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8990e307 |
1 | package Exporter; |
2 | |
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3 | require 5.006; |
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4 | |
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5 | # Be lean. |
6 | #use strict; |
7 | #no strict 'refs'; |
b75c8c73 |
8 | |
9 | our $Debug = 0; |
10 | our $ExportLevel = 0; |
11 | our $Verbose ||= 0; |
a29b0897 |
12 | our $VERSION = '5.58'; |
a6faae8d |
13 | our (%Cache); |
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14 | $Carp::Internal{Exporter} = 1; |
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15 | |
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16 | sub as_heavy { |
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17 | require Exporter::Heavy; |
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18 | # Unfortunately, this does not work if the caller is aliased as *name = \&foo |
19 | # Thus the need to create a lot of identical subroutines |
20 | my $c = (caller(1))[3]; |
21 | $c =~ s/.*:://; |
22 | \&{"Exporter::Heavy::heavy_$c"}; |
84902520 |
23 | } |
24 | |
4af1b167 |
25 | sub export { |
0e57b4e8 |
26 | goto &{as_heavy()}; |
a0d0e21e |
27 | } |
28 | |
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29 | sub import { |
30 | my $pkg = shift; |
31 | my $callpkg = caller($ExportLevel); |
b75c8c73 |
32 | |
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33 | if ($pkg eq "Exporter" and @_ and $_[0] eq "import") { |
34 | *{$callpkg."::import"} = \&import; |
35 | return; |
36 | } |
37 | |
4af1b167 |
38 | # We *need* to treat @{"$pkg\::EXPORT_FAIL"} since Carp uses it :-( |
a6faae8d |
39 | my($exports, $fail) = (\@{"$pkg\::EXPORT"}, \@{"$pkg\::EXPORT_FAIL"}); |
4af1b167 |
40 | return export $pkg, $callpkg, @_ |
b75c8c73 |
41 | if $Verbose or $Debug or @$fail > 1; |
a6faae8d |
42 | my $export_cache = ($Cache{$pkg} ||= {}); |
b75c8c73 |
43 | my $args = @_ or @_ = @$exports; |
732bb7c2 |
44 | |
45 | local $_; |
b75c8c73 |
46 | if ($args and not %$export_cache) { |
732bb7c2 |
47 | s/^&//, $export_cache->{$_} = 1 |
48 | foreach (@$exports, @{"$pkg\::EXPORT_OK"}); |
4af1b167 |
49 | } |
fa1bb02f |
50 | my $heavy; |
51 | # Try very hard not to use {} and hence have to enter scope on the foreach |
52 | # We bomb out of the loop with last as soon as heavy is set. |
53 | if ($args or $fail) { |
732bb7c2 |
54 | ($heavy = (/\W/ or $args and not exists $export_cache->{$_} |
fa1bb02f |
55 | or @$fail and $_ eq $fail->[0])) and last |
56 | foreach (@_); |
57 | } else { |
58 | ($heavy = /\W/) and last |
732bb7c2 |
59 | foreach (@_); |
4af1b167 |
60 | } |
732bb7c2 |
61 | return export $pkg, $callpkg, ($args ? @_ : ()) if $heavy; |
4af1b167 |
62 | local $SIG{__WARN__} = |
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63 | sub {require Carp; &Carp::carp}; |
732bb7c2 |
64 | # shortcut for the common case of no type character |
65 | *{"$callpkg\::$_"} = \&{"$pkg\::$_"} foreach @_; |
e50aee73 |
66 | } |
67 | |
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68 | # Default methods |
69 | |
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70 | sub export_fail { |
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71 | my $self = shift; |
72 | @_; |
2b5b2650 |
73 | } |
74 | |
0e57b4e8 |
75 | # Unfortunately, caller(1)[3] "does not work" if the caller is aliased as |
76 | # *name = \&foo. Thus the need to create a lot of identical subroutines |
77 | # Otherwise we could have aliased them to export(). |
b75c8c73 |
78 | |
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79 | sub export_to_level { |
80 | goto &{as_heavy()}; |
81 | } |
82 | |
83 | sub export_tags { |
84 | goto &{as_heavy()}; |
b75c8c73 |
85 | } |
86 | |
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87 | sub export_ok_tags { |
88 | goto &{as_heavy()}; |
89 | } |
90 | |
91 | sub require_version { |
92 | goto &{as_heavy()}; |
93 | } |
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94 | |
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95 | 1; |
732bb7c2 |
96 | __END__ |
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97 | |
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98 | =head1 NAME |
99 | |
100 | Exporter - Implements default import method for modules |
101 | |
102 | =head1 SYNOPSIS |
103 | |
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104 | In module YourModule.pm: |
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105 | |
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106 | package YourModule; |
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107 | require Exporter; |
108 | @ISA = qw(Exporter); |
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109 | @EXPORT_OK = qw(munge frobnicate); # symbols to export on request |
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110 | |
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111 | or |
112 | |
113 | package YourModule; |
114 | use Exporter 'import'; # gives you Exporter's import() method directly |
115 | @EXPORT_OK = qw(munge frobnicate); # symbols to export on request |
116 | |
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117 | In other files which wish to use YourModule: |
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118 | |
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119 | use ModuleName qw(frobnicate); # import listed symbols |
120 | frobnicate ($left, $right) # calls YourModule::frobnicate |
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121 | |
122 | =head1 DESCRIPTION |
123 | |
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124 | The Exporter module implements an C<import> method which allows a module |
125 | to export functions and variables to its users' namespaces. Many modules |
126 | use Exporter rather than implementing their own C<import> method because |
127 | Exporter provides a highly flexible interface, with an implementation optimised |
128 | for the common case. |
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129 | |
130 | Perl automatically calls the C<import> method when processing a |
131 | C<use> statement for a module. Modules and C<use> are documented |
132 | in L<perlfunc> and L<perlmod>. Understanding the concept of |
133 | modules and how the C<use> statement operates is important to |
134 | understanding the Exporter. |
135 | |
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136 | =head2 How to Export |
137 | |
138 | The arrays C<@EXPORT> and C<@EXPORT_OK> in a module hold lists of |
139 | symbols that are going to be exported into the users name space by |
140 | default, or which they can request to be exported, respectively. The |
141 | symbols can represent functions, scalars, arrays, hashes, or typeglobs. |
142 | The symbols must be given by full name with the exception that the |
143 | ampersand in front of a function is optional, e.g. |
144 | |
145 | @EXPORT = qw(afunc $scalar @array); # afunc is a function |
146 | @EXPORT_OK = qw(&bfunc %hash *typeglob); # explicit prefix on &bfunc |
147 | |
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148 | If you are only exporting function names it is recommended to omit the |
149 | ampersand, as the implementation is faster this way. |
150 | |
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151 | =head2 Selecting What To Export |
152 | |
153 | Do B<not> export method names! |
154 | |
155 | Do B<not> export anything else by default without a good reason! |
156 | |
157 | Exports pollute the namespace of the module user. If you must export |
158 | try to use @EXPORT_OK in preference to @EXPORT and avoid short or |
159 | common symbol names to reduce the risk of name clashes. |
160 | |
161 | Generally anything not exported is still accessible from outside the |
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162 | module using the ModuleName::item_name (or $blessed_ref-E<gt>method) |
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163 | syntax. By convention you can use a leading underscore on names to |
164 | informally indicate that they are 'internal' and not for public use. |
165 | |
166 | (It is actually possible to get private functions by saying: |
167 | |
168 | my $subref = sub { ... }; |
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169 | $subref->(@args); # Call it as a function |
170 | $obj->$subref(@args); # Use it as a method |
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171 | |
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172 | However if you use them for methods it is up to you to figure out |
173 | how to make inheritance work.) |
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174 | |
175 | As a general rule, if the module is trying to be object oriented |
176 | then export nothing. If it's just a collection of functions then |
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177 | @EXPORT_OK anything but use @EXPORT with caution. For function and |
178 | method names use barewords in preference to names prefixed with |
179 | ampersands for the export lists. |
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180 | |
181 | Other module design guidelines can be found in L<perlmod>. |
182 | |
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183 | =head2 How to Import |
184 | |
185 | In other files which wish to use your module there are three basic ways for |
186 | them to load your module and import its symbols: |
187 | |
188 | =over 4 |
189 | |
190 | =item C<use ModuleName;> |
191 | |
192 | This imports all the symbols from ModuleName's @EXPORT into the namespace |
193 | of the C<use> statement. |
194 | |
195 | =item C<use ModuleName ();> |
196 | |
197 | This causes perl to load your module but does not import any symbols. |
198 | |
199 | =item C<use ModuleName qw(...);> |
200 | |
201 | This imports only the symbols listed by the caller into their namespace. |
202 | All listed symbols must be in your @EXPORT or @EXPORT_OK, else an error |
203 | occurs. The advanced export features of Exporter are accessed like this, |
204 | but with list entries that are syntactically distinct from symbol names. |
205 | |
206 | =back |
207 | |
208 | Unless you want to use its advanced features, this is probably all you |
209 | need to know to use Exporter. |
210 | |
211 | =head1 Advanced features |
212 | |
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213 | =head2 Specialised Import Lists |
214 | |
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215 | If any of the entries in an import list begins with !, : or / then |
216 | the list is treated as a series of specifications which either add to |
217 | or delete from the list of names to import. They are processed left to |
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218 | right. Specifications are in the form: |
219 | |
220 | [!]name This name only |
221 | [!]:DEFAULT All names in @EXPORT |
222 | [!]:tag All names in $EXPORT_TAGS{tag} anonymous list |
223 | [!]/pattern/ All names in @EXPORT and @EXPORT_OK which match |
224 | |
225 | A leading ! indicates that matching names should be deleted from the |
226 | list of names to import. If the first specification is a deletion it |
227 | is treated as though preceded by :DEFAULT. If you just want to import |
228 | extra names in addition to the default set you will still need to |
229 | include :DEFAULT explicitly. |
230 | |
231 | e.g., Module.pm defines: |
232 | |
233 | @EXPORT = qw(A1 A2 A3 A4 A5); |
234 | @EXPORT_OK = qw(B1 B2 B3 B4 B5); |
235 | %EXPORT_TAGS = (T1 => [qw(A1 A2 B1 B2)], T2 => [qw(A1 A2 B3 B4)]); |
236 | |
237 | Note that you cannot use tags in @EXPORT or @EXPORT_OK. |
238 | Names in EXPORT_TAGS must also appear in @EXPORT or @EXPORT_OK. |
239 | |
240 | An application using Module can say something like: |
241 | |
242 | use Module qw(:DEFAULT :T2 !B3 A3); |
243 | |
244 | Other examples include: |
245 | |
246 | use Socket qw(!/^[AP]F_/ !SOMAXCONN !SOL_SOCKET); |
247 | use POSIX qw(:errno_h :termios_h !TCSADRAIN !/^EXIT/); |
248 | |
249 | Remember that most patterns (using //) will need to be anchored |
250 | with a leading ^, e.g., C</^EXIT/> rather than C</EXIT/>. |
251 | |
252 | You can say C<BEGIN { $Exporter::Verbose=1 }> to see how the |
253 | specifications are being processed and what is actually being imported |
254 | into modules. |
255 | |
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256 | =head2 Exporting without using Exporter's import method |
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257 | |
258 | Exporter has a special method, 'export_to_level' which is used in situations |
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259 | where you can't directly call Exporter's import method. The export_to_level |
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260 | method looks like: |
261 | |
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262 | MyPackage->export_to_level($where_to_export, $package, @what_to_export); |
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263 | |
264 | where $where_to_export is an integer telling how far up the calling stack |
265 | to export your symbols, and @what_to_export is an array telling what |
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266 | symbols *to* export (usually this is @_). The $package argument is |
267 | currently unused. |
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268 | |
269 | For example, suppose that you have a module, A, which already has an |
270 | import function: |
271 | |
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272 | package A; |
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273 | |
cec46e5a |
274 | @ISA = qw(Exporter); |
275 | @EXPORT_OK = qw ($b); |
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276 | |
cec46e5a |
277 | sub import |
278 | { |
279 | $A::b = 1; # not a very useful import method |
280 | } |
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281 | |
282 | and you want to Export symbol $A::b back to the module that called |
283 | package A. Since Exporter relies on the import method to work, via |
284 | inheritance, as it stands Exporter::import() will never get called. |
285 | Instead, say the following: |
286 | |
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287 | package A; |
288 | @ISA = qw(Exporter); |
289 | @EXPORT_OK = qw ($b); |
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290 | |
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291 | sub import |
292 | { |
293 | $A::b = 1; |
294 | A->export_to_level(1, @_); |
295 | } |
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296 | |
297 | This will export the symbols one level 'above' the current package - ie: to |
298 | the program or module that used package A. |
299 | |
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300 | Note: Be careful not to modify C<@_> at all before you call export_to_level |
84902520 |
301 | - or people using your package will get very unexplained results! |
302 | |
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303 | =head2 Exporting without inheriting from Exporter |
304 | |
305 | By including Exporter in your @ISA you inherit an Exporter's import() method |
306 | but you also inherit several other helper methods which you probably don't |
307 | want. To avoid this you can do |
308 | |
309 | package YourModule; |
310 | use Exporter qw( import ); |
311 | |
312 | which will export Exporter's own import() method into YourModule. |
313 | Everything will work as before but you won't need to include Exporter in |
314 | @YourModule::ISA. |
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315 | |
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316 | =head2 Module Version Checking |
317 | |
318 | The Exporter module will convert an attempt to import a number from a |
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319 | module into a call to $module_name-E<gt>require_version($value). This can |
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320 | be used to validate that the version of the module being used is |
321 | greater than or equal to the required version. |
322 | |
323 | The Exporter module supplies a default require_version method which |
324 | checks the value of $VERSION in the exporting module. |
325 | |
326 | Since the default require_version method treats the $VERSION number as |
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327 | a simple numeric value it will regard version 1.10 as lower than |
328 | 1.9. For this reason it is strongly recommended that you use numbers |
329 | with at least two decimal places, e.g., 1.09. |
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330 | |
331 | =head2 Managing Unknown Symbols |
332 | |
333 | In some situations you may want to prevent certain symbols from being |
334 | exported. Typically this applies to extensions which have functions |
335 | or constants that may not exist on some systems. |
336 | |
337 | The names of any symbols that cannot be exported should be listed |
338 | in the C<@EXPORT_FAIL> array. |
339 | |
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340 | If a module attempts to import any of these symbols the Exporter |
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341 | will give the module an opportunity to handle the situation before |
342 | generating an error. The Exporter will call an export_fail method |
343 | with a list of the failed symbols: |
344 | |
345 | @failed_symbols = $module_name->export_fail(@failed_symbols); |
346 | |
347 | If the export_fail method returns an empty list then no error is |
348 | recorded and all the requested symbols are exported. If the returned |
349 | list is not empty then an error is generated for each symbol and the |
350 | export fails. The Exporter provides a default export_fail method which |
351 | simply returns the list unchanged. |
352 | |
353 | Uses for the export_fail method include giving better error messages |
354 | for some symbols and performing lazy architectural checks (put more |
355 | symbols into @EXPORT_FAIL by default and then take them out if someone |
356 | actually tries to use them and an expensive check shows that they are |
357 | usable on that platform). |
358 | |
359 | =head2 Tag Handling Utility Functions |
360 | |
361 | Since the symbols listed within %EXPORT_TAGS must also appear in either |
362 | @EXPORT or @EXPORT_OK, two utility functions are provided which allow |
363 | you to easily add tagged sets of symbols to @EXPORT or @EXPORT_OK: |
364 | |
365 | %EXPORT_TAGS = (foo => [qw(aa bb cc)], bar => [qw(aa cc dd)]); |
366 | |
367 | Exporter::export_tags('foo'); # add aa, bb and cc to @EXPORT |
368 | Exporter::export_ok_tags('bar'); # add aa, cc and dd to @EXPORT_OK |
369 | |
370 | Any names which are not tags are added to @EXPORT or @EXPORT_OK |
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371 | unchanged but will trigger a warning (with C<-w>) to avoid misspelt tags |
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372 | names being silently added to @EXPORT or @EXPORT_OK. Future versions |
373 | may make this a fatal error. |
374 | |
d584343b |
375 | =head2 Generating combined tags |
376 | |
377 | If several symbol categories exist in %EXPORT_TAGS, it's usually |
378 | useful to create the utility ":all" to simplify "use" statements. |
379 | |
380 | The simplest way to do this is: |
381 | |
382 | %EXPORT_TAGS = (foo => [qw(aa bb cc)], bar => [qw(aa cc dd)]); |
383 | |
384 | # add all the other ":class" tags to the ":all" class, |
385 | # deleting duplicates |
386 | { |
387 | my %seen; |
388 | |
389 | push @{$EXPORT_TAGS{all}}, |
390 | grep {!$seen{$_}++} @{$EXPORT_TAGS{$_}} foreach keys %EXPORT_TAGS; |
391 | } |
392 | |
393 | CGI.pm creates an ":all" tag which contains some (but not really |
394 | all) of its categories. That could be done with one small |
395 | change: |
396 | |
397 | # add some of the other ":class" tags to the ":all" class, |
398 | # deleting duplicates |
399 | { |
400 | my %seen; |
401 | |
402 | push @{$EXPORT_TAGS{all}}, |
403 | grep {!$seen{$_}++} @{$EXPORT_TAGS{$_}} |
404 | foreach qw/html2 html3 netscape form cgi internal/; |
405 | } |
406 | |
407 | Note that the tag names in %EXPORT_TAGS don't have the leading ':'. |
408 | |
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409 | =head2 C<AUTOLOAD>ed Constants |
410 | |
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411 | Many modules make use of C<AUTOLOAD>ing for constant subroutines to |
412 | avoid having to compile and waste memory on rarely used values (see |
413 | L<perlsub> for details on constant subroutines). Calls to such |
414 | constant subroutines are not optimized away at compile time because |
415 | they can't be checked at compile time for constancy. |
416 | |
417 | Even if a prototype is available at compile time, the body of the |
418 | subroutine is not (it hasn't been C<AUTOLOAD>ed yet). perl needs to |
419 | examine both the C<()> prototype and the body of a subroutine at |
420 | compile time to detect that it can safely replace calls to that |
421 | subroutine with the constant value. |
5fea0f12 |
422 | |
423 | A workaround for this is to call the constants once in a C<BEGIN> block: |
424 | |
425 | package My ; |
426 | |
427 | use Socket ; |
428 | |
429 | foo( SO_LINGER ); ## SO_LINGER NOT optimized away; called at runtime |
430 | BEGIN { SO_LINGER } |
431 | foo( SO_LINGER ); ## SO_LINGER optimized away at compile time. |
432 | |
8b4c0206 |
433 | This forces the C<AUTOLOAD> for C<SO_LINGER> to take place before |
434 | SO_LINGER is encountered later in C<My> package. |
5fea0f12 |
435 | |
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436 | If you are writing a package that C<AUTOLOAD>s, consider forcing |
437 | an C<AUTOLOAD> for any constants explicitly imported by other packages |
438 | or which are usually used when your package is C<use>d. |
5fea0f12 |
439 | |
2b5b2650 |
440 | =cut |