6 # We go to a lot of trouble not to 'require Carp' at file scope,
7 # because Carp requires Exporter, and something has to give.
11 $Verbose = 0 unless $Verbose;
15 # First make import warnings look like they're coming from the "use".
16 local $SIG{__WARN__} = sub {
18 if ($text =~ s/ at \S*Exporter.pm line \d+.*\n//) {
20 local $Carp::CarpLevel = 1; # ignore package calling us too.
27 local $SIG{__DIE__} = sub {
29 local $Carp::CarpLevel = 1; # ignore package calling us too.
30 Carp::croak("$_[0]Illegal null symbol in \@${1}::EXPORT")
31 if $_[0] =~ /^Unable to create sub named "(.*?)::"/;
34 my($pkg, $callpkg, @imports) = @_;
35 my($type, $sym, $oops);
36 *exports = *{"${pkg}::EXPORT"};
40 grep(s/^&//, @exports);
41 @exports{@exports} = (1) x @exports;
42 my $ok = \@{"${pkg}::EXPORT_OK"};
45 @exports{@$ok} = (1) x @$ok;
49 if ($imports[0] =~ m#^[/!:]#){
50 my $tagsref = \%{"${pkg}::EXPORT_TAGS"};
53 my($remove, $spec, @names, @allexports);
54 # negated first item implies starting with default set:
55 unshift @imports, ':DEFAULT' if $imports[0] =~ m/^!/;
56 foreach $spec (@imports){
57 $remove = $spec =~ s/^!//;
60 if ($spec eq 'DEFAULT'){
63 elsif ($tagdata = $tagsref->{$spec}) {
67 warn qq["$spec" is not defined in %${pkg}::EXPORT_TAGS];
72 elsif ($spec =~ m:^/(.*)/$:){
74 @allexports = keys %exports unless @allexports; # only do keys once
75 @names = grep(/$patn/, @allexports); # not anchored by default
78 @names = ($spec); # is a normal symbol name
81 warn "Import ".($remove ? "del":"add").": @names "
85 foreach $sym (@names) { delete $imports{$sym} }
88 @imports{@names} = (1) x @names;
91 @imports = keys %imports;
94 foreach $sym (@imports) {
95 if (!$exports{$sym}) {
97 $pkg->require_version($sym);
98 # If the version number was the only thing specified
99 # then we should act as if nothing was specified:
104 # We need a way to emulate 'use Foo ()' but still
105 # allow an easy version check: "use Foo 1.23, ''";
106 if (@imports == 2 and !$imports[1]) {
110 } elsif ($sym !~ s/^&// || !$exports{$sym}) {
112 Carp::carp(qq["$sym" is not exported by the $pkg module]);
119 Carp::croak("Can't continue after import errors");
126 *fail = *{"${pkg}::EXPORT_FAIL"};
129 # Build cache of symbols. Optimise the lookup by adding
130 # barewords twice... both with and without a leading &.
131 # (Technique could be applied to %exports cache at cost of memory)
132 my @expanded = map { /^\w/ ? ($_, '&'.$_) : $_ } @fail;
133 warn "${pkg}::EXPORT_FAIL cached: @expanded" if $Verbose;
134 @fail{@expanded} = (1) x @expanded;
137 foreach $sym (@imports) { push(@failed, $sym) if $fail{$sym} }
139 @failed = $pkg->export_fail(@failed);
140 foreach $sym (@failed) {
142 Carp::carp(qq["$sym" is not implemented by the $pkg module ],
143 "on this architecture");
147 Carp::croak("Can't continue after import errors");
152 warn "Importing into $callpkg from $pkg: ",
153 join(", ",sort @imports) if $Verbose;
155 foreach $sym (@imports) {
156 # shortcut for the common case of no type character
157 (*{"${callpkg}::$sym"} = \&{"${pkg}::$sym"}, next)
158 unless $sym =~ s/^(\W)//;
160 *{"${callpkg}::$sym"} =
161 $type eq '&' ? \&{"${pkg}::$sym"} :
162 $type eq '$' ? \${"${pkg}::$sym"} :
163 $type eq '@' ? \@{"${pkg}::$sym"} :
164 $type eq '%' ? \%{"${pkg}::$sym"} :
165 $type eq '*' ? *{"${pkg}::$sym"} :
166 do { require Carp; Carp::croak("Can't export symbol: $type$sym") };
174 my $callpkg = caller($level);
175 $pkg->export($callpkg, @_);
180 my $callpkg = caller($ExportLevel);
181 export $pkg, $callpkg, @_;
189 my($pkg, $var, $syms) = @_;
191 *export_tags = \%{"${pkg}::EXPORT_TAGS"};
192 push(@{"${pkg}::$var"},
193 map { $export_tags{$_} ? @{$export_tags{$_}} : scalar(++$nontag,$_) }
194 (@$syms) ? @$syms : keys %export_tags);
195 if ($nontag and $^W) {
196 # This may change to a die one day
198 Carp::carp("Some names are not tags");
202 sub export_tags { _push_tags((caller)[0], "EXPORT", \@_) }
203 sub export_ok_tags { _push_tags((caller)[0], "EXPORT_OK", \@_) }
213 sub require_version {
214 my($self, $wanted) = @_;
215 my $pkg = ref $self || $self;
216 my $version = ${"${pkg}::VERSION"};
217 if (!$version or $version < $wanted) {
218 $version ||= "(undef)";
219 my $file = $INC{"$pkg.pm"};
220 $file &&= " ($file)";
222 Carp::croak("$pkg $wanted required--this is only version $version$file")
229 # A simple self test harness. Change 'require Carp' to 'use Carp ()' for testing.
230 # package main; eval(join('',<DATA>)) or die $@ unless caller;
233 $INC{'Exporter.pm'} = 1;
235 @EXPORT = qw(A1 A2 A3 A4 A5);
236 @EXPORT_OK = qw(B1 B2 B3 B4 B5);
237 %EXPORT_TAGS = (T1=>[qw(A1 A2 B1 B2)], T2=>[qw(A1 A2 B3 B4)], T3=>[qw(X3)]);
238 @EXPORT_FAIL = qw(B4);
239 Exporter::export_ok_tags('T3', 'unknown_tag');
241 map { "Test::$_" } @_ # edit symbols just as an example
245 $Exporter::Verbose = 1;
247 #import Test qw(X3); # export ok via export_ok_tags()
248 #import Test qw(:T1 !A2 /5/ !/3/ B5);
249 import Test qw(:T2 !B4);
250 import Test qw(:T2); # should fail
255 Exporter - Implements default import method for modules
259 In module ModuleName.pm:
265 @EXPORT = qw(...); # symbols to export by default
266 @EXPORT_OK = qw(...); # symbols to export on request
267 %EXPORT_TAGS = tag => [...]; # define names for sets of symbols
269 In other files which wish to use ModuleName:
271 use ModuleName; # import default symbols into my package
273 use ModuleName qw(...); # import listed symbols into my package
275 use ModuleName (); # do not import any symbols
279 The Exporter module implements a default C<import> method which
280 many modules choose to inherit rather than implement their own.
282 Perl automatically calls the C<import> method when processing a
283 C<use> statement for a module. Modules and C<use> are documented
284 in L<perlfunc> and L<perlmod>. Understanding the concept of
285 modules and how the C<use> statement operates is important to
286 understanding the Exporter.
288 =head2 Selecting What To Export
290 Do B<not> export method names!
292 Do B<not> export anything else by default without a good reason!
294 Exports pollute the namespace of the module user. If you must export
295 try to use @EXPORT_OK in preference to @EXPORT and avoid short or
296 common symbol names to reduce the risk of name clashes.
298 Generally anything not exported is still accessible from outside the
299 module using the ModuleName::item_name (or $blessed_ref-E<gt>method)
300 syntax. By convention you can use a leading underscore on names to
301 informally indicate that they are 'internal' and not for public use.
303 (It is actually possible to get private functions by saying:
305 my $subref = sub { ... };
308 But there's no way to call that directly as a method, since a method
309 must have a name in the symbol table.)
311 As a general rule, if the module is trying to be object oriented
312 then export nothing. If it's just a collection of functions then
313 @EXPORT_OK anything but use @EXPORT with caution.
315 Other module design guidelines can be found in L<perlmod>.
317 =head2 Specialised Import Lists
319 If the first entry in an import list begins with !, : or / then the
320 list is treated as a series of specifications which either add to or
321 delete from the list of names to import. They are processed left to
322 right. Specifications are in the form:
324 [!]name This name only
325 [!]:DEFAULT All names in @EXPORT
326 [!]:tag All names in $EXPORT_TAGS{tag} anonymous list
327 [!]/pattern/ All names in @EXPORT and @EXPORT_OK which match
329 A leading ! indicates that matching names should be deleted from the
330 list of names to import. If the first specification is a deletion it
331 is treated as though preceded by :DEFAULT. If you just want to import
332 extra names in addition to the default set you will still need to
333 include :DEFAULT explicitly.
335 e.g., Module.pm defines:
337 @EXPORT = qw(A1 A2 A3 A4 A5);
338 @EXPORT_OK = qw(B1 B2 B3 B4 B5);
339 %EXPORT_TAGS = (T1 => [qw(A1 A2 B1 B2)], T2 => [qw(A1 A2 B3 B4)]);
341 Note that you cannot use tags in @EXPORT or @EXPORT_OK.
342 Names in EXPORT_TAGS must also appear in @EXPORT or @EXPORT_OK.
344 An application using Module can say something like:
346 use Module qw(:DEFAULT :T2 !B3 A3);
348 Other examples include:
350 use Socket qw(!/^[AP]F_/ !SOMAXCONN !SOL_SOCKET);
351 use POSIX qw(:errno_h :termios_h !TCSADRAIN !/^EXIT/);
353 Remember that most patterns (using //) will need to be anchored
354 with a leading ^, e.g., C</^EXIT/> rather than C</EXIT/>.
356 You can say C<BEGIN { $Exporter::Verbose=1 }> to see how the
357 specifications are being processed and what is actually being imported
360 =head2 Exporting without using Export's import method
362 Exporter has a special method, 'export_to_level' which is used in situations
363 where you can't directly call Export's import method. The export_to_level
366 MyPackage->export_to_level($where_to_export, @what_to_export);
368 where $where_to_export is an integer telling how far up the calling stack
369 to export your symbols, and @what_to_export is an array telling what
370 symbols *to* export (usually this is @_).
372 For example, suppose that you have a module, A, which already has an
378 @EXPORT_OK = qw ($b);
382 $A::b = 1; # not a very useful import method
385 and you want to Export symbol $A::b back to the module that called
386 package A. Since Exporter relies on the import method to work, via
387 inheritance, as it stands Exporter::import() will never get called.
388 Instead, say the following:
392 @EXPORT_OK = qw ($b);
397 A->export_to_level(1, @_);
400 This will export the symbols one level 'above' the current package - ie: to
401 the program or module that used package A.
403 Note: Be careful not to modify '@_' at all before you call export_to_level
404 - or people using your package will get very unexplained results!
407 =head2 Module Version Checking
409 The Exporter module will convert an attempt to import a number from a
410 module into a call to $module_name-E<gt>require_version($value). This can
411 be used to validate that the version of the module being used is
412 greater than or equal to the required version.
414 The Exporter module supplies a default require_version method which
415 checks the value of $VERSION in the exporting module.
417 Since the default require_version method treats the $VERSION number as
418 a simple numeric value it will regard version 1.10 as lower than
419 1.9. For this reason it is strongly recommended that you use numbers
420 with at least two decimal places, e.g., 1.09.
422 =head2 Managing Unknown Symbols
424 In some situations you may want to prevent certain symbols from being
425 exported. Typically this applies to extensions which have functions
426 or constants that may not exist on some systems.
428 The names of any symbols that cannot be exported should be listed
429 in the C<@EXPORT_FAIL> array.
431 If a module attempts to import any of these symbols the Exporter
432 will give the module an opportunity to handle the situation before
433 generating an error. The Exporter will call an export_fail method
434 with a list of the failed symbols:
436 @failed_symbols = $module_name->export_fail(@failed_symbols);
438 If the export_fail method returns an empty list then no error is
439 recorded and all the requested symbols are exported. If the returned
440 list is not empty then an error is generated for each symbol and the
441 export fails. The Exporter provides a default export_fail method which
442 simply returns the list unchanged.
444 Uses for the export_fail method include giving better error messages
445 for some symbols and performing lazy architectural checks (put more
446 symbols into @EXPORT_FAIL by default and then take them out if someone
447 actually tries to use them and an expensive check shows that they are
448 usable on that platform).
450 =head2 Tag Handling Utility Functions
452 Since the symbols listed within %EXPORT_TAGS must also appear in either
453 @EXPORT or @EXPORT_OK, two utility functions are provided which allow
454 you to easily add tagged sets of symbols to @EXPORT or @EXPORT_OK:
456 %EXPORT_TAGS = (foo => [qw(aa bb cc)], bar => [qw(aa cc dd)]);
458 Exporter::export_tags('foo'); # add aa, bb and cc to @EXPORT
459 Exporter::export_ok_tags('bar'); # add aa, cc and dd to @EXPORT_OK
461 Any names which are not tags are added to @EXPORT or @EXPORT_OK
462 unchanged but will trigger a warning (with C<-w>) to avoid misspelt tags
463 names being silently added to @EXPORT or @EXPORT_OK. Future versions
464 may make this a fatal error.