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!
13 state => 'feature_state',
14 switch => 'feature_switch',
15 evalbytes => 'feature_evalbytes',
16 array_base => 'feature_arybase',
17 current_sub => 'feature___SUB__',
18 unicode_eval => 'feature_unieval',
19 unicode_strings => 'feature_unicode',
22 our %feature_bundle = (
23 "5.10" => [qw(array_base say state switch)],
24 "5.11" => [qw(array_base say state switch unicode_strings)],
25 "5.15" => [qw(current_sub evalbytes fc say state switch unicode_eval unicode_strings)],
26 "all" => [qw(array_base current_sub evalbytes fc say state switch unicode_eval unicode_strings)],
27 "default" => [qw(array_base)],
30 $feature_bundle{"5.12"} = $feature_bundle{"5.11"};
31 $feature_bundle{"5.13"} = $feature_bundle{"5.11"};
32 $feature_bundle{"5.14"} = $feature_bundle{"5.11"};
33 $feature_bundle{"5.16"} = $feature_bundle{"5.15"};
34 $feature_bundle{"5.17"} = $feature_bundle{"5.15"};
35 $feature_bundle{"5.18"} = $feature_bundle{"5.15"};
36 $feature_bundle{"5.9.5"} = $feature_bundle{"5.10"};
39 our $hint_mask = 0x1c000000;
40 our @hint_bundles = qw( default 5.10 5.11 5.15 );
42 # This gets set (for now) in $^H as well as in %^H,
43 # for runtime speed of the uc/lc/ucfirst/lcfirst functions.
44 # See HINT_UNI_8_BIT in perl.h.
45 our $hint_uni8bit = 0x00000800;
48 # - think about versioned features (use feature switch => 2)
52 feature - Perl pragma to enable new features
56 use feature qw(say switch);
58 when (1) { say "\$foo == 1" }
59 when ([2,3]) { say "\$foo == 2 || \$foo == 3" }
60 when (/^a[bc]d$/) { say "\$foo eq 'abd' || \$foo eq 'acd'" }
61 when ($_ > 100) { say "\$foo > 100" }
62 default { say "None of the above" }
65 use feature ':5.10'; # loads all features available in perl 5.10
67 use v5.10; # implicitly loads :5.10 feature bundle
71 It is usually impossible to add new syntax to Perl without breaking
72 some existing programs. This pragma provides a way to minimize that
73 risk. New syntactic constructs, or new semantic meanings to older
74 constructs, can be enabled by C<use feature 'foo'>, and will be parsed
75 only when the appropriate feature pragma is in scope. (Nevertheless, the
76 C<CORE::> prefix provides access to all Perl keywords, regardless of this
81 Like other pragmas (C<use strict>, for example), features have a lexical
82 effect. C<use feature qw(foo)> will only make the feature "foo" available
83 from that point to the end of the enclosing block.
87 say "say is available here";
89 print "But not here.\n";
93 Features can also be turned off by using C<no feature "foo">. This too
97 say "say is available here";
100 print "But not here.\n";
102 say "Yet it is here.";
104 C<no feature> with no features specified will reset to the default group. To
105 disable I<all> features (an unusual request!) use C<no feature ':all'>.
107 =head1 AVAILABLE FEATURES
109 =head2 The 'say' feature
111 C<use feature 'say'> tells the compiler to enable the Perl 6 style
114 See L<perlfunc/say> for details.
116 This feature is available starting with Perl 5.10.
118 =head2 The 'state' feature
120 C<use feature 'state'> tells the compiler to enable C<state>
123 See L<perlsub/"Persistent Private Variables"> for details.
125 This feature is available starting with Perl 5.10.
127 =head2 The 'switch' feature
129 C<use feature 'switch'> tells the compiler to enable the Perl 6
130 given/when construct.
132 See L<perlsyn/"Switch Statements"> for details.
134 This feature is available starting with Perl 5.10.
136 =head2 The 'unicode_strings' feature
138 C<use feature 'unicode_strings'> tells the compiler to use Unicode semantics
139 in all string operations executed within its scope (unless they are also
140 within the scope of either C<use locale> or C<use bytes>). The same applies
141 to all regular expressions compiled within the scope, even if executed outside
142 it. It does not change the internal representation of strings, but only how
143 they are interpreted.
145 C<no feature 'unicode_strings'> tells the compiler to use the traditional
146 Perl semantics wherein the native character set semantics is used unless it is
147 clear to Perl that Unicode is desired. This can lead to some surprises
148 when the behavior suddenly changes. (See
149 L<perlunicode/The "Unicode Bug"> for details.) For this reason, if you are
150 potentially using Unicode in your program, the
151 C<use feature 'unicode_strings'> subpragma is B<strongly> recommended.
153 This feature is available starting with Perl 5.12; was almost fully
154 implemented in Perl 5.14; and extended in Perl 5.16 to cover C<quotemeta>.
156 =head2 The 'unicode_eval' and 'evalbytes' features
158 Under the C<unicode_eval> feature, Perl's C<eval> function, when passed a
159 string, will evaluate it as a string of characters, ignoring any
160 C<use utf8> declarations. C<use utf8> exists to declare the encoding of
161 the script, which only makes sense for a stream of bytes, not a string of
162 characters. Source filters are forbidden, as they also really only make
163 sense on strings of bytes. Any attempt to activate a source filter will
166 The C<evalbytes> feature enables the C<evalbytes> keyword, which evaluates
167 the argument passed to it as a string of bytes. It dies if the string
168 contains any characters outside the 8-bit range. Source filters work
169 within C<evalbytes>: they apply to the contents of the string being
172 Together, these two features are intended to replace the historical C<eval>
173 function, which has (at least) two bugs in it, that cannot easily be fixed
174 without breaking existing programs:
180 C<eval> behaves differently depending on the internal encoding of the
181 string, sometimes treating its argument as a string of bytes, and sometimes
182 as a string of characters.
186 Source filters activated within C<eval> leak out into whichever I<file>
187 scope is currently being compiled. To give an example with the CPAN module
190 BEGIN { eval "use Semi::Semicolons; # not filtered here " }
193 C<evalbytes> fixes that to work the way one would expect:
195 use feature "evalbytes";
196 BEGIN { evalbytes "use Semi::Semicolons; # filtered " }
201 These two features are available starting with Perl 5.16.
203 =head2 The 'current_sub' feature
205 This provides the C<__SUB__> token that returns a reference to the current
206 subroutine or C<undef> outside of a subroutine.
208 This feature is available starting with Perl 5.16.
210 =head2 The 'array_base' feature
212 This feature supports the legacy C<$[> variable. See L<perlvar/$[> and
213 L<arybase>. It is on by default but disabled under C<use v5.16> (see
214 L</IMPLICIT LOADING>, below).
216 This feature is available under this name starting with Perl 5.16. In
217 previous versions, it was simply on all the time, and this pragma knew
220 =head2 The 'fc' feature
222 C<use feature 'fc'> tells the compiler to enable the C<fc> function,
223 which implements Unicode casefolding.
225 See L<perlfunc/fc> for details.
227 This feature is available from Perl 5.16 onwards.
229 =head1 FEATURE BUNDLES
231 It's possible to load multiple features together, using
232 a I<feature bundle>. The name of a feature bundle is prefixed with
233 a colon, to distinguish it from an actual feature.
237 The following feature bundles are available:
239 bundle features included
240 --------- -----------------
243 :5.10 say state switch array_base
245 :5.12 say state switch unicode_strings array_base
247 :5.14 say state switch unicode_strings array_base
249 :5.16 say state switch unicode_strings
250 unicode_eval evalbytes current_sub fc
252 :5.18 say state switch unicode_strings
253 unicode_eval evalbytes current_sub fc
255 The C<:default> bundle represents the feature set that is enabled before
256 any C<use feature> or C<no feature> declaration.
258 Specifying sub-versions such as the C<0> in C<5.14.0> in feature bundles has
259 no effect. Feature bundles are guaranteed to be the same for all sub-versions.
261 use feature ":5.14.0"; # same as ":5.14"
262 use feature ":5.14.1"; # same as ":5.14"
264 =head1 IMPLICIT LOADING
266 Instead of loading feature bundles by name, it is easier to let Perl do
267 implicit loading of a feature bundle for you.
269 There are two ways to load the C<feature> pragma implicitly:
275 By using the C<-E> switch on the Perl command-line instead of C<-e>.
276 That will enable the feature bundle for that version of Perl in the
277 main compilation unit (that is, the one-liner that follows C<-E>).
281 By explicitly requiring a minimum Perl version number for your program, with
282 the C<use VERSION> construct. That is,
291 and so on. Note how the trailing sub-version
292 is automatically stripped from the
295 But to avoid portability warnings (see L<perlfunc/use>), you may prefer:
299 with the same effect.
301 If the required version is older than Perl 5.10, the ":default" feature
302 bundle is automatically loaded instead.
312 croak("No features specified");
321 # A bare C<no feature> should reset to the default bundle
323 $^H &= ~($hint_uni8bit|$hint_mask);
333 my $bundle_number = $^H & $hint_mask;
334 my $features = $bundle_number != $hint_mask
335 && $feature_bundle{$hint_bundles[$bundle_number >> $hint_shift]};
337 # Features are enabled implicitly via bundle hints.
338 # Delete any keys that may be left over from last time.
339 delete @^H{ values(%feature) };
342 $^H{$feature{$_}} = 1;
343 $^H |= $hint_uni8bit if $_ eq 'unicode_strings';
348 if (substr($name, 0, 1) eq ":") {
349 my $v = substr($name, 1);
350 if (!exists $feature_bundle{$v}) {
351 $v =~ s/^([0-9]+)\.([0-9]+).[0-9]+$/$1.$2/;
352 if (!exists $feature_bundle{$v}) {
353 unknown_feature_bundle(substr($name, 1));
356 unshift @_, @{$feature_bundle{$v}};
359 if (!exists $feature{$name}) {
360 unknown_feature($name);
363 $^H{$feature{$name}} = 1;
364 $^H |= $hint_uni8bit if $name eq 'unicode_strings';
366 delete $^H{$feature{$name}};
367 $^H &= ~ $hint_uni8bit if $name eq 'unicode_strings';
372 sub unknown_feature {
374 croak(sprintf('Feature "%s" is not supported by Perl %vd',
378 sub unknown_feature_bundle {
380 croak(sprintf('Feature bundle "%s" is not supported by Perl %vd',