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"});
51 # Try very hard not to use {} and hence have to enter scope on the foreach
52 # 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 $fail->[0])) and last
58 ($heavy = /\W/) and last
61 return export $pkg, $callpkg, ($args ? @_ : ()) if $heavy;
62 local $SIG{__WARN__} =
63 sub {require Carp; &Carp::carp};
64 # shortcut for the common case of no type character
65 *{"$callpkg\::$_"} = \&{"$pkg\::$_"} foreach @_;
78 require Exporter::Heavy;
79 goto &Exporter::Heavy::require_version;
88 Exporter - Implements default import method for modules
92 In module ModuleName.pm:
98 @EXPORT = qw(...); # symbols to export by default
99 @EXPORT_OK = qw(...); # symbols to export on request
100 %EXPORT_TAGS = tag => [...]; # define names for sets of symbols
102 In other files which wish to use ModuleName:
104 use ModuleName; # import default symbols into my package
106 use ModuleName qw(...); # import listed symbols into my package
108 use ModuleName (); # do not import any symbols
112 The Exporter module implements a default C<import> method which
113 many modules choose to inherit rather than implement their own.
115 Perl automatically calls the C<import> method when processing a
116 C<use> statement for a module. Modules and C<use> are documented
117 in L<perlfunc> and L<perlmod>. Understanding the concept of
118 modules and how the C<use> statement operates is important to
119 understanding the Exporter.
123 The arrays C<@EXPORT> and C<@EXPORT_OK> in a module hold lists of
124 symbols that are going to be exported into the users name space by
125 default, or which they can request to be exported, respectively. The
126 symbols can represent functions, scalars, arrays, hashes, or typeglobs.
127 The symbols must be given by full name with the exception that the
128 ampersand in front of a function is optional, e.g.
130 @EXPORT = qw(afunc $scalar @array); # afunc is a function
131 @EXPORT_OK = qw(&bfunc %hash *typeglob); # explicit prefix on &bfunc
133 =head2 Selecting What To Export
135 Do B<not> export method names!
137 Do B<not> export anything else by default without a good reason!
139 Exports pollute the namespace of the module user. If you must export
140 try to use @EXPORT_OK in preference to @EXPORT and avoid short or
141 common symbol names to reduce the risk of name clashes.
143 Generally anything not exported is still accessible from outside the
144 module using the ModuleName::item_name (or $blessed_ref-E<gt>method)
145 syntax. By convention you can use a leading underscore on names to
146 informally indicate that they are 'internal' and not for public use.
148 (It is actually possible to get private functions by saying:
150 my $subref = sub { ... };
151 $subref->(@args); # Call it as a function
152 $obj->$subref(@args); # Use it as a method
154 However if you use them for methods it is up to you to figure out
155 how to make inheritance work.)
157 As a general rule, if the module is trying to be object oriented
158 then export nothing. If it's just a collection of functions then
159 @EXPORT_OK anything but use @EXPORT with caution.
161 Other module design guidelines can be found in L<perlmod>.
163 =head2 Specialised Import Lists
165 If the first entry in an import list begins with !, : or / then the
166 list is treated as a series of specifications which either add to or
167 delete from the list of names to import. They are processed left to
168 right. Specifications are in the form:
170 [!]name This name only
171 [!]:DEFAULT All names in @EXPORT
172 [!]:tag All names in $EXPORT_TAGS{tag} anonymous list
173 [!]/pattern/ All names in @EXPORT and @EXPORT_OK which match
175 A leading ! indicates that matching names should be deleted from the
176 list of names to import. If the first specification is a deletion it
177 is treated as though preceded by :DEFAULT. If you just want to import
178 extra names in addition to the default set you will still need to
179 include :DEFAULT explicitly.
181 e.g., Module.pm defines:
183 @EXPORT = qw(A1 A2 A3 A4 A5);
184 @EXPORT_OK = qw(B1 B2 B3 B4 B5);
185 %EXPORT_TAGS = (T1 => [qw(A1 A2 B1 B2)], T2 => [qw(A1 A2 B3 B4)]);
187 Note that you cannot use tags in @EXPORT or @EXPORT_OK.
188 Names in EXPORT_TAGS must also appear in @EXPORT or @EXPORT_OK.
190 An application using Module can say something like:
192 use Module qw(:DEFAULT :T2 !B3 A3);
194 Other examples include:
196 use Socket qw(!/^[AP]F_/ !SOMAXCONN !SOL_SOCKET);
197 use POSIX qw(:errno_h :termios_h !TCSADRAIN !/^EXIT/);
199 Remember that most patterns (using //) will need to be anchored
200 with a leading ^, e.g., C</^EXIT/> rather than C</EXIT/>.
202 You can say C<BEGIN { $Exporter::Verbose=1 }> to see how the
203 specifications are being processed and what is actually being imported
206 =head2 Exporting without using Export's import method
208 Exporter has a special method, 'export_to_level' which is used in situations
209 where you can't directly call Export's import method. The export_to_level
212 MyPackage->export_to_level($where_to_export, $package, @what_to_export);
214 where $where_to_export is an integer telling how far up the calling stack
215 to export your symbols, and @what_to_export is an array telling what
216 symbols *to* export (usually this is @_). The $package argument is
219 For example, suppose that you have a module, A, which already has an
225 @EXPORT_OK = qw ($b);
229 $A::b = 1; # not a very useful import method
232 and you want to Export symbol $A::b back to the module that called
233 package A. Since Exporter relies on the import method to work, via
234 inheritance, as it stands Exporter::import() will never get called.
235 Instead, say the following:
239 @EXPORT_OK = qw ($b);
244 A->export_to_level(1, @_);
247 This will export the symbols one level 'above' the current package - ie: to
248 the program or module that used package A.
250 Note: Be careful not to modify '@_' at all before you call export_to_level
251 - or people using your package will get very unexplained results!
254 =head2 Module Version Checking
256 The Exporter module will convert an attempt to import a number from a
257 module into a call to $module_name-E<gt>require_version($value). This can
258 be used to validate that the version of the module being used is
259 greater than or equal to the required version.
261 The Exporter module supplies a default require_version method which
262 checks the value of $VERSION in the exporting module.
264 Since the default require_version method treats the $VERSION number as
265 a simple numeric value it will regard version 1.10 as lower than
266 1.9. For this reason it is strongly recommended that you use numbers
267 with at least two decimal places, e.g., 1.09.
269 =head2 Managing Unknown Symbols
271 In some situations you may want to prevent certain symbols from being
272 exported. Typically this applies to extensions which have functions
273 or constants that may not exist on some systems.
275 The names of any symbols that cannot be exported should be listed
276 in the C<@EXPORT_FAIL> array.
278 If a module attempts to import any of these symbols the Exporter
279 will give the module an opportunity to handle the situation before
280 generating an error. The Exporter will call an export_fail method
281 with a list of the failed symbols:
283 @failed_symbols = $module_name->export_fail(@failed_symbols);
285 If the export_fail method returns an empty list then no error is
286 recorded and all the requested symbols are exported. If the returned
287 list is not empty then an error is generated for each symbol and the
288 export fails. The Exporter provides a default export_fail method which
289 simply returns the list unchanged.
291 Uses for the export_fail method include giving better error messages
292 for some symbols and performing lazy architectural checks (put more
293 symbols into @EXPORT_FAIL by default and then take them out if someone
294 actually tries to use them and an expensive check shows that they are
295 usable on that platform).
297 =head2 Tag Handling Utility Functions
299 Since the symbols listed within %EXPORT_TAGS must also appear in either
300 @EXPORT or @EXPORT_OK, two utility functions are provided which allow
301 you to easily add tagged sets of symbols to @EXPORT or @EXPORT_OK:
303 %EXPORT_TAGS = (foo => [qw(aa bb cc)], bar => [qw(aa cc dd)]);
305 Exporter::export_tags('foo'); # add aa, bb and cc to @EXPORT
306 Exporter::export_ok_tags('bar'); # add aa, cc and dd to @EXPORT_OK
308 Any names which are not tags are added to @EXPORT or @EXPORT_OK
309 unchanged but will trigger a warning (with C<-w>) to avoid misspelt tags
310 names being silently added to @EXPORT or @EXPORT_OK. Future versions
311 may make this a fatal error.
313 =head2 Generating combined tags
315 If several symbol categories exist in %EXPORT_TAGS, it's usually
316 useful to create the utility ":all" to simplify "use" statements.
318 The simplest way to do this is:
320 %EXPORT_TAGS = (foo => [qw(aa bb cc)], bar => [qw(aa cc dd)]);
322 # add all the other ":class" tags to the ":all" class,
323 # deleting duplicates
327 push @{$EXPORT_TAGS{all}},
328 grep {!$seen{$_}++} @{$EXPORT_TAGS{$_}} foreach keys %EXPORT_TAGS;
331 CGI.pm creates an ":all" tag which contains some (but not really
332 all) of its categories. That could be done with one small
335 # add some of the other ":class" tags to the ":all" class,
336 # deleting duplicates
340 push @{$EXPORT_TAGS{all}},
341 grep {!$seen{$_}++} @{$EXPORT_TAGS{$_}}
342 foreach qw/html2 html3 netscape form cgi internal/;
345 Note that the tag names in %EXPORT_TAGS don't have the leading ':'.
347 =head2 C<AUTOLOAD>ed Constants
349 Many modules make use of C<AUTOLOAD>ing for constant subroutines to
350 avoid having to compile and waste memory on rarely used values (see
351 L<perlsub> for details on constant subroutines). Calls to such
352 constant subroutines are not optimized away at compile time because
353 they can't be checked at compile time for constancy.
355 Even if a prototype is available at compile time, the body of the
356 subroutine is not (it hasn't been C<AUTOLOAD>ed yet). perl needs to
357 examine both the C<()> prototype and the body of a subroutine at
358 compile time to detect that it can safely replace calls to that
359 subroutine with the constant value.
361 A workaround for this is to call the constants once in a C<BEGIN> block:
367 foo( SO_LINGER ); ## SO_LINGER NOT optimized away; called at runtime
369 foo( SO_LINGER ); ## SO_LINGER optimized away at compile time.
371 This forces the C<AUTOLOAD> for C<SO_LINGER> to take place before
372 SO_LINGER is encountered later in C<My> package.
374 If you are writing a package that C<AUTOLOAD>s, consider forcing
375 an C<AUTOLOAD> for any constants explicitly imported by other packages
376 or which are usually used when your package is C<use>d.