our $Debug = 0;
our $ExportLevel = 0;
our $Verbose ||= 0;
-our $VERSION = '5.566';
-$Carp::Internal{Exporter} = 1;
+our $VERSION = '5.67';
+our (%Cache);
sub as_heavy {
require Exporter::Heavy;
my $pkg = shift;
my $callpkg = caller($ExportLevel);
+ if ($pkg eq "Exporter" and @_ and $_[0] eq "import") {
+ *{$callpkg."::import"} = \&import;
+ return;
+ }
+
# We *need* to treat @{"$pkg\::EXPORT_FAIL"} since Carp uses it :-(
- my($exports, $export_cache, $fail)
- = (\@{"$pkg\::EXPORT"}, \%{"$pkg\::EXPORT"}, \@{"$pkg\::EXPORT_FAIL"});
+ my $exports = \@{"$pkg\::EXPORT"};
+ # But, avoid creating things if they don't exist, which saves a couple of
+ # hundred bytes per package processed.
+ my $fail = ${$pkg . '::'}{EXPORT_FAIL} && \@{"$pkg\::EXPORT_FAIL"};
return export $pkg, $callpkg, @_
- if $Verbose or $Debug or @$fail > 1;
+ if $Verbose or $Debug or $fail && @$fail > 1;
+ my $export_cache = ($Cache{$pkg} ||= {});
my $args = @_ or @_ = @$exports;
- local $_;
if ($args and not %$export_cache) {
s/^&//, $export_cache->{$_} = 1
foreach (@$exports, @{"$pkg\::EXPORT_OK"});
# We bomb out of the loop with last as soon as heavy is set.
if ($args or $fail) {
($heavy = (/\W/ or $args and not exists $export_cache->{$_}
- or @$fail and $_ eq $fail->[0])) and last
+ or $fail and @$fail and $_ eq $fail->[0])) and last
foreach (@_);
} else {
($heavy = /\W/) and last
}
return export $pkg, $callpkg, ($args ? @_ : ()) if $heavy;
local $SIG{__WARN__} =
- sub {require Carp; &Carp::carp};
+ sub {require Carp; &Carp::carp} if not $SIG{__WARN__};
# shortcut for the common case of no type character
*{"$callpkg\::$_"} = \&{"$pkg\::$_"} foreach @_;
}
=head1 SYNOPSIS
-In module YourModule.pm:
+In module F<YourModule.pm>:
package YourModule;
require Exporter;
@ISA = qw(Exporter);
@EXPORT_OK = qw(munge frobnicate); # symbols to export on request
-In other files which wish to use YourModule:
+or
+
+ package YourModule;
+ use Exporter 'import'; # gives you Exporter's import() method directly
+ @EXPORT_OK = qw(munge frobnicate); # symbols to export on request
+
+In other files which wish to use C<YourModule>:
- use ModuleName qw(frobnicate); # import listed symbols
+ use YourModule qw(frobnicate); # import listed symbols
frobnicate ($left, $right) # calls YourModule::frobnicate
+Take a look at L</Good Practices> for some variants
+you will like to use in modern Perl code.
+
=head1 DESCRIPTION
The Exporter module implements an C<import> method which allows a module
-to export functions and variables to its users' namespaces. Many modules
+to export functions and variables to its users' namespaces. Many modules
use Exporter rather than implementing their own C<import> method because
Exporter provides a highly flexible interface, with an implementation optimised
for the common case.
Perl automatically calls the C<import> method when processing a
-C<use> statement for a module. Modules and C<use> are documented
-in L<perlfunc> and L<perlmod>. Understanding the concept of
+C<use> statement for a module. Modules and C<use> are documented
+in L<perlfunc> and L<perlmod>. Understanding the concept of
modules and how the C<use> statement operates is important to
understanding the Exporter.
Do B<not> export anything else by default without a good reason!
Exports pollute the namespace of the module user. If you must export
-try to use @EXPORT_OK in preference to @EXPORT and avoid short or
+try to use C<@EXPORT_OK> in preference to C<@EXPORT> and avoid short or
common symbol names to reduce the risk of name clashes.
Generally anything not exported is still accessible from outside the
-module using the ModuleName::item_name (or $blessed_ref-E<gt>method)
+module using the C<YourModule::item_name> (or C<< $blessed_ref->method >>)
syntax. By convention you can use a leading underscore on names to
informally indicate that they are 'internal' and not for public use.
how to make inheritance work.)
As a general rule, if the module is trying to be object oriented
-then export nothing. If it's just a collection of functions then
-@EXPORT_OK anything but use @EXPORT with caution. For function and
+then export nothing. If it's just a collection of functions then
+C<@EXPORT_OK> anything but use C<@EXPORT> with caution. For function and
method names use barewords in preference to names prefixed with
ampersands for the export lists.
=over 4
-=item C<use ModuleName;>
+=item C<use YourModule;>
-This imports all the symbols from ModuleName's @EXPORT into the namespace
+This imports all the symbols from YourModule's C<@EXPORT> into the namespace
of the C<use> statement.
-=item C<use ModuleName ();>
+=item C<use YourModule ();>
This causes perl to load your module but does not import any symbols.
-=item C<use ModuleName qw(...);>
+=item C<use YourModule qw(...);>
This imports only the symbols listed by the caller into their namespace.
-All listed symbols must be in your @EXPORT or @EXPORT_OK, else an error
-occurs. The advanced export features of Exporter are accessed like this,
+All listed symbols must be in your C<@EXPORT> or C<@EXPORT_OK>, else an error
+occurs. The advanced export features of Exporter are accessed like this,
but with list entries that are syntactically distinct from symbol names.
=back
=head2 Specialised Import Lists
-If the first entry in an import list begins with !, : or / then the
-list is treated as a series of specifications which either add to or
-delete from the list of names to import. They are processed left to
+If any of the entries in an import list begins with !, : or / then
+the list is treated as a series of specifications which either add to
+or delete from the list of names to import. They are processed left to
right. Specifications are in the form:
[!]name This name only
A leading ! indicates that matching names should be deleted from the
list of names to import. If the first specification is a deletion it
-is treated as though preceded by :DEFAULT. If you just want to import
+is treated as though preceded by :DEFAULT. If you just want to import
extra names in addition to the default set you will still need to
include :DEFAULT explicitly.
-e.g., Module.pm defines:
+e.g., F<Module.pm> defines:
@EXPORT = qw(A1 A2 A3 A4 A5);
@EXPORT_OK = qw(B1 B2 B3 B4 B5);
=head2 Exporting without using Exporter's import method
Exporter has a special method, 'export_to_level' which is used in situations
-where you can't directly call Exporter's import method. The export_to_level
+where you can't directly call Exporter's
+import method. The export_to_level
method looks like:
-MyPackage->export_to_level($where_to_export, $package, @what_to_export);
+ MyPackage->export_to_level($where_to_export, $package, @what_to_export);
-where $where_to_export is an integer telling how far up the calling stack
-to export your symbols, and @what_to_export is an array telling what
-symbols *to* export (usually this is @_). The $package argument is
+where C<$where_to_export> is an integer telling how far up the calling stack
+to export your symbols, and C<@what_to_export> is an array telling what
+symbols *to* export (usually this is C<@_>). The C<$package> argument is
currently unused.
For example, suppose that you have a module, A, which already has an
import function:
-package A;
+ package A;
-@ISA = qw(Exporter);
-@EXPORT_OK = qw ($b);
+ @ISA = qw(Exporter);
+ @EXPORT_OK = qw ($b);
-sub import
-{
- $A::b = 1; # not a very useful import method
-}
+ sub import
+ {
+ $A::b = 1; # not a very useful import method
+ }
-and you want to Export symbol $A::b back to the module that called
-package A. Since Exporter relies on the import method to work, via
+and you want to Export symbol C<$A::b> back to the module that called
+package A. Since Exporter relies on the import method to work, via
inheritance, as it stands Exporter::import() will never get called.
Instead, say the following:
-package A;
-@ISA = qw(Exporter);
-@EXPORT_OK = qw ($b);
+ package A;
+ @ISA = qw(Exporter);
+ @EXPORT_OK = qw ($b);
-sub import
-{
- $A::b = 1;
- A->export_to_level(1, @_);
-}
+ sub import
+ {
+ $A::b = 1;
+ A->export_to_level(1, @_);
+ }
This will export the symbols one level 'above' the current package - ie: to
the program or module that used package A.
-Note: Be careful not to modify '@_' at all before you call export_to_level
+Note: Be careful not to modify C<@_> at all before you call export_to_level
- or people using your package will get very unexplained results!
+=head2 Exporting without inheriting from Exporter
+
+By including Exporter in your C<@ISA> you inherit an Exporter's import() method
+but you also inherit several other helper methods which you probably don't
+want. To avoid this you can do
+
+ package YourModule;
+ use Exporter qw( import );
+
+which will export Exporter's own import() method into YourModule.
+Everything will work as before but you won't need to include Exporter in
+C<@YourModule::ISA>.
+
+Note: This feature was introduced in version 5.57
+of Exporter, released with perl 5.8.3.
=head2 Module Version Checking
The Exporter module will convert an attempt to import a number from a
-module into a call to $module_name-E<gt>require_version($value). This can
+module into a call to C<< $module_name->VERSION($value) >>. This can
be used to validate that the version of the module being used is
greater than or equal to the required version.
-The Exporter module supplies a default require_version method which
-checks the value of $VERSION in the exporting module.
-
-Since the default require_version method treats the $VERSION number as
+Since the C<UNIVERSAL::VERSION> method treats the C<$VERSION> number as
a simple numeric value it will regard version 1.10 as lower than
-1.9. For this reason it is strongly recommended that you use numbers
+1.9. For this reason it is strongly recommended that you use numbers
with at least two decimal places, e.g., 1.09.
=head2 Managing Unknown Symbols
In some situations you may want to prevent certain symbols from being
-exported. Typically this applies to extensions which have functions
+exported. Typically this applies to extensions which have functions
or constants that may not exist on some systems.
The names of any symbols that cannot be exported should be listed
If a module attempts to import any of these symbols the Exporter
will give the module an opportunity to handle the situation before
-generating an error. The Exporter will call an export_fail method
+generating an error. The Exporter will call an export_fail method
with a list of the failed symbols:
@failed_symbols = $module_name->export_fail(@failed_symbols);
-If the export_fail method returns an empty list then no error is
-recorded and all the requested symbols are exported. If the returned
+If the C<export_fail> method returns an empty list then no error is
+recorded and all the requested symbols are exported. If the returned
list is not empty then an error is generated for each symbol and the
-export fails. The Exporter provides a default export_fail method which
+export fails. The Exporter provides a default C<export_fail> method which
simply returns the list unchanged.
-Uses for the export_fail method include giving better error messages
+Uses for the C<export_fail> method include giving better error messages
for some symbols and performing lazy architectural checks (put more
-symbols into @EXPORT_FAIL by default and then take them out if someone
+symbols into C<@EXPORT_FAIL> by default and then take them out if someone
actually tries to use them and an expensive check shows that they are
usable on that platform).
=head2 Tag Handling Utility Functions
-Since the symbols listed within %EXPORT_TAGS must also appear in either
-@EXPORT or @EXPORT_OK, two utility functions are provided which allow
-you to easily add tagged sets of symbols to @EXPORT or @EXPORT_OK:
+Since the symbols listed within C<%EXPORT_TAGS> must also appear in either
+C<@EXPORT> or C<@EXPORT_OK>, two utility functions are provided which allow
+you to easily add tagged sets of symbols to C<@EXPORT> or C<@EXPORT_OK>:
%EXPORT_TAGS = (foo => [qw(aa bb cc)], bar => [qw(aa cc dd)]);
Exporter::export_tags('foo'); # add aa, bb and cc to @EXPORT
Exporter::export_ok_tags('bar'); # add aa, cc and dd to @EXPORT_OK
-Any names which are not tags are added to @EXPORT or @EXPORT_OK
+Any names which are not tags are added to C<@EXPORT> or C<@EXPORT_OK>
unchanged but will trigger a warning (with C<-w>) to avoid misspelt tags
-names being silently added to @EXPORT or @EXPORT_OK. Future versions
+names being silently added to C<@EXPORT> or C<@EXPORT_OK>. Future versions
may make this a fatal error.
=head2 Generating combined tags
-If several symbol categories exist in %EXPORT_TAGS, it's usually
+If several symbol categories exist in C<%EXPORT_TAGS>, it's usually
useful to create the utility ":all" to simplify "use" statements.
The simplest way to do this is:
grep {!$seen{$_}++} @{$EXPORT_TAGS{$_}} foreach keys %EXPORT_TAGS;
}
-CGI.pm creates an ":all" tag which contains some (but not really
+F<CGI.pm> creates an ":all" tag which contains some (but not really
all) of its categories. That could be done with one small
change:
foreach qw/html2 html3 netscape form cgi internal/;
}
-Note that the tag names in %EXPORT_TAGS don't have the leading ':'.
+Note that the tag names in C<%EXPORT_TAGS> don't have the leading ':'.
=head2 C<AUTOLOAD>ed Constants
they can't be checked at compile time for constancy.
Even if a prototype is available at compile time, the body of the
-subroutine is not (it hasn't been C<AUTOLOAD>ed yet). perl needs to
+subroutine is not (it hasn't been C<AUTOLOAD>ed yet). perl needs to
examine both the C<()> prototype and the body of a subroutine at
compile time to detect that it can safely replace calls to that
subroutine with the constant value.
an C<AUTOLOAD> for any constants explicitly imported by other packages
or which are usually used when your package is C<use>d.
+=head1 Good Practices
+
+=head2 Declaring C<@EXPORT_OK> and Friends
+
+When using C<Exporter> with the standard C<strict> and C<warnings>
+pragmas, the C<our> keyword is needed to declare the package
+variables C<@EXPORT_OK>, C<@EXPORT>, C<@ISA>, etc.
+
+ our @ISA = qw(Exporter);
+ our @EXPORT_OK = qw(munge frobnicate);
+
+If backward compatibility for Perls under 5.6 is important,
+one must write instead a C<use vars> statement.
+
+ use vars qw(@ISA @EXPORT_OK);
+ @ISA = qw(Exporter);
+ @EXPORT_OK = qw(munge frobnicate);
+
+=head2 Playing Safe
+
+There are some caveats with the use of runtime statements
+like C<require Exporter> and the assignment to package
+variables, which can very subtle for the unaware programmer.
+This may happen for instance with mutually recursive
+modules, which are affected by the time the relevant
+constructions are executed.
+
+The ideal (but a bit ugly) way to never have to think
+about that is to use C<BEGIN> blocks. So the first part
+of the L</SYNOPSIS> code could be rewritten as:
+
+ package YourModule;
+
+ use strict;
+ use warnings;
+
+ our (@ISA, @EXPORT_OK);
+ BEGIN {
+ require Exporter;
+ @ISA = qw(Exporter);
+ @EXPORT_OK = qw(munge frobnicate); # symbols to export on request
+ }
+
+The C<BEGIN> will assure that the loading of F<Exporter.pm>
+and the assignments to C<@ISA> and C<@EXPORT_OK> happen
+immediately, leaving no room for something to get awry
+or just plain wrong.
+
+With respect to loading C<Exporter> and inheriting, there
+are alternatives with the use of modules like C<base> and C<parent>.
+
+ use base qw( Exporter );
+ # or
+ use parent qw( Exporter );
+
+Any of these statements are nice replacements for
+C<BEGIN { require Exporter; @ISA = qw(Exporter); }>
+with the same compile-time effect. The basic difference
+is that C<base> code interacts with declared C<fields>
+while C<parent> is a streamlined version of the older
+C<base> code to just establish the IS-A relationship.
+
+For more details, see the documentation and code of
+L<base> and L<parent>.
+
+Another thorough remedy to that runtime
+vs. compile-time trap is to use L<Exporter::Easy>,
+which is a wrapper of Exporter that allows all
+boilerplate code at a single gulp in the
+use statement.
+
+ use Exporter::Easy (
+ OK => [ qw(munge frobnicate) ],
+ );
+ # @ISA setup is automatic
+ # all assignments happen at compile time
+
+=head2 What not to Export
+
+You have been warned already in L</Selecting What To Export>
+to not export:
+
+=over 4
+
+=item *
+
+method names (because you don't need to
+and that's likely to not do what you want),
+
+=item *
+
+anything by default (because you don't want to surprise your users...
+badly)
+
+=item *
+
+anything you don't need to (because less is more)
+
+=back
+
+There's one more item to add to this list. Do B<not>
+export variable names. Just because C<Exporter> lets you
+do that, it does not mean you should.
+
+ @EXPORT_OK = qw( $svar @avar %hvar ); # DON'T!
+
+Exporting variables is not a good idea. They can
+change under the hood, provoking horrible
+effects at-a-distance, that are too hard to track
+and to fix. Trust me: they are not worth it.
+
+To provide the capability to set/get class-wide
+settings, it is best instead to provide accessors
+as subroutines or class methods instead.
+
+=head1 SEE ALSO
+
+C<Exporter> is definitely not the only module with
+symbol exporter capabilities. At CPAN, you may find
+a bunch of them. Some are lighter. Some
+provide improved APIs and features. Peek the one
+that fits your needs. The following is
+a sample list of such modules.
+
+ Exporter::Easy
+ Exporter::Lite
+ Exporter::Renaming
+ Exporter::Tidy
+ Sub::Exporter / Sub::Installer
+ Perl6::Export / Perl6::Export::Attrs
+
+=head1 LICENSE
+
+This library is free software. You can redistribute it
+and/or modify it under the same terms as Perl itself.
+
=cut
+
+
+
https://perl5.git.perl.org / perl5.git / blobdiff