11 our $VERSION = '5.562';
14 require Exporter::Heavy;
15 goto &Exporter::Heavy::heavy_export_to_level;
19 require Exporter::Heavy;
20 goto &Exporter::Heavy::heavy_export;
24 require Exporter::Heavy;
25 Exporter::Heavy::_push_tags((caller)[0], "EXPORT", \@_);
29 require Exporter::Heavy;
30 Exporter::Heavy::_push_tags((caller)[0], "EXPORT_OK", \@_);
35 my $callpkg = caller($ExportLevel);
37 my($exports, $export_cache) = (\@{"$pkg\::EXPORT"},
39 # We *need* to treat @{"$pkg\::EXPORT_FAIL"} since Carp uses it :-(
40 my($fail) = \@{"$pkg\::EXPORT_FAIL"};
41 return export $pkg, $callpkg, @_
42 if $Verbose or $Debug or @$fail > 1;
43 my $args = @_ or @_ = @$exports;
45 if ($args and not %$export_cache) {
46 foreach my $sym (@$exports, @{"$pkg\::EXPORT_OK"}) {
48 $export_cache->{$sym} = 1;
51 if ($Verbose or $Debug
52 or grep {/\W/ or $args and not exists $export_cache->{$_}
53 or @$fail and $_ eq $fail->[0]
54 or (@{"$pkg\::EXPORT_OK"}
55 and $_ eq ${"$pkg\::EXPORT_OK"}[0])} @_) {
56 return export $pkg, $callpkg, ($args ? @_ : ());
58 local $SIG{__WARN__} =
59 sub {require Carp; local $Carp::CarpLevel = 1; &Carp::carp};
60 foreach my $sym (@_) {
61 # shortcut for the common case of no type character
62 *{"$callpkg\::$sym"} = \&{"$pkg\::$sym"};
76 require Exporter::Heavy;
77 goto &Exporter::Heavy::require_version;
86 Exporter - Implements default import method for modules
90 In module ModuleName.pm:
96 @EXPORT = qw(...); # symbols to export by default
97 @EXPORT_OK = qw(...); # symbols to export on request
98 %EXPORT_TAGS = tag => [...]; # define names for sets of symbols
100 In other files which wish to use ModuleName:
102 use ModuleName; # import default symbols into my package
104 use ModuleName qw(...); # import listed symbols into my package
106 use ModuleName (); # do not import any symbols
110 The Exporter module implements a default C<import> method which
111 many modules choose to inherit rather than implement their own.
113 Perl automatically calls the C<import> method when processing a
114 C<use> statement for a module. Modules and C<use> are documented
115 in L<perlfunc> and L<perlmod>. Understanding the concept of
116 modules and how the C<use> statement operates is important to
117 understanding the Exporter.
121 The arrays C<@EXPORT> and C<@EXPORT_OK> in a module hold lists of
122 symbols that are going to be exported into the users name space by
123 default, or which they can request to be exported, respectively. The
124 symbols can represent functions, scalars, arrays, hashes, or typeglobs.
125 The symbols must be given by full name with the exception that the
126 ampersand in front of a function is optional, e.g.
128 @EXPORT = qw(afunc $scalar @array); # afunc is a function
129 @EXPORT_OK = qw(&bfunc %hash *typeglob); # explicit prefix on &bfunc
131 =head2 Selecting What To Export
133 Do B<not> export method names!
135 Do B<not> export anything else by default without a good reason!
137 Exports pollute the namespace of the module user. If you must export
138 try to use @EXPORT_OK in preference to @EXPORT and avoid short or
139 common symbol names to reduce the risk of name clashes.
141 Generally anything not exported is still accessible from outside the
142 module using the ModuleName::item_name (or $blessed_ref-E<gt>method)
143 syntax. By convention you can use a leading underscore on names to
144 informally indicate that they are 'internal' and not for public use.
146 (It is actually possible to get private functions by saying:
148 my $subref = sub { ... };
151 But there's no way to call that directly as a method, since a method
152 must have a name in the symbol table.)
154 As a general rule, if the module is trying to be object oriented
155 then export nothing. If it's just a collection of functions then
156 @EXPORT_OK anything but use @EXPORT with caution.
158 Other module design guidelines can be found in L<perlmod>.
160 =head2 Specialised Import Lists
162 If the first entry in an import list begins with !, : or / then the
163 list is treated as a series of specifications which either add to or
164 delete from the list of names to import. They are processed left to
165 right. Specifications are in the form:
167 [!]name This name only
168 [!]:DEFAULT All names in @EXPORT
169 [!]:tag All names in $EXPORT_TAGS{tag} anonymous list
170 [!]/pattern/ All names in @EXPORT and @EXPORT_OK which match
172 A leading ! indicates that matching names should be deleted from the
173 list of names to import. If the first specification is a deletion it
174 is treated as though preceded by :DEFAULT. If you just want to import
175 extra names in addition to the default set you will still need to
176 include :DEFAULT explicitly.
178 e.g., Module.pm defines:
180 @EXPORT = qw(A1 A2 A3 A4 A5);
181 @EXPORT_OK = qw(B1 B2 B3 B4 B5);
182 %EXPORT_TAGS = (T1 => [qw(A1 A2 B1 B2)], T2 => [qw(A1 A2 B3 B4)]);
184 Note that you cannot use tags in @EXPORT or @EXPORT_OK.
185 Names in EXPORT_TAGS must also appear in @EXPORT or @EXPORT_OK.
187 An application using Module can say something like:
189 use Module qw(:DEFAULT :T2 !B3 A3);
191 Other examples include:
193 use Socket qw(!/^[AP]F_/ !SOMAXCONN !SOL_SOCKET);
194 use POSIX qw(:errno_h :termios_h !TCSADRAIN !/^EXIT/);
196 Remember that most patterns (using //) will need to be anchored
197 with a leading ^, e.g., C</^EXIT/> rather than C</EXIT/>.
199 You can say C<BEGIN { $Exporter::Verbose=1 }> to see how the
200 specifications are being processed and what is actually being imported
203 =head2 Exporting without using Export's import method
205 Exporter has a special method, 'export_to_level' which is used in situations
206 where you can't directly call Export's import method. The export_to_level
209 MyPackage->export_to_level($where_to_export, $package, @what_to_export);
211 where $where_to_export is an integer telling how far up the calling stack
212 to export your symbols, and @what_to_export is an array telling what
213 symbols *to* export (usually this is @_). The $package argument is
216 For example, suppose that you have a module, A, which already has an
222 @EXPORT_OK = qw ($b);
226 $A::b = 1; # not a very useful import method
229 and you want to Export symbol $A::b back to the module that called
230 package A. Since Exporter relies on the import method to work, via
231 inheritance, as it stands Exporter::import() will never get called.
232 Instead, say the following:
236 @EXPORT_OK = qw ($b);
241 A->export_to_level(1, @_);
244 This will export the symbols one level 'above' the current package - ie: to
245 the program or module that used package A.
247 Note: Be careful not to modify '@_' at all before you call export_to_level
248 - or people using your package will get very unexplained results!
251 =head2 Module Version Checking
253 The Exporter module will convert an attempt to import a number from a
254 module into a call to $module_name-E<gt>require_version($value). This can
255 be used to validate that the version of the module being used is
256 greater than or equal to the required version.
258 The Exporter module supplies a default require_version method which
259 checks the value of $VERSION in the exporting module.
261 Since the default require_version method treats the $VERSION number as
262 a simple numeric value it will regard version 1.10 as lower than
263 1.9. For this reason it is strongly recommended that you use numbers
264 with at least two decimal places, e.g., 1.09.
266 =head2 Managing Unknown Symbols
268 In some situations you may want to prevent certain symbols from being
269 exported. Typically this applies to extensions which have functions
270 or constants that may not exist on some systems.
272 The names of any symbols that cannot be exported should be listed
273 in the C<@EXPORT_FAIL> array.
275 If a module attempts to import any of these symbols the Exporter
276 will give the module an opportunity to handle the situation before
277 generating an error. The Exporter will call an export_fail method
278 with a list of the failed symbols:
280 @failed_symbols = $module_name->export_fail(@failed_symbols);
282 If the export_fail method returns an empty list then no error is
283 recorded and all the requested symbols are exported. If the returned
284 list is not empty then an error is generated for each symbol and the
285 export fails. The Exporter provides a default export_fail method which
286 simply returns the list unchanged.
288 Uses for the export_fail method include giving better error messages
289 for some symbols and performing lazy architectural checks (put more
290 symbols into @EXPORT_FAIL by default and then take them out if someone
291 actually tries to use them and an expensive check shows that they are
292 usable on that platform).
294 =head2 Tag Handling Utility Functions
296 Since the symbols listed within %EXPORT_TAGS must also appear in either
297 @EXPORT or @EXPORT_OK, two utility functions are provided which allow
298 you to easily add tagged sets of symbols to @EXPORT or @EXPORT_OK:
300 %EXPORT_TAGS = (foo => [qw(aa bb cc)], bar => [qw(aa cc dd)]);
302 Exporter::export_tags('foo'); # add aa, bb and cc to @EXPORT
303 Exporter::export_ok_tags('bar'); # add aa, cc and dd to @EXPORT_OK
305 Any names which are not tags are added to @EXPORT or @EXPORT_OK
306 unchanged but will trigger a warning (with C<-w>) to avoid misspelt tags
307 names being silently added to @EXPORT or @EXPORT_OK. Future versions
308 may make this a fatal error.