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1 | package feature; |
2 | |
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3 | our $VERSION = '1.01'; |
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4 | |
5 | # (feature name) => (internal name, used in %^H) |
6 | my %feature = ( |
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7 | switch => 'feature_switch', |
8 | "~~" => "feature_~~", |
9 | say => "feature_say", |
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10 | err => "feature_err", |
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11 | dor => "feature_err", |
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12 | state => "feature_state", |
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13 | ); |
14 | |
15 | my %feature_bundle = ( |
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16 | "5.10" => [qw(switch ~~ say err state)], |
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17 | ); |
18 | |
19 | |
20 | # Here are some notes that probably shouldn't be in the public |
21 | # documentation, but which it's useful to have somewhere. |
22 | # |
23 | # One side-effect of the change is that C<prototype("CORE::continue")> |
24 | # no longer throws the error C<Can't find an opnumber for "continue">. |
25 | # One of the tests in t/op/cproto.t had to be changed to accommodate |
26 | # this, but it really shouldn't affect real-world code. |
27 | # |
28 | # TODO: |
29 | # - sort out the smartmatch semantics |
30 | # - think about versioned features (use switch => 2) |
31 | # |
32 | # -- Robin 2005-12 |
33 | |
34 | =head1 NAME |
35 | |
36 | feature - Perl pragma to enable new syntactic features |
37 | |
38 | =head1 SYNOPSIS |
39 | |
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40 | use feature qw(switch say); |
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41 | given ($foo) { |
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42 | when (1) { say "\$foo == 1" } |
43 | when ([2,3]) { say "\$foo == 2 || \$foo == 3" } |
44 | when (/^a[bc]d$/) { say "\$foo eq 'abd' || \$foo eq 'acd'" } |
45 | when ($_ > 100) { say "\$foo > 100" } |
46 | default { say "None of the above" } |
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47 | } |
48 | |
49 | =head1 DESCRIPTION |
50 | |
51 | It is usually impossible to add new syntax to Perl without breaking |
52 | some existing programs. This pragma provides a way to minimize that |
53 | risk. New syntactic constructs can be enabled by C<use feature 'foo'>, |
54 | and will be parsed only when the appropriate feature pragma is in |
55 | scope. |
56 | |
57 | =head2 The 'switch' feature |
58 | |
59 | C<use feature 'switch'> tells the compiler to enable the Perl 6 |
60 | given/when construct from here to the end of the enclosing BLOCK. |
61 | |
62 | See L<perlsyn/"Switch statements"> for details. |
63 | |
64 | =head2 The '~~' feature |
65 | |
66 | C<use feature '~~'> tells the compiler to enable the Perl 6 |
67 | smart match C<~~> operator from here to the end of the enclosing BLOCK. |
68 | |
69 | See L<perlsyn/"Smart Matching in Detail"> for details. |
70 | |
71 | =head2 The 'say' feature |
72 | |
73 | C<use feature 'say'> tells the compiler to enable the Perl 6 |
74 | C<say> function from here to the end of the enclosing BLOCK. |
75 | |
76 | See L<perlfunc/say> for details. |
77 | |
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78 | =head2 the 'err' feature |
79 | |
80 | C<use feature 'err'> tells the compiler to enable the C<err> |
81 | operator from here to the end of the enclosing BLOCK. |
82 | |
83 | C<err> is a low-precedence variant of the C<//> operator: |
84 | see C<perlop> for details. |
85 | |
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86 | =head2 the 'dor' feature |
87 | |
88 | The 'dor' feature is an alias for the 'err' feature. |
89 | |
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90 | =head2 the 'state' feature |
91 | |
92 | C<use feature 'state'> tells the compiler to enable C<state> |
93 | variables from here to the end of the enclosing BLOCK. |
94 | |
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95 | See L<perlsub/"Persistent Private Variables"> for details. |
96 | |
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97 | =head1 FEATURE BUNDLES |
98 | |
99 | It's possible to load a whole slew of features in one go, using |
100 | a I<feature bundle>. The name of a feature bundle is prefixed with |
101 | a colon, to distinguish it from an actual feature. At present, the |
102 | only feature bundle is C<use feature ":5.10">, which is equivalent |
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103 | to C<use feature qw(switch ~~ say err state)>. |
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104 | |
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105 | =cut |
106 | |
107 | sub import { |
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108 | my $class = shift; |
109 | if (@_ == 0) { |
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110 | croak("No features specified"); |
111 | } |
112 | while (@_) { |
113 | my $name = shift(@_); |
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114 | if ($name =~ /^:(.*)/) { |
115 | if (!exists $feature_bundle{$1}) { |
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116 | unknown_feature_bundle($1); |
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117 | } |
118 | unshift @_, @{$feature_bundle{$1}}; |
119 | next; |
120 | } |
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121 | if (!exists $feature{$name}) { |
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122 | unknown_feature($name); |
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123 | } |
124 | $^H{$feature{$name}} = 1; |
125 | } |
126 | } |
127 | |
128 | sub unimport { |
129 | my $class = shift; |
130 | |
131 | # A bare C<no feature> should disable *all* features |
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132 | if (!@_) { |
133 | delete @^H{ values(%feature) }; |
134 | return; |
135 | } |
136 | |
137 | while (@_) { |
138 | my $name = shift; |
139 | if ($name =~ /^:(.*)/) { |
140 | if (!exists $feature_bundle{$1}) { |
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141 | unknown_feature_bundle($1); |
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142 | } |
143 | unshift @_, @{$feature_bundle{$1}}; |
144 | next; |
145 | } |
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146 | if (!exists($feature{$name})) { |
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147 | unknown_feature($name); |
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148 | } |
149 | else { |
150 | delete $^H{$feature{$name}}; |
151 | } |
152 | } |
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153 | } |
154 | |
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155 | sub unknown_feature { |
156 | my $feature = shift; |
157 | croak(sprintf('Feature "%s" is not supported by Perl %vd', |
158 | $feature, $^V)); |
159 | } |
160 | |
161 | sub unknown_feature_bundle { |
162 | my $feature = shift; |
163 | croak(sprintf('Feature bundle "%s" is not supported by Perl %vd', |
164 | $feature, $^V)); |
165 | } |
166 | |
167 | sub croak { |
168 | require Carp; |
169 | Carp::croak(@_); |
170 | } |
171 | |
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172 | 1; |