11 our $VERSION = '5.564';
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 my($exports, $export_cache) = (\@{"$pkg\::EXPORT"},
40 # We *need* to treat @{"$pkg\::EXPORT_FAIL"} since Carp uses it :-(
41 my($fail) = \@{"$pkg\::EXPORT_FAIL"};
42 return export $pkg, $callpkg, @_
43 if $Verbose or $Debug or @$fail > 1;
44 my $args = @_ or @_ = @$exports;
46 if ($args and not %$export_cache) {
47 foreach my $sym (@$exports, @{"$pkg\::EXPORT_OK"}) {
49 $export_cache->{$sym} = 1;
52 if ($Verbose or $Debug
53 or grep {/\W/ or $args and not exists $export_cache->{$_}
54 or @$fail and $_ eq $fail->[0]
55 or (@{"$pkg\::EXPORT_OK"}
56 and $_ eq ${"$pkg\::EXPORT_OK"}[0])} @_) {
57 return export $pkg, $callpkg, ($args ? @_ : ());
59 local $SIG{__WARN__} =
60 sub {require Carp; &Carp::carp};
61 foreach my $sym (@_) {
62 # shortcut for the common case of no type character
63 *{"$callpkg\::$sym"} = \&{"$pkg\::$sym"};
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 { ... };
152 But there's no way to call that directly as a method, since a method
153 must have a name in the symbol table.)
155 As a general rule, if the module is trying to be object oriented
156 then export nothing. If it's just a collection of functions then
157 @EXPORT_OK anything but use @EXPORT with caution.
159 Other module design guidelines can be found in L<perlmod>.
161 =head2 Specialised Import Lists
163 If the first entry in an import list begins with !, : or / then the
164 list is treated as a series of specifications which either add to or
165 delete from the list of names to import. They are processed left to
166 right. Specifications are in the form:
168 [!]name This name only
169 [!]:DEFAULT All names in @EXPORT
170 [!]:tag All names in $EXPORT_TAGS{tag} anonymous list
171 [!]/pattern/ All names in @EXPORT and @EXPORT_OK which match
173 A leading ! indicates that matching names should be deleted from the
174 list of names to import. If the first specification is a deletion it
175 is treated as though preceded by :DEFAULT. If you just want to import
176 extra names in addition to the default set you will still need to
177 include :DEFAULT explicitly.
179 e.g., Module.pm defines:
181 @EXPORT = qw(A1 A2 A3 A4 A5);
182 @EXPORT_OK = qw(B1 B2 B3 B4 B5);
183 %EXPORT_TAGS = (T1 => [qw(A1 A2 B1 B2)], T2 => [qw(A1 A2 B3 B4)]);
185 Note that you cannot use tags in @EXPORT or @EXPORT_OK.
186 Names in EXPORT_TAGS must also appear in @EXPORT or @EXPORT_OK.
188 An application using Module can say something like:
190 use Module qw(:DEFAULT :T2 !B3 A3);
192 Other examples include:
194 use Socket qw(!/^[AP]F_/ !SOMAXCONN !SOL_SOCKET);
195 use POSIX qw(:errno_h :termios_h !TCSADRAIN !/^EXIT/);
197 Remember that most patterns (using //) will need to be anchored
198 with a leading ^, e.g., C</^EXIT/> rather than C</EXIT/>.
200 You can say C<BEGIN { $Exporter::Verbose=1 }> to see how the
201 specifications are being processed and what is actually being imported
204 =head2 Exporting without using Export's import method
206 Exporter has a special method, 'export_to_level' which is used in situations
207 where you can't directly call Export's import method. The export_to_level
210 MyPackage->export_to_level($where_to_export, $package, @what_to_export);
212 where $where_to_export is an integer telling how far up the calling stack
213 to export your symbols, and @what_to_export is an array telling what
214 symbols *to* export (usually this is @_). The $package argument is
217 For example, suppose that you have a module, A, which already has an
223 @EXPORT_OK = qw ($b);
227 $A::b = 1; # not a very useful import method
230 and you want to Export symbol $A::b back to the module that called
231 package A. Since Exporter relies on the import method to work, via
232 inheritance, as it stands Exporter::import() will never get called.
233 Instead, say the following:
237 @EXPORT_OK = qw ($b);
242 A->export_to_level(1, @_);
245 This will export the symbols one level 'above' the current package - ie: to
246 the program or module that used package A.
248 Note: Be careful not to modify '@_' at all before you call export_to_level
249 - or people using your package will get very unexplained results!
252 =head2 Module Version Checking
254 The Exporter module will convert an attempt to import a number from a
255 module into a call to $module_name-E<gt>require_version($value). This can
256 be used to validate that the version of the module being used is
257 greater than or equal to the required version.
259 The Exporter module supplies a default require_version method which
260 checks the value of $VERSION in the exporting module.
262 Since the default require_version method treats the $VERSION number as
263 a simple numeric value it will regard version 1.10 as lower than
264 1.9. For this reason it is strongly recommended that you use numbers
265 with at least two decimal places, e.g., 1.09.
267 =head2 Managing Unknown Symbols
269 In some situations you may want to prevent certain symbols from being
270 exported. Typically this applies to extensions which have functions
271 or constants that may not exist on some systems.
273 The names of any symbols that cannot be exported should be listed
274 in the C<@EXPORT_FAIL> array.
276 If a module attempts to import any of these symbols the Exporter
277 will give the module an opportunity to handle the situation before
278 generating an error. The Exporter will call an export_fail method
279 with a list of the failed symbols:
281 @failed_symbols = $module_name->export_fail(@failed_symbols);
283 If the export_fail method returns an empty list then no error is
284 recorded and all the requested symbols are exported. If the returned
285 list is not empty then an error is generated for each symbol and the
286 export fails. The Exporter provides a default export_fail method which
287 simply returns the list unchanged.
289 Uses for the export_fail method include giving better error messages
290 for some symbols and performing lazy architectural checks (put more
291 symbols into @EXPORT_FAIL by default and then take them out if someone
292 actually tries to use them and an expensive check shows that they are
293 usable on that platform).
295 =head2 Tag Handling Utility Functions
297 Since the symbols listed within %EXPORT_TAGS must also appear in either
298 @EXPORT or @EXPORT_OK, two utility functions are provided which allow
299 you to easily add tagged sets of symbols to @EXPORT or @EXPORT_OK:
301 %EXPORT_TAGS = (foo => [qw(aa bb cc)], bar => [qw(aa cc dd)]);
303 Exporter::export_tags('foo'); # add aa, bb and cc to @EXPORT
304 Exporter::export_ok_tags('bar'); # add aa, cc and dd to @EXPORT_OK
306 Any names which are not tags are added to @EXPORT or @EXPORT_OK
307 unchanged but will trigger a warning (with C<-w>) to avoid misspelt tags
308 names being silently added to @EXPORT or @EXPORT_OK. Future versions
309 may make this a fatal error.
311 =head2 C<AUTOLOAD>ed Constants
313 Many modules make use of C<AUTOLOAD>ing for constant subroutines to
314 avoid having to compile and waste memory on rarely used values (see
315 L<perlsub> for details on constant subroutines). Calls to such
316 constant subroutines are not optimized away at compile time because
317 they can't be checked at compile time for constancy.
319 Even if a prototype is available at compile time, the body of the
320 subroutine is not (it hasn't been C<AUTOLOAD>ed yet). perl needs to
321 examine both the C<()> prototype and the body of a subroutine at
322 compile time to detect that it can safely replace calls to that
323 subroutine with the constant value.
325 A workaround for this is to call the constants once in a C<BEGIN> block:
331 foo( SO_LINGER ); ## SO_LINGER NOT optimized away; called at runtime
333 foo( SO_LINGER ); ## SO_LINGER optimized away at compile time.
335 This forces the C<AUTOLOAD> for C<SO_LINGER> to take place before
336 SO_LINGER is encountered later in C<My> package.
338 If you are writing a package that C<AUTOLOAD>s, consider forcing
339 an C<AUTOLOAD> for any constants explicitly imported by other packages
340 or which are usually used when your package is C<use>d.