Profile of feature.pm

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For bin/dpath
Run on Tue Jun 5 15:31:33 2012
Reported on Tue Jun 5 15:31:52 2012

Filename | /home/ss5/perl5/perlbrew/perls/perl-5.14.1/lib/5.14.1/feature.pm
Statements | Executed 30 statements in 182µs

Subroutines
Calls | P | F | Exclusive Time | Inclusive Time | Subroutine
--- | --- | --- | --- | --- | ---
1 | 1 | 1 | 87µs | 87µs | feature::::importfeature::import
0 | 0 | 0 | 0s | 0s | feature::::croakfeature::croak
0 | 0 | 0 | 0s | 0s | feature::::unimportfeature::unimport
0 | 0 | 0 | 0s | 0s | feature::::unknown_featurefeature::unknown_feature
0 | 0 | 0 | 0s | 0s | feature::::unknown_feature_bundlefeature::unknown_feature_bundle

Call graph for these subroutines as a Graphviz dot language file.

Line | State ments | Time on line | Calls | Time in subs | Code
--- | --- | --- | --- | --- | ---
1 |  |  |  |  | package feature;
2 |  |  |  |  |
3 | 1 | 3µs |  |  | our $VERSION = '1.20';
4 |  |  |  |  |
5 |  |  |  |  | # (feature name) => (internal name, used in %^H)
6 | 1 | 14µs |  |  | my %feature = (
7 |  |  |  |  | switch => 'feature_switch',
8 |  |  |  |  | say => "feature_say",
9 |  |  |  |  | state => "feature_state",
10 |  |  |  |  | unicode_strings => "feature_unicode",
11 |  |  |  |  | );
12 |  |  |  |  |
13 |  |  |  |  | # This gets set (for now) in $^H as well as in %^H,
14 |  |  |  |  | # for runtime speed of the uc/lc/ucfirst/lcfirst functions.
15 |  |  |  |  | # See HINT_UNI_8_BIT in perl.h.
16 | 1 | 2µs |  |  | our $hint_uni8bit = 0x00000800;
17 |  |  |  |  |
18 |  |  |  |  | # NB. the latest bundle must be loaded by the -E switch (see toke.c)
19 |  |  |  |  |
20 | 1 | 22µs |  |  | my %feature_bundle = (
21 |  |  |  |  | "5.10" => [qw(switch say state)],
22 |  |  |  |  | "5.11" => [qw(switch say state unicode_strings)],
23 |  |  |  |  | "5.12" => [qw(switch say state unicode_strings)],
24 |  |  |  |  | "5.13" => [qw(switch say state unicode_strings)],
25 |  |  |  |  | "5.14" => [qw(switch say state unicode_strings)],
26 |  |  |  |  | );
27 |  |  |  |  |
28 |  |  |  |  | # special case
29 | 1 | 4µs |  |  | $feature_bundle{"5.9.5"} = $feature_bundle{"5.10"};
30 |  |  |  |  |
31 |  |  |  |  | # TODO:
32 |  |  |  |  | # - think about versioned features (use feature switch => 2)
33 |  |  |  |  |
34 |  |  |  |  | =head1 NAME
35 |  |  |  |  |
36 |  |  |  |  | feature - Perl pragma to enable new features
37 |  |  |  |  |
38 |  |  |  |  | =head1 SYNOPSIS
39 |  |  |  |  |
40 |  |  |  |  | use feature qw(switch say);
41 |  |  |  |  | given ($foo) {
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" }
47 |  |  |  |  | }
48 |  |  |  |  |
49 |  |  |  |  | use feature ':5.10'; # loads all features available in perl 5.10
50 |  |  |  |  |
51 |  |  |  |  | =head1 DESCRIPTION
52 |  |  |  |  |
53 |  |  |  |  | It is usually impossible to add new syntax to Perl without breaking
54 |  |  |  |  | some existing programs. This pragma provides a way to minimize that
55 |  |  |  |  | risk. New syntactic constructs, or new semantic meanings to older
56 |  |  |  |  | constructs, can be enabled by C<use feature 'foo'>, and will be parsed
57 |  |  |  |  | only when the appropriate feature pragma is in scope.
58 |  |  |  |  |
59 |  |  |  |  | =head2 Lexical effect
60 |  |  |  |  |
61 |  |  |  |  | Like other pragmas (C<use strict>, for example), features have a lexical
62 |  |  |  |  | effect. C<use feature qw(foo)> will only make the feature "foo" available
63 |  |  |  |  | from that point to the end of the enclosing block.
64 |  |  |  |  |
65 |  |  |  |  | {
66 |  |  |  |  | use feature 'say';
67 |  |  |  |  | say "say is available here";
68 |  |  |  |  | }
69 |  |  |  |  | print "But not here.\n";
70 |  |  |  |  |
71 |  |  |  |  | =head2 C<no feature>
72 |  |  |  |  |
73 |  |  |  |  | Features can also be turned off by using C<no feature "foo">. This too
74 |  |  |  |  | has lexical effect.
75 |  |  |  |  |
76 |  |  |  |  | use feature 'say';
77 |  |  |  |  | say "say is available here";
78 |  |  |  |  | {
79 |  |  |  |  | no feature 'say';
80 |  |  |  |  | print "But not here.\n";
81 |  |  |  |  | }
82 |  |  |  |  | say "Yet it is here.";
83 |  |  |  |  |
84 |  |  |  |  | C<no feature> with no features specified will turn off all features.
85 |  |  |  |  |
86 |  |  |  |  | =head2 The 'switch' feature
87 |  |  |  |  |
88 |  |  |  |  | C<use feature 'switch'> tells the compiler to enable the Perl 6
89 |  |  |  |  | given/when construct.
90 |  |  |  |  |
91 |  |  |  |  | See L<perlsyn/"Switch statements"> for details.
92 |  |  |  |  |
93 |  |  |  |  | =head2 The 'say' feature
94 |  |  |  |  |
95 |  |  |  |  | C<use feature 'say'> tells the compiler to enable the Perl 6
96 |  |  |  |  | C<say> function.
97 |  |  |  |  |
98 |  |  |  |  | See L<perlfunc/say> for details.
99 |  |  |  |  |
100 |  |  |  |  | =head2 the 'state' feature
101 |  |  |  |  |
102 |  |  |  |  | C<use feature 'state'> tells the compiler to enable C<state>
103 |  |  |  |  | variables.
104 |  |  |  |  |
105 |  |  |  |  | See L<perlsub/"Persistent Private Variables"> for details.
106 |  |  |  |  |
107 |  |  |  |  | =head2 the 'unicode_strings' feature
108 |  |  |  |  |
109 |  |  |  |  | C<use feature 'unicode_strings'> tells the compiler to use Unicode semantics
110 |  |  |  |  | in all string operations executed within its scope (unless they are also
111 |  |  |  |  | within the scope of either C<use locale> or C<use bytes>). The same applies
112 |  |  |  |  | to all regular expressions compiled within the scope, even if executed outside
113 |  |  |  |  | it.
114 |  |  |  |  |
115 |  |  |  |  | C<no feature 'unicode_strings'> tells the compiler to use the traditional
116 |  |  |  |  | Perl semantics wherein the native character set semantics is used unless it is
117 |  |  |  |  | clear to Perl that Unicode is desired. This can lead to some surprises
118 |  |  |  |  | when the behavior suddenly changes. (See
119 |  |  |  |  | L<perlunicode/The "Unicode Bug"> for details.) For this reason, if you are
120 |  |  |  |  | potentially using Unicode in your program, the
121 |  |  |  |  | C<use feature 'unicode_strings'> subpragma is B<strongly> recommended.
122 |  |  |  |  |
123 |  |  |  |  | This subpragma is available starting with Perl 5.11.3, but was not fully
124 |  |  |  |  | implemented until 5.13.8.
125 |  |  |  |  |
126 |  |  |  |  | =head1 FEATURE BUNDLES
127 |  |  |  |  |
128 |  |  |  |  | It's possible to load a whole slew of features in one go, using
129 |  |  |  |  | a I<feature bundle>. The name of a feature bundle is prefixed with
130 |  |  |  |  | a colon, to distinguish it from an actual feature. At present, the
131 |  |  |  |  | only feature bundle is C<use feature ":5.10"> which is equivalent
132 |  |  |  |  | to C<use feature qw(switch say state)>.
133 |  |  |  |  |
134 |  |  |  |  | Specifying sub-versions such as the C<0> in C<5.10.0> in feature bundles has
135 |  |  |  |  | no effect: feature bundles are guaranteed to be the same for all sub-versions.
136 |  |  |  |  |
137 |  |  |  |  | =head1 IMPLICIT LOADING
138 |  |  |  |  |
139 |  |  |  |  | There are two ways to load the C<feature> pragma implicitly :
140 |  |  |  |  |
141 |  |  |  |  | =over 4
142 |  |  |  |  |
143 |  |  |  |  | =item *
144 |  |  |  |  |
145 |  |  |  |  | By using the C<-E> switch on the command-line instead of C<-e>. It enables
146 |  |  |  |  | all available features in the main compilation unit (that is, the one-liner.)
147 |  |  |  |  |
148 |  |  |  |  | =item *
149 |  |  |  |  |
150 |  |  |  |  | By requiring explicitly a minimal Perl version number for your program, with
151 |  |  |  |  | the C<use VERSION> construct, and when the version is higher than or equal to
152 |  |  |  |  | 5.10.0. That is,
153 |  |  |  |  |
154 |  |  |  |  | use 5.10.0;
155 |  |  |  |  |
156 |  |  |  |  | will do an implicit
157 |  |  |  |  |
158 |  |  |  |  | use feature ':5.10';
159 |  |  |  |  |
160 |  |  |  |  | and so on. Note how the trailing sub-version is automatically stripped from the
161 |  |  |  |  | version.
162 |  |  |  |  |
163 |  |  |  |  | But to avoid portability warnings (see L<perlfunc/use>), you may prefer:
164 |  |  |  |  |
165 |  |  |  |  | use 5.010;
166 |  |  |  |  |
167 |  |  |  |  | with the same effect.
168 |  |  |  |  |
169 |  |  |  |  | =back
170 |  |  |  |  |
171 |  |  |  |  | =cut
172 |  |  |  |  |
173 |  |  |  |  | # spent 87µs within feature::import which was called: # once (87µs+0s) by SelfLoader::BEGIN@1.6 at line 1 of (eval 31)[SelfLoader.pm:12] sub import {
174 | 1 | 3µs |  |  | my $class = shift;
175 | 1 | 4µs |  |  | if (@_ == 0) {
176 |  |  |  |  | croak("No features specified");
177 |  |  |  |  | }
178 | 1 | 31µs |  |  | while (@_) {
179 | 4 | 7µs |  |  | my $name = shift(@_);
180 | 4 | 10µs |  |  | if (substr($name, 0, 1) eq ":") {
181 | 1 | 2µs |  |  | my $v = substr($name, 1);
182 | 1 | 2µs |  |  | if (!exists $feature_bundle{$v}) {
183 |  |  |  |  | $v =~ s/^([0-9]+)\.([0-9]+).[0-9]+$/$1.$2/;
184 |  |  |  |  | if (!exists $feature_bundle{$v}) {
185 |  |  |  |  | unknown_feature_bundle(substr($name, 1));
186 |  |  |  |  | }
187 |  |  |  |  | }
188 | 1 | 8µs |  |  | unshift @_, @{$feature_bundle{$v}};
189 | 1 | 4µs |  |  | next;
190 |  |  |  |  | }
191 | 3 | 3µs |  |  | if (!exists $feature{$name}) {
192 |  |  |  |  | unknown_feature($name);
193 |  |  |  |  | }
194 | 3 | 23µs |  |  | $^H{$feature{$name}} = 1;
195 | 3 | 7µs |  |  | $^H |= $hint_uni8bit if $name eq 'unicode_strings';
196 |  |  |  |  | }
197 |  |  |  |  | }
198 |  |  |  |  |
199 |  |  |  |  | sub unimport {
200 |  |  |  |  | my $class = shift;
201 |  |  |  |  |
202 |  |  |  |  | # A bare C<no feature> should disable *all* features
203 |  |  |  |  | if (!@_) {
204 |  |  |  |  | delete @^H{ values(%feature) };
205 |  |  |  |  | $^H &= ~ $hint_uni8bit;
206 |  |  |  |  | return;
207 |  |  |  |  | }
208 |  |  |  |  |
209 |  |  |  |  | while (@_) {
210 |  |  |  |  | my $name = shift;
211 |  |  |  |  | if (substr($name, 0, 1) eq ":") {
212 |  |  |  |  | my $v = substr($name, 1);
213 |  |  |  |  | if (!exists $feature_bundle{$v}) {
214 |  |  |  |  | $v =~ s/^([0-9]+)\.([0-9]+).[0-9]+$/$1.$2/;
215 |  |  |  |  | if (!exists $feature_bundle{$v}) {
216 |  |  |  |  | unknown_feature_bundle(substr($name, 1));
217 |  |  |  |  | }
218 |  |  |  |  | }
219 |  |  |  |  | unshift @_, @{$feature_bundle{$v}};
220 |  |  |  |  | next;
221 |  |  |  |  | }
222 |  |  |  |  | if (!exists($feature{$name})) {
223 |  |  |  |  | unknown_feature($name);
224 |  |  |  |  | }
225 |  |  |  |  | else {
226 |  |  |  |  | delete $^H{$feature{$name}};
227 |  |  |  |  | $^H &= ~ $hint_uni8bit if $name eq 'unicode_strings';
228 |  |  |  |  | }
229 |  |  |  |  | }
230 |  |  |  |  | }
231 |  |  |  |  |
232 |  |  |  |  | sub unknown_feature {
233 |  |  |  |  | my $feature = shift;
234 |  |  |  |  | croak(sprintf('Feature "%s" is not supported by Perl %vd',
235 |  |  |  |  | $feature, $^V));
236 |  |  |  |  | }
237 |  |  |  |  |
238 |  |  |  |  | sub unknown_feature_bundle {
239 |  |  |  |  | my $feature = shift;
240 |  |  |  |  | croak(sprintf('Feature bundle "%s" is not supported by Perl %vd',
241 |  |  |  |  | $feature, $^V));
242 |  |  |  |  | }
243 |  |  |  |  |
244 |  |  |  |  | sub croak {
245 |  |  |  |  | require Carp;
246 |  |  |  |  | Carp::croak(@_);
247 |  |  |  |  | }
248 |  |  |  |  |
249 | 1 | 33µs |  |  | 1;