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0d863452 RH |
1 | package feature; |
2 | ||
8fd870d9 | 3 | our $VERSION = '1.10'; |
0d863452 RH |
4 | |
5 | # (feature name) => (internal name, used in %^H) | |
6 | my %feature = ( | |
7b9ef140 | 7 | switch => 'feature_switch', |
7b9ef140 | 8 | say => "feature_say", |
bc9b29db | 9 | err => "feature_err", |
712d05cf | 10 | state => "feature_state", |
bc9b29db RH |
11 | ); |
12 | ||
13 | my %feature_bundle = ( | |
3e7dd34d | 14 | "5.10.0" => [qw(switch say err state)], |
0d863452 | 15 | ); |
8fd870d9 RGS |
16 | # latest version here |
17 | # keep it harcoded until we actually bump the version number to 5.10 | |
18 | $feature_bundle{"5.10"} = $feature_bundle{"5.10.0"}; | |
19 | #$feature_bundle{"5.10"} = $feature_bundle{sprintf("%vd",$^V)}; | |
0d863452 | 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 | ||
39 | =head1 DESCRIPTION | |
40 | ||
41 | It is usually impossible to add new syntax to Perl without breaking | |
42 | some existing programs. This pragma provides a way to minimize that | |
43 | risk. New syntactic constructs can be enabled by C<use feature 'foo'>, | |
44 | and will be parsed only when the appropriate feature pragma is in | |
45 | scope. | |
46 | ||
9eb27be9 RGS |
47 | =head2 Lexical effect |
48 | ||
49 | Like other pragmas (C<use strict>, for example), features have a lexical | |
5e36ed56 | 50 | effect. C<use feature qw(foo)> will only make the feature "foo" available |
9eb27be9 RGS |
51 | from that point to the end of the enclosing block. |
52 | ||
53 | { | |
54 | use feature 'say'; | |
55 | say "say is available here"; | |
56 | } | |
57 | print "But not here.\n"; | |
58 | ||
5e36ed56 RGS |
59 | =head2 C<no feature> |
60 | ||
61 | Features can also be turned off by using C<no feature "foo">. This too | |
62 | has lexical effect. | |
63 | ||
64 | use feature 'say'; | |
65 | say "say is available here"; | |
66 | { | |
67 | no feature 'say'; | |
68 | print "But not here.\n"; | |
69 | } | |
70 | say "Yet it is here."; | |
71 | ||
72 | C<no feature> with no features specified will turn off all features. | |
73 | ||
0d863452 RH |
74 | =head2 The 'switch' feature |
75 | ||
76 | C<use feature 'switch'> tells the compiler to enable the Perl 6 | |
9eb27be9 | 77 | given/when construct. |
0d863452 RH |
78 | |
79 | See L<perlsyn/"Switch statements"> for details. | |
80 | ||
0d863452 RH |
81 | =head2 The 'say' feature |
82 | ||
83 | C<use feature 'say'> tells the compiler to enable the Perl 6 | |
9eb27be9 | 84 | C<say> function. |
0d863452 RH |
85 | |
86 | See L<perlfunc/say> for details. | |
87 | ||
bc9b29db RH |
88 | =head2 the 'err' feature |
89 | ||
90 | C<use feature 'err'> tells the compiler to enable the C<err> | |
9eb27be9 | 91 | operator. |
bc9b29db RH |
92 | |
93 | C<err> is a low-precedence variant of the C<//> operator: | |
94 | see C<perlop> for details. | |
95 | ||
712d05cf RGS |
96 | =head2 the 'state' feature |
97 | ||
98 | C<use feature 'state'> tells the compiler to enable C<state> | |
9eb27be9 | 99 | variables. |
712d05cf | 100 | |
e60bcc8b RGS |
101 | See L<perlsub/"Persistent Private Variables"> for details. |
102 | ||
bc9b29db RH |
103 | =head1 FEATURE BUNDLES |
104 | ||
105 | It's possible to load a whole slew of features in one go, using | |
106 | a I<feature bundle>. The name of a feature bundle is prefixed with | |
107 | a colon, to distinguish it from an actual feature. At present, the | |
8fd870d9 | 108 | only feature bundles are C<use feature ":5.10"> and C<use feature ":5.10.0">, |
3e7dd34d | 109 | which both are equivalent to C<use feature qw(switch say err state)>. |
8fd870d9 RGS |
110 | |
111 | In the forthcoming 5.10.X perl releases, C<use feature ":5.10"> will be | |
112 | equivalent to the latest C<use feature ":5.10.X">. | |
bc9b29db | 113 | |
0d863452 RH |
114 | =cut |
115 | ||
116 | sub import { | |
0d863452 RH |
117 | my $class = shift; |
118 | if (@_ == 0) { | |
0d863452 RH |
119 | croak("No features specified"); |
120 | } | |
121 | while (@_) { | |
122 | my $name = shift(@_); | |
bc9b29db RH |
123 | if ($name =~ /^:(.*)/) { |
124 | if (!exists $feature_bundle{$1}) { | |
b42943c4 | 125 | unknown_feature_bundle($1); |
bc9b29db RH |
126 | } |
127 | unshift @_, @{$feature_bundle{$1}}; | |
128 | next; | |
129 | } | |
0d863452 | 130 | if (!exists $feature{$name}) { |
b42943c4 | 131 | unknown_feature($name); |
0d863452 RH |
132 | } |
133 | $^H{$feature{$name}} = 1; | |
134 | } | |
135 | } | |
136 | ||
137 | sub unimport { | |
138 | my $class = shift; | |
139 | ||
140 | # A bare C<no feature> should disable *all* features | |
bc9b29db RH |
141 | if (!@_) { |
142 | delete @^H{ values(%feature) }; | |
143 | return; | |
144 | } | |
145 | ||
146 | while (@_) { | |
147 | my $name = shift; | |
148 | if ($name =~ /^:(.*)/) { | |
149 | if (!exists $feature_bundle{$1}) { | |
b42943c4 | 150 | unknown_feature_bundle($1); |
bc9b29db RH |
151 | } |
152 | unshift @_, @{$feature_bundle{$1}}; | |
153 | next; | |
154 | } | |
0d863452 | 155 | if (!exists($feature{$name})) { |
b42943c4 | 156 | unknown_feature($name); |
0d863452 RH |
157 | } |
158 | else { | |
159 | delete $^H{$feature{$name}}; | |
160 | } | |
161 | } | |
0d863452 RH |
162 | } |
163 | ||
b42943c4 RGS |
164 | sub unknown_feature { |
165 | my $feature = shift; | |
166 | croak(sprintf('Feature "%s" is not supported by Perl %vd', | |
167 | $feature, $^V)); | |
168 | } | |
169 | ||
170 | sub unknown_feature_bundle { | |
171 | my $feature = shift; | |
172 | croak(sprintf('Feature bundle "%s" is not supported by Perl %vd', | |
173 | $feature, $^V)); | |
174 | } | |
175 | ||
176 | sub croak { | |
177 | require Carp; | |
178 | Carp::croak(@_); | |
179 | } | |
180 | ||
0d863452 | 181 | 1; |