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; | |
23b51b60 | 12 | our $VERSION = '5.67'; |
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 | 46 | |
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 $export_cache->{$_} |
2d7e78b1 | 56 | or $fail and @$fail and $_ eq $fail->[0])) and last |
fa1bb02f NC |
57 | foreach (@_); |
58 | } else { | |
59 | ($heavy = /\W/) and last | |
732bb7c2 | 60 | foreach (@_); |
4af1b167 | 61 | } |
732bb7c2 | 62 | return export $pkg, $callpkg, ($args ? @_ : ()) if $heavy; |
4af1b167 | 63 | local $SIG{__WARN__} = |
9b86bb5c | 64 | sub {require Carp; &Carp::carp} if not $SIG{__WARN__}; |
732bb7c2 NC |
65 | # shortcut for the common case of no type character |
66 | *{"$callpkg\::$_"} = \&{"$pkg\::$_"} foreach @_; | |
e50aee73 AD |
67 | } |
68 | ||
b75c8c73 MS |
69 | # Default methods |
70 | ||
2b5b2650 | 71 | sub export_fail { |
b75c8c73 MS |
72 | my $self = shift; |
73 | @_; | |
2b5b2650 | 74 | } |
75 | ||
0e57b4e8 IZ |
76 | # Unfortunately, caller(1)[3] "does not work" if the caller is aliased as |
77 | # *name = \&foo. Thus the need to create a lot of identical subroutines | |
78 | # Otherwise we could have aliased them to export(). | |
b75c8c73 | 79 | |
0e57b4e8 IZ |
80 | sub export_to_level { |
81 | goto &{as_heavy()}; | |
82 | } | |
83 | ||
84 | sub export_tags { | |
85 | goto &{as_heavy()}; | |
b75c8c73 MS |
86 | } |
87 | ||
0e57b4e8 IZ |
88 | sub export_ok_tags { |
89 | goto &{as_heavy()}; | |
90 | } | |
91 | ||
92 | sub require_version { | |
93 | goto &{as_heavy()}; | |
94 | } | |
b75c8c73 | 95 | |
2b5b2650 | 96 | 1; |
732bb7c2 | 97 | __END__ |
b75c8c73 | 98 | |
2b5b2650 | 99 | =head1 NAME |
100 | ||
101 | Exporter - Implements default import method for modules | |
102 | ||
103 | =head1 SYNOPSIS | |
104 | ||
3e927c50 | 105 | In module F<YourModule.pm>: |
2b5b2650 | 106 | |
65503211 | 107 | package YourModule; |
2b5b2650 | 108 | require Exporter; |
109 | @ISA = qw(Exporter); | |
65503211 | 110 | @EXPORT_OK = qw(munge frobnicate); # symbols to export on request |
2b5b2650 | 111 | |
fe43f860 FD |
112 | or |
113 | ||
114 | package YourModule; | |
115 | use Exporter 'import'; # gives you Exporter's import() method directly | |
116 | @EXPORT_OK = qw(munge frobnicate); # symbols to export on request | |
117 | ||
3e927c50 | 118 | In other files which wish to use C<YourModule>: |
2b5b2650 | 119 | |
3e927c50 | 120 | use YourModule qw(frobnicate); # import listed symbols |
65503211 | 121 | frobnicate ($left, $right) # calls YourModule::frobnicate |
2b5b2650 | 122 | |
47f97feb AF |
123 | Take a look at L</Good Practices> for some variants |
124 | you will like to use in modern Perl code. | |
125 | ||
2b5b2650 | 126 | =head1 DESCRIPTION |
127 | ||
65503211 | 128 | The Exporter module implements an C<import> method which allows a module |
5b2cfa76 | 129 | to export functions and variables to its users' namespaces. Many modules |
65503211 NC |
130 | use Exporter rather than implementing their own C<import> method because |
131 | Exporter provides a highly flexible interface, with an implementation optimised | |
132 | for the common case. | |
2b5b2650 | 133 | |
134 | Perl automatically calls the C<import> method when processing a | |
5b2cfa76 FC |
135 | C<use> statement for a module. Modules and C<use> are documented |
136 | in L<perlfunc> and L<perlmod>. Understanding the concept of | |
2b5b2650 | 137 | modules and how the C<use> statement operates is important to |
138 | understanding the Exporter. | |
139 | ||
4fddf32b GS |
140 | =head2 How to Export |
141 | ||
142 | The arrays C<@EXPORT> and C<@EXPORT_OK> in a module hold lists of | |
143 | symbols that are going to be exported into the users name space by | |
144 | default, or which they can request to be exported, respectively. The | |
145 | symbols can represent functions, scalars, arrays, hashes, or typeglobs. | |
146 | The symbols must be given by full name with the exception that the | |
147 | ampersand in front of a function is optional, e.g. | |
148 | ||
149 | @EXPORT = qw(afunc $scalar @array); # afunc is a function | |
150 | @EXPORT_OK = qw(&bfunc %hash *typeglob); # explicit prefix on &bfunc | |
151 | ||
65503211 NC |
152 | If you are only exporting function names it is recommended to omit the |
153 | ampersand, as the implementation is faster this way. | |
154 | ||
ec6b919e | 155 | =head2 Selecting What to Export |
2b5b2650 | 156 | |
157 | Do B<not> export method names! | |
158 | ||
159 | Do B<not> export anything else by default without a good reason! | |
160 | ||
161 | Exports pollute the namespace of the module user. If you must export | |
3e927c50 | 162 | try to use C<@EXPORT_OK> in preference to C<@EXPORT> and avoid short or |
2b5b2650 | 163 | common symbol names to reduce the risk of name clashes. |
164 | ||
165 | Generally anything not exported is still accessible from outside the | |
3e927c50 | 166 | module using the C<YourModule::item_name> (or C<< $blessed_ref->method >>) |
2b5b2650 | 167 | syntax. By convention you can use a leading underscore on names to |
168 | informally indicate that they are 'internal' and not for public use. | |
169 | ||
170 | (It is actually possible to get private functions by saying: | |
171 | ||
172 | my $subref = sub { ... }; | |
e60ce172 BT |
173 | $subref->(@args); # Call it as a function |
174 | $obj->$subref(@args); # Use it as a method | |
2b5b2650 | 175 | |
e60ce172 BT |
176 | However if you use them for methods it is up to you to figure out |
177 | how to make inheritance work.) | |
2b5b2650 | 178 | |
179 | As a general rule, if the module is trying to be object oriented | |
5b2cfa76 FC |
180 | then export nothing. If it's just a collection of functions then |
181 | C<@EXPORT_OK> anything but use C<@EXPORT> with caution. For function and | |
65503211 NC |
182 | method names use barewords in preference to names prefixed with |
183 | ampersands for the export lists. | |
2b5b2650 | 184 | |
185 | Other module design guidelines can be found in L<perlmod>. | |
186 | ||
65503211 NC |
187 | =head2 How to Import |
188 | ||
189 | In other files which wish to use your module there are three basic ways for | |
190 | them to load your module and import its symbols: | |
191 | ||
192 | =over 4 | |
193 | ||
3e927c50 | 194 | =item C<use YourModule;> |
65503211 | 195 | |
3e927c50 | 196 | This imports all the symbols from YourModule's C<@EXPORT> into the namespace |
65503211 NC |
197 | of the C<use> statement. |
198 | ||
3e927c50 | 199 | =item C<use YourModule ();> |
65503211 NC |
200 | |
201 | This causes perl to load your module but does not import any symbols. | |
202 | ||
3e927c50 | 203 | =item C<use YourModule qw(...);> |
65503211 NC |
204 | |
205 | This imports only the symbols listed by the caller into their namespace. | |
3e927c50 | 206 | All listed symbols must be in your C<@EXPORT> or C<@EXPORT_OK>, else an error |
5b2cfa76 | 207 | occurs. The advanced export features of Exporter are accessed like this, |
65503211 NC |
208 | but with list entries that are syntactically distinct from symbol names. |
209 | ||
210 | =back | |
211 | ||
212 | Unless you want to use its advanced features, this is probably all you | |
213 | need to know to use Exporter. | |
214 | ||
ec6b919e | 215 | =head1 Advanced Features |
65503211 | 216 | |
2b5b2650 | 217 | =head2 Specialised Import Lists |
218 | ||
a29b0897 MB |
219 | If any of the entries in an import list begins with !, : or / then |
220 | the list is treated as a series of specifications which either add to | |
5b2cfa76 | 221 | or delete from the list of names to import. They are processed left to |
2b5b2650 | 222 | right. Specifications are in the form: |
223 | ||
224 | [!]name This name only | |
225 | [!]:DEFAULT All names in @EXPORT | |
226 | [!]:tag All names in $EXPORT_TAGS{tag} anonymous list | |
227 | [!]/pattern/ All names in @EXPORT and @EXPORT_OK which match | |
228 | ||
229 | A leading ! indicates that matching names should be deleted from the | |
230 | list of names to import. If the first specification is a deletion it | |
5b2cfa76 | 231 | is treated as though preceded by :DEFAULT. If you just want to import |
2b5b2650 | 232 | extra names in addition to the default set you will still need to |
233 | include :DEFAULT explicitly. | |
234 | ||
3e927c50 | 235 | e.g., F<Module.pm> defines: |
2b5b2650 | 236 | |
237 | @EXPORT = qw(A1 A2 A3 A4 A5); | |
238 | @EXPORT_OK = qw(B1 B2 B3 B4 B5); | |
239 | %EXPORT_TAGS = (T1 => [qw(A1 A2 B1 B2)], T2 => [qw(A1 A2 B3 B4)]); | |
240 | ||
9dcb3660 C |
241 | Note that you cannot use tags in @EXPORT or @EXPORT_OK. |
242 | ||
243 | Names in EXPORT_TAGS must also appear in @EXPORT or @EXPORT_OK. | |
2b5b2650 | 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 | ||
ec6b919e | 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 | |
5b2cfa76 FC |
264 | where you can't directly call Exporter's |
265 | import method. The export_to_level | |
84902520 TB |
266 | method looks like: |
267 | ||
e8c1f67a FC |
268 | MyPackage->export_to_level( |
269 | $where_to_export, $package, @what_to_export | |
270 | ); | |
84902520 | 271 | |
3e927c50 AF |
272 | where C<$where_to_export> is an integer telling how far up the calling stack |
273 | to export your symbols, and C<@what_to_export> is an array telling what | |
274 | symbols *to* export (usually this is C<@_>). The C<$package> argument is | |
ba5725f8 | 275 | currently unused. |
84902520 TB |
276 | |
277 | For example, suppose that you have a module, A, which already has an | |
278 | import function: | |
279 | ||
cec46e5a | 280 | package A; |
84902520 | 281 | |
cec46e5a RGS |
282 | @ISA = qw(Exporter); |
283 | @EXPORT_OK = qw ($b); | |
84902520 | 284 | |
cec46e5a RGS |
285 | sub import |
286 | { | |
287 | $A::b = 1; # not a very useful import method | |
288 | } | |
84902520 | 289 | |
3e927c50 | 290 | and you want to Export symbol C<$A::b> back to the module that called |
5b2cfa76 | 291 | package A. Since Exporter relies on the import method to work, via |
84902520 TB |
292 | inheritance, as it stands Exporter::import() will never get called. |
293 | Instead, say the following: | |
294 | ||
cec46e5a RGS |
295 | package A; |
296 | @ISA = qw(Exporter); | |
297 | @EXPORT_OK = qw ($b); | |
84902520 | 298 | |
cec46e5a RGS |
299 | sub import |
300 | { | |
301 | $A::b = 1; | |
302 | A->export_to_level(1, @_); | |
303 | } | |
84902520 TB |
304 | |
305 | This will export the symbols one level 'above' the current package - ie: to | |
306 | the program or module that used package A. | |
307 | ||
fe43f860 | 308 | Note: Be careful not to modify C<@_> at all before you call export_to_level |
84902520 TB |
309 | - or people using your package will get very unexplained results! |
310 | ||
ec6b919e | 311 | =head2 Exporting Without Inheriting from Exporter |
fe43f860 | 312 | |
3e927c50 | 313 | By including Exporter in your C<@ISA> you inherit an Exporter's import() method |
fe43f860 | 314 | but you also inherit several other helper methods which you probably don't |
5b2cfa76 | 315 | want. To avoid this you can do |
fe43f860 FD |
316 | |
317 | package YourModule; | |
318 | use Exporter qw( import ); | |
319 | ||
320 | which will export Exporter's own import() method into YourModule. | |
321 | Everything will work as before but you won't need to include Exporter in | |
3e927c50 | 322 | C<@YourModule::ISA>. |
84902520 | 323 | |
47f97feb AF |
324 | Note: This feature was introduced in version 5.57 |
325 | of Exporter, released with perl 5.8.3. | |
326 | ||
2b5b2650 | 327 | =head2 Module Version Checking |
328 | ||
329 | The Exporter module will convert an attempt to import a number from a | |
5b2cfa76 | 330 | module into a call to C<< $module_name->VERSION($value) >>. This can |
2b5b2650 | 331 | be used to validate that the version of the module being used is |
332 | greater than or equal to the required version. | |
333 | ||
53592368 FC |
334 | For historical reasons, Exporter supplies a C<require_version> method that |
335 | simply delegates to C<VERSION>. Originally, before C<UNIVERSAL::VERSION> | |
336 | existed, Exporter would call C<require_version>. | |
337 | ||
1c0201fc | 338 | Since the C<UNIVERSAL::VERSION> method treats the C<$VERSION> number as |
d5e40bcc | 339 | a simple numeric value it will regard version 1.10 as lower than |
5b2cfa76 | 340 | 1.9. For this reason it is strongly recommended that you use numbers |
d5e40bcc | 341 | with at least two decimal places, e.g., 1.09. |
2b5b2650 | 342 | |
343 | =head2 Managing Unknown Symbols | |
344 | ||
345 | In some situations you may want to prevent certain symbols from being | |
5b2cfa76 | 346 | exported. Typically this applies to extensions which have functions |
2b5b2650 | 347 | or constants that may not exist on some systems. |
348 | ||
349 | The names of any symbols that cannot be exported should be listed | |
350 | in the C<@EXPORT_FAIL> array. | |
351 | ||
7a2e2cd6 | 352 | If a module attempts to import any of these symbols the Exporter |
2b5b2650 | 353 | will give the module an opportunity to handle the situation before |
5b2cfa76 | 354 | generating an error. The Exporter will call an export_fail method |
2b5b2650 | 355 | with a list of the failed symbols: |
356 | ||
357 | @failed_symbols = $module_name->export_fail(@failed_symbols); | |
358 | ||
3e927c50 | 359 | If the C<export_fail> method returns an empty list then no error is |
5b2cfa76 | 360 | recorded and all the requested symbols are exported. If the returned |
2b5b2650 | 361 | list is not empty then an error is generated for each symbol and the |
5b2cfa76 | 362 | export fails. The Exporter provides a default C<export_fail> method which |
2b5b2650 | 363 | simply returns the list unchanged. |
364 | ||
3e927c50 | 365 | Uses for the C<export_fail> method include giving better error messages |
2b5b2650 | 366 | for some symbols and performing lazy architectural checks (put more |
3e927c50 | 367 | symbols into C<@EXPORT_FAIL> by default and then take them out if someone |
2b5b2650 | 368 | actually tries to use them and an expensive check shows that they are |
369 | usable on that platform). | |
370 | ||
371 | =head2 Tag Handling Utility Functions | |
372 | ||
3e927c50 AF |
373 | Since the symbols listed within C<%EXPORT_TAGS> must also appear in either |
374 | C<@EXPORT> or C<@EXPORT_OK>, two utility functions are provided which allow | |
375 | you to easily add tagged sets of symbols to C<@EXPORT> or C<@EXPORT_OK>: | |
2b5b2650 | 376 | |
377 | %EXPORT_TAGS = (foo => [qw(aa bb cc)], bar => [qw(aa cc dd)]); | |
378 | ||
379 | Exporter::export_tags('foo'); # add aa, bb and cc to @EXPORT | |
380 | Exporter::export_ok_tags('bar'); # add aa, cc and dd to @EXPORT_OK | |
381 | ||
3e927c50 | 382 | Any names which are not tags are added to C<@EXPORT> or C<@EXPORT_OK> |
d5e40bcc | 383 | unchanged but will trigger a warning (with C<-w>) to avoid misspelt tags |
5b2cfa76 | 384 | names being silently added to C<@EXPORT> or C<@EXPORT_OK>. Future versions |
2b5b2650 | 385 | may make this a fatal error. |
386 | ||
ec6b919e | 387 | =head2 Generating Combined Tags |
d584343b | 388 | |
3e927c50 | 389 | If several symbol categories exist in C<%EXPORT_TAGS>, it's usually |
d584343b MG |
390 | useful to create the utility ":all" to simplify "use" statements. |
391 | ||
392 | The simplest way to do this is: | |
393 | ||
394 | %EXPORT_TAGS = (foo => [qw(aa bb cc)], bar => [qw(aa cc dd)]); | |
395 | ||
396 | # add all the other ":class" tags to the ":all" class, | |
397 | # deleting duplicates | |
398 | { | |
399 | my %seen; | |
400 | ||
401 | push @{$EXPORT_TAGS{all}}, | |
402 | grep {!$seen{$_}++} @{$EXPORT_TAGS{$_}} foreach keys %EXPORT_TAGS; | |
403 | } | |
404 | ||
3e927c50 | 405 | F<CGI.pm> creates an ":all" tag which contains some (but not really |
d584343b MG |
406 | all) of its categories. That could be done with one small |
407 | change: | |
408 | ||
409 | # add some of the other ":class" tags to the ":all" class, | |
410 | # deleting duplicates | |
411 | { | |
412 | my %seen; | |
413 | ||
414 | push @{$EXPORT_TAGS{all}}, | |
415 | grep {!$seen{$_}++} @{$EXPORT_TAGS{$_}} | |
416 | foreach qw/html2 html3 netscape form cgi internal/; | |
417 | } | |
418 | ||
3e927c50 | 419 | Note that the tag names in C<%EXPORT_TAGS> don't have the leading ':'. |
d584343b | 420 | |
5fea0f12 BS |
421 | =head2 C<AUTOLOAD>ed Constants |
422 | ||
8b4c0206 T |
423 | Many modules make use of C<AUTOLOAD>ing for constant subroutines to |
424 | avoid having to compile and waste memory on rarely used values (see | |
425 | L<perlsub> for details on constant subroutines). Calls to such | |
426 | constant subroutines are not optimized away at compile time because | |
427 | they can't be checked at compile time for constancy. | |
428 | ||
429 | Even if a prototype is available at compile time, the body of the | |
5b2cfa76 | 430 | subroutine is not (it hasn't been C<AUTOLOAD>ed yet). perl needs to |
8b4c0206 T |
431 | examine both the C<()> prototype and the body of a subroutine at |
432 | compile time to detect that it can safely replace calls to that | |
433 | subroutine with the constant value. | |
5fea0f12 BS |
434 | |
435 | A workaround for this is to call the constants once in a C<BEGIN> block: | |
436 | ||
437 | package My ; | |
438 | ||
439 | use Socket ; | |
440 | ||
e8c1f67a | 441 | foo( SO_LINGER ); ## SO_LINGER NOT optimized away; called at runtime |
5fea0f12 | 442 | BEGIN { SO_LINGER } |
e8c1f67a | 443 | foo( SO_LINGER ); ## SO_LINGER optimized away at compile time. |
5fea0f12 | 444 | |
8b4c0206 T |
445 | This forces the C<AUTOLOAD> for C<SO_LINGER> to take place before |
446 | SO_LINGER is encountered later in C<My> package. | |
5fea0f12 | 447 | |
8b4c0206 T |
448 | If you are writing a package that C<AUTOLOAD>s, consider forcing |
449 | an C<AUTOLOAD> for any constants explicitly imported by other packages | |
450 | or which are usually used when your package is C<use>d. | |
5fea0f12 | 451 | |
47f97feb AF |
452 | =head1 Good Practices |
453 | ||
454 | =head2 Declaring C<@EXPORT_OK> and Friends | |
455 | ||
456 | When using C<Exporter> with the standard C<strict> and C<warnings> | |
457 | pragmas, the C<our> keyword is needed to declare the package | |
458 | variables C<@EXPORT_OK>, C<@EXPORT>, C<@ISA>, etc. | |
459 | ||
460 | our @ISA = qw(Exporter); | |
461 | our @EXPORT_OK = qw(munge frobnicate); | |
462 | ||
463 | If backward compatibility for Perls under 5.6 is important, | |
464 | one must write instead a C<use vars> statement. | |
465 | ||
466 | use vars qw(@ISA @EXPORT_OK); | |
467 | @ISA = qw(Exporter); | |
468 | @EXPORT_OK = qw(munge frobnicate); | |
469 | ||
470 | =head2 Playing Safe | |
471 | ||
472 | There are some caveats with the use of runtime statements | |
473 | like C<require Exporter> and the assignment to package | |
474 | variables, which can very subtle for the unaware programmer. | |
475 | This may happen for instance with mutually recursive | |
476 | modules, which are affected by the time the relevant | |
477 | constructions are executed. | |
478 | ||
479 | The ideal (but a bit ugly) way to never have to think | |
5b2cfa76 | 480 | about that is to use C<BEGIN> blocks. So the first part |
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481 | of the L</SYNOPSIS> code could be rewritten as: |
482 | ||
483 | package YourModule; | |
484 | ||
485 | use strict; | |
486 | use warnings; | |
487 | ||
488 | our (@ISA, @EXPORT_OK); | |
489 | BEGIN { | |
490 | require Exporter; | |
491 | @ISA = qw(Exporter); | |
492 | @EXPORT_OK = qw(munge frobnicate); # symbols to export on request | |
493 | } | |
494 | ||
495 | The C<BEGIN> will assure that the loading of F<Exporter.pm> | |
496 | and the assignments to C<@ISA> and C<@EXPORT_OK> happen | |
497 | immediately, leaving no room for something to get awry | |
498 | or just plain wrong. | |
499 | ||
500 | With respect to loading C<Exporter> and inheriting, there | |
501 | are alternatives with the use of modules like C<base> and C<parent>. | |
502 | ||
503 | use base qw( Exporter ); | |
504 | # or | |
505 | use parent qw( Exporter ); | |
506 | ||
507 | Any of these statements are nice replacements for | |
508 | C<BEGIN { require Exporter; @ISA = qw(Exporter); }> | |
5b2cfa76 | 509 | with the same compile-time effect. The basic difference |
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510 | is that C<base> code interacts with declared C<fields> |
511 | while C<parent> is a streamlined version of the older | |
512 | C<base> code to just establish the IS-A relationship. | |
513 | ||
514 | For more details, see the documentation and code of | |
515 | L<base> and L<parent>. | |
516 | ||
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517 | Another thorough remedy to that runtime |
518 | vs. compile-time trap is to use L<Exporter::Easy>, | |
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519 | which is a wrapper of Exporter that allows all |
520 | boilerplate code at a single gulp in the | |
521 | use statement. | |
522 | ||
523 | use Exporter::Easy ( | |
524 | OK => [ qw(munge frobnicate) ], | |
525 | ); | |
526 | # @ISA setup is automatic | |
527 | # all assignments happen at compile time | |
528 | ||
ec6b919e | 529 | =head2 What Not to Export |
47f97feb | 530 | |
9ff2e302 | 531 | You have been warned already in L</Selecting What to Export> |
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532 | to not export: |
533 | ||
534 | =over 4 | |
535 | ||
536 | =item * | |
537 | ||
44ddc072 | 538 | method names (because you don't need to |
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539 | and that's likely to not do what you want), |
540 | ||
541 | =item * | |
542 | ||
543 | anything by default (because you don't want to surprise your users... | |
544 | badly) | |
545 | ||
546 | =item * | |
547 | ||
548 | anything you don't need to (because less is more) | |
549 | ||
550 | =back | |
551 | ||
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552 | There's one more item to add to this list. Do B<not> |
553 | export variable names. Just because C<Exporter> lets you | |
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554 | do that, it does not mean you should. |
555 | ||
556 | @EXPORT_OK = qw( $svar @avar %hvar ); # DON'T! | |
557 | ||
5b2cfa76 | 558 | Exporting variables is not a good idea. They can |
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559 | change under the hood, provoking horrible |
560 | effects at-a-distance, that are too hard to track | |
5b2cfa76 | 561 | and to fix. Trust me: they are not worth it. |
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562 | |
563 | To provide the capability to set/get class-wide | |
564 | settings, it is best instead to provide accessors | |
565 | as subroutines or class methods instead. | |
566 | ||
567 | =head1 SEE ALSO | |
568 | ||
569 | C<Exporter> is definitely not the only module with | |
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570 | symbol exporter capabilities. At CPAN, you may find |
571 | a bunch of them. Some are lighter. Some | |
572 | provide improved APIs and features. Peek the one | |
573 | that fits your needs. The following is | |
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574 | a sample list of such modules. |
575 | ||
576 | Exporter::Easy | |
577 | Exporter::Lite | |
578 | Exporter::Renaming | |
579 | Exporter::Tidy | |
580 | Sub::Exporter / Sub::Installer | |
581 | Perl6::Export / Perl6::Export::Attrs | |
582 | ||
583 | =head1 LICENSE | |
584 | ||
5b2cfa76 | 585 | This library is free software. You can redistribute it |
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586 | and/or modify it under the same terms as Perl itself. |
587 | ||
2b5b2650 | 588 | =cut |
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589 | |
590 | ||
591 |