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; | |
09e96b99 | 12 | our $VERSION = '5.59'; |
a6faae8d | 13 | our (%Cache); |
09e96b99 JC |
14 | # Carp does this now for us, so we can finally live w/o Carp |
15 | #$Carp::Internal{Exporter} = 1; | |
2b5b2650 | 16 | |
0e57b4e8 | 17 | sub as_heavy { |
4af1b167 | 18 | require Exporter::Heavy; |
0e57b4e8 IZ |
19 | # Unfortunately, this does not work if the caller is aliased as *name = \&foo |
20 | # Thus the need to create a lot of identical subroutines | |
21 | my $c = (caller(1))[3]; | |
22 | $c =~ s/.*:://; | |
23 | \&{"Exporter::Heavy::heavy_$c"}; | |
84902520 TB |
24 | } |
25 | ||
4af1b167 | 26 | sub export { |
0e57b4e8 | 27 | goto &{as_heavy()}; |
a0d0e21e LW |
28 | } |
29 | ||
4af1b167 IZ |
30 | sub import { |
31 | my $pkg = shift; | |
32 | my $callpkg = caller($ExportLevel); | |
b75c8c73 | 33 | |
fe43f860 FD |
34 | if ($pkg eq "Exporter" and @_ and $_[0] eq "import") { |
35 | *{$callpkg."::import"} = \&import; | |
36 | return; | |
37 | } | |
38 | ||
4af1b167 | 39 | # We *need* to treat @{"$pkg\::EXPORT_FAIL"} since Carp uses it :-( |
a6faae8d | 40 | my($exports, $fail) = (\@{"$pkg\::EXPORT"}, \@{"$pkg\::EXPORT_FAIL"}); |
4af1b167 | 41 | return export $pkg, $callpkg, @_ |
b75c8c73 | 42 | if $Verbose or $Debug or @$fail > 1; |
a6faae8d | 43 | my $export_cache = ($Cache{$pkg} ||= {}); |
b75c8c73 | 44 | my $args = @_ or @_ = @$exports; |
732bb7c2 NC |
45 | |
46 | local $_; | |
b75c8c73 | 47 | if ($args and not %$export_cache) { |
732bb7c2 NC |
48 | s/^&//, $export_cache->{$_} = 1 |
49 | foreach (@$exports, @{"$pkg\::EXPORT_OK"}); | |
4af1b167 | 50 | } |
fa1bb02f NC |
51 | my $heavy; |
52 | # Try very hard not to use {} and hence have to enter scope on the foreach | |
53 | # We bomb out of the loop with last as soon as heavy is set. | |
54 | if ($args or $fail) { | |
732bb7c2 | 55 | ($heavy = (/\W/ or $args and not exists $export_cache->{$_} |
fa1bb02f NC |
56 | or @$fail and $_ eq $fail->[0])) and last |
57 | foreach (@_); | |
58 | } else { | |
59 | ($heavy = /\W/) and last | |
732bb7c2 | 60 | foreach (@_); |
4af1b167 | 61 | } |
732bb7c2 | 62 | return export $pkg, $callpkg, ($args ? @_ : ()) if $heavy; |
4af1b167 | 63 | local $SIG{__WARN__} = |
bb2cbcd1 | 64 | sub {require Carp; &Carp::carp}; |
732bb7c2 NC |
65 | # shortcut for the common case of no type character |
66 | *{"$callpkg\::$_"} = \&{"$pkg\::$_"} foreach @_; | |
e50aee73 AD |
67 | } |
68 | ||
b75c8c73 MS |
69 | # Default methods |
70 | ||
2b5b2650 | 71 | sub export_fail { |
b75c8c73 MS |
72 | my $self = shift; |
73 | @_; | |
2b5b2650 | 74 | } |
75 | ||
0e57b4e8 IZ |
76 | # Unfortunately, caller(1)[3] "does not work" if the caller is aliased as |
77 | # *name = \&foo. Thus the need to create a lot of identical subroutines | |
78 | # Otherwise we could have aliased them to export(). | |
b75c8c73 | 79 | |
0e57b4e8 IZ |
80 | sub export_to_level { |
81 | goto &{as_heavy()}; | |
82 | } | |
83 | ||
84 | sub export_tags { | |
85 | goto &{as_heavy()}; | |
b75c8c73 MS |
86 | } |
87 | ||
0e57b4e8 IZ |
88 | sub export_ok_tags { |
89 | goto &{as_heavy()}; | |
90 | } | |
91 | ||
92 | sub require_version { | |
93 | goto &{as_heavy()}; | |
94 | } | |
b75c8c73 | 95 | |
2b5b2650 | 96 | 1; |
732bb7c2 | 97 | __END__ |
b75c8c73 | 98 | |
2b5b2650 | 99 | =head1 NAME |
100 | ||
101 | Exporter - Implements default import method for modules | |
102 | ||
103 | =head1 SYNOPSIS | |
104 | ||
65503211 | 105 | In module YourModule.pm: |
2b5b2650 | 106 | |
65503211 | 107 | package YourModule; |
2b5b2650 | 108 | require Exporter; |
109 | @ISA = qw(Exporter); | |
65503211 | 110 | @EXPORT_OK = qw(munge frobnicate); # symbols to export on request |
2b5b2650 | 111 | |
fe43f860 FD |
112 | or |
113 | ||
114 | package YourModule; | |
115 | use Exporter 'import'; # gives you Exporter's import() method directly | |
116 | @EXPORT_OK = qw(munge frobnicate); # symbols to export on request | |
117 | ||
65503211 | 118 | In other files which wish to use YourModule: |
2b5b2650 | 119 | |
65503211 NC |
120 | use ModuleName qw(frobnicate); # import listed symbols |
121 | frobnicate ($left, $right) # calls YourModule::frobnicate | |
2b5b2650 | 122 | |
123 | =head1 DESCRIPTION | |
124 | ||
65503211 NC |
125 | The Exporter module implements an C<import> method which allows a module |
126 | to export functions and variables to its users' namespaces. Many modules | |
127 | use Exporter rather than implementing their own C<import> method because | |
128 | Exporter provides a highly flexible interface, with an implementation optimised | |
129 | for the common case. | |
2b5b2650 | 130 | |
131 | Perl automatically calls the C<import> method when processing a | |
132 | C<use> statement for a module. Modules and C<use> are documented | |
133 | in L<perlfunc> and L<perlmod>. Understanding the concept of | |
134 | modules and how the C<use> statement operates is important to | |
135 | understanding the Exporter. | |
136 | ||
4fddf32b GS |
137 | =head2 How to Export |
138 | ||
139 | The arrays C<@EXPORT> and C<@EXPORT_OK> in a module hold lists of | |
140 | symbols that are going to be exported into the users name space by | |
141 | default, or which they can request to be exported, respectively. The | |
142 | symbols can represent functions, scalars, arrays, hashes, or typeglobs. | |
143 | The symbols must be given by full name with the exception that the | |
144 | ampersand in front of a function is optional, e.g. | |
145 | ||
146 | @EXPORT = qw(afunc $scalar @array); # afunc is a function | |
147 | @EXPORT_OK = qw(&bfunc %hash *typeglob); # explicit prefix on &bfunc | |
148 | ||
65503211 NC |
149 | If you are only exporting function names it is recommended to omit the |
150 | ampersand, as the implementation is faster this way. | |
151 | ||
2b5b2650 | 152 | =head2 Selecting What To Export |
153 | ||
154 | Do B<not> export method names! | |
155 | ||
156 | Do B<not> export anything else by default without a good reason! | |
157 | ||
158 | Exports pollute the namespace of the module user. If you must export | |
159 | try to use @EXPORT_OK in preference to @EXPORT and avoid short or | |
160 | common symbol names to reduce the risk of name clashes. | |
161 | ||
162 | Generally anything not exported is still accessible from outside the | |
1fef88e7 | 163 | module using the ModuleName::item_name (or $blessed_ref-E<gt>method) |
2b5b2650 | 164 | syntax. By convention you can use a leading underscore on names to |
165 | informally indicate that they are 'internal' and not for public use. | |
166 | ||
167 | (It is actually possible to get private functions by saying: | |
168 | ||
169 | my $subref = sub { ... }; | |
e60ce172 BT |
170 | $subref->(@args); # Call it as a function |
171 | $obj->$subref(@args); # Use it as a method | |
2b5b2650 | 172 | |
e60ce172 BT |
173 | However if you use them for methods it is up to you to figure out |
174 | how to make inheritance work.) | |
2b5b2650 | 175 | |
176 | As a general rule, if the module is trying to be object oriented | |
177 | then export nothing. If it's just a collection of functions then | |
65503211 NC |
178 | @EXPORT_OK anything but use @EXPORT with caution. For function and |
179 | method names use barewords in preference to names prefixed with | |
180 | ampersands for the export lists. | |
2b5b2650 | 181 | |
182 | Other module design guidelines can be found in L<perlmod>. | |
183 | ||
65503211 NC |
184 | =head2 How to Import |
185 | ||
186 | In other files which wish to use your module there are three basic ways for | |
187 | them to load your module and import its symbols: | |
188 | ||
189 | =over 4 | |
190 | ||
191 | =item C<use ModuleName;> | |
192 | ||
193 | This imports all the symbols from ModuleName's @EXPORT into the namespace | |
194 | of the C<use> statement. | |
195 | ||
196 | =item C<use ModuleName ();> | |
197 | ||
198 | This causes perl to load your module but does not import any symbols. | |
199 | ||
200 | =item C<use ModuleName qw(...);> | |
201 | ||
202 | This imports only the symbols listed by the caller into their namespace. | |
203 | All listed symbols must be in your @EXPORT or @EXPORT_OK, else an error | |
204 | occurs. The advanced export features of Exporter are accessed like this, | |
205 | but with list entries that are syntactically distinct from symbol names. | |
206 | ||
207 | =back | |
208 | ||
209 | Unless you want to use its advanced features, this is probably all you | |
210 | need to know to use Exporter. | |
211 | ||
212 | =head1 Advanced features | |
213 | ||
2b5b2650 | 214 | =head2 Specialised Import Lists |
215 | ||
a29b0897 MB |
216 | If any of the entries in an import list begins with !, : or / then |
217 | the list is treated as a series of specifications which either add to | |
218 | or delete from the list of names to import. They are processed left to | |
2b5b2650 | 219 | right. Specifications are in the form: |
220 | ||
221 | [!]name This name only | |
222 | [!]:DEFAULT All names in @EXPORT | |
223 | [!]:tag All names in $EXPORT_TAGS{tag} anonymous list | |
224 | [!]/pattern/ All names in @EXPORT and @EXPORT_OK which match | |
225 | ||
226 | A leading ! indicates that matching names should be deleted from the | |
227 | list of names to import. If the first specification is a deletion it | |
228 | is treated as though preceded by :DEFAULT. If you just want to import | |
229 | extra names in addition to the default set you will still need to | |
230 | include :DEFAULT explicitly. | |
231 | ||
232 | e.g., Module.pm defines: | |
233 | ||
234 | @EXPORT = qw(A1 A2 A3 A4 A5); | |
235 | @EXPORT_OK = qw(B1 B2 B3 B4 B5); | |
236 | %EXPORT_TAGS = (T1 => [qw(A1 A2 B1 B2)], T2 => [qw(A1 A2 B3 B4)]); | |
237 | ||
238 | Note that you cannot use tags in @EXPORT or @EXPORT_OK. | |
239 | Names in EXPORT_TAGS must also appear in @EXPORT or @EXPORT_OK. | |
240 | ||
241 | An application using Module can say something like: | |
242 | ||
243 | use Module qw(:DEFAULT :T2 !B3 A3); | |
244 | ||
245 | Other examples include: | |
246 | ||
247 | use Socket qw(!/^[AP]F_/ !SOMAXCONN !SOL_SOCKET); | |
248 | use POSIX qw(:errno_h :termios_h !TCSADRAIN !/^EXIT/); | |
249 | ||
250 | Remember that most patterns (using //) will need to be anchored | |
251 | with a leading ^, e.g., C</^EXIT/> rather than C</EXIT/>. | |
252 | ||
253 | You can say C<BEGIN { $Exporter::Verbose=1 }> to see how the | |
254 | specifications are being processed and what is actually being imported | |
255 | into modules. | |
256 | ||
65503211 | 257 | =head2 Exporting without using Exporter's import method |
84902520 TB |
258 | |
259 | Exporter has a special method, 'export_to_level' which is used in situations | |
65503211 | 260 | where you can't directly call Exporter's import method. The export_to_level |
84902520 TB |
261 | method looks like: |
262 | ||
cec46e5a | 263 | MyPackage->export_to_level($where_to_export, $package, @what_to_export); |
84902520 TB |
264 | |
265 | where $where_to_export is an integer telling how far up the calling stack | |
266 | to export your symbols, and @what_to_export is an array telling what | |
ba5725f8 GS |
267 | symbols *to* export (usually this is @_). The $package argument is |
268 | currently unused. | |
84902520 TB |
269 | |
270 | For example, suppose that you have a module, A, which already has an | |
271 | import function: | |
272 | ||
cec46e5a | 273 | package A; |
84902520 | 274 | |
cec46e5a RGS |
275 | @ISA = qw(Exporter); |
276 | @EXPORT_OK = qw ($b); | |
84902520 | 277 | |
cec46e5a RGS |
278 | sub import |
279 | { | |
280 | $A::b = 1; # not a very useful import method | |
281 | } | |
84902520 TB |
282 | |
283 | and you want to Export symbol $A::b back to the module that called | |
284 | package A. Since Exporter relies on the import method to work, via | |
285 | inheritance, as it stands Exporter::import() will never get called. | |
286 | Instead, say the following: | |
287 | ||
cec46e5a RGS |
288 | package A; |
289 | @ISA = qw(Exporter); | |
290 | @EXPORT_OK = qw ($b); | |
84902520 | 291 | |
cec46e5a RGS |
292 | sub import |
293 | { | |
294 | $A::b = 1; | |
295 | A->export_to_level(1, @_); | |
296 | } | |
84902520 TB |
297 | |
298 | This will export the symbols one level 'above' the current package - ie: to | |
299 | the program or module that used package A. | |
300 | ||
fe43f860 | 301 | Note: Be careful not to modify C<@_> at all before you call export_to_level |
84902520 TB |
302 | - or people using your package will get very unexplained results! |
303 | ||
fe43f860 FD |
304 | =head2 Exporting without inheriting from Exporter |
305 | ||
306 | By including Exporter in your @ISA you inherit an Exporter's import() method | |
307 | but you also inherit several other helper methods which you probably don't | |
308 | want. To avoid this you can do | |
309 | ||
310 | package YourModule; | |
311 | use Exporter qw( import ); | |
312 | ||
313 | which will export Exporter's own import() method into YourModule. | |
314 | Everything will work as before but you won't need to include Exporter in | |
315 | @YourModule::ISA. | |
84902520 | 316 | |
2b5b2650 | 317 | =head2 Module Version Checking |
318 | ||
319 | The Exporter module will convert an attempt to import a number from a | |
1fef88e7 | 320 | module into a call to $module_name-E<gt>require_version($value). This can |
2b5b2650 | 321 | be used to validate that the version of the module being used is |
322 | greater than or equal to the required version. | |
323 | ||
324 | The Exporter module supplies a default require_version method which | |
325 | checks the value of $VERSION in the exporting module. | |
326 | ||
327 | Since the default require_version method treats the $VERSION number as | |
d5e40bcc | 328 | a simple numeric value it will regard version 1.10 as lower than |
329 | 1.9. For this reason it is strongly recommended that you use numbers | |
330 | with at least two decimal places, e.g., 1.09. | |
2b5b2650 | 331 | |
332 | =head2 Managing Unknown Symbols | |
333 | ||
334 | In some situations you may want to prevent certain symbols from being | |
335 | exported. Typically this applies to extensions which have functions | |
336 | or constants that may not exist on some systems. | |
337 | ||
338 | The names of any symbols that cannot be exported should be listed | |
339 | in the C<@EXPORT_FAIL> array. | |
340 | ||
7a2e2cd6 | 341 | If a module attempts to import any of these symbols the Exporter |
2b5b2650 | 342 | will give the module an opportunity to handle the situation before |
343 | generating an error. The Exporter will call an export_fail method | |
344 | with a list of the failed symbols: | |
345 | ||
346 | @failed_symbols = $module_name->export_fail(@failed_symbols); | |
347 | ||
348 | If the export_fail method returns an empty list then no error is | |
349 | recorded and all the requested symbols are exported. If the returned | |
350 | list is not empty then an error is generated for each symbol and the | |
351 | export fails. The Exporter provides a default export_fail method which | |
352 | simply returns the list unchanged. | |
353 | ||
354 | Uses for the export_fail method include giving better error messages | |
355 | for some symbols and performing lazy architectural checks (put more | |
356 | symbols into @EXPORT_FAIL by default and then take them out if someone | |
357 | actually tries to use them and an expensive check shows that they are | |
358 | usable on that platform). | |
359 | ||
360 | =head2 Tag Handling Utility Functions | |
361 | ||
362 | Since the symbols listed within %EXPORT_TAGS must also appear in either | |
363 | @EXPORT or @EXPORT_OK, two utility functions are provided which allow | |
364 | you to easily add tagged sets of symbols to @EXPORT or @EXPORT_OK: | |
365 | ||
366 | %EXPORT_TAGS = (foo => [qw(aa bb cc)], bar => [qw(aa cc dd)]); | |
367 | ||
368 | Exporter::export_tags('foo'); # add aa, bb and cc to @EXPORT | |
369 | Exporter::export_ok_tags('bar'); # add aa, cc and dd to @EXPORT_OK | |
370 | ||
371 | Any names which are not tags are added to @EXPORT or @EXPORT_OK | |
d5e40bcc | 372 | unchanged but will trigger a warning (with C<-w>) to avoid misspelt tags |
2b5b2650 | 373 | names being silently added to @EXPORT or @EXPORT_OK. Future versions |
374 | may make this a fatal error. | |
375 | ||
d584343b MG |
376 | =head2 Generating combined tags |
377 | ||
378 | If several symbol categories exist in %EXPORT_TAGS, it's usually | |
379 | useful to create the utility ":all" to simplify "use" statements. | |
380 | ||
381 | The simplest way to do this is: | |
382 | ||
383 | %EXPORT_TAGS = (foo => [qw(aa bb cc)], bar => [qw(aa cc dd)]); | |
384 | ||
385 | # add all the other ":class" tags to the ":all" class, | |
386 | # deleting duplicates | |
387 | { | |
388 | my %seen; | |
389 | ||
390 | push @{$EXPORT_TAGS{all}}, | |
391 | grep {!$seen{$_}++} @{$EXPORT_TAGS{$_}} foreach keys %EXPORT_TAGS; | |
392 | } | |
393 | ||
394 | CGI.pm creates an ":all" tag which contains some (but not really | |
395 | all) of its categories. That could be done with one small | |
396 | change: | |
397 | ||
398 | # add some of the other ":class" tags to the ":all" class, | |
399 | # deleting duplicates | |
400 | { | |
401 | my %seen; | |
402 | ||
403 | push @{$EXPORT_TAGS{all}}, | |
404 | grep {!$seen{$_}++} @{$EXPORT_TAGS{$_}} | |
405 | foreach qw/html2 html3 netscape form cgi internal/; | |
406 | } | |
407 | ||
408 | Note that the tag names in %EXPORT_TAGS don't have the leading ':'. | |
409 | ||
5fea0f12 BS |
410 | =head2 C<AUTOLOAD>ed Constants |
411 | ||
8b4c0206 T |
412 | Many modules make use of C<AUTOLOAD>ing for constant subroutines to |
413 | avoid having to compile and waste memory on rarely used values (see | |
414 | L<perlsub> for details on constant subroutines). Calls to such | |
415 | constant subroutines are not optimized away at compile time because | |
416 | they can't be checked at compile time for constancy. | |
417 | ||
418 | Even if a prototype is available at compile time, the body of the | |
419 | subroutine is not (it hasn't been C<AUTOLOAD>ed yet). perl needs to | |
420 | examine both the C<()> prototype and the body of a subroutine at | |
421 | compile time to detect that it can safely replace calls to that | |
422 | subroutine with the constant value. | |
5fea0f12 BS |
423 | |
424 | A workaround for this is to call the constants once in a C<BEGIN> block: | |
425 | ||
426 | package My ; | |
427 | ||
428 | use Socket ; | |
429 | ||
430 | foo( SO_LINGER ); ## SO_LINGER NOT optimized away; called at runtime | |
431 | BEGIN { SO_LINGER } | |
432 | foo( SO_LINGER ); ## SO_LINGER optimized away at compile time. | |
433 | ||
8b4c0206 T |
434 | This forces the C<AUTOLOAD> for C<SO_LINGER> to take place before |
435 | SO_LINGER is encountered later in C<My> package. | |
5fea0f12 | 436 | |
8b4c0206 T |
437 | If you are writing a package that C<AUTOLOAD>s, consider forcing |
438 | an C<AUTOLOAD> for any constants explicitly imported by other packages | |
439 | or which are usually used when your package is C<use>d. | |
5fea0f12 | 440 | |
2b5b2650 | 441 | =cut |