Commit | Line | Data |
0d863452 |
1 | package feature; |
2 | |
712d05cf |
3 | our $VERSION = '1.01'; |
0d863452 |
4 | |
5 | # (feature name) => (internal name, used in %^H) |
6 | my %feature = ( |
7b9ef140 |
7 | switch => 'feature_switch', |
8 | "~~" => "feature_~~", |
9 | say => "feature_say", |
bc9b29db |
10 | err => "feature_err", |
712d05cf |
11 | state => "feature_state", |
bc9b29db |
12 | ); |
13 | |
14 | my %feature_bundle = ( |
712d05cf |
15 | "5.10" => [qw(switch ~~ say err state)], |
0d863452 |
16 | ); |
17 | |
18 | |
19 | # Here are some notes that probably shouldn't be in the public |
20 | # documentation, but which it's useful to have somewhere. |
21 | # |
22 | # One side-effect of the change is that C<prototype("CORE::continue")> |
23 | # no longer throws the error C<Can't find an opnumber for "continue">. |
24 | # One of the tests in t/op/cproto.t had to be changed to accommodate |
25 | # this, but it really shouldn't affect real-world code. |
26 | # |
27 | # TODO: |
28 | # - sort out the smartmatch semantics |
29 | # - think about versioned features (use switch => 2) |
30 | # |
31 | # -- Robin 2005-12 |
32 | |
33 | =head1 NAME |
34 | |
35 | feature - Perl pragma to enable new syntactic features |
36 | |
37 | =head1 SYNOPSIS |
38 | |
bc9b29db |
39 | use feature qw(switch say); |
0d863452 |
40 | given ($foo) { |
bc9b29db |
41 | when (1) { say "\$foo == 1" } |
42 | when ([2,3]) { say "\$foo == 2 || \$foo == 3" } |
43 | when (/^a[bc]d$/) { say "\$foo eq 'abd' || \$foo eq 'acd'" } |
44 | when ($_ > 100) { say "\$foo > 100" } |
45 | default { say "None of the above" } |
0d863452 |
46 | } |
47 | |
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 |
52 | risk. New syntactic constructs can be enabled by C<use feature 'foo'>, |
53 | and will be parsed only when the appropriate feature pragma is in |
54 | scope. |
55 | |
56 | =head2 The 'switch' feature |
57 | |
58 | C<use feature 'switch'> tells the compiler to enable the Perl 6 |
59 | given/when construct from here to the end of the enclosing BLOCK. |
60 | |
61 | See L<perlsyn/"Switch statements"> for details. |
62 | |
63 | =head2 The '~~' feature |
64 | |
65 | C<use feature '~~'> tells the compiler to enable the Perl 6 |
66 | smart match C<~~> operator from here to the end of the enclosing BLOCK. |
67 | |
68 | See L<perlsyn/"Smart Matching in Detail"> for details. |
69 | |
70 | =head2 The 'say' feature |
71 | |
72 | C<use feature 'say'> tells the compiler to enable the Perl 6 |
73 | C<say> function from here to the end of the enclosing BLOCK. |
74 | |
75 | See L<perlfunc/say> for details. |
76 | |
bc9b29db |
77 | =head2 the 'err' feature |
78 | |
79 | C<use feature 'err'> tells the compiler to enable the C<err> |
80 | operator from here to the end of the enclosing BLOCK. |
81 | |
82 | C<err> is a low-precedence variant of the C<//> operator: |
83 | see C<perlop> for details. |
84 | |
712d05cf |
85 | =head2 the 'state' feature |
86 | |
87 | C<use feature 'state'> tells the compiler to enable C<state> |
88 | variables from here to the end of the enclosing BLOCK. |
89 | |
bc9b29db |
90 | =head1 FEATURE BUNDLES |
91 | |
92 | It's possible to load a whole slew of features in one go, using |
93 | a I<feature bundle>. The name of a feature bundle is prefixed with |
94 | a colon, to distinguish it from an actual feature. At present, the |
95 | only feature bundle is C<use feature ":5.10">, which is equivalent |
712d05cf |
96 | to C<use feature qw(switch ~~ say err state)>. |
bc9b29db |
97 | |
0d863452 |
98 | =cut |
99 | |
100 | sub import { |
0d863452 |
101 | my $class = shift; |
102 | if (@_ == 0) { |
103 | require Carp; |
104 | Carp->import("croak"); |
105 | croak("No features specified"); |
106 | } |
107 | while (@_) { |
108 | my $name = shift(@_); |
bc9b29db |
109 | if ($name =~ /^:(.*)/) { |
110 | if (!exists $feature_bundle{$1}) { |
111 | require Carp; |
112 | Carp->import("croak"); |
113 | croak(sprintf('Feature bundle "%s" is not supported by Perl %vd', |
114 | $1, $^V)); |
115 | } |
116 | unshift @_, @{$feature_bundle{$1}}; |
117 | next; |
118 | } |
0d863452 |
119 | if (!exists $feature{$name}) { |
120 | require Carp; |
121 | Carp->import("croak"); |
122 | croak(sprintf('Feature "%s" is not supported by Perl %vd', |
123 | $name, $^V)); |
124 | } |
125 | $^H{$feature{$name}} = 1; |
126 | } |
127 | } |
128 | |
129 | sub unimport { |
130 | my $class = shift; |
131 | |
132 | # A bare C<no feature> should disable *all* features |
bc9b29db |
133 | if (!@_) { |
134 | delete @^H{ values(%feature) }; |
135 | return; |
136 | } |
137 | |
138 | while (@_) { |
139 | my $name = shift; |
140 | if ($name =~ /^:(.*)/) { |
141 | if (!exists $feature_bundle{$1}) { |
142 | require Carp; |
143 | Carp->import("croak"); |
144 | croak(sprintf('Feature bundle "%s" is not supported by Perl %vd', |
145 | $1, $^V)); |
146 | } |
147 | unshift @_, @{$feature_bundle{$1}}; |
148 | next; |
149 | } |
0d863452 |
150 | if (!exists($feature{$name})) { |
151 | require Carp; |
152 | Carp->import("croak"); |
153 | croak(sprintf('Feature "%s" is not supported by Perl %vd', |
154 | $name, $^V)); |
155 | } |
156 | else { |
157 | delete $^H{$feature{$name}}; |
158 | } |
159 | } |
0d863452 |
160 | } |
161 | |
162 | 1; |