Commit | Line | Data |
0d863452 |
1 | package feature; |
2 | |
0a0b870a |
3 | our $VERSION = '1.15'; |
0d863452 |
4 | |
5 | # (feature name) => (internal name, used in %^H) |
6 | my %feature = ( |
1863b879 |
7 | switch => 'feature_switch', |
8 | say => "feature_say", |
9 | state => "feature_state", |
10 | unicode_strings => "feature_unicode", |
bc9b29db |
11 | ); |
12 | |
1863b879 |
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 |
16 | our $hint_uni8bit = 0x00000800; |
17 | |
13a7998c |
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)], |
0d863452 |
23 | ); |
d052521a |
24 | |
82cfb3a2 |
25 | # special case |
26 | $feature_bundle{"5.9.5"} = $feature_bundle{"5.10"}; |
7dfde25d |
27 | |
0d863452 |
28 | # TODO: |
1c321dc6 |
29 | # - think about versioned features (use feature switch => 2) |
0d863452 |
30 | |
31 | =head1 NAME |
32 | |
e1b711da |
33 | feature - Perl pragma to enable new features |
0d863452 |
34 | |
35 | =head1 SYNOPSIS |
36 | |
bc9b29db |
37 | use feature qw(switch say); |
0d863452 |
38 | given ($foo) { |
bc9b29db |
39 | when (1) { say "\$foo == 1" } |
40 | when ([2,3]) { say "\$foo == 2 || \$foo == 3" } |
41 | when (/^a[bc]d$/) { say "\$foo eq 'abd' || \$foo eq 'acd'" } |
42 | when ($_ > 100) { say "\$foo > 100" } |
43 | default { say "None of the above" } |
0d863452 |
44 | } |
45 | |
ec488c7f |
46 | use feature ':5.10'; # loads all features available in perl 5.10 |
47 | |
0d863452 |
48 | =head1 DESCRIPTION |
49 | |
50 | It is usually impossible to add new syntax to Perl without breaking |
51 | some existing programs. This pragma provides a way to minimize that |
1863b879 |
52 | risk. New syntactic constructs, or new semantic meanings to older |
53 | constructs, can be enabled by C<use feature 'foo'>, and will be parsed |
54 | only when the appropriate feature pragma is in scope. |
0d863452 |
55 | |
9eb27be9 |
56 | =head2 Lexical effect |
57 | |
58 | Like other pragmas (C<use strict>, for example), features have a lexical |
5e36ed56 |
59 | effect. C<use feature qw(foo)> will only make the feature "foo" available |
9eb27be9 |
60 | from that point to the end of the enclosing block. |
61 | |
62 | { |
63 | use feature 'say'; |
64 | say "say is available here"; |
65 | } |
66 | print "But not here.\n"; |
67 | |
5e36ed56 |
68 | =head2 C<no feature> |
69 | |
70 | Features can also be turned off by using C<no feature "foo">. This too |
71 | has lexical effect. |
72 | |
73 | use feature 'say'; |
74 | say "say is available here"; |
75 | { |
76 | no feature 'say'; |
77 | print "But not here.\n"; |
78 | } |
79 | say "Yet it is here."; |
80 | |
81 | C<no feature> with no features specified will turn off all features. |
82 | |
0d863452 |
83 | =head2 The 'switch' feature |
84 | |
85 | C<use feature 'switch'> tells the compiler to enable the Perl 6 |
9eb27be9 |
86 | given/when construct. |
0d863452 |
87 | |
88 | See L<perlsyn/"Switch statements"> for details. |
89 | |
0d863452 |
90 | =head2 The 'say' feature |
91 | |
92 | C<use feature 'say'> tells the compiler to enable the Perl 6 |
9eb27be9 |
93 | C<say> function. |
0d863452 |
94 | |
95 | See L<perlfunc/say> for details. |
96 | |
712d05cf |
97 | =head2 the 'state' feature |
98 | |
99 | C<use feature 'state'> tells the compiler to enable C<state> |
9eb27be9 |
100 | variables. |
712d05cf |
101 | |
e60bcc8b |
102 | See L<perlsub/"Persistent Private Variables"> for details. |
103 | |
1863b879 |
104 | =head2 the 'unicode_strings' feature |
105 | |
106 | C<use feature 'unicode_strings'> tells the compiler to treat |
e1b711da |
107 | all strings outside of C<use locale> and C<use bytes> as Unicode. It is |
108 | available starting with Perl 5.11.3. |
1863b879 |
109 | |
e1b711da |
110 | See L<perlunicode/The "Unicode Bug"> for details. |
1863b879 |
111 | |
bc9b29db |
112 | =head1 FEATURE BUNDLES |
113 | |
114 | It's possible to load a whole slew of features in one go, using |
115 | a I<feature bundle>. The name of a feature bundle is prefixed with |
116 | a colon, to distinguish it from an actual feature. At present, the |
82cfb3a2 |
117 | only feature bundle is C<use feature ":5.10"> which is equivalent |
118 | to C<use feature qw(switch say state)>. |
8fd870d9 |
119 | |
82cfb3a2 |
120 | Specifying sub-versions such as the C<0> in C<5.10.0> in feature bundles has |
121 | no effect: feature bundles are guaranteed to be the same for all sub-versions. |
bc9b29db |
122 | |
7dfde25d |
123 | =head1 IMPLICIT LOADING |
124 | |
125 | There are two ways to load the C<feature> pragma implicitly : |
126 | |
127 | =over 4 |
128 | |
129 | =item * |
130 | |
131 | By using the C<-E> switch on the command-line instead of C<-e>. It enables |
132 | all available features in the main compilation unit (that is, the one-liner.) |
133 | |
134 | =item * |
135 | |
136 | By requiring explicitly a minimal Perl version number for your program, with |
137 | the C<use VERSION> construct, and when the version is higher than or equal to |
8d115822 |
138 | 5.10.0. That is, |
7dfde25d |
139 | |
8d115822 |
140 | use 5.10.0; |
7dfde25d |
141 | |
142 | will do an implicit |
143 | |
82cfb3a2 |
144 | use feature ':5.10'; |
7dfde25d |
145 | |
82cfb3a2 |
146 | and so on. Note how the trailing sub-version is automatically stripped from the |
147 | version. |
7dfde25d |
148 | |
8d115822 |
149 | But to avoid portability warnings (see L<perlfunc/use>), you may prefer: |
150 | |
151 | use 5.010; |
152 | |
153 | with the same effect. |
154 | |
7dfde25d |
155 | =back |
156 | |
0d863452 |
157 | =cut |
158 | |
159 | sub import { |
0d863452 |
160 | my $class = shift; |
161 | if (@_ == 0) { |
0d863452 |
162 | croak("No features specified"); |
163 | } |
164 | while (@_) { |
165 | my $name = shift(@_); |
89c3975a |
166 | if (substr($name, 0, 1) eq ":") { |
167 | my $v = substr($name, 1); |
7be54ea7 |
168 | if (!exists $feature_bundle{$v}) { |
82cfb3a2 |
169 | $v =~ s/^([0-9]+)\.([0-9]+).[0-9]+$/$1.$2/; |
170 | if (!exists $feature_bundle{$v}) { |
171 | unknown_feature_bundle(substr($name, 1)); |
172 | } |
bc9b29db |
173 | } |
7be54ea7 |
174 | unshift @_, @{$feature_bundle{$v}}; |
bc9b29db |
175 | next; |
176 | } |
0d863452 |
177 | if (!exists $feature{$name}) { |
b42943c4 |
178 | unknown_feature($name); |
0d863452 |
179 | } |
180 | $^H{$feature{$name}} = 1; |
1863b879 |
181 | $^H |= $hint_uni8bit if $name eq 'unicode_strings'; |
0d863452 |
182 | } |
183 | } |
184 | |
185 | sub unimport { |
186 | my $class = shift; |
187 | |
188 | # A bare C<no feature> should disable *all* features |
bc9b29db |
189 | if (!@_) { |
190 | delete @^H{ values(%feature) }; |
1863b879 |
191 | $^H &= ~ $hint_uni8bit; |
bc9b29db |
192 | return; |
193 | } |
194 | |
195 | while (@_) { |
196 | my $name = shift; |
89c3975a |
197 | if (substr($name, 0, 1) eq ":") { |
198 | my $v = substr($name, 1); |
7be54ea7 |
199 | if (!exists $feature_bundle{$v}) { |
82cfb3a2 |
200 | $v =~ s/^([0-9]+)\.([0-9]+).[0-9]+$/$1.$2/; |
201 | if (!exists $feature_bundle{$v}) { |
202 | unknown_feature_bundle(substr($name, 1)); |
203 | } |
bc9b29db |
204 | } |
7be54ea7 |
205 | unshift @_, @{$feature_bundle{$v}}; |
bc9b29db |
206 | next; |
207 | } |
0d863452 |
208 | if (!exists($feature{$name})) { |
b42943c4 |
209 | unknown_feature($name); |
0d863452 |
210 | } |
211 | else { |
212 | delete $^H{$feature{$name}}; |
1863b879 |
213 | $^H &= ~ $hint_uni8bit if $name eq 'unicode_strings'; |
0d863452 |
214 | } |
215 | } |
0d863452 |
216 | } |
217 | |
b42943c4 |
218 | sub unknown_feature { |
219 | my $feature = shift; |
220 | croak(sprintf('Feature "%s" is not supported by Perl %vd', |
221 | $feature, $^V)); |
222 | } |
223 | |
224 | sub unknown_feature_bundle { |
225 | my $feature = shift; |
226 | croak(sprintf('Feature bundle "%s" is not supported by Perl %vd', |
227 | $feature, $^V)); |
228 | } |
229 | |
230 | sub croak { |
231 | require Carp; |
232 | Carp::croak(@_); |
233 | } |
234 | |
0d863452 |
235 | 1; |