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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'; |
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8 | |
9 | our $Debug = 0; |
10 | our $ExportLevel = 0; |
11 | our $Verbose ||= 0; |
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12 | our $VERSION = '5.567'; |
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"}; |
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23 | } |
24 | |
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25 | sub export { |
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26 | goto &{as_heavy()}; |
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27 | } |
28 | |
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29 | sub import { |
30 | my $pkg = shift; |
31 | my $callpkg = caller($ExportLevel); |
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32 | |
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33 | # We *need* to treat @{"$pkg\::EXPORT_FAIL"} since Carp uses it :-( |
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34 | my($exports, $fail) = (\@{"$pkg\::EXPORT"}, \@{"$pkg\::EXPORT_FAIL"}); |
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35 | return export $pkg, $callpkg, @_ |
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36 | if $Verbose or $Debug or @$fail > 1; |
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37 | my $export_cache = ($Cache{$pkg} ||= {}); |
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38 | my $args = @_ or @_ = @$exports; |
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39 | |
40 | local $_; |
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41 | if ($args and not %$export_cache) { |
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42 | s/^&//, $export_cache->{$_} = 1 |
43 | foreach (@$exports, @{"$pkg\::EXPORT_OK"}); |
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44 | } |
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45 | my $heavy; |
46 | # Try very hard not to use {} and hence have to enter scope on the foreach |
47 | # We bomb out of the loop with last as soon as heavy is set. |
48 | if ($args or $fail) { |
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49 | ($heavy = (/\W/ or $args and not exists $export_cache->{$_} |
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50 | or @$fail and $_ eq $fail->[0])) and last |
51 | foreach (@_); |
52 | } else { |
53 | ($heavy = /\W/) and last |
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54 | foreach (@_); |
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55 | } |
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56 | return export $pkg, $callpkg, ($args ? @_ : ()) if $heavy; |
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57 | local $SIG{__WARN__} = |
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58 | sub {require Carp; &Carp::carp}; |
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59 | # shortcut for the common case of no type character |
60 | *{"$callpkg\::$_"} = \&{"$pkg\::$_"} foreach @_; |
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61 | } |
62 | |
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63 | # Default methods |
64 | |
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65 | sub export_fail { |
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66 | my $self = shift; |
67 | @_; |
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68 | } |
69 | |
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70 | # Unfortunately, caller(1)[3] "does not work" if the caller is aliased as |
71 | # *name = \&foo. Thus the need to create a lot of identical subroutines |
72 | # Otherwise we could have aliased them to export(). |
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73 | |
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74 | sub export_to_level { |
75 | goto &{as_heavy()}; |
76 | } |
77 | |
78 | sub export_tags { |
79 | goto &{as_heavy()}; |
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80 | } |
81 | |
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82 | sub export_ok_tags { |
83 | goto &{as_heavy()}; |
84 | } |
85 | |
86 | sub require_version { |
87 | goto &{as_heavy()}; |
88 | } |
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89 | |
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90 | 1; |
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91 | __END__ |
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92 | |
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93 | =head1 NAME |
94 | |
95 | Exporter - Implements default import method for modules |
96 | |
97 | =head1 SYNOPSIS |
98 | |
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99 | In module YourModule.pm: |
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100 | |
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101 | package YourModule; |
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102 | require Exporter; |
103 | @ISA = qw(Exporter); |
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104 | @EXPORT_OK = qw(munge frobnicate); # symbols to export on request |
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105 | |
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106 | In other files which wish to use YourModule: |
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107 | |
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108 | use ModuleName qw(frobnicate); # import listed symbols |
109 | frobnicate ($left, $right) # calls YourModule::frobnicate |
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110 | |
111 | =head1 DESCRIPTION |
112 | |
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113 | The Exporter module implements an C<import> method which allows a module |
114 | to export functions and variables to its users' namespaces. Many modules |
115 | use Exporter rather than implementing their own C<import> method because |
116 | Exporter provides a highly flexible interface, with an implementation optimised |
117 | for the common case. |
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118 | |
119 | Perl automatically calls the C<import> method when processing a |
120 | C<use> statement for a module. Modules and C<use> are documented |
121 | in L<perlfunc> and L<perlmod>. Understanding the concept of |
122 | modules and how the C<use> statement operates is important to |
123 | understanding the Exporter. |
124 | |
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125 | =head2 How to Export |
126 | |
127 | The arrays C<@EXPORT> and C<@EXPORT_OK> in a module hold lists of |
128 | symbols that are going to be exported into the users name space by |
129 | default, or which they can request to be exported, respectively. The |
130 | symbols can represent functions, scalars, arrays, hashes, or typeglobs. |
131 | The symbols must be given by full name with the exception that the |
132 | ampersand in front of a function is optional, e.g. |
133 | |
134 | @EXPORT = qw(afunc $scalar @array); # afunc is a function |
135 | @EXPORT_OK = qw(&bfunc %hash *typeglob); # explicit prefix on &bfunc |
136 | |
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137 | If you are only exporting function names it is recommended to omit the |
138 | ampersand, as the implementation is faster this way. |
139 | |
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140 | =head2 Selecting What To Export |
141 | |
142 | Do B<not> export method names! |
143 | |
144 | Do B<not> export anything else by default without a good reason! |
145 | |
146 | Exports pollute the namespace of the module user. If you must export |
147 | try to use @EXPORT_OK in preference to @EXPORT and avoid short or |
148 | common symbol names to reduce the risk of name clashes. |
149 | |
150 | Generally anything not exported is still accessible from outside the |
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151 | module using the ModuleName::item_name (or $blessed_ref-E<gt>method) |
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152 | syntax. By convention you can use a leading underscore on names to |
153 | informally indicate that they are 'internal' and not for public use. |
154 | |
155 | (It is actually possible to get private functions by saying: |
156 | |
157 | my $subref = sub { ... }; |
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158 | $subref->(@args); # Call it as a function |
159 | $obj->$subref(@args); # Use it as a method |
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160 | |
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161 | However if you use them for methods it is up to you to figure out |
162 | how to make inheritance work.) |
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163 | |
164 | As a general rule, if the module is trying to be object oriented |
165 | then export nothing. If it's just a collection of functions then |
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166 | @EXPORT_OK anything but use @EXPORT with caution. For function and |
167 | method names use barewords in preference to names prefixed with |
168 | ampersands for the export lists. |
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169 | |
170 | Other module design guidelines can be found in L<perlmod>. |
171 | |
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172 | =head2 How to Import |
173 | |
174 | In other files which wish to use your module there are three basic ways for |
175 | them to load your module and import its symbols: |
176 | |
177 | =over 4 |
178 | |
179 | =item C<use ModuleName;> |
180 | |
181 | This imports all the symbols from ModuleName's @EXPORT into the namespace |
182 | of the C<use> statement. |
183 | |
184 | =item C<use ModuleName ();> |
185 | |
186 | This causes perl to load your module but does not import any symbols. |
187 | |
188 | =item C<use ModuleName qw(...);> |
189 | |
190 | This imports only the symbols listed by the caller into their namespace. |
191 | All listed symbols must be in your @EXPORT or @EXPORT_OK, else an error |
192 | occurs. The advanced export features of Exporter are accessed like this, |
193 | but with list entries that are syntactically distinct from symbol names. |
194 | |
195 | =back |
196 | |
197 | Unless you want to use its advanced features, this is probably all you |
198 | need to know to use Exporter. |
199 | |
200 | =head1 Advanced features |
201 | |
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202 | =head2 Specialised Import Lists |
203 | |
204 | If the first entry in an import list begins with !, : or / then the |
205 | list is treated as a series of specifications which either add to or |
206 | delete from the list of names to import. They are processed left to |
207 | right. Specifications are in the form: |
208 | |
209 | [!]name This name only |
210 | [!]:DEFAULT All names in @EXPORT |
211 | [!]:tag All names in $EXPORT_TAGS{tag} anonymous list |
212 | [!]/pattern/ All names in @EXPORT and @EXPORT_OK which match |
213 | |
214 | A leading ! indicates that matching names should be deleted from the |
215 | list of names to import. If the first specification is a deletion it |
216 | is treated as though preceded by :DEFAULT. If you just want to import |
217 | extra names in addition to the default set you will still need to |
218 | include :DEFAULT explicitly. |
219 | |
220 | e.g., Module.pm defines: |
221 | |
222 | @EXPORT = qw(A1 A2 A3 A4 A5); |
223 | @EXPORT_OK = qw(B1 B2 B3 B4 B5); |
224 | %EXPORT_TAGS = (T1 => [qw(A1 A2 B1 B2)], T2 => [qw(A1 A2 B3 B4)]); |
225 | |
226 | Note that you cannot use tags in @EXPORT or @EXPORT_OK. |
227 | Names in EXPORT_TAGS must also appear in @EXPORT or @EXPORT_OK. |
228 | |
229 | An application using Module can say something like: |
230 | |
231 | use Module qw(:DEFAULT :T2 !B3 A3); |
232 | |
233 | Other examples include: |
234 | |
235 | use Socket qw(!/^[AP]F_/ !SOMAXCONN !SOL_SOCKET); |
236 | use POSIX qw(:errno_h :termios_h !TCSADRAIN !/^EXIT/); |
237 | |
238 | Remember that most patterns (using //) will need to be anchored |
239 | with a leading ^, e.g., C</^EXIT/> rather than C</EXIT/>. |
240 | |
241 | You can say C<BEGIN { $Exporter::Verbose=1 }> to see how the |
242 | specifications are being processed and what is actually being imported |
243 | into modules. |
244 | |
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245 | =head2 Exporting without using Exporter's import method |
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246 | |
247 | Exporter has a special method, 'export_to_level' which is used in situations |
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248 | where you can't directly call Exporter's import method. The export_to_level |
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249 | method looks like: |
250 | |
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251 | MyPackage->export_to_level($where_to_export, $package, @what_to_export); |
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252 | |
253 | where $where_to_export is an integer telling how far up the calling stack |
254 | to export your symbols, and @what_to_export is an array telling what |
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255 | symbols *to* export (usually this is @_). The $package argument is |
256 | currently unused. |
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257 | |
258 | For example, suppose that you have a module, A, which already has an |
259 | import function: |
260 | |
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261 | package A; |
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262 | |
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263 | @ISA = qw(Exporter); |
264 | @EXPORT_OK = qw ($b); |
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265 | |
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266 | sub import |
267 | { |
268 | $A::b = 1; # not a very useful import method |
269 | } |
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270 | |
271 | and you want to Export symbol $A::b back to the module that called |
272 | package A. Since Exporter relies on the import method to work, via |
273 | inheritance, as it stands Exporter::import() will never get called. |
274 | Instead, say the following: |
275 | |
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276 | package A; |
277 | @ISA = qw(Exporter); |
278 | @EXPORT_OK = qw ($b); |
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279 | |
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280 | sub import |
281 | { |
282 | $A::b = 1; |
283 | A->export_to_level(1, @_); |
284 | } |
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285 | |
286 | This will export the symbols one level 'above' the current package - ie: to |
287 | the program or module that used package A. |
288 | |
289 | Note: Be careful not to modify '@_' at all before you call export_to_level |
290 | - or people using your package will get very unexplained results! |
291 | |
292 | |
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293 | =head2 Module Version Checking |
294 | |
295 | The Exporter module will convert an attempt to import a number from a |
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296 | module into a call to $module_name-E<gt>require_version($value). This can |
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297 | be used to validate that the version of the module being used is |
298 | greater than or equal to the required version. |
299 | |
300 | The Exporter module supplies a default require_version method which |
301 | checks the value of $VERSION in the exporting module. |
302 | |
303 | Since the default require_version method treats the $VERSION number as |
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304 | a simple numeric value it will regard version 1.10 as lower than |
305 | 1.9. For this reason it is strongly recommended that you use numbers |
306 | with at least two decimal places, e.g., 1.09. |
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307 | |
308 | =head2 Managing Unknown Symbols |
309 | |
310 | In some situations you may want to prevent certain symbols from being |
311 | exported. Typically this applies to extensions which have functions |
312 | or constants that may not exist on some systems. |
313 | |
314 | The names of any symbols that cannot be exported should be listed |
315 | in the C<@EXPORT_FAIL> array. |
316 | |
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317 | If a module attempts to import any of these symbols the Exporter |
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318 | will give the module an opportunity to handle the situation before |
319 | generating an error. The Exporter will call an export_fail method |
320 | with a list of the failed symbols: |
321 | |
322 | @failed_symbols = $module_name->export_fail(@failed_symbols); |
323 | |
324 | If the export_fail method returns an empty list then no error is |
325 | recorded and all the requested symbols are exported. If the returned |
326 | list is not empty then an error is generated for each symbol and the |
327 | export fails. The Exporter provides a default export_fail method which |
328 | simply returns the list unchanged. |
329 | |
330 | Uses for the export_fail method include giving better error messages |
331 | for some symbols and performing lazy architectural checks (put more |
332 | symbols into @EXPORT_FAIL by default and then take them out if someone |
333 | actually tries to use them and an expensive check shows that they are |
334 | usable on that platform). |
335 | |
336 | =head2 Tag Handling Utility Functions |
337 | |
338 | Since the symbols listed within %EXPORT_TAGS must also appear in either |
339 | @EXPORT or @EXPORT_OK, two utility functions are provided which allow |
340 | you to easily add tagged sets of symbols to @EXPORT or @EXPORT_OK: |
341 | |
342 | %EXPORT_TAGS = (foo => [qw(aa bb cc)], bar => [qw(aa cc dd)]); |
343 | |
344 | Exporter::export_tags('foo'); # add aa, bb and cc to @EXPORT |
345 | Exporter::export_ok_tags('bar'); # add aa, cc and dd to @EXPORT_OK |
346 | |
347 | Any names which are not tags are added to @EXPORT or @EXPORT_OK |
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348 | unchanged but will trigger a warning (with C<-w>) to avoid misspelt tags |
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349 | names being silently added to @EXPORT or @EXPORT_OK. Future versions |
350 | may make this a fatal error. |
351 | |
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352 | =head2 Generating combined tags |
353 | |
354 | If several symbol categories exist in %EXPORT_TAGS, it's usually |
355 | useful to create the utility ":all" to simplify "use" statements. |
356 | |
357 | The simplest way to do this is: |
358 | |
359 | %EXPORT_TAGS = (foo => [qw(aa bb cc)], bar => [qw(aa cc dd)]); |
360 | |
361 | # add all the other ":class" tags to the ":all" class, |
362 | # deleting duplicates |
363 | { |
364 | my %seen; |
365 | |
366 | push @{$EXPORT_TAGS{all}}, |
367 | grep {!$seen{$_}++} @{$EXPORT_TAGS{$_}} foreach keys %EXPORT_TAGS; |
368 | } |
369 | |
370 | CGI.pm creates an ":all" tag which contains some (but not really |
371 | all) of its categories. That could be done with one small |
372 | change: |
373 | |
374 | # add some of the other ":class" tags to the ":all" class, |
375 | # deleting duplicates |
376 | { |
377 | my %seen; |
378 | |
379 | push @{$EXPORT_TAGS{all}}, |
380 | grep {!$seen{$_}++} @{$EXPORT_TAGS{$_}} |
381 | foreach qw/html2 html3 netscape form cgi internal/; |
382 | } |
383 | |
384 | Note that the tag names in %EXPORT_TAGS don't have the leading ':'. |
385 | |
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386 | =head2 C<AUTOLOAD>ed Constants |
387 | |
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388 | Many modules make use of C<AUTOLOAD>ing for constant subroutines to |
389 | avoid having to compile and waste memory on rarely used values (see |
390 | L<perlsub> for details on constant subroutines). Calls to such |
391 | constant subroutines are not optimized away at compile time because |
392 | they can't be checked at compile time for constancy. |
393 | |
394 | Even if a prototype is available at compile time, the body of the |
395 | subroutine is not (it hasn't been C<AUTOLOAD>ed yet). perl needs to |
396 | examine both the C<()> prototype and the body of a subroutine at |
397 | compile time to detect that it can safely replace calls to that |
398 | subroutine with the constant value. |
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399 | |
400 | A workaround for this is to call the constants once in a C<BEGIN> block: |
401 | |
402 | package My ; |
403 | |
404 | use Socket ; |
405 | |
406 | foo( SO_LINGER ); ## SO_LINGER NOT optimized away; called at runtime |
407 | BEGIN { SO_LINGER } |
408 | foo( SO_LINGER ); ## SO_LINGER optimized away at compile time. |
409 | |
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410 | This forces the C<AUTOLOAD> for C<SO_LINGER> to take place before |
411 | SO_LINGER is encountered later in C<My> package. |
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412 | |
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413 | If you are writing a package that C<AUTOLOAD>s, consider forcing |
414 | an C<AUTOLOAD> for any constants explicitly imported by other packages |
415 | or which are usually used when your package is C<use>d. |
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416 | |
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417 | =cut |