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; | |
3247c188 | 12 | our $VERSION = '5.64_01'; |
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 @{"$pkg\::EXPORT_FAIL"} since Carp uses it :-( |
a6faae8d | 38 | my($exports, $fail) = (\@{"$pkg\::EXPORT"}, \@{"$pkg\::EXPORT_FAIL"}); |
4af1b167 | 39 | return export $pkg, $callpkg, @_ |
b75c8c73 | 40 | if $Verbose or $Debug or @$fail > 1; |
a6faae8d | 41 | my $export_cache = ($Cache{$pkg} ||= {}); |
b75c8c73 | 42 | my $args = @_ or @_ = @$exports; |
732bb7c2 NC |
43 | |
44 | local $_; | |
b75c8c73 | 45 | if ($args and not %$export_cache) { |
732bb7c2 NC |
46 | s/^&//, $export_cache->{$_} = 1 |
47 | foreach (@$exports, @{"$pkg\::EXPORT_OK"}); | |
4af1b167 | 48 | } |
fa1bb02f NC |
49 | my $heavy; |
50 | # Try very hard not to use {} and hence have to enter scope on the foreach | |
51 | # We bomb out of the loop with last as soon as heavy is set. | |
52 | if ($args or $fail) { | |
732bb7c2 | 53 | ($heavy = (/\W/ or $args and not exists $export_cache->{$_} |
fa1bb02f NC |
54 | or @$fail and $_ eq $fail->[0])) and last |
55 | foreach (@_); | |
56 | } else { | |
57 | ($heavy = /\W/) and last | |
732bb7c2 | 58 | foreach (@_); |
4af1b167 | 59 | } |
732bb7c2 | 60 | return export $pkg, $callpkg, ($args ? @_ : ()) if $heavy; |
4af1b167 | 61 | local $SIG{__WARN__} = |
bb2cbcd1 | 62 | sub {require Carp; &Carp::carp}; |
732bb7c2 NC |
63 | # shortcut for the common case of no type character |
64 | *{"$callpkg\::$_"} = \&{"$pkg\::$_"} foreach @_; | |
e50aee73 AD |
65 | } |
66 | ||
b75c8c73 MS |
67 | # Default methods |
68 | ||
2b5b2650 | 69 | sub export_fail { |
b75c8c73 MS |
70 | my $self = shift; |
71 | @_; | |
2b5b2650 | 72 | } |
73 | ||
0e57b4e8 IZ |
74 | # Unfortunately, caller(1)[3] "does not work" if the caller is aliased as |
75 | # *name = \&foo. Thus the need to create a lot of identical subroutines | |
76 | # Otherwise we could have aliased them to export(). | |
b75c8c73 | 77 | |
0e57b4e8 IZ |
78 | sub export_to_level { |
79 | goto &{as_heavy()}; | |
80 | } | |
81 | ||
82 | sub export_tags { | |
83 | goto &{as_heavy()}; | |
b75c8c73 MS |
84 | } |
85 | ||
0e57b4e8 IZ |
86 | sub export_ok_tags { |
87 | goto &{as_heavy()}; | |
88 | } | |
89 | ||
90 | sub require_version { | |
91 | goto &{as_heavy()}; | |
92 | } | |
b75c8c73 | 93 | |
2b5b2650 | 94 | 1; |
732bb7c2 | 95 | __END__ |
b75c8c73 | 96 | |
2b5b2650 | 97 | =head1 NAME |
98 | ||
99 | Exporter - Implements default import method for modules | |
100 | ||
101 | =head1 SYNOPSIS | |
102 | ||
3e927c50 | 103 | In module F<YourModule.pm>: |
2b5b2650 | 104 | |
65503211 | 105 | package YourModule; |
2b5b2650 | 106 | require Exporter; |
107 | @ISA = qw(Exporter); | |
65503211 | 108 | @EXPORT_OK = qw(munge frobnicate); # symbols to export on request |
2b5b2650 | 109 | |
fe43f860 FD |
110 | or |
111 | ||
112 | package YourModule; | |
113 | use Exporter 'import'; # gives you Exporter's import() method directly | |
114 | @EXPORT_OK = qw(munge frobnicate); # symbols to export on request | |
115 | ||
3e927c50 | 116 | In other files which wish to use C<YourModule>: |
2b5b2650 | 117 | |
3e927c50 | 118 | use YourModule qw(frobnicate); # import listed symbols |
65503211 | 119 | frobnicate ($left, $right) # calls YourModule::frobnicate |
2b5b2650 | 120 | |
47f97feb AF |
121 | Take a look at L</Good Practices> for some variants |
122 | you will like to use in modern Perl code. | |
123 | ||
2b5b2650 | 124 | =head1 DESCRIPTION |
125 | ||
65503211 NC |
126 | The Exporter module implements an C<import> method which allows a module |
127 | to export functions and variables to its users' namespaces. Many modules | |
128 | use Exporter rather than implementing their own C<import> method because | |
129 | Exporter provides a highly flexible interface, with an implementation optimised | |
130 | for the common case. | |
2b5b2650 | 131 | |
132 | Perl automatically calls the C<import> method when processing a | |
133 | C<use> statement for a module. Modules and C<use> are documented | |
134 | in L<perlfunc> and L<perlmod>. Understanding the concept of | |
135 | modules and how the C<use> statement operates is important to | |
136 | understanding the Exporter. | |
137 | ||
4fddf32b GS |
138 | =head2 How to Export |
139 | ||
140 | The arrays C<@EXPORT> and C<@EXPORT_OK> in a module hold lists of | |
141 | symbols that are going to be exported into the users name space by | |
142 | default, or which they can request to be exported, respectively. The | |
143 | symbols can represent functions, scalars, arrays, hashes, or typeglobs. | |
144 | The symbols must be given by full name with the exception that the | |
145 | ampersand in front of a function is optional, e.g. | |
146 | ||
147 | @EXPORT = qw(afunc $scalar @array); # afunc is a function | |
148 | @EXPORT_OK = qw(&bfunc %hash *typeglob); # explicit prefix on &bfunc | |
149 | ||
65503211 NC |
150 | If you are only exporting function names it is recommended to omit the |
151 | ampersand, as the implementation is faster this way. | |
152 | ||
2b5b2650 | 153 | =head2 Selecting What To Export |
154 | ||
155 | Do B<not> export method names! | |
156 | ||
157 | Do B<not> export anything else by default without a good reason! | |
158 | ||
159 | Exports pollute the namespace of the module user. If you must export | |
3e927c50 | 160 | try to use C<@EXPORT_OK> in preference to C<@EXPORT> and avoid short or |
2b5b2650 | 161 | common symbol names to reduce the risk of name clashes. |
162 | ||
163 | Generally anything not exported is still accessible from outside the | |
3e927c50 | 164 | module using the C<YourModule::item_name> (or C<< $blessed_ref->method >>) |
2b5b2650 | 165 | syntax. By convention you can use a leading underscore on names to |
166 | informally indicate that they are 'internal' and not for public use. | |
167 | ||
168 | (It is actually possible to get private functions by saying: | |
169 | ||
170 | my $subref = sub { ... }; | |
e60ce172 BT |
171 | $subref->(@args); # Call it as a function |
172 | $obj->$subref(@args); # Use it as a method | |
2b5b2650 | 173 | |
e60ce172 BT |
174 | However if you use them for methods it is up to you to figure out |
175 | how to make inheritance work.) | |
2b5b2650 | 176 | |
177 | As a general rule, if the module is trying to be object oriented | |
178 | then export nothing. If it's just a collection of functions then | |
3e927c50 | 179 | C<@EXPORT_OK> anything but use C<@EXPORT> with caution. For function and |
65503211 NC |
180 | method names use barewords in preference to names prefixed with |
181 | ampersands for the export lists. | |
2b5b2650 | 182 | |
183 | Other module design guidelines can be found in L<perlmod>. | |
184 | ||
65503211 NC |
185 | =head2 How to Import |
186 | ||
187 | In other files which wish to use your module there are three basic ways for | |
188 | them to load your module and import its symbols: | |
189 | ||
190 | =over 4 | |
191 | ||
3e927c50 | 192 | =item C<use YourModule;> |
65503211 | 193 | |
3e927c50 | 194 | This imports all the symbols from YourModule's C<@EXPORT> into the namespace |
65503211 NC |
195 | of the C<use> statement. |
196 | ||
3e927c50 | 197 | =item C<use YourModule ();> |
65503211 NC |
198 | |
199 | This causes perl to load your module but does not import any symbols. | |
200 | ||
3e927c50 | 201 | =item C<use YourModule qw(...);> |
65503211 NC |
202 | |
203 | This imports only the symbols listed by the caller into their namespace. | |
3e927c50 | 204 | All listed symbols must be in your C<@EXPORT> or C<@EXPORT_OK>, else an error |
65503211 NC |
205 | occurs. The advanced export features of Exporter are accessed like this, |
206 | but with list entries that are syntactically distinct from symbol names. | |
207 | ||
208 | =back | |
209 | ||
210 | Unless you want to use its advanced features, this is probably all you | |
211 | need to know to use Exporter. | |
212 | ||
213 | =head1 Advanced features | |
214 | ||
2b5b2650 | 215 | =head2 Specialised Import Lists |
216 | ||
a29b0897 MB |
217 | If any of the entries in an import list begins with !, : or / then |
218 | the list is treated as a series of specifications which either add to | |
219 | or delete from the list of names to import. They are processed left to | |
2b5b2650 | 220 | right. Specifications are in the form: |
221 | ||
222 | [!]name This name only | |
223 | [!]:DEFAULT All names in @EXPORT | |
224 | [!]:tag All names in $EXPORT_TAGS{tag} anonymous list | |
225 | [!]/pattern/ All names in @EXPORT and @EXPORT_OK which match | |
226 | ||
227 | A leading ! indicates that matching names should be deleted from the | |
228 | list of names to import. If the first specification is a deletion it | |
229 | is treated as though preceded by :DEFAULT. If you just want to import | |
230 | extra names in addition to the default set you will still need to | |
231 | include :DEFAULT explicitly. | |
232 | ||
3e927c50 | 233 | e.g., F<Module.pm> defines: |
2b5b2650 | 234 | |
235 | @EXPORT = qw(A1 A2 A3 A4 A5); | |
236 | @EXPORT_OK = qw(B1 B2 B3 B4 B5); | |
237 | %EXPORT_TAGS = (T1 => [qw(A1 A2 B1 B2)], T2 => [qw(A1 A2 B3 B4)]); | |
238 | ||
239 | Note that you cannot use tags in @EXPORT or @EXPORT_OK. | |
240 | Names in EXPORT_TAGS must also appear in @EXPORT or @EXPORT_OK. | |
241 | ||
242 | An application using Module can say something like: | |
243 | ||
244 | use Module qw(:DEFAULT :T2 !B3 A3); | |
245 | ||
246 | Other examples include: | |
247 | ||
248 | use Socket qw(!/^[AP]F_/ !SOMAXCONN !SOL_SOCKET); | |
249 | use POSIX qw(:errno_h :termios_h !TCSADRAIN !/^EXIT/); | |
250 | ||
251 | Remember that most patterns (using //) will need to be anchored | |
252 | with a leading ^, e.g., C</^EXIT/> rather than C</EXIT/>. | |
253 | ||
254 | You can say C<BEGIN { $Exporter::Verbose=1 }> to see how the | |
255 | specifications are being processed and what is actually being imported | |
256 | into modules. | |
257 | ||
65503211 | 258 | =head2 Exporting without using Exporter's import method |
84902520 TB |
259 | |
260 | Exporter has a special method, 'export_to_level' which is used in situations | |
65503211 | 261 | where you can't directly call Exporter's import method. The export_to_level |
84902520 TB |
262 | method looks like: |
263 | ||
cec46e5a | 264 | MyPackage->export_to_level($where_to_export, $package, @what_to_export); |
84902520 | 265 | |
3e927c50 AF |
266 | where C<$where_to_export> is an integer telling how far up the calling stack |
267 | to export your symbols, and C<@what_to_export> is an array telling what | |
268 | symbols *to* export (usually this is C<@_>). The C<$package> argument is | |
ba5725f8 | 269 | currently unused. |
84902520 TB |
270 | |
271 | For example, suppose that you have a module, A, which already has an | |
272 | import function: | |
273 | ||
cec46e5a | 274 | package A; |
84902520 | 275 | |
cec46e5a RGS |
276 | @ISA = qw(Exporter); |
277 | @EXPORT_OK = qw ($b); | |
84902520 | 278 | |
cec46e5a RGS |
279 | sub import |
280 | { | |
281 | $A::b = 1; # not a very useful import method | |
282 | } | |
84902520 | 283 | |
3e927c50 | 284 | and you want to Export symbol C<$A::b> back to the module that called |
84902520 TB |
285 | package A. Since Exporter relies on the import method to work, via |
286 | inheritance, as it stands Exporter::import() will never get called. | |
287 | Instead, say the following: | |
288 | ||
cec46e5a RGS |
289 | package A; |
290 | @ISA = qw(Exporter); | |
291 | @EXPORT_OK = qw ($b); | |
84902520 | 292 | |
cec46e5a RGS |
293 | sub import |
294 | { | |
295 | $A::b = 1; | |
296 | A->export_to_level(1, @_); | |
297 | } | |
84902520 TB |
298 | |
299 | This will export the symbols one level 'above' the current package - ie: to | |
300 | the program or module that used package A. | |
301 | ||
fe43f860 | 302 | Note: Be careful not to modify C<@_> at all before you call export_to_level |
84902520 TB |
303 | - or people using your package will get very unexplained results! |
304 | ||
fe43f860 FD |
305 | =head2 Exporting without inheriting from Exporter |
306 | ||
3e927c50 | 307 | By including Exporter in your C<@ISA> you inherit an Exporter's import() method |
fe43f860 FD |
308 | but you also inherit several other helper methods which you probably don't |
309 | want. To avoid this you can do | |
310 | ||
311 | package YourModule; | |
312 | use Exporter qw( import ); | |
313 | ||
314 | which will export Exporter's own import() method into YourModule. | |
315 | Everything will work as before but you won't need to include Exporter in | |
3e927c50 | 316 | C<@YourModule::ISA>. |
84902520 | 317 | |
47f97feb AF |
318 | Note: This feature was introduced in version 5.57 |
319 | of Exporter, released with perl 5.8.3. | |
320 | ||
2b5b2650 | 321 | =head2 Module Version Checking |
322 | ||
323 | The Exporter module will convert an attempt to import a number from a | |
3e927c50 | 324 | module into a call to C<< $module_name->require_version($value) >>. This can |
2b5b2650 | 325 | be used to validate that the version of the module being used is |
326 | greater than or equal to the required version. | |
327 | ||
3e927c50 AF |
328 | The Exporter module supplies a default C<require_version> method which |
329 | checks the value of C<$VERSION> in the exporting module. | |
2b5b2650 | 330 | |
3e927c50 | 331 | Since the default C<require_version> method treats the C<$VERSION> number as |
d5e40bcc | 332 | a simple numeric value it will regard version 1.10 as lower than |
333 | 1.9. For this reason it is strongly recommended that you use numbers | |
334 | with at least two decimal places, e.g., 1.09. | |
2b5b2650 | 335 | |
336 | =head2 Managing Unknown Symbols | |
337 | ||
338 | In some situations you may want to prevent certain symbols from being | |
339 | exported. Typically this applies to extensions which have functions | |
340 | or constants that may not exist on some systems. | |
341 | ||
342 | The names of any symbols that cannot be exported should be listed | |
343 | in the C<@EXPORT_FAIL> array. | |
344 | ||
7a2e2cd6 | 345 | If a module attempts to import any of these symbols the Exporter |
2b5b2650 | 346 | will give the module an opportunity to handle the situation before |
347 | generating an error. The Exporter will call an export_fail method | |
348 | with a list of the failed symbols: | |
349 | ||
350 | @failed_symbols = $module_name->export_fail(@failed_symbols); | |
351 | ||
3e927c50 | 352 | If the C<export_fail> method returns an empty list then no error is |
2b5b2650 | 353 | recorded and all the requested symbols are exported. If the returned |
354 | list is not empty then an error is generated for each symbol and the | |
3e927c50 | 355 | export fails. The Exporter provides a default C<export_fail> method which |
2b5b2650 | 356 | simply returns the list unchanged. |
357 | ||
3e927c50 | 358 | Uses for the C<export_fail> method include giving better error messages |
2b5b2650 | 359 | for some symbols and performing lazy architectural checks (put more |
3e927c50 | 360 | symbols into C<@EXPORT_FAIL> by default and then take them out if someone |
2b5b2650 | 361 | actually tries to use them and an expensive check shows that they are |
362 | usable on that platform). | |
363 | ||
364 | =head2 Tag Handling Utility Functions | |
365 | ||
3e927c50 AF |
366 | Since the symbols listed within C<%EXPORT_TAGS> must also appear in either |
367 | C<@EXPORT> or C<@EXPORT_OK>, two utility functions are provided which allow | |
368 | you to easily add tagged sets of symbols to C<@EXPORT> or C<@EXPORT_OK>: | |
2b5b2650 | 369 | |
370 | %EXPORT_TAGS = (foo => [qw(aa bb cc)], bar => [qw(aa cc dd)]); | |
371 | ||
372 | Exporter::export_tags('foo'); # add aa, bb and cc to @EXPORT | |
373 | Exporter::export_ok_tags('bar'); # add aa, cc and dd to @EXPORT_OK | |
374 | ||
3e927c50 | 375 | Any names which are not tags are added to C<@EXPORT> or C<@EXPORT_OK> |
d5e40bcc | 376 | unchanged but will trigger a warning (with C<-w>) to avoid misspelt tags |
3e927c50 | 377 | names being silently added to C<@EXPORT> or C<@EXPORT_OK>. Future versions |
2b5b2650 | 378 | may make this a fatal error. |
379 | ||
d584343b MG |
380 | =head2 Generating combined tags |
381 | ||
3e927c50 | 382 | If several symbol categories exist in C<%EXPORT_TAGS>, it's usually |
d584343b MG |
383 | useful to create the utility ":all" to simplify "use" statements. |
384 | ||
385 | The simplest way to do this is: | |
386 | ||
387 | %EXPORT_TAGS = (foo => [qw(aa bb cc)], bar => [qw(aa cc dd)]); | |
388 | ||
389 | # add all the other ":class" tags to the ":all" class, | |
390 | # deleting duplicates | |
391 | { | |
392 | my %seen; | |
393 | ||
394 | push @{$EXPORT_TAGS{all}}, | |
395 | grep {!$seen{$_}++} @{$EXPORT_TAGS{$_}} foreach keys %EXPORT_TAGS; | |
396 | } | |
397 | ||
3e927c50 | 398 | F<CGI.pm> creates an ":all" tag which contains some (but not really |
d584343b MG |
399 | all) of its categories. That could be done with one small |
400 | change: | |
401 | ||
402 | # add some of the other ":class" tags to the ":all" class, | |
403 | # deleting duplicates | |
404 | { | |
405 | my %seen; | |
406 | ||
407 | push @{$EXPORT_TAGS{all}}, | |
408 | grep {!$seen{$_}++} @{$EXPORT_TAGS{$_}} | |
409 | foreach qw/html2 html3 netscape form cgi internal/; | |
410 | } | |
411 | ||
3e927c50 | 412 | Note that the tag names in C<%EXPORT_TAGS> don't have the leading ':'. |
d584343b | 413 | |
5fea0f12 BS |
414 | =head2 C<AUTOLOAD>ed Constants |
415 | ||
8b4c0206 T |
416 | Many modules make use of C<AUTOLOAD>ing for constant subroutines to |
417 | avoid having to compile and waste memory on rarely used values (see | |
418 | L<perlsub> for details on constant subroutines). Calls to such | |
419 | constant subroutines are not optimized away at compile time because | |
420 | they can't be checked at compile time for constancy. | |
421 | ||
422 | Even if a prototype is available at compile time, the body of the | |
423 | subroutine is not (it hasn't been C<AUTOLOAD>ed yet). perl needs to | |
424 | examine both the C<()> prototype and the body of a subroutine at | |
425 | compile time to detect that it can safely replace calls to that | |
426 | subroutine with the constant value. | |
5fea0f12 BS |
427 | |
428 | A workaround for this is to call the constants once in a C<BEGIN> block: | |
429 | ||
430 | package My ; | |
431 | ||
432 | use Socket ; | |
433 | ||
434 | foo( SO_LINGER ); ## SO_LINGER NOT optimized away; called at runtime | |
435 | BEGIN { SO_LINGER } | |
436 | foo( SO_LINGER ); ## SO_LINGER optimized away at compile time. | |
437 | ||
8b4c0206 T |
438 | This forces the C<AUTOLOAD> for C<SO_LINGER> to take place before |
439 | SO_LINGER is encountered later in C<My> package. | |
5fea0f12 | 440 | |
8b4c0206 T |
441 | If you are writing a package that C<AUTOLOAD>s, consider forcing |
442 | an C<AUTOLOAD> for any constants explicitly imported by other packages | |
443 | or which are usually used when your package is C<use>d. | |
5fea0f12 | 444 | |
47f97feb AF |
445 | =head1 Good Practices |
446 | ||
447 | =head2 Declaring C<@EXPORT_OK> and Friends | |
448 | ||
449 | When using C<Exporter> with the standard C<strict> and C<warnings> | |
450 | pragmas, the C<our> keyword is needed to declare the package | |
451 | variables C<@EXPORT_OK>, C<@EXPORT>, C<@ISA>, etc. | |
452 | ||
453 | our @ISA = qw(Exporter); | |
454 | our @EXPORT_OK = qw(munge frobnicate); | |
455 | ||
456 | If backward compatibility for Perls under 5.6 is important, | |
457 | one must write instead a C<use vars> statement. | |
458 | ||
459 | use vars qw(@ISA @EXPORT_OK); | |
460 | @ISA = qw(Exporter); | |
461 | @EXPORT_OK = qw(munge frobnicate); | |
462 | ||
463 | =head2 Playing Safe | |
464 | ||
465 | There are some caveats with the use of runtime statements | |
466 | like C<require Exporter> and the assignment to package | |
467 | variables, which can very subtle for the unaware programmer. | |
468 | This may happen for instance with mutually recursive | |
469 | modules, which are affected by the time the relevant | |
470 | constructions are executed. | |
471 | ||
472 | The ideal (but a bit ugly) way to never have to think | |
473 | about that is to use C<BEGIN> blocks. So the first part | |
474 | of the L</SYNOPSIS> code could be rewritten as: | |
475 | ||
476 | package YourModule; | |
477 | ||
478 | use strict; | |
479 | use warnings; | |
480 | ||
481 | our (@ISA, @EXPORT_OK); | |
482 | BEGIN { | |
483 | require Exporter; | |
484 | @ISA = qw(Exporter); | |
485 | @EXPORT_OK = qw(munge frobnicate); # symbols to export on request | |
486 | } | |
487 | ||
488 | The C<BEGIN> will assure that the loading of F<Exporter.pm> | |
489 | and the assignments to C<@ISA> and C<@EXPORT_OK> happen | |
490 | immediately, leaving no room for something to get awry | |
491 | or just plain wrong. | |
492 | ||
493 | With respect to loading C<Exporter> and inheriting, there | |
494 | are alternatives with the use of modules like C<base> and C<parent>. | |
495 | ||
496 | use base qw( Exporter ); | |
497 | # or | |
498 | use parent qw( Exporter ); | |
499 | ||
500 | Any of these statements are nice replacements for | |
501 | C<BEGIN { require Exporter; @ISA = qw(Exporter); }> | |
502 | with the same compile-time effect. The basic difference | |
503 | is that C<base> code interacts with declared C<fields> | |
504 | while C<parent> is a streamlined version of the older | |
505 | C<base> code to just establish the IS-A relationship. | |
506 | ||
507 | For more details, see the documentation and code of | |
508 | L<base> and L<parent>. | |
509 | ||
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510 | Another thorough remedy to that runtime vs. |
511 | compile-time trap is to use L<Exporter::Easy>, | |
512 | which is a wrapper of Exporter that allows all | |
513 | boilerplate code at a single gulp in the | |
514 | use statement. | |
515 | ||
516 | use Exporter::Easy ( | |
517 | OK => [ qw(munge frobnicate) ], | |
518 | ); | |
519 | # @ISA setup is automatic | |
520 | # all assignments happen at compile time | |
521 | ||
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522 | =head2 What not to Export |
523 | ||
af30f7a9 | 524 | You have been warned already in L</Selecting What To Export> |
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525 | to not export: |
526 | ||
527 | =over 4 | |
528 | ||
529 | =item * | |
530 | ||
44ddc072 | 531 | method names (because you don't need to |
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532 | and that's likely to not do what you want), |
533 | ||
534 | =item * | |
535 | ||
536 | anything by default (because you don't want to surprise your users... | |
537 | badly) | |
538 | ||
539 | =item * | |
540 | ||
541 | anything you don't need to (because less is more) | |
542 | ||
543 | =back | |
544 | ||
545 | There's one more item to add to this list. Do B<not> | |
546 | export variable names. Just because C<Exporter> lets you | |
547 | do that, it does not mean you should. | |
548 | ||
549 | @EXPORT_OK = qw( $svar @avar %hvar ); # DON'T! | |
550 | ||
551 | Exporting variables is not a good idea. They can | |
552 | change under the hood, provoking horrible | |
553 | effects at-a-distance, that are too hard to track | |
554 | and to fix. Trust me: they are not worth it. | |
555 | ||
556 | To provide the capability to set/get class-wide | |
557 | settings, it is best instead to provide accessors | |
558 | as subroutines or class methods instead. | |
559 | ||
560 | =head1 SEE ALSO | |
561 | ||
562 | C<Exporter> is definitely not the only module with | |
563 | symbol exporter capabilities. At CPAN, you may find | |
564 | a bunch of them. Some are lighter. Some | |
565 | provide improved APIs and features. Peek the one | |
566 | that fits your needs. The following is | |
567 | a sample list of such modules. | |
568 | ||
569 | Exporter::Easy | |
570 | Exporter::Lite | |
571 | Exporter::Renaming | |
572 | Exporter::Tidy | |
573 | Sub::Exporter / Sub::Installer | |
574 | Perl6::Export / Perl6::Export::Attrs | |
575 | ||
576 | =head1 LICENSE | |
577 | ||
578 | This library is free software. You can redistribute it | |
579 | and/or modify it under the same terms as Perl itself. | |
580 | ||
2b5b2650 | 581 | =cut |
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582 | |
583 | ||
584 |