Commit | Line | Data |
0d863452 |
1 | package feature; |
2 | |
3 | our $VERSION = '1.00'; |
4 | $feature::hint_bits = 0x04020000; # HINT_LOCALIZE_HH | HINT_HH_FOR_EVAL |
5 | |
6 | # (feature name) => (internal name, used in %^H) |
7 | my %feature = ( |
8 | switch => 'switch', |
9 | "~~" => "~~", |
10 | say => "say", |
11 | ); |
12 | |
13 | |
14 | # Here are some notes that probably shouldn't be in the public |
15 | # documentation, but which it's useful to have somewhere. |
16 | # |
17 | # One side-effect of the change is that C<prototype("CORE::continue")> |
18 | # no longer throws the error C<Can't find an opnumber for "continue">. |
19 | # One of the tests in t/op/cproto.t had to be changed to accommodate |
20 | # this, but it really shouldn't affect real-world code. |
21 | # |
22 | # TODO: |
23 | # - sort out the smartmatch semantics |
24 | # - think about versioned features (use switch => 2) |
25 | # |
26 | # -- Robin 2005-12 |
27 | |
28 | =head1 NAME |
29 | |
30 | feature - Perl pragma to enable new syntactic features |
31 | |
32 | =head1 SYNOPSIS |
33 | |
34 | use feature 'switch'; |
35 | given ($foo) { |
36 | when (1) { print "\$foo == 1\n" } |
37 | when ([2,3]) { print "\$foo == 2 || \$foo == 3\n" } |
38 | when (/^a[bc]d$/) { print "\$foo eq 'abd' || \$foo eq 'acd'\n" } |
39 | when ($_ > 100) { print "\$foo > 100\n" } |
40 | default { print "None of the above\n" } |
41 | } |
42 | |
43 | =head1 DESCRIPTION |
44 | |
45 | It is usually impossible to add new syntax to Perl without breaking |
46 | some existing programs. This pragma provides a way to minimize that |
47 | risk. New syntactic constructs can be enabled by C<use feature 'foo'>, |
48 | and will be parsed only when the appropriate feature pragma is in |
49 | scope. |
50 | |
51 | =head2 The 'switch' feature |
52 | |
53 | C<use feature 'switch'> tells the compiler to enable the Perl 6 |
54 | given/when construct from here to the end of the enclosing BLOCK. |
55 | |
56 | See L<perlsyn/"Switch statements"> for details. |
57 | |
58 | =head2 The '~~' feature |
59 | |
60 | C<use feature '~~'> tells the compiler to enable the Perl 6 |
61 | smart match C<~~> operator from here to the end of the enclosing BLOCK. |
62 | |
63 | See L<perlsyn/"Smart Matching in Detail"> for details. |
64 | |
65 | =head2 The 'say' feature |
66 | |
67 | C<use feature 'say'> tells the compiler to enable the Perl 6 |
68 | C<say> function from here to the end of the enclosing BLOCK. |
69 | |
70 | See L<perlfunc/say> for details. |
71 | |
72 | =cut |
73 | |
74 | sub import { |
75 | $^H |= $feature::hint_bits; # Need this or %^H won't work |
76 | |
77 | my $class = shift; |
78 | if (@_ == 0) { |
79 | require Carp; |
80 | Carp->import("croak"); |
81 | croak("No features specified"); |
82 | } |
83 | while (@_) { |
84 | my $name = shift(@_); |
85 | if (!exists $feature{$name}) { |
86 | require Carp; |
87 | Carp->import("croak"); |
88 | croak(sprintf('Feature "%s" is not supported by Perl %vd', |
89 | $name, $^V)); |
90 | } |
91 | $^H{$feature{$name}} = 1; |
92 | } |
93 | } |
94 | |
95 | sub unimport { |
96 | my $class = shift; |
97 | |
98 | # A bare C<no feature> should disable *all* features |
99 | for my $name (@_) { |
100 | if (!exists($feature{$name})) { |
101 | require Carp; |
102 | Carp->import("croak"); |
103 | croak(sprintf('Feature "%s" is not supported by Perl %vd', |
104 | $name, $^V)); |
105 | } |
106 | else { |
107 | delete $^H{$feature{$name}}; |
108 | } |
109 | } |
110 | |
111 | if(!@_) { |
112 | delete @^H{ values(%feature) }; |
113 | } |
114 | } |
115 | |
116 | 1; |