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; | |
f87cd9fa | 12 | our $VERSION = '5.65'; |
a6faae8d | 13 | our (%Cache); |
3e927c50 | 14 | |
0e57b4e8 | 15 | sub as_heavy { |
4af1b167 | 16 | require Exporter::Heavy; |
0e57b4e8 IZ |
17 | # Unfortunately, this does not work if the caller is aliased as *name = \&foo |
18 | # Thus the need to create a lot of identical subroutines | |
19 | my $c = (caller(1))[3]; | |
20 | $c =~ s/.*:://; | |
21 | \&{"Exporter::Heavy::heavy_$c"}; | |
84902520 TB |
22 | } |
23 | ||
4af1b167 | 24 | sub export { |
0e57b4e8 | 25 | goto &{as_heavy()}; |
a0d0e21e LW |
26 | } |
27 | ||
4af1b167 IZ |
28 | sub import { |
29 | my $pkg = shift; | |
30 | my $callpkg = caller($ExportLevel); | |
b75c8c73 | 31 | |
fe43f860 FD |
32 | if ($pkg eq "Exporter" and @_ and $_[0] eq "import") { |
33 | *{$callpkg."::import"} = \&import; | |
34 | return; | |
35 | } | |
36 | ||
4af1b167 | 37 | # We *need* to treat @{"$pkg\::EXPORT_FAIL"} since Carp uses it :-( |
2d7e78b1 NC |
38 | my $exports = \@{"$pkg\::EXPORT"}; |
39 | # But, avoid creating things if they don't exist, which saves a couple of | |
40 | # hundred bytes per package processed. | |
41 | my $fail = ${$pkg . '::'}{EXPORT_FAIL} && \@{"$pkg\::EXPORT_FAIL"}; | |
4af1b167 | 42 | return export $pkg, $callpkg, @_ |
2d7e78b1 | 43 | if $Verbose or $Debug or $fail && @$fail > 1; |
a6faae8d | 44 | my $export_cache = ($Cache{$pkg} ||= {}); |
b75c8c73 | 45 | my $args = @_ or @_ = @$exports; |
732bb7c2 NC |
46 | |
47 | local $_; | |
b75c8c73 | 48 | if ($args and not %$export_cache) { |
732bb7c2 NC |
49 | s/^&//, $export_cache->{$_} = 1 |
50 | foreach (@$exports, @{"$pkg\::EXPORT_OK"}); | |
4af1b167 | 51 | } |
fa1bb02f NC |
52 | my $heavy; |
53 | # Try very hard not to use {} and hence have to enter scope on the foreach | |
54 | # We bomb out of the loop with last as soon as heavy is set. | |
55 | if ($args or $fail) { | |
732bb7c2 | 56 | ($heavy = (/\W/ or $args and not exists $export_cache->{$_} |
2d7e78b1 | 57 | or $fail and @$fail and $_ eq $fail->[0])) and last |
fa1bb02f NC |
58 | foreach (@_); |
59 | } else { | |
60 | ($heavy = /\W/) and last | |
732bb7c2 | 61 | foreach (@_); |
4af1b167 | 62 | } |
732bb7c2 | 63 | return export $pkg, $callpkg, ($args ? @_ : ()) if $heavy; |
4af1b167 | 64 | local $SIG{__WARN__} = |
9b86bb5c | 65 | sub {require Carp; &Carp::carp} if not $SIG{__WARN__}; |
732bb7c2 NC |
66 | # shortcut for the common case of no type character |
67 | *{"$callpkg\::$_"} = \&{"$pkg\::$_"} foreach @_; | |
e50aee73 AD |
68 | } |
69 | ||
b75c8c73 MS |
70 | # Default methods |
71 | ||
2b5b2650 | 72 | sub export_fail { |
b75c8c73 MS |
73 | my $self = shift; |
74 | @_; | |
2b5b2650 | 75 | } |
76 | ||
0e57b4e8 IZ |
77 | # Unfortunately, caller(1)[3] "does not work" if the caller is aliased as |
78 | # *name = \&foo. Thus the need to create a lot of identical subroutines | |
79 | # Otherwise we could have aliased them to export(). | |
b75c8c73 | 80 | |
0e57b4e8 IZ |
81 | sub export_to_level { |
82 | goto &{as_heavy()}; | |
83 | } | |
84 | ||
85 | sub export_tags { | |
86 | goto &{as_heavy()}; | |
b75c8c73 MS |
87 | } |
88 | ||
0e57b4e8 IZ |
89 | sub export_ok_tags { |
90 | goto &{as_heavy()}; | |
91 | } | |
92 | ||
93 | sub require_version { | |
94 | goto &{as_heavy()}; | |
95 | } | |
b75c8c73 | 96 | |
2b5b2650 | 97 | 1; |
732bb7c2 | 98 | __END__ |
b75c8c73 | 99 | |
2b5b2650 | 100 | =head1 NAME |
101 | ||
102 | Exporter - Implements default import method for modules | |
103 | ||
104 | =head1 SYNOPSIS | |
105 | ||
3e927c50 | 106 | In module F<YourModule.pm>: |
2b5b2650 | 107 | |
65503211 | 108 | package YourModule; |
2b5b2650 | 109 | require Exporter; |
110 | @ISA = qw(Exporter); | |
65503211 | 111 | @EXPORT_OK = qw(munge frobnicate); # symbols to export on request |
2b5b2650 | 112 | |
fe43f860 FD |
113 | or |
114 | ||
115 | package YourModule; | |
116 | use Exporter 'import'; # gives you Exporter's import() method directly | |
117 | @EXPORT_OK = qw(munge frobnicate); # symbols to export on request | |
118 | ||
3e927c50 | 119 | In other files which wish to use C<YourModule>: |
2b5b2650 | 120 | |
3e927c50 | 121 | use YourModule qw(frobnicate); # import listed symbols |
65503211 | 122 | frobnicate ($left, $right) # calls YourModule::frobnicate |
2b5b2650 | 123 | |
47f97feb AF |
124 | Take a look at L</Good Practices> for some variants |
125 | you will like to use in modern Perl code. | |
126 | ||
2b5b2650 | 127 | =head1 DESCRIPTION |
128 | ||
65503211 NC |
129 | The Exporter module implements an C<import> method which allows a module |
130 | to export functions and variables to its users' namespaces. Many modules | |
131 | use Exporter rather than implementing their own C<import> method because | |
132 | Exporter provides a highly flexible interface, with an implementation optimised | |
133 | for the common case. | |
2b5b2650 | 134 | |
135 | Perl automatically calls the C<import> method when processing a | |
136 | C<use> statement for a module. Modules and C<use> are documented | |
137 | in L<perlfunc> and L<perlmod>. Understanding the concept of | |
138 | modules and how the C<use> statement operates is important to | |
139 | understanding the Exporter. | |
140 | ||
4fddf32b GS |
141 | =head2 How to Export |
142 | ||
143 | The arrays C<@EXPORT> and C<@EXPORT_OK> in a module hold lists of | |
144 | symbols that are going to be exported into the users name space by | |
145 | default, or which they can request to be exported, respectively. The | |
146 | symbols can represent functions, scalars, arrays, hashes, or typeglobs. | |
147 | The symbols must be given by full name with the exception that the | |
148 | ampersand in front of a function is optional, e.g. | |
149 | ||
150 | @EXPORT = qw(afunc $scalar @array); # afunc is a function | |
151 | @EXPORT_OK = qw(&bfunc %hash *typeglob); # explicit prefix on &bfunc | |
152 | ||
65503211 NC |
153 | If you are only exporting function names it is recommended to omit the |
154 | ampersand, as the implementation is faster this way. | |
155 | ||
2b5b2650 | 156 | =head2 Selecting What To Export |
157 | ||
158 | Do B<not> export method names! | |
159 | ||
160 | Do B<not> export anything else by default without a good reason! | |
161 | ||
162 | Exports pollute the namespace of the module user. If you must export | |
3e927c50 | 163 | try to use C<@EXPORT_OK> in preference to C<@EXPORT> and avoid short or |
2b5b2650 | 164 | common symbol names to reduce the risk of name clashes. |
165 | ||
166 | Generally anything not exported is still accessible from outside the | |
3e927c50 | 167 | module using the C<YourModule::item_name> (or C<< $blessed_ref->method >>) |
2b5b2650 | 168 | syntax. By convention you can use a leading underscore on names to |
169 | informally indicate that they are 'internal' and not for public use. | |
170 | ||
171 | (It is actually possible to get private functions by saying: | |
172 | ||
173 | my $subref = sub { ... }; | |
e60ce172 BT |
174 | $subref->(@args); # Call it as a function |
175 | $obj->$subref(@args); # Use it as a method | |
2b5b2650 | 176 | |
e60ce172 BT |
177 | However if you use them for methods it is up to you to figure out |
178 | how to make inheritance work.) | |
2b5b2650 | 179 | |
180 | As a general rule, if the module is trying to be object oriented | |
181 | then export nothing. If it's just a collection of functions then | |
3e927c50 | 182 | C<@EXPORT_OK> anything but use C<@EXPORT> with caution. For function and |
65503211 NC |
183 | method names use barewords in preference to names prefixed with |
184 | ampersands for the export lists. | |
2b5b2650 | 185 | |
186 | Other module design guidelines can be found in L<perlmod>. | |
187 | ||
65503211 NC |
188 | =head2 How to Import |
189 | ||
190 | In other files which wish to use your module there are three basic ways for | |
191 | them to load your module and import its symbols: | |
192 | ||
193 | =over 4 | |
194 | ||
3e927c50 | 195 | =item C<use YourModule;> |
65503211 | 196 | |
3e927c50 | 197 | This imports all the symbols from YourModule's C<@EXPORT> into the namespace |
65503211 NC |
198 | of the C<use> statement. |
199 | ||
3e927c50 | 200 | =item C<use YourModule ();> |
65503211 NC |
201 | |
202 | This causes perl to load your module but does not import any symbols. | |
203 | ||
3e927c50 | 204 | =item C<use YourModule qw(...);> |
65503211 NC |
205 | |
206 | This imports only the symbols listed by the caller into their namespace. | |
3e927c50 | 207 | All listed symbols must be in your C<@EXPORT> or C<@EXPORT_OK>, else an error |
65503211 NC |
208 | occurs. The advanced export features of Exporter are accessed like this, |
209 | but with list entries that are syntactically distinct from symbol names. | |
210 | ||
211 | =back | |
212 | ||
213 | Unless you want to use its advanced features, this is probably all you | |
214 | need to know to use Exporter. | |
215 | ||
216 | =head1 Advanced features | |
217 | ||
2b5b2650 | 218 | =head2 Specialised Import Lists |
219 | ||
a29b0897 MB |
220 | If any of the entries in an import list begins with !, : or / then |
221 | the list is treated as a series of specifications which either add to | |
222 | or delete from the list of names to import. They are processed left to | |
2b5b2650 | 223 | right. Specifications are in the form: |
224 | ||
225 | [!]name This name only | |
226 | [!]:DEFAULT All names in @EXPORT | |
227 | [!]:tag All names in $EXPORT_TAGS{tag} anonymous list | |
228 | [!]/pattern/ All names in @EXPORT and @EXPORT_OK which match | |
229 | ||
230 | A leading ! indicates that matching names should be deleted from the | |
231 | list of names to import. If the first specification is a deletion it | |
232 | is treated as though preceded by :DEFAULT. If you just want to import | |
233 | extra names in addition to the default set you will still need to | |
234 | include :DEFAULT explicitly. | |
235 | ||
3e927c50 | 236 | e.g., F<Module.pm> defines: |
2b5b2650 | 237 | |
238 | @EXPORT = qw(A1 A2 A3 A4 A5); | |
239 | @EXPORT_OK = qw(B1 B2 B3 B4 B5); | |
240 | %EXPORT_TAGS = (T1 => [qw(A1 A2 B1 B2)], T2 => [qw(A1 A2 B3 B4)]); | |
241 | ||
242 | Note that you cannot use tags in @EXPORT or @EXPORT_OK. | |
243 | Names in EXPORT_TAGS must also appear in @EXPORT or @EXPORT_OK. | |
244 | ||
245 | An application using Module can say something like: | |
246 | ||
247 | use Module qw(:DEFAULT :T2 !B3 A3); | |
248 | ||
249 | Other examples include: | |
250 | ||
251 | use Socket qw(!/^[AP]F_/ !SOMAXCONN !SOL_SOCKET); | |
252 | use POSIX qw(:errno_h :termios_h !TCSADRAIN !/^EXIT/); | |
253 | ||
254 | Remember that most patterns (using //) will need to be anchored | |
255 | with a leading ^, e.g., C</^EXIT/> rather than C</EXIT/>. | |
256 | ||
257 | You can say C<BEGIN { $Exporter::Verbose=1 }> to see how the | |
258 | specifications are being processed and what is actually being imported | |
259 | into modules. | |
260 | ||
65503211 | 261 | =head2 Exporting without using Exporter's import method |
84902520 TB |
262 | |
263 | Exporter has a special method, 'export_to_level' which is used in situations | |
65503211 | 264 | where you can't directly call Exporter's import method. The export_to_level |
84902520 TB |
265 | method looks like: |
266 | ||
cec46e5a | 267 | MyPackage->export_to_level($where_to_export, $package, @what_to_export); |
84902520 | 268 | |
3e927c50 AF |
269 | where C<$where_to_export> is an integer telling how far up the calling stack |
270 | to export your symbols, and C<@what_to_export> is an array telling what | |
271 | symbols *to* export (usually this is C<@_>). The C<$package> argument is | |
ba5725f8 | 272 | currently unused. |
84902520 TB |
273 | |
274 | For example, suppose that you have a module, A, which already has an | |
275 | import function: | |
276 | ||
cec46e5a | 277 | package A; |
84902520 | 278 | |
cec46e5a RGS |
279 | @ISA = qw(Exporter); |
280 | @EXPORT_OK = qw ($b); | |
84902520 | 281 | |
cec46e5a RGS |
282 | sub import |
283 | { | |
284 | $A::b = 1; # not a very useful import method | |
285 | } | |
84902520 | 286 | |
3e927c50 | 287 | and you want to Export symbol C<$A::b> back to the module that called |
84902520 TB |
288 | package A. Since Exporter relies on the import method to work, via |
289 | inheritance, as it stands Exporter::import() will never get called. | |
290 | Instead, say the following: | |
291 | ||
cec46e5a RGS |
292 | package A; |
293 | @ISA = qw(Exporter); | |
294 | @EXPORT_OK = qw ($b); | |
84902520 | 295 | |
cec46e5a RGS |
296 | sub import |
297 | { | |
298 | $A::b = 1; | |
299 | A->export_to_level(1, @_); | |
300 | } | |
84902520 TB |
301 | |
302 | This will export the symbols one level 'above' the current package - ie: to | |
303 | the program or module that used package A. | |
304 | ||
fe43f860 | 305 | Note: Be careful not to modify C<@_> at all before you call export_to_level |
84902520 TB |
306 | - or people using your package will get very unexplained results! |
307 | ||
fe43f860 FD |
308 | =head2 Exporting without inheriting from Exporter |
309 | ||
3e927c50 | 310 | By including Exporter in your C<@ISA> you inherit an Exporter's import() method |
fe43f860 FD |
311 | but you also inherit several other helper methods which you probably don't |
312 | want. To avoid this you can do | |
313 | ||
314 | package YourModule; | |
315 | use Exporter qw( import ); | |
316 | ||
317 | which will export Exporter's own import() method into YourModule. | |
318 | Everything will work as before but you won't need to include Exporter in | |
3e927c50 | 319 | C<@YourModule::ISA>. |
84902520 | 320 | |
47f97feb AF |
321 | Note: This feature was introduced in version 5.57 |
322 | of Exporter, released with perl 5.8.3. | |
323 | ||
2b5b2650 | 324 | =head2 Module Version Checking |
325 | ||
326 | The Exporter module will convert an attempt to import a number from a | |
3e927c50 | 327 | module into a call to C<< $module_name->require_version($value) >>. This can |
2b5b2650 | 328 | be used to validate that the version of the module being used is |
329 | greater than or equal to the required version. | |
330 | ||
3e927c50 AF |
331 | The Exporter module supplies a default C<require_version> method which |
332 | checks the value of C<$VERSION> in the exporting module. | |
2b5b2650 | 333 | |
3e927c50 | 334 | Since the default C<require_version> method treats the C<$VERSION> number as |
d5e40bcc | 335 | a simple numeric value it will regard version 1.10 as lower than |
336 | 1.9. For this reason it is strongly recommended that you use numbers | |
337 | with at least two decimal places, e.g., 1.09. | |
2b5b2650 | 338 | |
339 | =head2 Managing Unknown Symbols | |
340 | ||
341 | In some situations you may want to prevent certain symbols from being | |
342 | exported. Typically this applies to extensions which have functions | |
343 | or constants that may not exist on some systems. | |
344 | ||
345 | The names of any symbols that cannot be exported should be listed | |
346 | in the C<@EXPORT_FAIL> array. | |
347 | ||
7a2e2cd6 | 348 | If a module attempts to import any of these symbols the Exporter |
2b5b2650 | 349 | will give the module an opportunity to handle the situation before |
350 | generating an error. The Exporter will call an export_fail method | |
351 | with a list of the failed symbols: | |
352 | ||
353 | @failed_symbols = $module_name->export_fail(@failed_symbols); | |
354 | ||
3e927c50 | 355 | If the C<export_fail> method returns an empty list then no error is |
2b5b2650 | 356 | recorded and all the requested symbols are exported. If the returned |
357 | list is not empty then an error is generated for each symbol and the | |
3e927c50 | 358 | export fails. The Exporter provides a default C<export_fail> method which |
2b5b2650 | 359 | simply returns the list unchanged. |
360 | ||
3e927c50 | 361 | Uses for the C<export_fail> method include giving better error messages |
2b5b2650 | 362 | for some symbols and performing lazy architectural checks (put more |
3e927c50 | 363 | symbols into C<@EXPORT_FAIL> by default and then take them out if someone |
2b5b2650 | 364 | actually tries to use them and an expensive check shows that they are |
365 | usable on that platform). | |
366 | ||
367 | =head2 Tag Handling Utility Functions | |
368 | ||
3e927c50 AF |
369 | Since the symbols listed within C<%EXPORT_TAGS> must also appear in either |
370 | C<@EXPORT> or C<@EXPORT_OK>, two utility functions are provided which allow | |
371 | you to easily add tagged sets of symbols to C<@EXPORT> or C<@EXPORT_OK>: | |
2b5b2650 | 372 | |
373 | %EXPORT_TAGS = (foo => [qw(aa bb cc)], bar => [qw(aa cc dd)]); | |
374 | ||
375 | Exporter::export_tags('foo'); # add aa, bb and cc to @EXPORT | |
376 | Exporter::export_ok_tags('bar'); # add aa, cc and dd to @EXPORT_OK | |
377 | ||
3e927c50 | 378 | Any names which are not tags are added to C<@EXPORT> or C<@EXPORT_OK> |
d5e40bcc | 379 | unchanged but will trigger a warning (with C<-w>) to avoid misspelt tags |
3e927c50 | 380 | names being silently added to C<@EXPORT> or C<@EXPORT_OK>. Future versions |
2b5b2650 | 381 | may make this a fatal error. |
382 | ||
d584343b MG |
383 | =head2 Generating combined tags |
384 | ||
3e927c50 | 385 | If several symbol categories exist in C<%EXPORT_TAGS>, it's usually |
d584343b MG |
386 | useful to create the utility ":all" to simplify "use" statements. |
387 | ||
388 | The simplest way to do this is: | |
389 | ||
390 | %EXPORT_TAGS = (foo => [qw(aa bb cc)], bar => [qw(aa cc dd)]); | |
391 | ||
392 | # add all the other ":class" tags to the ":all" class, | |
393 | # deleting duplicates | |
394 | { | |
395 | my %seen; | |
396 | ||
397 | push @{$EXPORT_TAGS{all}}, | |
398 | grep {!$seen{$_}++} @{$EXPORT_TAGS{$_}} foreach keys %EXPORT_TAGS; | |
399 | } | |
400 | ||
3e927c50 | 401 | F<CGI.pm> creates an ":all" tag which contains some (but not really |
d584343b MG |
402 | all) of its categories. That could be done with one small |
403 | change: | |
404 | ||
405 | # add some of the other ":class" tags to the ":all" class, | |
406 | # deleting duplicates | |
407 | { | |
408 | my %seen; | |
409 | ||
410 | push @{$EXPORT_TAGS{all}}, | |
411 | grep {!$seen{$_}++} @{$EXPORT_TAGS{$_}} | |
412 | foreach qw/html2 html3 netscape form cgi internal/; | |
413 | } | |
414 | ||
3e927c50 | 415 | Note that the tag names in C<%EXPORT_TAGS> don't have the leading ':'. |
d584343b | 416 | |
5fea0f12 BS |
417 | =head2 C<AUTOLOAD>ed Constants |
418 | ||
8b4c0206 T |
419 | Many modules make use of C<AUTOLOAD>ing for constant subroutines to |
420 | avoid having to compile and waste memory on rarely used values (see | |
421 | L<perlsub> for details on constant subroutines). Calls to such | |
422 | constant subroutines are not optimized away at compile time because | |
423 | they can't be checked at compile time for constancy. | |
424 | ||
425 | Even if a prototype is available at compile time, the body of the | |
426 | subroutine is not (it hasn't been C<AUTOLOAD>ed yet). perl needs to | |
427 | examine both the C<()> prototype and the body of a subroutine at | |
428 | compile time to detect that it can safely replace calls to that | |
429 | subroutine with the constant value. | |
5fea0f12 BS |
430 | |
431 | A workaround for this is to call the constants once in a C<BEGIN> block: | |
432 | ||
433 | package My ; | |
434 | ||
435 | use Socket ; | |
436 | ||
437 | foo( SO_LINGER ); ## SO_LINGER NOT optimized away; called at runtime | |
438 | BEGIN { SO_LINGER } | |
439 | foo( SO_LINGER ); ## SO_LINGER optimized away at compile time. | |
440 | ||
8b4c0206 T |
441 | This forces the C<AUTOLOAD> for C<SO_LINGER> to take place before |
442 | SO_LINGER is encountered later in C<My> package. | |
5fea0f12 | 443 | |
8b4c0206 T |
444 | If you are writing a package that C<AUTOLOAD>s, consider forcing |
445 | an C<AUTOLOAD> for any constants explicitly imported by other packages | |
446 | or which are usually used when your package is C<use>d. | |
5fea0f12 | 447 | |
47f97feb AF |
448 | =head1 Good Practices |
449 | ||
450 | =head2 Declaring C<@EXPORT_OK> and Friends | |
451 | ||
452 | When using C<Exporter> with the standard C<strict> and C<warnings> | |
453 | pragmas, the C<our> keyword is needed to declare the package | |
454 | variables C<@EXPORT_OK>, C<@EXPORT>, C<@ISA>, etc. | |
455 | ||
456 | our @ISA = qw(Exporter); | |
457 | our @EXPORT_OK = qw(munge frobnicate); | |
458 | ||
459 | If backward compatibility for Perls under 5.6 is important, | |
460 | one must write instead a C<use vars> statement. | |
461 | ||
462 | use vars qw(@ISA @EXPORT_OK); | |
463 | @ISA = qw(Exporter); | |
464 | @EXPORT_OK = qw(munge frobnicate); | |
465 | ||
466 | =head2 Playing Safe | |
467 | ||
468 | There are some caveats with the use of runtime statements | |
469 | like C<require Exporter> and the assignment to package | |
470 | variables, which can very subtle for the unaware programmer. | |
471 | This may happen for instance with mutually recursive | |
472 | modules, which are affected by the time the relevant | |
473 | constructions are executed. | |
474 | ||
475 | The ideal (but a bit ugly) way to never have to think | |
476 | about that is to use C<BEGIN> blocks. So the first part | |
477 | of the L</SYNOPSIS> code could be rewritten as: | |
478 | ||
479 | package YourModule; | |
480 | ||
481 | use strict; | |
482 | use warnings; | |
483 | ||
484 | our (@ISA, @EXPORT_OK); | |
485 | BEGIN { | |
486 | require Exporter; | |
487 | @ISA = qw(Exporter); | |
488 | @EXPORT_OK = qw(munge frobnicate); # symbols to export on request | |
489 | } | |
490 | ||
491 | The C<BEGIN> will assure that the loading of F<Exporter.pm> | |
492 | and the assignments to C<@ISA> and C<@EXPORT_OK> happen | |
493 | immediately, leaving no room for something to get awry | |
494 | or just plain wrong. | |
495 | ||
496 | With respect to loading C<Exporter> and inheriting, there | |
497 | are alternatives with the use of modules like C<base> and C<parent>. | |
498 | ||
499 | use base qw( Exporter ); | |
500 | # or | |
501 | use parent qw( Exporter ); | |
502 | ||
503 | Any of these statements are nice replacements for | |
504 | C<BEGIN { require Exporter; @ISA = qw(Exporter); }> | |
505 | with the same compile-time effect. The basic difference | |
506 | is that C<base> code interacts with declared C<fields> | |
507 | while C<parent> is a streamlined version of the older | |
508 | C<base> code to just establish the IS-A relationship. | |
509 | ||
510 | For more details, see the documentation and code of | |
511 | L<base> and L<parent>. | |
512 | ||
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513 | Another thorough remedy to that runtime vs. |
514 | compile-time trap is to use L<Exporter::Easy>, | |
515 | which is a wrapper of Exporter that allows all | |
516 | boilerplate code at a single gulp in the | |
517 | use statement. | |
518 | ||
519 | use Exporter::Easy ( | |
520 | OK => [ qw(munge frobnicate) ], | |
521 | ); | |
522 | # @ISA setup is automatic | |
523 | # all assignments happen at compile time | |
524 | ||
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525 | =head2 What not to Export |
526 | ||
af30f7a9 | 527 | You have been warned already in L</Selecting What To Export> |
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528 | to not export: |
529 | ||
530 | =over 4 | |
531 | ||
532 | =item * | |
533 | ||
44ddc072 | 534 | method names (because you don't need to |
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535 | and that's likely to not do what you want), |
536 | ||
537 | =item * | |
538 | ||
539 | anything by default (because you don't want to surprise your users... | |
540 | badly) | |
541 | ||
542 | =item * | |
543 | ||
544 | anything you don't need to (because less is more) | |
545 | ||
546 | =back | |
547 | ||
548 | There's one more item to add to this list. Do B<not> | |
549 | export variable names. Just because C<Exporter> lets you | |
550 | do that, it does not mean you should. | |
551 | ||
552 | @EXPORT_OK = qw( $svar @avar %hvar ); # DON'T! | |
553 | ||
554 | Exporting variables is not a good idea. They can | |
555 | change under the hood, provoking horrible | |
556 | effects at-a-distance, that are too hard to track | |
557 | and to fix. Trust me: they are not worth it. | |
558 | ||
559 | To provide the capability to set/get class-wide | |
560 | settings, it is best instead to provide accessors | |
561 | as subroutines or class methods instead. | |
562 | ||
563 | =head1 SEE ALSO | |
564 | ||
565 | C<Exporter> is definitely not the only module with | |
566 | symbol exporter capabilities. At CPAN, you may find | |
567 | a bunch of them. Some are lighter. Some | |
568 | provide improved APIs and features. Peek the one | |
569 | that fits your needs. The following is | |
570 | a sample list of such modules. | |
571 | ||
572 | Exporter::Easy | |
573 | Exporter::Lite | |
574 | Exporter::Renaming | |
575 | Exporter::Tidy | |
576 | Sub::Exporter / Sub::Installer | |
577 | Perl6::Export / Perl6::Export::Attrs | |
578 | ||
579 | =head1 LICENSE | |
580 | ||
581 | This library is free software. You can redistribute it | |
582 | and/or modify it under the same terms as Perl itself. | |
583 | ||
2b5b2650 | 584 | =cut |
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585 | |
586 | ||
587 |