package Exporter;
-=head1 Comments
+require 5.006;
-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
+# Be lean.
+#use strict;
+#no strict 'refs';
+
+our $Debug = 0;
+our $ExportLevel = 0;
+our $Verbose ||= 0;
+our $VERSION = '5.67';
+our (%Cache);
+
+sub as_heavy {
+ require Exporter::Heavy;
+ # Unfortunately, this does not work if the caller is aliased as *name = \&foo
+ # Thus the need to create a lot of identical subroutines
+ my $c = (caller(1))[3];
+ $c =~ s/.*:://;
+ \&{"Exporter::Heavy::heavy_$c"};
+}
+
+sub export {
+ goto &{as_heavy()};
+}
+
+sub import {
+ 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 $exports = \@{"$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 $fail && @$fail > 1;
+ my $export_cache = ($Cache{$pkg} ||= {});
+ my $args = @_ or @_ = @$exports;
+
+ if ($args and not %$export_cache) {
+ s/^&//, $export_cache->{$_} = 1
+ foreach (@$exports, @{"$pkg\::EXPORT_OK"});
+ }
+ my $heavy;
+ # Try very hard not to use {} and hence have to enter scope on the foreach
+ # We bomb out of the loop with last as soon as heavy is set.
+ if ($args or $fail) {
+ ($heavy = (/\W/ or $args and not exists $export_cache->{$_}
+ or $fail and @$fail and $_ eq $fail->[0])) and last
+ foreach (@_);
+ } else {
+ ($heavy = /\W/) and last
+ foreach (@_);
+ }
+ return export $pkg, $callpkg, ($args ? @_ : ()) if $heavy;
+ local $SIG{__WARN__} =
+ sub {require Carp; &Carp::carp} if not $SIG{__WARN__};
+ # shortcut for the common case of no type character
+ *{"$callpkg\::$_"} = \&{"$pkg\::$_"} foreach @_;
+}
+
+# Default methods
+
+sub export_fail {
+ my $self = shift;
+ @_;
+}
+
+# Unfortunately, caller(1)[3] "does not work" if the caller is aliased as
+# *name = \&foo. Thus the need to create a lot of identical subroutines
+# Otherwise we could have aliased them to export().
+
+sub export_to_level {
+ goto &{as_heavy()};
+}
+
+sub export_tags {
+ goto &{as_heavy()};
+}
+
+sub export_ok_tags {
+ goto &{as_heavy()};
+}
+
+sub require_version {
+ goto &{as_heavy()};
+}
+
+1;
+__END__
+
+=head1 NAME
+
+Exporter - Implements default import method for modules
+
+=head1 SYNOPSIS
+
+In module F<YourModule.pm>:
+
+ package YourModule;
+ require Exporter;
+ @ISA = qw(Exporter);
+ @EXPORT_OK = qw(munge frobnicate); # symbols to export on request
+
+or
+
+ package YourModule;
+ use Exporter 'import'; # gives you Exporter's import() method directly
+ @EXPORT_OK = qw(munge frobnicate); # symbols to export on request
+
+In other files which wish to use C<YourModule>:
+
+ use YourModule qw(frobnicate); # import listed symbols
+ frobnicate ($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
+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
+modules and how the C<use> statement operates is important to
+understanding the Exporter.
+
+=head2 How to Export
+
+The arrays C<@EXPORT> and C<@EXPORT_OK> in a module hold lists of
+symbols that are going to be exported into the users name space by
+default, or which they can request to be exported, respectively. The
+symbols can represent functions, scalars, arrays, hashes, or typeglobs.
+The symbols must be given by full name with the exception that the
+ampersand in front of a function is optional, e.g.
+
+ @EXPORT = qw(afunc $scalar @array); # afunc is a function
+ @EXPORT_OK = qw(&bfunc %hash *typeglob); # explicit prefix on &bfunc
+
+If you are only exporting function names it is recommended to omit the
+ampersand, as the implementation is faster this way.
+
+=head2 Selecting What To Export
+
+Do B<not> export method names!
+
+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 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 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.
+
+(It is actually possible to get private functions by saying:
+
+ my $subref = sub { ... };
+ $subref->(@args); # Call it as a function
+ $obj->$subref(@args); # Use it as a method
+
+However if you use them for methods it is up to you to figure out
+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
+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.
+
+Other module design guidelines can be found in L<perlmod>.
+
+=head2 How to Import
+
+In other files which wish to use your module there are three basic ways for
+them to load your module and import its symbols:
+
+=over 4
+
+=item C<use YourModule;>
+
+This imports all the symbols from YourModule's C<@EXPORT> into the namespace
+of the C<use> statement.
+
+=item C<use YourModule ();>
+
+This causes perl to load your module but does not import any symbols.
+
+=item C<use YourModule qw(...);>
+
+This imports only the symbols listed by the caller into their namespace.
+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
+
+Unless you want to use its advanced features, this is probably all you
+need to know to use Exporter.
+
+=head1 Advanced features
+
+=head2 Specialised Import Lists
+
+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);
Note that you cannot use tags in @EXPORT or @EXPORT_OK.
Names in EXPORT_TAGS must also appear in @EXPORT or @EXPORT_OK.
-Application says:
+An application using Module can say something like:
use Module qw(:DEFAULT :T2 !B3 A3);
+
+Other examples include:
+
use Socket qw(!/^[AP]F_/ !SOMAXCONN !SOL_SOCKET);
- use POSIX qw(/^S_/ acos asin atan /^E/ !/^EXIT/);
+ use POSIX qw(:errno_h :termios_h !TCSADRAIN !/^EXIT/);
+
+Remember that most patterns (using //) will need to be anchored
+with a leading ^, e.g., C</^EXIT/> rather than C</EXIT/>.
+
+You can say C<BEGIN { $Exporter::Verbose=1 }> to see how the
+specifications are being processed and what is actually being imported
+into modules.
+
+=head2 Exporting without using Exporter's import method
+
+Exporter has a special method, 'export_to_level' which is used in situations
+where you can't directly call Exporter's
+import method. The export_to_level
+method looks like:
+
+ MyPackage->export_to_level($where_to_export, $package, @what_to_export);
+
+where C<$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<$package> argument is
+currently unused.
+
+For example, suppose that you have a module, A, which already has an
+import function:
+
+ package A;
+
+ @ISA = qw(Exporter);
+ @EXPORT_OK = qw ($b);
+
+ sub import
+ {
+ $A::b = 1; # not a very useful import method
+ }
+
+and you want to Export symbol C<$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 ($b);
-You can set C<$Exporter::Verbose=1;> to see how the specifications are
-being processed and what is actually being imported into modules.
+ 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 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 $module_name->require_version($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 $VERSION in the exporting module.
+Since the C<UNIVERSAL::VERSION> method treats the C<$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
+with at least two decimal places, e.g., 1.09.
-=cut
+=head2 Managing Unknown Symbols
-require 5.001;
+In some situations you may want to prevent certain symbols from being
+exported. Typically this applies to extensions which have functions
+or constants that may not exist on some systems.
-$ExportLevel = 0;
-$Verbose = 0;
+The names of any symbols that cannot be exported should be listed
+in the C<@EXPORT_FAIL> array.
-require Carp;
+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
+with a list of the failed symbols:
-sub export {
+ @failed_symbols = $module_name->export_fail(@failed_symbols);
- # First make import warnings look like they're coming from the "use".
- local $SIG{__WARN__} = sub {
- my $text = shift;
- $text =~ s/ at \S*Exporter.pm line \d+.\n//;
- local $Carp::CarpLevel = 1; # ignore package calling us too.
- Carp::carp($text);
- };
-
- my $pkg = shift;
- my $callpkg = shift;
- my @imports = @_;
- my($type, $sym);
- *exports = \@{"${pkg}::EXPORT"};
- if (@imports) {
- my $oops;
- *exports = \%{"${pkg}::EXPORT"};
- if (!%exports) {
- grep(s/^&//, @exports);
- @exports{@exports} = (1) x @exports;
- foreach $extra (@{"${pkg}::EXPORT_OK"}) {
- $exports{$extra} = 1;
- }
- }
-
- if ($imports[0] =~ m#^[/!:]#){
- my(@allexports) = keys %exports;
- my $tagsref = \%{"${pkg}::EXPORT_TAGS"};
- my $tagdata;
- my %imports;
- # negated first item implies starting with default set:
- unshift(@imports, ':DEFAULT') if $imports[0] =~ m/^!/;
- foreach (@imports){
- my(@names);
- my($mode,$spec) = m/^(!)?(.*)/;
- $mode = '+' unless defined $mode;
-
- @names = ($spec); # default, maybe overridden below
-
- if ($spec =~ m:^/(.*)/$:){
- my $patn = $1;
- @names = grep(/$patn/, @allexports); # XXX anchor by default?
- }
- elsif ($spec =~ m#^:(.*)# and $tagsref){
- if ($1 eq 'DEFAULT'){
- @names = @exports;
- }
- elsif ($tagsref and $tagdata = $tagsref->{$1}) {
- @names = @$tagdata;
- }
- }
-
- warn "Import Mode $mode, Spec $spec, Names @names\n" if $Verbose;
- if ($mode eq '!') {
- map {delete $imports{$_}} @names; # delete @imports{@names} would be handy :-)
- }
- else {
- @imports{@names} = (1) x @names;
- }
- }
- @imports = keys %imports;
- }
-
- foreach $sym (@imports) {
- if (!$exports{$sym}) {
- if ($sym =~ m/^\d/) {
- $pkg->require_version($sym);
- # If the version number was the only thing specified
- # then we should act as if nothing was specified:
- if (@imports == 1) {
- @imports = @exports;
- last;
- }
- } elsif ($sym !~ s/^&// || !$exports{$sym}) {
- warn qq["$sym" is not exported by the $pkg module ],
- "at $callfile line $callline\n";
- $oops++;
- next;
- }
- }
- }
- Carp::croak("Can't continue with import errors.\n") if $oops;
- }
- else {
- @imports = @exports;
- }
- warn "Importing from $pkg into $callpkg: ",
- join(", ",@imports),"\n" if ($Verbose && @imports);
- foreach $sym (@imports) {
- $type = '&';
- $type = $1 if $sym =~ s/^(\W)//;
- *{"${callpkg}::$sym"} =
- $type eq '&' ? \&{"${pkg}::$sym"} :
- $type eq '$' ? \${"${pkg}::$sym"} :
- $type eq '@' ? \@{"${pkg}::$sym"} :
- $type eq '%' ? \%{"${pkg}::$sym"} :
- $type eq '*' ? *{"${pkg}::$sym"} :
- warn "Can't export symbol: $type$sym\n";
- }
-};
+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 C<export_fail> method which
+simply returns the list unchanged.
-sub import {
- local ($callpkg, $callfile, $callline) = caller($ExportLevel);
- my $pkg = shift;
- export $pkg, $callpkg, @_;
-}
+Uses for the C<export_fail> method include giving better error messages
+for some symbols and performing lazy architectural checks (put more
+symbols into C<@EXPORT_FAIL> by default and then take them out if someone
+actually tries to use them and an expensive check shows that they are
+usable on that platform).
+
+=head2 Tag Handling Utility Functions
+
+Since the symbols listed within C<%EXPORT_TAGS> must also appear in either
+C<@EXPORT> or C<@EXPORT_OK>, two utility functions are provided which allow
+you to easily add tagged sets of symbols to C<@EXPORT> or C<@EXPORT_OK>:
+
+ %EXPORT_TAGS = (foo => [qw(aa bb cc)], bar => [qw(aa cc dd)]);
+
+ Exporter::export_tags('foo'); # add aa, bb and cc to @EXPORT
+ Exporter::export_ok_tags('bar'); # add aa, cc and dd to @EXPORT_OK
+
+Any names which are not tags are added to C<@EXPORT> or C<@EXPORT_OK>
+unchanged but will trigger a warning (with C<-w>) to avoid misspelt tags
+names being silently added to C<@EXPORT> or C<@EXPORT_OK>. Future versions
+may make this a fatal error.
+
+=head2 Generating combined tags
+
+If several symbol categories exist in C<%EXPORT_TAGS>, it's usually
+useful to create the utility ":all" to simplify "use" statements.
+
+The simplest way to do this is:
+
+ %EXPORT_TAGS = (foo => [qw(aa bb cc)], bar => [qw(aa cc dd)]);
+
+ # add all the other ":class" tags to the ":all" class,
+ # deleting duplicates
+ {
+ my %seen;
+
+ push @{$EXPORT_TAGS{all}},
+ grep {!$seen{$_}++} @{$EXPORT_TAGS{$_}} foreach keys %EXPORT_TAGS;
+ }
+
+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:
+
+ # add some of the other ":class" tags to the ":all" class,
+ # deleting duplicates
+ {
+ my %seen;
+
+ push @{$EXPORT_TAGS{all}},
+ grep {!$seen{$_}++} @{$EXPORT_TAGS{$_}}
+ foreach qw/html2 html3 netscape form cgi internal/;
+ }
+
+Note that the tag names in C<%EXPORT_TAGS> don't have the leading ':'.
+
+=head2 C<AUTOLOAD>ed Constants
+
+Many modules make use of C<AUTOLOAD>ing for constant subroutines to
+avoid having to compile and waste memory on rarely used values (see
+L<perlsub> for details on constant subroutines). Calls to such
+constant subroutines are not optimized away at compile time because
+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
+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.
+
+A workaround for this is to call the constants once in a C<BEGIN> block:
+
+ package My ;
+
+ use Socket ;
+
+ foo( SO_LINGER ); ## SO_LINGER NOT optimized away; called at runtime
+ BEGIN { SO_LINGER }
+ foo( SO_LINGER ); ## SO_LINGER optimized away at compile time.
+
+This forces the C<AUTOLOAD> for C<SO_LINGER> to take place before
+SO_LINGER is encountered later in C<My> package.
+
+If you are writing a package that C<AUTOLOAD>s, consider forcing
+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( $svar @avar %hvar ); # DON'T!
+
+Exporting variables is not a good idea. They can
+change under the hood, provoking horrible
+effects at-a-distance, that are too hard to track
+and to fix. Trust me: they are not worth it.
+
+To provide the capability to set/get class-wide
+settings, it is best instead to provide accessors
+as subroutines or class methods instead.
+
+=head1 SEE ALSO
+
+C<Exporter> is definitely not the only module with
+symbol exporter capabilities. At CPAN, you may find
+a bunch of them. Some are lighter. Some
+provide improved APIs and features. Peek the one
+that fits your needs. The following is
+a sample list of such modules.
+
+ Exporter::Easy
+ Exporter::Lite
+ Exporter::Renaming
+ Exporter::Tidy
+ Sub::Exporter / Sub::Installer
+ Perl6::Export / Perl6::Export::Attrs
+
+=head1 LICENSE
+
+This library is free software. You can redistribute it
+and/or modify it under the same terms as Perl itself.
+
+=cut
-sub export_tags {
- my ($pkg) = caller;
- *tags = \%{"${pkg}::EXPORT_TAGS"};
- push(@{"${pkg}::EXPORT"},
- map {$tags{$_} ? @{$tags{$_}} : $_} @_ ? @_ : keys %tags);
-}
-sub require_version {
- my($self, $wanted) = @_;
- my $pkg = ref $self || $self;
- my $version = ${"${pkg}::VERSION"} || "(undef)";
- Carp::croak("$pkg $wanted required--this is only version $version")
- if $version < $wanted;
- $version;
-}
-1;
https://perl5.git.perl.org / perl5.git / blobdiff