11 our $VERSION = '5.565';
12 $Carp::Internal{Exporter} = 1;
15 require Exporter::Heavy;
16 goto &Exporter::Heavy::heavy_export_to_level;
20 require Exporter::Heavy;
21 goto &Exporter::Heavy::heavy_export;
25 require Exporter::Heavy;
26 Exporter::Heavy::_push_tags((caller)[0], "EXPORT", \@_);
30 require Exporter::Heavy;
31 Exporter::Heavy::_push_tags((caller)[0], "EXPORT_OK", \@_);
36 my $callpkg = caller($ExportLevel);
38 # We *need* to treat @{"$pkg\::EXPORT_FAIL"} since Carp uses it :-(
39 my($exports, $export_cache, $fail)
40 = (\@{"$pkg\::EXPORT"}, \%{"$pkg\::EXPORT"}, \@{"$pkg\::EXPORT_FAIL"});
41 return export $pkg, $callpkg, @_
42 if $Verbose or $Debug or @$fail > 1;
43 my $args = @_ or @_ = @$exports;
46 if ($args and not %$export_cache) {
47 s/^&//, $export_cache->{$_} = 1
48 foreach (@$exports, @{"$pkg\::EXPORT_OK"});
50 my $heavy = $Verbose || $Debug;
52 # Try very hard not to use {} and hence have to enter scope on the foreach
53 # We bomb out of the loop with last as soon as heavy is set.
54 ($heavy = (/\W/ or $args and not exists $export_cache->{$_}
55 or @$fail and $_ eq $fail->[0]
56 or (@{"$pkg\::EXPORT_OK"} and $_ eq ${"$pkg\::EXPORT_OK"}[0])))
60 return export $pkg, $callpkg, ($args ? @_ : ()) if $heavy;
61 local $SIG{__WARN__} =
62 sub {require Carp; &Carp::carp};
63 # shortcut for the common case of no type character
64 *{"$callpkg\::$_"} = \&{"$pkg\::$_"} foreach @_;
77 require Exporter::Heavy;
78 goto &Exporter::Heavy::require_version;
87 Exporter - Implements default import method for modules
91 In module ModuleName.pm:
97 @EXPORT = qw(...); # symbols to export by default
98 @EXPORT_OK = qw(...); # symbols to export on request
99 %EXPORT_TAGS = tag => [...]; # define names for sets of symbols
101 In other files which wish to use ModuleName:
103 use ModuleName; # import default symbols into my package
105 use ModuleName qw(...); # import listed symbols into my package
107 use ModuleName (); # do not import any symbols
111 The Exporter module implements a default C<import> method which
112 many modules choose to inherit rather than implement their own.
114 Perl automatically calls the C<import> method when processing a
115 C<use> statement for a module. Modules and C<use> are documented
116 in L<perlfunc> and L<perlmod>. Understanding the concept of
117 modules and how the C<use> statement operates is important to
118 understanding the Exporter.
122 The arrays C<@EXPORT> and C<@EXPORT_OK> in a module hold lists of
123 symbols that are going to be exported into the users name space by
124 default, or which they can request to be exported, respectively. The
125 symbols can represent functions, scalars, arrays, hashes, or typeglobs.
126 The symbols must be given by full name with the exception that the
127 ampersand in front of a function is optional, e.g.
129 @EXPORT = qw(afunc $scalar @array); # afunc is a function
130 @EXPORT_OK = qw(&bfunc %hash *typeglob); # explicit prefix on &bfunc
132 =head2 Selecting What To Export
134 Do B<not> export method names!
136 Do B<not> export anything else by default without a good reason!
138 Exports pollute the namespace of the module user. If you must export
139 try to use @EXPORT_OK in preference to @EXPORT and avoid short or
140 common symbol names to reduce the risk of name clashes.
142 Generally anything not exported is still accessible from outside the
143 module using the ModuleName::item_name (or $blessed_ref-E<gt>method)
144 syntax. By convention you can use a leading underscore on names to
145 informally indicate that they are 'internal' and not for public use.
147 (It is actually possible to get private functions by saying:
149 my $subref = sub { ... };
150 $subref->(@args); # Call it as a function
151 $obj->$subref(@args); # Use it as a method
153 However if you use them for methods it is up to you to figure out
154 how to make inheritance work.)
156 As a general rule, if the module is trying to be object oriented
157 then export nothing. If it's just a collection of functions then
158 @EXPORT_OK anything but use @EXPORT with caution.
160 Other module design guidelines can be found in L<perlmod>.
162 =head2 Specialised Import Lists
164 If the first entry in an import list begins with !, : or / then the
165 list is treated as a series of specifications which either add to or
166 delete from the list of names to import. They are processed left to
167 right. Specifications are in the form:
169 [!]name This name only
170 [!]:DEFAULT All names in @EXPORT
171 [!]:tag All names in $EXPORT_TAGS{tag} anonymous list
172 [!]/pattern/ All names in @EXPORT and @EXPORT_OK which match
174 A leading ! indicates that matching names should be deleted from the
175 list of names to import. If the first specification is a deletion it
176 is treated as though preceded by :DEFAULT. If you just want to import
177 extra names in addition to the default set you will still need to
178 include :DEFAULT explicitly.
180 e.g., Module.pm defines:
182 @EXPORT = qw(A1 A2 A3 A4 A5);
183 @EXPORT_OK = qw(B1 B2 B3 B4 B5);
184 %EXPORT_TAGS = (T1 => [qw(A1 A2 B1 B2)], T2 => [qw(A1 A2 B3 B4)]);
186 Note that you cannot use tags in @EXPORT or @EXPORT_OK.
187 Names in EXPORT_TAGS must also appear in @EXPORT or @EXPORT_OK.
189 An application using Module can say something like:
191 use Module qw(:DEFAULT :T2 !B3 A3);
193 Other examples include:
195 use Socket qw(!/^[AP]F_/ !SOMAXCONN !SOL_SOCKET);
196 use POSIX qw(:errno_h :termios_h !TCSADRAIN !/^EXIT/);
198 Remember that most patterns (using //) will need to be anchored
199 with a leading ^, e.g., C</^EXIT/> rather than C</EXIT/>.
201 You can say C<BEGIN { $Exporter::Verbose=1 }> to see how the
202 specifications are being processed and what is actually being imported
205 =head2 Exporting without using Export's import method
207 Exporter has a special method, 'export_to_level' which is used in situations
208 where you can't directly call Export's import method. The export_to_level
211 MyPackage->export_to_level($where_to_export, $package, @what_to_export);
213 where $where_to_export is an integer telling how far up the calling stack
214 to export your symbols, and @what_to_export is an array telling what
215 symbols *to* export (usually this is @_). The $package argument is
218 For example, suppose that you have a module, A, which already has an
224 @EXPORT_OK = qw ($b);
228 $A::b = 1; # not a very useful import method
231 and you want to Export symbol $A::b back to the module that called
232 package A. Since Exporter relies on the import method to work, via
233 inheritance, as it stands Exporter::import() will never get called.
234 Instead, say the following:
238 @EXPORT_OK = qw ($b);
243 A->export_to_level(1, @_);
246 This will export the symbols one level 'above' the current package - ie: to
247 the program or module that used package A.
249 Note: Be careful not to modify '@_' at all before you call export_to_level
250 - or people using your package will get very unexplained results!
253 =head2 Module Version Checking
255 The Exporter module will convert an attempt to import a number from a
256 module into a call to $module_name-E<gt>require_version($value). This can
257 be used to validate that the version of the module being used is
258 greater than or equal to the required version.
260 The Exporter module supplies a default require_version method which
261 checks the value of $VERSION in the exporting module.
263 Since the default require_version method treats the $VERSION number as
264 a simple numeric value it will regard version 1.10 as lower than
265 1.9. For this reason it is strongly recommended that you use numbers
266 with at least two decimal places, e.g., 1.09.
268 =head2 Managing Unknown Symbols
270 In some situations you may want to prevent certain symbols from being
271 exported. Typically this applies to extensions which have functions
272 or constants that may not exist on some systems.
274 The names of any symbols that cannot be exported should be listed
275 in the C<@EXPORT_FAIL> array.
277 If a module attempts to import any of these symbols the Exporter
278 will give the module an opportunity to handle the situation before
279 generating an error. The Exporter will call an export_fail method
280 with a list of the failed symbols:
282 @failed_symbols = $module_name->export_fail(@failed_symbols);
284 If the export_fail method returns an empty list then no error is
285 recorded and all the requested symbols are exported. If the returned
286 list is not empty then an error is generated for each symbol and the
287 export fails. The Exporter provides a default export_fail method which
288 simply returns the list unchanged.
290 Uses for the export_fail method include giving better error messages
291 for some symbols and performing lazy architectural checks (put more
292 symbols into @EXPORT_FAIL by default and then take them out if someone
293 actually tries to use them and an expensive check shows that they are
294 usable on that platform).
296 =head2 Tag Handling Utility Functions
298 Since the symbols listed within %EXPORT_TAGS must also appear in either
299 @EXPORT or @EXPORT_OK, two utility functions are provided which allow
300 you to easily add tagged sets of symbols to @EXPORT or @EXPORT_OK:
302 %EXPORT_TAGS = (foo => [qw(aa bb cc)], bar => [qw(aa cc dd)]);
304 Exporter::export_tags('foo'); # add aa, bb and cc to @EXPORT
305 Exporter::export_ok_tags('bar'); # add aa, cc and dd to @EXPORT_OK
307 Any names which are not tags are added to @EXPORT or @EXPORT_OK
308 unchanged but will trigger a warning (with C<-w>) to avoid misspelt tags
309 names being silently added to @EXPORT or @EXPORT_OK. Future versions
310 may make this a fatal error.
312 =head2 C<AUTOLOAD>ed Constants
314 Many modules make use of C<AUTOLOAD>ing for constant subroutines to
315 avoid having to compile and waste memory on rarely used values (see
316 L<perlsub> for details on constant subroutines). Calls to such
317 constant subroutines are not optimized away at compile time because
318 they can't be checked at compile time for constancy.
320 Even if a prototype is available at compile time, the body of the
321 subroutine is not (it hasn't been C<AUTOLOAD>ed yet). perl needs to
322 examine both the C<()> prototype and the body of a subroutine at
323 compile time to detect that it can safely replace calls to that
324 subroutine with the constant value.
326 A workaround for this is to call the constants once in a C<BEGIN> block:
332 foo( SO_LINGER ); ## SO_LINGER NOT optimized away; called at runtime
334 foo( SO_LINGER ); ## SO_LINGER optimized away at compile time.
336 This forces the C<AUTOLOAD> for C<SO_LINGER> to take place before
337 SO_LINGER is encountered later in C<My> package.
339 If you are writing a package that C<AUTOLOAD>s, consider forcing
340 an C<AUTOLOAD> for any constants explicitly imported by other packages
341 or which are usually used when your package is C<use>d.