Commit | Line | Data |
---|---|---|
8990e307 LW |
1 | package Exporter; |
2 | ||
732bb7c2 | 3 | require 5.006; |
8990e307 | 4 | |
0e57b4e8 IZ |
5 | # Be lean. |
6 | #use strict; | |
7 | #no strict 'refs'; | |
b75c8c73 MS |
8 | |
9 | our $Debug = 0; | |
10 | our $ExportLevel = 0; | |
11 | our $Verbose ||= 0; | |
a29b0897 | 12 | our $VERSION = '5.58'; |
a6faae8d | 13 | our (%Cache); |
bb2cbcd1 | 14 | $Carp::Internal{Exporter} = 1; |
2b5b2650 | 15 | |
0e57b4e8 | 16 | sub as_heavy { |
4af1b167 | 17 | require Exporter::Heavy; |
0e57b4e8 IZ |
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 TB |
23 | } |
24 | ||
4af1b167 | 25 | sub export { |
0e57b4e8 | 26 | goto &{as_heavy()}; |
a0d0e21e LW |
27 | } |
28 | ||
4af1b167 IZ |
29 | sub import { |
30 | my $pkg = shift; | |
31 | my $callpkg = caller($ExportLevel); | |
b75c8c73 | 32 | |
fe43f860 FD |
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 NC |
44 | |
45 | local $_; | |
b75c8c73 | 46 | if ($args and not %$export_cache) { |
732bb7c2 NC |
47 | s/^&//, $export_cache->{$_} = 1 |
48 | foreach (@$exports, @{"$pkg\::EXPORT_OK"}); | |
4af1b167 | 49 | } |
fa1bb02f NC |
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 NC |
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 $SIG{__WARN__} = |
bb2cbcd1 | 63 | sub {require Carp; &Carp::carp}; |
732bb7c2 NC |
64 | # shortcut for the common case of no type character |
65 | *{"$callpkg\::$_"} = \&{"$pkg\::$_"} foreach @_; | |
e50aee73 AD |
66 | } |
67 | ||
b75c8c73 MS |
68 | # Default methods |
69 | ||
2b5b2650 | 70 | sub export_fail { |
b75c8c73 MS |
71 | my $self = shift; |
72 | @_; | |
2b5b2650 | 73 | } |
74 | ||
0e57b4e8 IZ |
75 | # Unfortunately, caller(1)[3] "does not work" if the caller is aliased as |
76 | # *name = \&foo. Thus the need to create a lot of identical subroutines | |
77 | # Otherwise we could have aliased them to export(). | |
b75c8c73 | 78 | |
0e57b4e8 IZ |
79 | sub export_to_level { |
80 | goto &{as_heavy()}; | |
81 | } | |
82 | ||
83 | sub export_tags { | |
84 | goto &{as_heavy()}; | |
b75c8c73 MS |
85 | } |
86 | ||
0e57b4e8 IZ |
87 | sub export_ok_tags { |
88 | goto &{as_heavy()}; | |
89 | } | |
90 | ||
91 | sub require_version { | |
92 | goto &{as_heavy()}; | |
93 | } | |
b75c8c73 | 94 | |
2b5b2650 | 95 | 1; |
732bb7c2 | 96 | __END__ |
b75c8c73 | 97 | |
2b5b2650 | 98 | =head1 NAME |
99 | ||
100 | Exporter - Implements default import method for modules | |
101 | ||
102 | =head1 SYNOPSIS | |
103 | ||
65503211 | 104 | In module YourModule.pm: |
2b5b2650 | 105 | |
65503211 | 106 | package YourModule; |
2b5b2650 | 107 | require Exporter; |
108 | @ISA = qw(Exporter); | |
65503211 | 109 | @EXPORT_OK = qw(munge frobnicate); # symbols to export on request |
2b5b2650 | 110 | |
fe43f860 FD |
111 | or |
112 | ||
113 | package YourModule; | |
114 | use Exporter 'import'; # gives you Exporter's import() method directly | |
115 | @EXPORT_OK = qw(munge frobnicate); # symbols to export on request | |
116 | ||
65503211 | 117 | In other files which wish to use YourModule: |
2b5b2650 | 118 | |
65503211 NC |
119 | use ModuleName qw(frobnicate); # import listed symbols |
120 | frobnicate ($left, $right) # calls YourModule::frobnicate | |
2b5b2650 | 121 | |
122 | =head1 DESCRIPTION | |
123 | ||
65503211 NC |
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. | |
2b5b2650 | 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 | ||
4fddf32b GS |
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 | ||
65503211 NC |
148 | If you are only exporting function names it is recommended to omit the |
149 | ampersand, as the implementation is faster this way. | |
150 | ||
2b5b2650 | 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 | |
1fef88e7 | 162 | module using the ModuleName::item_name (or $blessed_ref-E<gt>method) |
2b5b2650 | 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 { ... }; | |
e60ce172 BT |
169 | $subref->(@args); # Call it as a function |
170 | $obj->$subref(@args); # Use it as a method | |
2b5b2650 | 171 | |
e60ce172 BT |
172 | However if you use them for methods it is up to you to figure out |
173 | how to make inheritance work.) | |
2b5b2650 | 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 | |
65503211 NC |
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. | |
2b5b2650 | 180 | |
181 | Other module design guidelines can be found in L<perlmod>. | |
182 | ||
65503211 NC |
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 | ||
2b5b2650 | 213 | =head2 Specialised Import Lists |
214 | ||
a29b0897 MB |
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 | |
2b5b2650 | 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 { $Exporter::Verbose=1 }> to see how the | |
253 | specifications are being processed and what is actually being imported | |
254 | into modules. | |
255 | ||
65503211 | 256 | =head2 Exporting without using Exporter's import method |
84902520 TB |
257 | |
258 | Exporter has a special method, 'export_to_level' which is used in situations | |
65503211 | 259 | where you can't directly call Exporter's import method. The export_to_level |
84902520 TB |
260 | method looks like: |
261 | ||
cec46e5a | 262 | MyPackage->export_to_level($where_to_export, $package, @what_to_export); |
84902520 TB |
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 | |
ba5725f8 GS |
266 | symbols *to* export (usually this is @_). The $package argument is |
267 | currently unused. | |
84902520 TB |
268 | |
269 | For example, suppose that you have a module, A, which already has an | |
270 | import function: | |
271 | ||
cec46e5a | 272 | package A; |
84902520 | 273 | |
cec46e5a RGS |
274 | @ISA = qw(Exporter); |
275 | @EXPORT_OK = qw ($b); | |
84902520 | 276 | |
cec46e5a RGS |
277 | sub import |
278 | { | |
279 | $A::b = 1; # not a very useful import method | |
280 | } | |
84902520 TB |
281 | |
282 | and you want to Export symbol $A::b back to the module that called | |
283 | package A. Since Exporter relies on the import method to work, via | |
284 | inheritance, as it stands Exporter::import() will never get called. | |
285 | Instead, say the following: | |
286 | ||
cec46e5a RGS |
287 | package A; |
288 | @ISA = qw(Exporter); | |
289 | @EXPORT_OK = qw ($b); | |
84902520 | 290 | |
cec46e5a RGS |
291 | sub import |
292 | { | |
293 | $A::b = 1; | |
294 | A->export_to_level(1, @_); | |
295 | } | |
84902520 TB |
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 | ||
fe43f860 | 300 | Note: Be careful not to modify C<@_> at all before you call export_to_level |
84902520 TB |
301 | - or people using your package will get very unexplained results! |
302 | ||
fe43f860 FD |
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. | |
84902520 | 315 | |
2b5b2650 | 316 | =head2 Module Version Checking |
317 | ||
318 | The Exporter module will convert an attempt to import a number from a | |
1fef88e7 | 319 | module into a call to $module_name-E<gt>require_version($value). This can |
2b5b2650 | 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 | |
d5e40bcc | 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. | |
2b5b2650 | 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 | ||
7a2e2cd6 | 340 | If a module attempts to import any of these symbols the Exporter |
2b5b2650 | 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 | |
d5e40bcc | 371 | unchanged but will trigger a warning (with C<-w>) to avoid misspelt tags |
2b5b2650 | 372 | names being silently added to @EXPORT or @EXPORT_OK. Future versions |
373 | may make this a fatal error. | |
374 | ||
d584343b MG |
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 | ||
5fea0f12 BS |
409 | =head2 C<AUTOLOAD>ed Constants |
410 | ||
8b4c0206 T |
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 BS |
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 T |
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 | |
8b4c0206 T |
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 |