12 our $VERSION = '5.566';
13 $Carp::Internal{Exporter} = 1;
16 require Exporter::Heavy;
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 $c = (caller(1))[3];
21 \&{"Exporter::Heavy::heavy_$c"};
30 my $callpkg = caller($ExportLevel);
32 # We *need* to treat @{"$pkg\::EXPORT_FAIL"} since Carp uses it :-(
33 my($exports, $export_cache, $fail)
34 = (\@{"$pkg\::EXPORT"}, \%{"$pkg\::EXPORT"}, \@{"$pkg\::EXPORT_FAIL"});
35 return export $pkg, $callpkg, @_
36 if $Verbose or $Debug or @$fail > 1;
37 my $args = @_ or @_ = @$exports;
40 if ($args and not %$export_cache) {
41 s/^&//, $export_cache->{$_} = 1
42 foreach (@$exports, @{"$pkg\::EXPORT_OK"});
45 # Try very hard not to use {} and hence have to enter scope on the foreach
46 # We bomb out of the loop with last as soon as heavy is set.
48 ($heavy = (/\W/ or $args and not exists $export_cache->{$_}
49 or @$fail and $_ eq $fail->[0])) and last
52 ($heavy = /\W/) and last
55 return export $pkg, $callpkg, ($args ? @_ : ()) if $heavy;
56 local $SIG{__WARN__} =
57 sub {require Carp; &Carp::carp};
58 # shortcut for the common case of no type character
59 *{"$callpkg\::$_"} = \&{"$pkg\::$_"} foreach @_;
69 # Unfortunately, caller(1)[3] "does not work" if the caller is aliased as
70 # *name = \&foo. Thus the need to create a lot of identical subroutines
71 # Otherwise we could have aliased them to export().
94 Exporter - Implements default import method for modules
98 In module ModuleName.pm:
104 @EXPORT = qw(...); # symbols to export by default
105 @EXPORT_OK = qw(...); # symbols to export on request
106 %EXPORT_TAGS = tag => [...]; # define names for sets of symbols
108 In other files which wish to use ModuleName:
110 use ModuleName; # import default symbols into my package
112 use ModuleName qw(...); # import listed symbols into my package
114 use ModuleName (); # do not import any symbols
118 The Exporter module implements a default C<import> method which
119 many modules choose to inherit rather than implement their own.
121 Perl automatically calls the C<import> method when processing a
122 C<use> statement for a module. Modules and C<use> are documented
123 in L<perlfunc> and L<perlmod>. Understanding the concept of
124 modules and how the C<use> statement operates is important to
125 understanding the Exporter.
129 The arrays C<@EXPORT> and C<@EXPORT_OK> in a module hold lists of
130 symbols that are going to be exported into the users name space by
131 default, or which they can request to be exported, respectively. The
132 symbols can represent functions, scalars, arrays, hashes, or typeglobs.
133 The symbols must be given by full name with the exception that the
134 ampersand in front of a function is optional, e.g.
136 @EXPORT = qw(afunc $scalar @array); # afunc is a function
137 @EXPORT_OK = qw(&bfunc %hash *typeglob); # explicit prefix on &bfunc
139 =head2 Selecting What To Export
141 Do B<not> export method names!
143 Do B<not> export anything else by default without a good reason!
145 Exports pollute the namespace of the module user. If you must export
146 try to use @EXPORT_OK in preference to @EXPORT and avoid short or
147 common symbol names to reduce the risk of name clashes.
149 Generally anything not exported is still accessible from outside the
150 module using the ModuleName::item_name (or $blessed_ref-E<gt>method)
151 syntax. By convention you can use a leading underscore on names to
152 informally indicate that they are 'internal' and not for public use.
154 (It is actually possible to get private functions by saying:
156 my $subref = sub { ... };
157 $subref->(@args); # Call it as a function
158 $obj->$subref(@args); # Use it as a method
160 However if you use them for methods it is up to you to figure out
161 how to make inheritance work.)
163 As a general rule, if the module is trying to be object oriented
164 then export nothing. If it's just a collection of functions then
165 @EXPORT_OK anything but use @EXPORT with caution.
167 Other module design guidelines can be found in L<perlmod>.
169 =head2 Specialised Import Lists
171 If the first entry in an import list begins with !, : or / then the
172 list is treated as a series of specifications which either add to or
173 delete from the list of names to import. They are processed left to
174 right. Specifications are in the form:
176 [!]name This name only
177 [!]:DEFAULT All names in @EXPORT
178 [!]:tag All names in $EXPORT_TAGS{tag} anonymous list
179 [!]/pattern/ All names in @EXPORT and @EXPORT_OK which match
181 A leading ! indicates that matching names should be deleted from the
182 list of names to import. If the first specification is a deletion it
183 is treated as though preceded by :DEFAULT. If you just want to import
184 extra names in addition to the default set you will still need to
185 include :DEFAULT explicitly.
187 e.g., Module.pm defines:
189 @EXPORT = qw(A1 A2 A3 A4 A5);
190 @EXPORT_OK = qw(B1 B2 B3 B4 B5);
191 %EXPORT_TAGS = (T1 => [qw(A1 A2 B1 B2)], T2 => [qw(A1 A2 B3 B4)]);
193 Note that you cannot use tags in @EXPORT or @EXPORT_OK.
194 Names in EXPORT_TAGS must also appear in @EXPORT or @EXPORT_OK.
196 An application using Module can say something like:
198 use Module qw(:DEFAULT :T2 !B3 A3);
200 Other examples include:
202 use Socket qw(!/^[AP]F_/ !SOMAXCONN !SOL_SOCKET);
203 use POSIX qw(:errno_h :termios_h !TCSADRAIN !/^EXIT/);
205 Remember that most patterns (using //) will need to be anchored
206 with a leading ^, e.g., C</^EXIT/> rather than C</EXIT/>.
208 You can say C<BEGIN { $Exporter::Verbose=1 }> to see how the
209 specifications are being processed and what is actually being imported
212 =head2 Exporting without using Export's import method
214 Exporter has a special method, 'export_to_level' which is used in situations
215 where you can't directly call Export's import method. The export_to_level
218 MyPackage->export_to_level($where_to_export, $package, @what_to_export);
220 where $where_to_export is an integer telling how far up the calling stack
221 to export your symbols, and @what_to_export is an array telling what
222 symbols *to* export (usually this is @_). The $package argument is
225 For example, suppose that you have a module, A, which already has an
231 @EXPORT_OK = qw ($b);
235 $A::b = 1; # not a very useful import method
238 and you want to Export symbol $A::b back to the module that called
239 package A. Since Exporter relies on the import method to work, via
240 inheritance, as it stands Exporter::import() will never get called.
241 Instead, say the following:
245 @EXPORT_OK = qw ($b);
250 A->export_to_level(1, @_);
253 This will export the symbols one level 'above' the current package - ie: to
254 the program or module that used package A.
256 Note: Be careful not to modify '@_' at all before you call export_to_level
257 - or people using your package will get very unexplained results!
260 =head2 Module Version Checking
262 The Exporter module will convert an attempt to import a number from a
263 module into a call to $module_name-E<gt>require_version($value). This can
264 be used to validate that the version of the module being used is
265 greater than or equal to the required version.
267 The Exporter module supplies a default require_version method which
268 checks the value of $VERSION in the exporting module.
270 Since the default require_version method treats the $VERSION number as
271 a simple numeric value it will regard version 1.10 as lower than
272 1.9. For this reason it is strongly recommended that you use numbers
273 with at least two decimal places, e.g., 1.09.
275 =head2 Managing Unknown Symbols
277 In some situations you may want to prevent certain symbols from being
278 exported. Typically this applies to extensions which have functions
279 or constants that may not exist on some systems.
281 The names of any symbols that cannot be exported should be listed
282 in the C<@EXPORT_FAIL> array.
284 If a module attempts to import any of these symbols the Exporter
285 will give the module an opportunity to handle the situation before
286 generating an error. The Exporter will call an export_fail method
287 with a list of the failed symbols:
289 @failed_symbols = $module_name->export_fail(@failed_symbols);
291 If the export_fail method returns an empty list then no error is
292 recorded and all the requested symbols are exported. If the returned
293 list is not empty then an error is generated for each symbol and the
294 export fails. The Exporter provides a default export_fail method which
295 simply returns the list unchanged.
297 Uses for the export_fail method include giving better error messages
298 for some symbols and performing lazy architectural checks (put more
299 symbols into @EXPORT_FAIL by default and then take them out if someone
300 actually tries to use them and an expensive check shows that they are
301 usable on that platform).
303 =head2 Tag Handling Utility Functions
305 Since the symbols listed within %EXPORT_TAGS must also appear in either
306 @EXPORT or @EXPORT_OK, two utility functions are provided which allow
307 you to easily add tagged sets of symbols to @EXPORT or @EXPORT_OK:
309 %EXPORT_TAGS = (foo => [qw(aa bb cc)], bar => [qw(aa cc dd)]);
311 Exporter::export_tags('foo'); # add aa, bb and cc to @EXPORT
312 Exporter::export_ok_tags('bar'); # add aa, cc and dd to @EXPORT_OK
314 Any names which are not tags are added to @EXPORT or @EXPORT_OK
315 unchanged but will trigger a warning (with C<-w>) to avoid misspelt tags
316 names being silently added to @EXPORT or @EXPORT_OK. Future versions
317 may make this a fatal error.
319 =head2 Generating combined tags
321 If several symbol categories exist in %EXPORT_TAGS, it's usually
322 useful to create the utility ":all" to simplify "use" statements.
324 The simplest way to do this is:
326 %EXPORT_TAGS = (foo => [qw(aa bb cc)], bar => [qw(aa cc dd)]);
328 # add all the other ":class" tags to the ":all" class,
329 # deleting duplicates
333 push @{$EXPORT_TAGS{all}},
334 grep {!$seen{$_}++} @{$EXPORT_TAGS{$_}} foreach keys %EXPORT_TAGS;
337 CGI.pm creates an ":all" tag which contains some (but not really
338 all) of its categories. That could be done with one small
341 # add some of the other ":class" tags to the ":all" class,
342 # deleting duplicates
346 push @{$EXPORT_TAGS{all}},
347 grep {!$seen{$_}++} @{$EXPORT_TAGS{$_}}
348 foreach qw/html2 html3 netscape form cgi internal/;
351 Note that the tag names in %EXPORT_TAGS don't have the leading ':'.
353 =head2 C<AUTOLOAD>ed Constants
355 Many modules make use of C<AUTOLOAD>ing for constant subroutines to
356 avoid having to compile and waste memory on rarely used values (see
357 L<perlsub> for details on constant subroutines). Calls to such
358 constant subroutines are not optimized away at compile time because
359 they can't be checked at compile time for constancy.
361 Even if a prototype is available at compile time, the body of the
362 subroutine is not (it hasn't been C<AUTOLOAD>ed yet). perl needs to
363 examine both the C<()> prototype and the body of a subroutine at
364 compile time to detect that it can safely replace calls to that
365 subroutine with the constant value.
367 A workaround for this is to call the constants once in a C<BEGIN> block:
373 foo( SO_LINGER ); ## SO_LINGER NOT optimized away; called at runtime
375 foo( SO_LINGER ); ## SO_LINGER optimized away at compile time.
377 This forces the C<AUTOLOAD> for C<SO_LINGER> to take place before
378 SO_LINGER is encountered later in C<My> package.
380 If you are writing a package that C<AUTOLOAD>s, consider forcing
381 an C<AUTOLOAD> for any constants explicitly imported by other packages
382 or which are usually used when your package is C<use>d.