 | This feature is available starting with Perl 5.10. |
121 | ||
122 | =head2 The 'state' feature | |
712d05cf RGS |
123 | |
124 | C<use feature 'state'> tells the compiler to enable C<state> | |
9eb27be9 | 125 | variables. |
712d05cf | 126 | |
e60bcc8b RGS |
127 | See L<perlsub/"Persistent Private Variables"> for details. |
128 | ||
0b25e784 DG |
129 | This feature is available starting with Perl 5.10. |
130 | ||
47e9d84a EB |
131 | =head2 The 'switch' feature |
132 | ||
133 | C<use feature 'switch'> tells the compiler to enable the Perl 6 | |
134 | given/when construct. | |
135 | ||
48238296 | 136 | See L<perlsyn/"Switch Statements"> for details. |
47e9d84a | 137 | |
0b25e784 DG |
138 | This feature is available starting with Perl 5.10. |
139 | ||
140 | =head2 The 'unicode_strings' feature | |
1863b879 | 141 | |
20db7501 KW |
142 | C<use feature 'unicode_strings'> tells the compiler to use Unicode semantics |
143 | in all string operations executed within its scope (unless they are also | |
144 | within the scope of either C<use locale> or C<use bytes>). The same applies | |
145 | to all regular expressions compiled within the scope, even if executed outside | |
2269d15c KW |
146 | it. It does not change the internal representation of strings, but only how |
147 | they are interpreted. | |
20db7501 KW |
148 | |
149 | C<no feature 'unicode_strings'> tells the compiler to use the traditional | |
150 | Perl semantics wherein the native character set semantics is used unless it is | |
151 | clear to Perl that Unicode is desired. This can lead to some surprises | |
152 | when the behavior suddenly changes. (See | |
153 | L<perlunicode/The "Unicode Bug"> for details.) For this reason, if you are | |
154 | potentially using Unicode in your program, the | |
155 | C<use feature 'unicode_strings'> subpragma is B<strongly> recommended. | |
156 | ||
2e2b2571 KW |
157 | This feature is available starting with Perl 5.12; was almost fully |
158 | implemented in Perl 5.14; and extended in Perl 5.16 to cover C<quotemeta>. | |
1863b879 | 159 | |
0b25e784 | 160 | =head2 The 'unicode_eval' and 'evalbytes' features |
7289c5e6 FC |
161 | |
162 | Under the C<unicode_eval> feature, Perl's C<eval> function, when passed a | |
163 | string, will evaluate it as a string of characters, ignoring any | |
164 | C<use utf8> declarations. C<use utf8> exists to declare the encoding of | |
165 | the script, which only makes sense for a stream of bytes, not a string of | |
166 | characters. Source filters are forbidden, as they also really only make | |
167 | sense on strings of bytes. Any attempt to activate a source filter will | |
168 | result in an error. | |
169 | ||
170 | The C<evalbytes> feature enables the C<evalbytes> keyword, which evaluates | |
171 | the argument passed to it as a string of bytes. It dies if the string | |
172 | contains any characters outside the 8-bit range. Source filters work | |
173 | within C<evalbytes>: they apply to the contents of the string being | |
174 | evaluated. | |
175 | ||
176 | Together, these two features are intended to replace the historical C<eval> | |
177 | function, which has (at least) two bugs in it, that cannot easily be fixed | |
178 | without breaking existing programs: | |
179 | ||
180 | =over | |
181 | ||
182 | =item * | |
183 | ||
184 | C<eval> behaves differently depending on the internal encoding of the | |
185 | string, sometimes treating its argument as a string of bytes, and sometimes | |
186 | as a string of characters. | |
187 | ||
188 | =item * | |
189 | ||
190 | Source filters activated within C<eval> leak out into whichever I<file> | |
191 | scope is currently being compiled. To give an example with the CPAN module | |
192 | L<Semi::Semicolons>: | |
193 | ||
194 | BEGIN { eval "use Semi::Semicolons; # not filtered here " } | |
195 | # filtered here! | |
196 | ||
197 | C<evalbytes> fixes that to work the way one would expect: | |
198 | ||
199 | use feature "evalbytes"; | |
200 | BEGIN { evalbytes "use Semi::Semicolons; # filtered " } | |
201 | # not filtered | |
202 | ||
203 | =back | |
204 | ||
205 | These two features are available starting with Perl 5.16. | |
206 | ||
84ed0108 FC |
207 | =head2 The 'current_sub' feature |
208 | ||
209 | This provides the C<__SUB__> token that returns a reference to the current | |
210 | subroutine or C<undef> outside of a subroutine. | |
211 | ||
212 | This feature is available starting with Perl 5.16. | |
213 | ||
01868d00 FC |
214 | =head2 The 'array_base' feature |
215 | ||
216 | This feature supports the legacy C<$[> variable. See L<perlvar/$[> and | |
217 | L<arybase>. It is on by default but disabled under C<use v5.16> (see | |
218 | L</IMPLICIT LOADING>, below). | |
219 | ||
220 | This feature is available under this name starting with Perl 5.16. In | |
221 | previous versions, it was simply on all the time, and this pragma knew | |
222 | nothing about it. | |
223 | ||
2a4315f8 BF |
224 | =head2 The 'fc' feature |
225 | ||
226 | C<use feature 'fc'> tells the compiler to enable the C<fc> function, | |
227 | which implements Unicode casefolding. | |
228 | ||
229 | See L<perlfunc/fc> for details. | |
230 | ||
231 | This feature is available from Perl 5.16 onwards. | |
232 | ||
bc9b29db RH |
233 | =head1 FEATURE BUNDLES |
234 | ||
0b25e784 | 235 | It's possible to load multiple features together, using |
b22bbcf0 | 236 | a I<feature bundle>. The name of a feature bundle is prefixed with |
0b25e784 DG |
237 | a colon, to distinguish it from an actual feature. |
238 | ||
239 | use feature ":5.10"; | |
240 | ||
241 | The following feature bundles are available: | |
242 | ||
243 | bundle features included | |
244 | --------- ----------------- | |
01868d00 | 245 | :default array_base |
0b25e784 | 246 | |
01868d00 | 247 | :5.10 say state switch array_base |
0b25e784 | 248 | |
01868d00 | 249 | :5.12 say state switch unicode_strings array_base |
0b25e784 | 250 | |
01868d00 | 251 | :5.14 say state switch unicode_strings array_base |
0b25e784 DG |
252 | |
253 | :5.16 say state switch unicode_strings | |
2a4315f8 | 254 | unicode_eval evalbytes current_sub fc |
0b25e784 | 255 | |
52fc5c56 FC |
256 | :5.18 say state switch unicode_strings |
257 | unicode_eval evalbytes current_sub fc | |
258 | ||
01868d00 FC |
259 | The C<:default> bundle represents the feature set that is enabled before |
260 | any C<use feature> or C<no feature> declaration. | |
a3a91442 JV |
261 | |
262 | Specifying sub-versions such as the C<0> in C<5.14.0> in feature bundles has | |
b22bbcf0 | 263 | no effect. Feature bundles are guaranteed to be the same for all sub-versions. |
bc9b29db | 264 | |
0b25e784 DG |
265 | use feature ":5.14.0"; # same as ":5.14" |
266 | use feature ":5.14.1"; # same as ":5.14" | |
a3a91442 | 267 | |
7dfde25d RGS |
268 | =head1 IMPLICIT LOADING |
269 | ||
0b25e784 DG |
270 | Instead of loading feature bundles by name, it is easier to let Perl do |
271 | implicit loading of a feature bundle for you. | |
272 | ||
273 | There are two ways to load the C<feature> pragma implicitly: | |
7dfde25d RGS |
274 | |
275 | =over 4 | |
276 | ||
277 | =item * | |
278 | ||
0b25e784 DG |
279 | By using the C<-E> switch on the Perl command-line instead of C<-e>. |
280 | That will enable the feature bundle for that version of Perl in the | |
281 | main compilation unit (that is, the one-liner that follows C<-E>). | |
7dfde25d RGS |
282 | |
283 | =item * | |
284 | ||
0b25e784 | 285 | By explicitly requiring a minimum Perl version number for your program, with |
b22bbcf0 | 286 | the C<use VERSION> construct. That is, |
7dfde25d | 287 | |
0b25e784 | 288 | use v5.10.0; |
7dfde25d RGS |
289 | |
290 | will do an implicit | |
291 | ||
39ec54a5 | 292 | no feature ':all'; |
82cfb3a2 | 293 | use feature ':5.10'; |
7dfde25d | 294 | |
b22bbcf0 FC |
295 | and so on. Note how the trailing sub-version |
296 | is automatically stripped from the | |
82cfb3a2 | 297 | version. |
7dfde25d | 298 | |
8d115822 RB |
299 | But to avoid portability warnings (see L<perlfunc/use>), you may prefer: |
300 | ||
301 | use 5.010; | |
302 | ||
303 | with the same effect. | |
304 | ||
0b25e784 | 305 | If the required version is older than Perl 5.10, the ":default" feature |
01868d00 | 306 | bundle is automatically loaded instead. |
70397346 | 307 | |
7dfde25d RGS |
308 | =back |
309 | ||
0d863452 RH |
310 | =cut |
311 | ||
312 | sub import { | |
0d863452 | 313 | my $class = shift; |
36143a0c NC |
314 | |
315 | if (!@_) { | |
0b25e784 | 316 | croak("No features specified"); |
0d863452 | 317 | } |
36143a0c | 318 | |
d3757264 | 319 | __common(1, @_); |
0d863452 RH |
320 | } |
321 | ||
322 | sub unimport { | |
323 | my $class = shift; | |
324 | ||
39ec54a5 | 325 | # A bare C<no feature> should reset to the default bundle |
bc9b29db | 326 | if (!@_) { |
39ec54a5 RS |
327 | $^H &= ~($hint_uni8bit|$hint_mask); |
328 | return; | |
bc9b29db RH |
329 | } |
330 | ||
d3757264 NC |
331 | __common(0, @_); |
332 | } | |
333 | ||
334 | ||
335 | sub __common { | |
336 | my $import = shift; | |
0c8d5017 NC |
337 | my $bundle_number = $^H & $hint_mask; |
338 | my $features = $bundle_number != $hint_mask | |
339 | && $feature_bundle{$hint_bundles[$bundle_number >> $hint_shift]}; | |
340 | if ($features) { | |
da5b5421 | 341 | # Features are enabled implicitly via bundle hints. |
d9ee6ccb NC |
342 | # Delete any keys that may be left over from last time. |
343 | delete @^H{ values(%feature) }; | |
344 | $^H |= $hint_mask; | |
345 | for (@$features) { | |
346 | $^H{$feature{$_}} = 1; | |
347 | $^H |= $hint_uni8bit if $_ eq 'unicode_strings'; | |
348 | } | |
da5b5421 | 349 | } |
bc9b29db | 350 | while (@_) { |
0b25e784 DG |
351 | my $name = shift; |
352 | if (substr($name, 0, 1) eq ":") { | |
353 | my $v = substr($name, 1); | |
354 | if (!exists $feature_bundle{$v}) { | |
355 | $v =~ s/^([0-9]+)\.([0-9]+).[0-9]+$/$1.$2/; | |
356 | if (!exists $feature_bundle{$v}) { | |
357 | unknown_feature_bundle(substr($name, 1)); | |
358 | } | |
359 | } | |
360 | unshift @_, @{$feature_bundle{$v}}; | |
361 | next; | |
362 | } | |
36143a0c | 363 | if (!exists $feature{$name}) { |
0b25e784 DG |
364 | unknown_feature($name); |
365 | } | |
d3757264 NC |
366 | if ($import) { |
367 | $^H{$feature{$name}} = 1; | |
368 | $^H |= $hint_uni8bit if $name eq 'unicode_strings'; | |
ebd25686 FC |
369 | if ($experimental{$name}) { |
370 | require warnings; | |
371 | warnings::warnif("experimental:$name", | |
372 | "The $name feature is experimental"); | |
373 | } | |
d3757264 | 374 | } else { |
0b25e784 | 375 | delete $^H{$feature{$name}}; |
1863b879 | 376 | $^H &= ~ $hint_uni8bit if $name eq 'unicode_strings'; |
0b25e784 | 377 | } |
0d863452 | 378 | } |
0d863452 RH |
379 | } |
380 | ||
b42943c4 RGS |
381 | sub unknown_feature { |
382 | my $feature = shift; | |
383 | croak(sprintf('Feature "%s" is not supported by Perl %vd', | |
0b25e784 | 384 | $feature, $^V)); |
b42943c4 RGS |
385 | } |
386 | ||
387 | sub unknown_feature_bundle { | |
388 | my $feature = shift; | |
389 | croak(sprintf('Feature bundle "%s" is not supported by Perl %vd', | |
0b25e784 | 390 | $feature, $^V)); |
b42943c4 RGS |
391 | } |
392 | ||
393 | sub croak { | |
394 | require Carp; | |
395 | Carp::croak(@_); | |
396 | } | |
397 | ||
0d863452 | 398 | 1; |
69bcf1d3 FC |
399 | |
400 | # ex: set ro: |