12 our $VERSION = '5.567';
14 $Carp::Internal{Exporter} = 1;
17 require Exporter::Heavy;
18 # Unfortunately, this does not work if the caller is aliased as *name = \&foo
19 # Thus the need to create a lot of identical subroutines
20 my $c = (caller(1))[3];
22 \&{"Exporter::Heavy::heavy_$c"};
31 my $callpkg = caller($ExportLevel);
33 # We *need* to treat @{"$pkg\::EXPORT_FAIL"} since Carp uses it :-(
34 my($exports, $fail) = (\@{"$pkg\::EXPORT"}, \@{"$pkg\::EXPORT_FAIL"});
35 return export $pkg, $callpkg, @_
36 if $Verbose or $Debug or @$fail > 1;
37 my $export_cache = ($Cache{$pkg} ||= {});
38 my $args = @_ or @_ = @$exports;
41 if ($args and not %$export_cache) {
42 s/^&//, $export_cache->{$_} = 1
43 foreach (@$exports, @{"$pkg\::EXPORT_OK"});
46 # Try very hard not to use {} and hence have to enter scope on the foreach
47 # We bomb out of the loop with last as soon as heavy is set.
49 ($heavy = (/\W/ or $args and not exists $export_cache->{$_}
50 or @$fail and $_ eq $fail->[0])) and last
53 ($heavy = /\W/) and last
56 return export $pkg, $callpkg, ($args ? @_ : ()) if $heavy;
57 local $SIG{__WARN__} =
58 sub {require Carp; &Carp::carp};
59 # shortcut for the common case of no type character
60 *{"$callpkg\::$_"} = \&{"$pkg\::$_"} foreach @_;
70 # Unfortunately, caller(1)[3] "does not work" if the caller is aliased as
71 # *name = \&foo. Thus the need to create a lot of identical subroutines
72 # Otherwise we could have aliased them to export().
95 Exporter - Implements default import method for modules
99 In module YourModule.pm:
104 @EXPORT_OK = qw(munge frobnicate); # symbols to export on request
106 In other files which wish to use YourModule:
108 use ModuleName qw(frobnicate); # import listed symbols
109 frobnicate ($left, $right) # calls YourModule::frobnicate
113 The Exporter module implements an C<import> method which allows a module
114 to export functions and variables to its users' namespaces. Many modules
115 use Exporter rather than implementing their own C<import> method because
116 Exporter provides a highly flexible interface, with an implementation optimised
119 Perl automatically calls the C<import> method when processing a
120 C<use> statement for a module. Modules and C<use> are documented
121 in L<perlfunc> and L<perlmod>. Understanding the concept of
122 modules and how the C<use> statement operates is important to
123 understanding the Exporter.
127 The arrays C<@EXPORT> and C<@EXPORT_OK> in a module hold lists of
128 symbols that are going to be exported into the users name space by
129 default, or which they can request to be exported, respectively. The
130 symbols can represent functions, scalars, arrays, hashes, or typeglobs.
131 The symbols must be given by full name with the exception that the
132 ampersand in front of a function is optional, e.g.
134 @EXPORT = qw(afunc $scalar @array); # afunc is a function
135 @EXPORT_OK = qw(&bfunc %hash *typeglob); # explicit prefix on &bfunc
137 If you are only exporting function names it is recommended to omit the
138 ampersand, as the implementation is faster this way.
140 =head2 Selecting What To Export
142 Do B<not> export method names!
144 Do B<not> export anything else by default without a good reason!
146 Exports pollute the namespace of the module user. If you must export
147 try to use @EXPORT_OK in preference to @EXPORT and avoid short or
148 common symbol names to reduce the risk of name clashes.
150 Generally anything not exported is still accessible from outside the
151 module using the ModuleName::item_name (or $blessed_ref-E<gt>method)
152 syntax. By convention you can use a leading underscore on names to
153 informally indicate that they are 'internal' and not for public use.
155 (It is actually possible to get private functions by saying:
157 my $subref = sub { ... };
158 $subref->(@args); # Call it as a function
159 $obj->$subref(@args); # Use it as a method
161 However if you use them for methods it is up to you to figure out
162 how to make inheritance work.)
164 As a general rule, if the module is trying to be object oriented
165 then export nothing. If it's just a collection of functions then
166 @EXPORT_OK anything but use @EXPORT with caution. For function and
167 method names use barewords in preference to names prefixed with
168 ampersands for the export lists.
170 Other module design guidelines can be found in L<perlmod>.
174 In other files which wish to use your module there are three basic ways for
175 them to load your module and import its symbols:
179 =item C<use ModuleName;>
181 This imports all the symbols from ModuleName's @EXPORT into the namespace
182 of the C<use> statement.
184 =item C<use ModuleName ();>
186 This causes perl to load your module but does not import any symbols.
188 =item C<use ModuleName qw(...);>
190 This imports only the symbols listed by the caller into their namespace.
191 All listed symbols must be in your @EXPORT or @EXPORT_OK, else an error
192 occurs. The advanced export features of Exporter are accessed like this,
193 but with list entries that are syntactically distinct from symbol names.
197 Unless you want to use its advanced features, this is probably all you
198 need to know to use Exporter.
200 =head1 Advanced features
202 =head2 Specialised Import Lists
204 If the first entry in an import list begins with !, : or / then the
205 list is treated as a series of specifications which either add to or
206 delete from the list of names to import. They are processed left to
207 right. Specifications are in the form:
209 [!]name This name only
210 [!]:DEFAULT All names in @EXPORT
211 [!]:tag All names in $EXPORT_TAGS{tag} anonymous list
212 [!]/pattern/ All names in @EXPORT and @EXPORT_OK which match
214 A leading ! indicates that matching names should be deleted from the
215 list of names to import. If the first specification is a deletion it
216 is treated as though preceded by :DEFAULT. If you just want to import
217 extra names in addition to the default set you will still need to
218 include :DEFAULT explicitly.
220 e.g., Module.pm defines:
222 @EXPORT = qw(A1 A2 A3 A4 A5);
223 @EXPORT_OK = qw(B1 B2 B3 B4 B5);
224 %EXPORT_TAGS = (T1 => [qw(A1 A2 B1 B2)], T2 => [qw(A1 A2 B3 B4)]);
226 Note that you cannot use tags in @EXPORT or @EXPORT_OK.
227 Names in EXPORT_TAGS must also appear in @EXPORT or @EXPORT_OK.
229 An application using Module can say something like:
231 use Module qw(:DEFAULT :T2 !B3 A3);
233 Other examples include:
235 use Socket qw(!/^[AP]F_/ !SOMAXCONN !SOL_SOCKET);
236 use POSIX qw(:errno_h :termios_h !TCSADRAIN !/^EXIT/);
238 Remember that most patterns (using //) will need to be anchored
239 with a leading ^, e.g., C</^EXIT/> rather than C</EXIT/>.
241 You can say C<BEGIN { $Exporter::Verbose=1 }> to see how the
242 specifications are being processed and what is actually being imported
245 =head2 Exporting without using Exporter's import method
247 Exporter has a special method, 'export_to_level' which is used in situations
248 where you can't directly call Exporter's import method. The export_to_level
251 MyPackage->export_to_level($where_to_export, $package, @what_to_export);
253 where $where_to_export is an integer telling how far up the calling stack
254 to export your symbols, and @what_to_export is an array telling what
255 symbols *to* export (usually this is @_). The $package argument is
258 For example, suppose that you have a module, A, which already has an
264 @EXPORT_OK = qw ($b);
268 $A::b = 1; # not a very useful import method
271 and you want to Export symbol $A::b back to the module that called
272 package A. Since Exporter relies on the import method to work, via
273 inheritance, as it stands Exporter::import() will never get called.
274 Instead, say the following:
278 @EXPORT_OK = qw ($b);
283 A->export_to_level(1, @_);
286 This will export the symbols one level 'above' the current package - ie: to
287 the program or module that used package A.
289 Note: Be careful not to modify '@_' at all before you call export_to_level
290 - or people using your package will get very unexplained results!
293 =head2 Module Version Checking
295 The Exporter module will convert an attempt to import a number from a
296 module into a call to $module_name-E<gt>require_version($value). This can
297 be used to validate that the version of the module being used is
298 greater than or equal to the required version.
300 The Exporter module supplies a default require_version method which
301 checks the value of $VERSION in the exporting module.
303 Since the default require_version method treats the $VERSION number as
304 a simple numeric value it will regard version 1.10 as lower than
305 1.9. For this reason it is strongly recommended that you use numbers
306 with at least two decimal places, e.g., 1.09.
308 =head2 Managing Unknown Symbols
310 In some situations you may want to prevent certain symbols from being
311 exported. Typically this applies to extensions which have functions
312 or constants that may not exist on some systems.
314 The names of any symbols that cannot be exported should be listed
315 in the C<@EXPORT_FAIL> array.
317 If a module attempts to import any of these symbols the Exporter
318 will give the module an opportunity to handle the situation before
319 generating an error. The Exporter will call an export_fail method
320 with a list of the failed symbols:
322 @failed_symbols = $module_name->export_fail(@failed_symbols);
324 If the export_fail method returns an empty list then no error is
325 recorded and all the requested symbols are exported. If the returned
326 list is not empty then an error is generated for each symbol and the
327 export fails. The Exporter provides a default export_fail method which
328 simply returns the list unchanged.
330 Uses for the export_fail method include giving better error messages
331 for some symbols and performing lazy architectural checks (put more
332 symbols into @EXPORT_FAIL by default and then take them out if someone
333 actually tries to use them and an expensive check shows that they are
334 usable on that platform).
336 =head2 Tag Handling Utility Functions
338 Since the symbols listed within %EXPORT_TAGS must also appear in either
339 @EXPORT or @EXPORT_OK, two utility functions are provided which allow
340 you to easily add tagged sets of symbols to @EXPORT or @EXPORT_OK:
342 %EXPORT_TAGS = (foo => [qw(aa bb cc)], bar => [qw(aa cc dd)]);
344 Exporter::export_tags('foo'); # add aa, bb and cc to @EXPORT
345 Exporter::export_ok_tags('bar'); # add aa, cc and dd to @EXPORT_OK
347 Any names which are not tags are added to @EXPORT or @EXPORT_OK
348 unchanged but will trigger a warning (with C<-w>) to avoid misspelt tags
349 names being silently added to @EXPORT or @EXPORT_OK. Future versions
350 may make this a fatal error.
352 =head2 Generating combined tags
354 If several symbol categories exist in %EXPORT_TAGS, it's usually
355 useful to create the utility ":all" to simplify "use" statements.
357 The simplest way to do this is:
359 %EXPORT_TAGS = (foo => [qw(aa bb cc)], bar => [qw(aa cc dd)]);
361 # add all the other ":class" tags to the ":all" class,
362 # deleting duplicates
366 push @{$EXPORT_TAGS{all}},
367 grep {!$seen{$_}++} @{$EXPORT_TAGS{$_}} foreach keys %EXPORT_TAGS;
370 CGI.pm creates an ":all" tag which contains some (but not really
371 all) of its categories. That could be done with one small
374 # add some of the other ":class" tags to the ":all" class,
375 # deleting duplicates
379 push @{$EXPORT_TAGS{all}},
380 grep {!$seen{$_}++} @{$EXPORT_TAGS{$_}}
381 foreach qw/html2 html3 netscape form cgi internal/;
384 Note that the tag names in %EXPORT_TAGS don't have the leading ':'.
386 =head2 C<AUTOLOAD>ed Constants
388 Many modules make use of C<AUTOLOAD>ing for constant subroutines to
389 avoid having to compile and waste memory on rarely used values (see
390 L<perlsub> for details on constant subroutines). Calls to such
391 constant subroutines are not optimized away at compile time because
392 they can't be checked at compile time for constancy.
394 Even if a prototype is available at compile time, the body of the
395 subroutine is not (it hasn't been C<AUTOLOAD>ed yet). perl needs to
396 examine both the C<()> prototype and the body of a subroutine at
397 compile time to detect that it can safely replace calls to that
398 subroutine with the constant value.
400 A workaround for this is to call the constants once in a C<BEGIN> block:
406 foo( SO_LINGER ); ## SO_LINGER NOT optimized away; called at runtime
408 foo( SO_LINGER ); ## SO_LINGER optimized away at compile time.
410 This forces the C<AUTOLOAD> for C<SO_LINGER> to take place before
411 SO_LINGER is encountered later in C<My> package.
413 If you are writing a package that C<AUTOLOAD>s, consider forcing
414 an C<AUTOLOAD> for any constants explicitly imported by other packages
415 or which are usually used when your package is C<use>d.