314 lines
10 KiB
Perl
314 lines
10 KiB
Perl
package Exporter;
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require 5.001;
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$ExportLevel = 0;
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$Verbose ||= 0;
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$VERSION = '5.562';
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sub export_to_level {
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require Exporter::Heavy;
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goto &heavy_export_to_level;
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}
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sub export {
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require Exporter::Heavy;
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goto &heavy_export;
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}
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sub export_tags {
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require Exporter::Heavy;
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_push_tags((caller)[0], "EXPORT", \@_);
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}
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sub export_ok_tags {
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require Exporter::Heavy;
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_push_tags((caller)[0], "EXPORT_OK", \@_);
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}
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sub import {
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my $pkg = shift;
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my $callpkg = caller($ExportLevel);
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*exports = *{"$pkg\::EXPORT"};
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# We *need* to treat @{"$pkg\::EXPORT_FAIL"} since Carp uses it :-(
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*fail = *{"$pkg\::EXPORT_FAIL"};
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return export $pkg, $callpkg, @_
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if $Verbose or $Debug or @fail > 1;
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my $args = @_ or @_ = @exports;
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if ($args and not %exports) {
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foreach my $sym (@exports, @{"$pkg\::EXPORT_OK"}) {
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$sym =~ s/^&//;
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$exports{$sym} = 1;
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}
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}
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if ($Verbose or $Debug
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or grep {/\W/ or $args and not exists $exports{$_}
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or @fail and $_ eq $fail[0]
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or (@{"$pkg\::EXPORT_OK"}
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and $_ eq ${"$pkg\::EXPORT_OK"}[0])} @_) {
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return export $pkg, $callpkg, ($args ? @_ : ());
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}
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#local $SIG{__WARN__} = sub {require Carp; goto &Carp::carp};
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local $SIG{__WARN__} =
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sub {require Carp; local $Carp::CarpLevel = 1; &Carp::carp};
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foreach $sym (@_) {
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# shortcut for the common case of no type character
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*{"$callpkg\::$sym"} = \&{"$pkg\::$sym"};
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}
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}
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1;
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# A simple self test harness. Change 'require Carp' to 'use Carp ()' for testing.
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# package main; eval(join('',<DATA>)) or die $@ unless caller;
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__END__
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package Test;
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$INC{'Exporter.pm'} = 1;
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@ISA = qw(Exporter);
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@EXPORT = qw(A1 A2 A3 A4 A5);
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@EXPORT_OK = qw(B1 B2 B3 B4 B5);
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%EXPORT_TAGS = (T1=>[qw(A1 A2 B1 B2)], T2=>[qw(A1 A2 B3 B4)], T3=>[qw(X3)]);
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@EXPORT_FAIL = qw(B4);
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Exporter::export_ok_tags('T3', 'unknown_tag');
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sub export_fail {
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map { "Test::$_" } @_ # edit symbols just as an example
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}
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package main;
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$Exporter::Verbose = 1;
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#import Test;
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#import Test qw(X3); # export ok via export_ok_tags()
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#import Test qw(:T1 !A2 /5/ !/3/ B5);
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import Test qw(:T2 !B4);
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import Test qw(:T2); # should fail
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1;
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=head1 NAME
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Exporter - Implements default import method for modules
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=head1 SYNOPSIS
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In module ModuleName.pm:
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package ModuleName;
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require Exporter;
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@ISA = qw(Exporter);
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@EXPORT = qw(...); # symbols to export by default
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@EXPORT_OK = qw(...); # symbols to export on request
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%EXPORT_TAGS = tag => [...]; # define names for sets of symbols
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In other files which wish to use ModuleName:
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use ModuleName; # import default symbols into my package
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use ModuleName qw(...); # import listed symbols into my package
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use ModuleName (); # do not import any symbols
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=head1 DESCRIPTION
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The Exporter module implements a default C<import> method which
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many modules choose to inherit rather than implement their own.
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Perl automatically calls the C<import> method when processing a
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C<use> statement for a module. Modules and C<use> are documented
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in L<perlfunc> and L<perlmod>. Understanding the concept of
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modules and how the C<use> statement operates is important to
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understanding the Exporter.
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=head2 How to Export
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The arrays C<@EXPORT> and C<@EXPORT_OK> in a module hold lists of
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symbols that are going to be exported into the users name space by
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default, or which they can request to be exported, respectively. The
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symbols can represent functions, scalars, arrays, hashes, or typeglobs.
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The symbols must be given by full name with the exception that the
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ampersand in front of a function is optional, e.g.
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@EXPORT = qw(afunc $scalar @array); # afunc is a function
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@EXPORT_OK = qw(&bfunc %hash *typeglob); # explicit prefix on &bfunc
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=head2 Selecting What To Export
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Do B<not> export method names!
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Do B<not> export anything else by default without a good reason!
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Exports pollute the namespace of the module user. If you must export
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try to use @EXPORT_OK in preference to @EXPORT and avoid short or
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common symbol names to reduce the risk of name clashes.
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Generally anything not exported is still accessible from outside the
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module using the ModuleName::item_name (or $blessed_ref-E<gt>method)
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syntax. By convention you can use a leading underscore on names to
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informally indicate that they are 'internal' and not for public use.
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(It is actually possible to get private functions by saying:
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my $subref = sub { ... };
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&$subref;
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But there's no way to call that directly as a method, since a method
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must have a name in the symbol table.)
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As a general rule, if the module is trying to be object oriented
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then export nothing. If it's just a collection of functions then
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@EXPORT_OK anything but use @EXPORT with caution.
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Other module design guidelines can be found in L<perlmod>.
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=head2 Specialised Import Lists
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If the first entry in an import list begins with !, : or / then the
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list is treated as a series of specifications which either add to or
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delete from the list of names to import. They are processed left to
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right. Specifications are in the form:
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[!]name This name only
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[!]:DEFAULT All names in @EXPORT
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[!]:tag All names in $EXPORT_TAGS{tag} anonymous list
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[!]/pattern/ All names in @EXPORT and @EXPORT_OK which match
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A leading ! indicates that matching names should be deleted from the
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list of names to import. If the first specification is a deletion it
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is treated as though preceded by :DEFAULT. If you just want to import
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extra names in addition to the default set you will still need to
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include :DEFAULT explicitly.
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e.g., Module.pm defines:
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@EXPORT = qw(A1 A2 A3 A4 A5);
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@EXPORT_OK = qw(B1 B2 B3 B4 B5);
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%EXPORT_TAGS = (T1 => [qw(A1 A2 B1 B2)], T2 => [qw(A1 A2 B3 B4)]);
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Note that you cannot use tags in @EXPORT or @EXPORT_OK.
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Names in EXPORT_TAGS must also appear in @EXPORT or @EXPORT_OK.
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An application using Module can say something like:
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use Module qw(:DEFAULT :T2 !B3 A3);
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Other examples include:
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use Socket qw(!/^[AP]F_/ !SOMAXCONN !SOL_SOCKET);
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use POSIX qw(:errno_h :termios_h !TCSADRAIN !/^EXIT/);
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Remember that most patterns (using //) will need to be anchored
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with a leading ^, e.g., C</^EXIT/> rather than C</EXIT/>.
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You can say C<BEGIN { $Exporter::Verbose=1 }> to see how the
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specifications are being processed and what is actually being imported
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into modules.
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=head2 Exporting without using Export's import method
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Exporter has a special method, 'export_to_level' which is used in situations
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where you can't directly call Export's import method. The export_to_level
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method looks like:
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MyPackage->export_to_level($where_to_export, $package, @what_to_export);
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where $where_to_export is an integer telling how far up the calling stack
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to export your symbols, and @what_to_export is an array telling what
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symbols *to* export (usually this is @_). The $package argument is
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currently unused.
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For example, suppose that you have a module, A, which already has an
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import function:
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package A;
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@ISA = qw(Exporter);
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@EXPORT_OK = qw ($b);
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sub import
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{
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$A::b = 1; # not a very useful import method
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}
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and you want to Export symbol $A::b back to the module that called
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package A. Since Exporter relies on the import method to work, via
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inheritance, as it stands Exporter::import() will never get called.
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Instead, say the following:
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package A;
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@ISA = qw(Exporter);
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@EXPORT_OK = qw ($b);
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sub import
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{
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$A::b = 1;
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A->export_to_level(1, @_);
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}
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This will export the symbols one level 'above' the current package - ie: to
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the program or module that used package A.
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Note: Be careful not to modify '@_' at all before you call export_to_level
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- or people using your package will get very unexplained results!
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=head2 Module Version Checking
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The Exporter module will convert an attempt to import a number from a
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module into a call to $module_name-E<gt>require_version($value). This can
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be used to validate that the version of the module being used is
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greater than or equal to the required version.
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The Exporter module supplies a default require_version method which
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checks the value of $VERSION in the exporting module.
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Since the default require_version method treats the $VERSION number as
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a simple numeric value it will regard version 1.10 as lower than
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1.9. For this reason it is strongly recommended that you use numbers
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with at least two decimal places, e.g., 1.09.
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=head2 Managing Unknown Symbols
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In some situations you may want to prevent certain symbols from being
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exported. Typically this applies to extensions which have functions
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or constants that may not exist on some systems.
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The names of any symbols that cannot be exported should be listed
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in the C<@EXPORT_FAIL> array.
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If a module attempts to import any of these symbols the Exporter
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will give the module an opportunity to handle the situation before
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generating an error. The Exporter will call an export_fail method
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with a list of the failed symbols:
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@failed_symbols = $module_name->export_fail(@failed_symbols);
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If the export_fail method returns an empty list then no error is
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recorded and all the requested symbols are exported. If the returned
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list is not empty then an error is generated for each symbol and the
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export fails. The Exporter provides a default export_fail method which
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simply returns the list unchanged.
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Uses for the export_fail method include giving better error messages
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for some symbols and performing lazy architectural checks (put more
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symbols into @EXPORT_FAIL by default and then take them out if someone
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actually tries to use them and an expensive check shows that they are
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usable on that platform).
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=head2 Tag Handling Utility Functions
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Since the symbols listed within %EXPORT_TAGS must also appear in either
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@EXPORT or @EXPORT_OK, two utility functions are provided which allow
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you to easily add tagged sets of symbols to @EXPORT or @EXPORT_OK:
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%EXPORT_TAGS = (foo => [qw(aa bb cc)], bar => [qw(aa cc dd)]);
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Exporter::export_tags('foo'); # add aa, bb and cc to @EXPORT
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Exporter::export_ok_tags('bar'); # add aa, cc and dd to @EXPORT_OK
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Any names which are not tags are added to @EXPORT or @EXPORT_OK
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unchanged but will trigger a warning (with C<-w>) to avoid misspelt tags
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names being silently added to @EXPORT or @EXPORT_OK. Future versions
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may make this a fatal error.
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=cut
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