perl/lib/AutoLoader.pm - chromium/deps/perl - Git at Google

 package AutoLoader;

 use strict;
 use 5.006_001;

 our($VERSION, $AUTOLOAD);

 my $is_dosish;
 my $is_epoc;
 my $is_vms;
 my $is_macos;

 BEGIN {
     $is_dosish = $^O eq 'dos' || $^O eq 'os2' || $^O eq 'MSWin32' || $^O eq 'NetWare';
     $is_epoc = $^O eq 'epoc';
     $is_vms = $^O eq 'VMS';
     $is_macos = $^O eq 'MacOS';
     $VERSION = '5.72';
 }

 AUTOLOAD {
     my $sub = $AUTOLOAD;
     my $filename = AutoLoader::find_filename( $sub );

     my $save = $@;
     local $!; # Do not munge the value.
     eval { local $SIG{__DIE__}; require $filename };
     if ($@) {
 	if (substr($sub,-9) eq '::DESTROY') {
 	    no strict 'refs';
 	    *$sub = sub {};
 	    $@ = undef;
 	} elsif ($@ =~ /^Can't locate/) {
 	    # The load might just have failed because the filename was too
 	    # long for some old SVR3 systems which treat long names as errors.
 	    # If we can successfully truncate a long name then it's worth a go.
 	    # There is a slight risk that we could pick up the wrong file here
 	    # but autosplit should have warned about that when splitting.
 	    if ($filename =~ s/(\w{12,})\.al$/substr($1,0,11).".al"/e){
 		eval { local $SIG{__DIE__}; require $filename };
 	    }
 	}
 	if ($@){
 	    $@ =~ s/ at .*\n//;
 	    my $error = $@;
 	    require Carp;
 	    Carp::croak($error);
 	}
     }
     $@ = $save;
     goto &$sub;
 }

 sub find_filename {
     my $sub = shift;
     my $filename;
     # Braces used to preserve $1 et al.
     {
 	# Try to find the autoloaded file from the package-qualified
 	# name of the sub. e.g., if the sub needed is
 	# Getopt::Long::GetOptions(), then $INC{Getopt/Long.pm} is
 	# something like '/usr/lib/perl5/Getopt/Long.pm', and the
 	# autoload file is '/usr/lib/perl5/auto/Getopt/Long/GetOptions.al'.
 	#
 	# However, if @INC is a relative path, this might not work.  If,
 	# for example, @INC = ('lib'), then $INC{Getopt/Long.pm} is
 	# 'lib/Getopt/Long.pm', and we want to require
 	# 'auto/Getopt/Long/GetOptions.al' (without the leading 'lib').
 	# In this case, we simple prepend the 'auto/' and let the
 	# C<require> take care of the searching for us.

 	my ($pkg,$func) = ($sub =~ /(.*)::([^:]+)$/);
 	$pkg =~ s#::#/#g;
 	if (defined($filename = $INC{"$pkg.pm"})) {
 	    if ($is_macos) {
 		$pkg =~ tr#/#:#;
 		$filename = undef
 		  unless $filename =~ s#^(.*)$pkg\.pm\z#$1auto:$pkg:$func.al#s;
 	    } else {
 		$filename = undef
 		  unless $filename =~ s#^(.*)$pkg\.pm\z#$1auto/$pkg/$func.al#s;
 	    }

 	    # if the file exists, then make sure that it is a
 	    # a fully anchored path (i.e either '/usr/lib/auto/foo/bar.al',
 	    # or './lib/auto/foo/bar.al'.  This avoids C<require> searching
 	    # (and failing) to find the 'lib/auto/foo/bar.al' because it
 	    # looked for 'lib/lib/auto/foo/bar.al', given @INC = ('lib').

 	    if (defined $filename and -r $filename) {
 		unless ($filename =~ m|^/|s) {
 		    if ($is_dosish) {
 			unless ($filename =~ m{^([a-z]:)?[\\/]}is) {
 			    if ($^O ne 'NetWare') {
 				$filename = "./$filename";
 			    } else {
 				$filename = "$filename";
 			    }
 			}
 		    }
 		    elsif ($is_epoc) {
 			unless ($filename =~ m{^([a-z?]:)?[\\/]}is) {
 			     $filename = "./$filename";
 			}
 		    }
 		    elsif ($is_vms) {
 			# XXX todo by VMSmiths
 			$filename = "./$filename";
 		    }
 		    elsif (!$is_macos) {
 			$filename = "./$filename";
 		    }
 		}
 	    }
 	    else {
 		$filename = undef;
 	    }
 	}
 	unless (defined $filename) {
 	    # let C<require> do the searching
 	    $filename = "auto/$sub.al";
 	    $filename =~ s#::#/#g;
 	}
     }
     return $filename;
 }

 sub import {
     my $pkg = shift;
     my $callpkg = caller;

     #
     # Export symbols, but not by accident of inheritance.
     #

     if ($pkg eq 'AutoLoader') {
 	if ( @_ and $_[0] =~ /^&?AUTOLOAD$/ ) {
 	    no strict 'refs';
 	    *{ $callpkg . '::AUTOLOAD' } = \&AUTOLOAD;
 	}
     }

     #
     # Try to find the autosplit index file.  Eg., if the call package
     # is POSIX, then $INC{POSIX.pm} is something like
     # '/usr/local/lib/perl5/POSIX.pm', and the autosplit index file is in
     # '/usr/local/lib/perl5/auto/POSIX/autosplit.ix', so we require that.
     #
     # However, if @INC is a relative path, this might not work.  If,
     # for example, @INC = ('lib'), then
     # $INC{POSIX.pm} is 'lib/POSIX.pm', and we want to require
     # 'auto/POSIX/autosplit.ix' (without the leading 'lib').
     #

     (my $calldir = $callpkg) =~ s#::#/#g;
     my $path = $INC{$calldir . '.pm'};
     if (defined($path)) {
 	# Try absolute path name, but only eval it if the
         # transformation from module path to autosplit.ix path
         # succeeded!
 	my $replaced_okay;
 	if ($is_macos) {
 	    (my $malldir = $calldir) =~ tr#/#:#;
 	    $replaced_okay = ($path =~ s#^(.*)$malldir\.pm\z#$1auto:$malldir:autosplit.ix#s);
 	} else {
 	    $replaced_okay = ($path =~ s#^(.*)$calldir\.pm\z#$1auto/$calldir/autosplit.ix#);
 	}

 	eval { require $path; } if $replaced_okay;
 	# If that failed, try relative path with normal @INC searching.
 	if (!$replaced_okay or $@) {
 	    $path ="auto/$calldir/autosplit.ix";
 	    eval { require $path; };
 	}
 	if ($@) {
 	    my $error = $@;
 	    require Carp;
 	    Carp::carp($error);
 	}
     }
 }

 sub unimport {
     my $callpkg = caller;

     no strict 'refs';

     for my $exported (qw( AUTOLOAD )) {
 	my $symname = $callpkg . '::' . $exported;
 	undef *{ $symname } if \&{ $symname } == \&{ $exported };
 	*{ $symname } = \&{ $symname };
     }
 }

 1;

 __END__

 =head1 NAME

 AutoLoader - load subroutines only on demand

 =head1 SYNOPSIS

     package Foo;
     use AutoLoader 'AUTOLOAD';   # import the default AUTOLOAD subroutine

     package Bar;
     use AutoLoader;              # don't import AUTOLOAD, define our own
     sub AUTOLOAD {
         ...
         $AutoLoader::AUTOLOAD = "...";
         goto &AutoLoader::AUTOLOAD;
     }

 =head1 DESCRIPTION

 The B<AutoLoader> module works with the B<AutoSplit> module and the
 C<__END__> token to defer the loading of some subroutines until they are
 used rather than loading them all at once.

 To use B<AutoLoader>, the author of a module has to place the
 definitions of subroutines to be autoloaded after an C<__END__> token.
 (See L<perldata>.)  The B<AutoSplit> module can then be run manually to
 extract the definitions into individual files F<auto/funcname.al>.

 B<AutoLoader> implements an AUTOLOAD subroutine.  When an undefined
 subroutine in is called in a client module of B<AutoLoader>,
 B<AutoLoader>'s AUTOLOAD subroutine attempts to locate the subroutine in a
 file with a name related to the location of the file from which the
 client module was read.  As an example, if F<POSIX.pm> is located in
 F</usr/local/lib/perl5/POSIX.pm>, B<AutoLoader> will look for perl
 subroutines B<POSIX> in F</usr/local/lib/perl5/auto/POSIX/*.al>, where
 the C<.al> file has the same name as the subroutine, sans package.  If
 such a file exists, AUTOLOAD will read and evaluate it,
 thus (presumably) defining the needed subroutine.  AUTOLOAD will then
 C<goto> the newly defined subroutine.

 Once this process completes for a given function, it is defined, so
 future calls to the subroutine will bypass the AUTOLOAD mechanism.

 =head2 Subroutine Stubs

 In order for object method lookup and/or prototype checking to operate
 correctly even when methods have not yet been defined it is necessary to
 "forward declare" each subroutine (as in C<sub NAME;>).  See
 L<perlsub/"SYNOPSIS">.  Such forward declaration creates "subroutine
 stubs", which are place holders with no code.

 The AutoSplit and B<AutoLoader> modules automate the creation of forward
 declarations.  The AutoSplit module creates an 'index' file containing
 forward declarations of all the AutoSplit subroutines.  When the
 AutoLoader module is 'use'd it loads these declarations into its callers
 package.

 Because of this mechanism it is important that B<AutoLoader> is always
 C<use>d and not C<require>d.

 =head2 Using B<AutoLoader>'s AUTOLOAD Subroutine

 In order to use B<AutoLoader>'s AUTOLOAD subroutine you I<must>
 explicitly import it:

     use AutoLoader 'AUTOLOAD';

 =head2 Overriding B<AutoLoader>'s AUTOLOAD Subroutine

 Some modules, mainly extensions, provide their own AUTOLOAD subroutines.
 They typically need to check for some special cases (such as constants)
 and then fallback to B<AutoLoader>'s AUTOLOAD for the rest.

 Such modules should I<not> import B<AutoLoader>'s AUTOLOAD subroutine.
 Instead, they should define their own AUTOLOAD subroutines along these
 lines:

     use AutoLoader;
     use Carp;

     sub AUTOLOAD {
         my $sub = $AUTOLOAD;
         (my $constname = $sub) =~ s/.*:://;
         my $val = constant($constname, @_ ? $_[0] : 0);
         if ($! != 0) {
             if ($! =~ /Invalid/ || $!{EINVAL}) {
                 $AutoLoader::AUTOLOAD = $sub;
                 goto &AutoLoader::AUTOLOAD;
             }
             else {
                 croak "Your vendor has not defined constant $constname";
             }
         }
         *$sub = sub { $val }; # same as: eval "sub $sub { $val }";
         goto &$sub;
     }

 If any module's own AUTOLOAD subroutine has no need to fallback to the
 AutoLoader's AUTOLOAD subroutine (because it doesn't have any AutoSplit
 subroutines), then that module should not use B<AutoLoader> at all.

 =head2 Package Lexicals

 Package lexicals declared with C<my> in the main block of a package
 using B<AutoLoader> will not be visible to auto-loaded subroutines, due to
 the fact that the given scope ends at the C<__END__> marker.  A module
 using such variables as package globals will not work properly under the
 B<AutoLoader>.

 The C<vars> pragma (see L<perlmod/"vars">) may be used in such
 situations as an alternative to explicitly qualifying all globals with
 the package namespace.  Variables pre-declared with this pragma will be
 visible to any autoloaded routines (but will not be invisible outside
 the package, unfortunately).

 =head2 Not Using AutoLoader

 You can stop using AutoLoader by simply

 	no AutoLoader;

 =head2 B<AutoLoader> vs. B<SelfLoader>

 The B<AutoLoader> is similar in purpose to B<SelfLoader>: both delay the
 loading of subroutines.

 B<SelfLoader> uses the C<__DATA__> marker rather than C<__END__>.
 While this avoids the use of a hierarchy of disk files and the
 associated open/close for each routine loaded, B<SelfLoader> suffers a
 startup speed disadvantage in the one-time parsing of the lines after
 C<__DATA__>, after which routines are cached.  B<SelfLoader> can also
 handle multiple packages in a file.

 B<AutoLoader> only reads code as it is requested, and in many cases
 should be faster, but requires a mechanism like B<AutoSplit> be used to
 create the individual files.  L<ExtUtils::MakeMaker> will invoke
 B<AutoSplit> automatically if B<AutoLoader> is used in a module source
 file.

 =head1 CAVEATS

 AutoLoaders prior to Perl 5.002 had a slightly different interface.  Any
 old modules which use B<AutoLoader> should be changed to the new calling
 style.  Typically this just means changing a require to a use, adding
 the explicit C<'AUTOLOAD'> import if needed, and removing B<AutoLoader>
 from C<@ISA>.

 On systems with restrictions on file name length, the file corresponding
 to a subroutine may have a shorter name that the routine itself.  This
 can lead to conflicting file names.  The I<AutoSplit> package warns of
 these potential conflicts when used to split a module.

 AutoLoader may fail to find the autosplit files (or even find the wrong
 ones) in cases where C<@INC> contains relative paths, B<and> the program
 does C<chdir>.

 =head1 SEE ALSO

 L<SelfLoader> - an autoloader that doesn't use external files.

 =head1 AUTHOR

 C<AutoLoader> is maintained by the perl5-porters. Please direct
 any questions to the canonical mailing list. Anything that
 is applicable to the CPAN release can be sent to its maintainer,
 though.

 Author and Maintainer: The Perl5-Porters <perl5-porters@perl.org>

 Maintainer of the CPAN release: Steffen Mueller <smueller@cpan.org>

 =head1 COPYRIGHT AND LICENSE

 This package has been part of the perl core since the first release
 of perl5. It has been released separately to CPAN so older installations
 can benefit from bug fixes.

 This package has the same copyright and license as the perl core:

              Copyright (C) 1993, 1994, 1995, 1996, 1997, 1998, 1999,
         2000, 2001, 2002, 2003, 2004, 2005, 2006, 2007, 2008, 2009, 2011
         by Larry Wall and others

 			    All rights reserved.

     This program is free software; you can redistribute it and/or modify
     it under the terms of either:

 	a) the GNU General Public License as published by the Free
 	Software Foundation; either version 1, or (at your option) any
 	later version, or

 	b) the "Artistic License" which comes with this Kit.

     This program is distributed in the hope that it will be useful,
     but WITHOUT ANY WARRANTY; without even the implied warranty of
     MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See either
     the GNU General Public License or the Artistic License for more details.

     You should have received a copy of the Artistic License with this
     Kit, in the file named "Artistic".  If not, I'll be glad to provide one.

     You should also have received a copy of the GNU General Public License
     along with this program in the file named "Copying". If not, write to the
     Free Software Foundation, Inc., 51 Franklin St, Fifth Floor, Boston,
     MA 02110-1301, USA or visit their web page on the internet at
     http://www.gnu.org/copyleft/gpl.html.

     For those of you that choose to use the GNU General Public License,
     my interpretation of the GNU General Public License is that no Perl
     script falls under the terms of the GPL unless you explicitly put
     said script under the terms of the GPL yourself.  Furthermore, any
     object code linked with perl does not automatically fall under the
     terms of the GPL, provided such object code only adds definitions
     of subroutines and variables, and does not otherwise impair the
     resulting interpreter from executing any standard Perl script.  I
     consider linking in C subroutines in this manner to be the moral
     equivalent of defining subroutines in the Perl language itself.  You
     may sell such an object file as proprietary provided that you provide
     or offer to provide the Perl source, as specified by the GNU General
     Public License.  (This is merely an alternate way of specifying input
     to the program.)  You may also sell a binary produced by the dumping of
     a running Perl script that belongs to you, provided that you provide or
     offer to provide the Perl source as specified by the GPL.  (The
     fact that a Perl interpreter and your code are in the same binary file
     is, in this case, a form of mere aggregation.)  This is my interpretation
     of the GPL.  If you still have concerns or difficulties understanding
     my intent, feel free to contact me.  Of course, the Artistic License
     spells all this out for your protection, so you may prefer to use that.

 =cut
	package AutoLoader;

	use strict;
	use 5.006_001;

	our($VERSION, $AUTOLOAD);

	my $is_dosish;
	my $is_epoc;
	my $is_vms;
	my $is_macos;

	BEGIN {
	$is_dosish = $^O eq 'dos' \|\| $^O eq 'os2' \|\| $^O eq 'MSWin32' \|\| $^O eq 'NetWare';
	$is_epoc = $^O eq 'epoc';
	$is_vms = $^O eq 'VMS';
	$is_macos = $^O eq 'MacOS';
	$VERSION = '5.72';
	}

	AUTOLOAD {
	my $sub = $AUTOLOAD;
	my $filename = AutoLoader::find_filename( $sub );

	my $save = $@;
	local $!; # Do not munge the value.
	eval { local $SIG{__DIE__}; require $filename };
	if ($@) {
	if (substr($sub,-9) eq '::DESTROY') {
	no strict 'refs';
	*$sub = sub {};
	$@ = undef;
	} elsif ($@ =~ /^Can't locate/) {
	# The load might just have failed because the filename was too
	# long for some old SVR3 systems which treat long names as errors.
	# If we can successfully truncate a long name then it's worth a go.
	# There is a slight risk that we could pick up the wrong file here
	# but autosplit should have warned about that when splitting.
	if ($filename =~ s/(\w{12,})\.al$/substr($1,0,11).".al"/e){
	eval { local $SIG{__DIE__}; require $filename };
	}
	}
	if ($@){
	$@ =~ s/ at .*\n//;
	my $error = $@;
	require Carp;
	Carp::croak($error);
	}
	}
	$@ = $save;
	goto &$sub;
	}

	sub find_filename {
	my $sub = shift;
	my $filename;
	# Braces used to preserve $1 et al.
	{
	# Try to find the autoloaded file from the package-qualified
	# name of the sub. e.g., if the sub needed is
	# Getopt::Long::GetOptions(), then $INC{Getopt/Long.pm} is
	# something like '/usr/lib/perl5/Getopt/Long.pm', and the
	# autoload file is '/usr/lib/perl5/auto/Getopt/Long/GetOptions.al'.
	#
	# However, if @INC is a relative path, this might not work. If,
	# for example, @INC = ('lib'), then $INC{Getopt/Long.pm} is
	# 'lib/Getopt/Long.pm', and we want to require
	# 'auto/Getopt/Long/GetOptions.al' (without the leading 'lib').
	# In this case, we simple prepend the 'auto/' and let the
	# C<require> take care of the searching for us.

	my ($pkg,$func) = ($sub =~ /(.*)::([^:]+)$/);
	$pkg =~ s#::#/#g;
	if (defined($filename = $INC{"$pkg.pm"})) {
	if ($is_macos) {
	$pkg =~ tr#/#:#;
	$filename = undef
	unless $filename =~ s#^(.*)$pkg\.pm\z#$1auto:$pkg:$func.al#s;
	} else {
	$filename = undef
	unless $filename =~ s#^(.*)$pkg\.pm\z#$1auto/$pkg/$func.al#s;
	}

	# if the file exists, then make sure that it is a
	# a fully anchored path (i.e either '/usr/lib/auto/foo/bar.al',
	# or './lib/auto/foo/bar.al'. This avoids C<require> searching
	# (and failing) to find the 'lib/auto/foo/bar.al' because it
	# looked for 'lib/lib/auto/foo/bar.al', given @INC = ('lib').

	if (defined $filename and -r $filename) {
	unless ($filename =~ m\|^/\|s) {
	if ($is_dosish) {
	unless ($filename =~ m{^([a-z]:)?[\\/]}is) {
	if ($^O ne 'NetWare') {
	$filename = "./$filename";
	} else {
	$filename = "$filename";
	}
	}
	}
	elsif ($is_epoc) {
	unless ($filename =~ m{^([a-z?]:)?[\\/]}is) {
	$filename = "./$filename";
	}
	}
	elsif ($is_vms) {
	# XXX todo by VMSmiths
	$filename = "./$filename";
	}
	elsif (!$is_macos) {
	$filename = "./$filename";
	}
	}
	}
	else {
	$filename = undef;
	}
	}
	unless (defined $filename) {
	# let C<require> do the searching
	$filename = "auto/$sub.al";
	$filename =~ s#::#/#g;
	}
	}
	return $filename;
	}

	sub import {
	my $pkg = shift;
	my $callpkg = caller;

	#
	# Export symbols, but not by accident of inheritance.
	#

	if ($pkg eq 'AutoLoader') {
	if ( @_ and $_[0] =~ /^&?AUTOLOAD$/ ) {
	no strict 'refs';
	*{ $callpkg . '::AUTOLOAD' } = \&AUTOLOAD;
	}
	}

	#
	# Try to find the autosplit index file. Eg., if the call package
	# is POSIX, then $INC{POSIX.pm} is something like
	# '/usr/local/lib/perl5/POSIX.pm', and the autosplit index file is in
	# '/usr/local/lib/perl5/auto/POSIX/autosplit.ix', so we require that.
	#
	# However, if @INC is a relative path, this might not work. If,
	# for example, @INC = ('lib'), then
	# $INC{POSIX.pm} is 'lib/POSIX.pm', and we want to require
	# 'auto/POSIX/autosplit.ix' (without the leading 'lib').
	#

	(my $calldir = $callpkg) =~ s#::#/#g;
	my $path = $INC{$calldir . '.pm'};
	if (defined($path)) {
	# Try absolute path name, but only eval it if the
	# transformation from module path to autosplit.ix path
	# succeeded!
	my $replaced_okay;
	if ($is_macos) {
	(my $malldir = $calldir) =~ tr#/#:#;
	$replaced_okay = ($path =~ s#^(.*)$malldir\.pm\z#$1auto:$malldir:autosplit.ix#s);
	} else {
	$replaced_okay = ($path =~ s#^(.*)$calldir\.pm\z#$1auto/$calldir/autosplit.ix#);
	}

	eval { require $path; } if $replaced_okay;
	# If that failed, try relative path with normal @INC searching.
	if (!$replaced_okay or $@) {
	$path ="auto/$calldir/autosplit.ix";
	eval { require $path; };
	}
	if ($@) {
	my $error = $@;
	require Carp;
	Carp::carp($error);
	}
	}
	}

	sub unimport {
	my $callpkg = caller;

	no strict 'refs';

	for my $exported (qw( AUTOLOAD )) {
	my $symname = $callpkg . '::' . $exported;
	undef *{ $symname } if \&{ $symname } == \&{ $exported };
	*{ $symname } = \&{ $symname };
	}
	}

	1;

	__END__

	=head1 NAME

	AutoLoader - load subroutines only on demand

	=head1 SYNOPSIS

	package Foo;
	use AutoLoader 'AUTOLOAD'; # import the default AUTOLOAD subroutine

	package Bar;
	use AutoLoader; # don't import AUTOLOAD, define our own
	sub AUTOLOAD {
	...
	$AutoLoader::AUTOLOAD = "...";
	goto &AutoLoader::AUTOLOAD;
	}

	=head1 DESCRIPTION

	The B<AutoLoader> module works with the B<AutoSplit> module and the
	C<__END__> token to defer the loading of some subroutines until they are
	used rather than loading them all at once.

	To use B<AutoLoader>, the author of a module has to place the
	definitions of subroutines to be autoloaded after an C<__END__> token.
	(See L<perldata>.) The B<AutoSplit> module can then be run manually to
	extract the definitions into individual files F<auto/funcname.al>.

	B<AutoLoader> implements an AUTOLOAD subroutine. When an undefined
	subroutine in is called in a client module of B<AutoLoader>,
	B<AutoLoader>'s AUTOLOAD subroutine attempts to locate the subroutine in a
	file with a name related to the location of the file from which the
	client module was read. As an example, if F<POSIX.pm> is located in
	F</usr/local/lib/perl5/POSIX.pm>, B<AutoLoader> will look for perl
	subroutines B<POSIX> in F</usr/local/lib/perl5/auto/POSIX/*.al>, where
	the C<.al> file has the same name as the subroutine, sans package. If
	such a file exists, AUTOLOAD will read and evaluate it,
	thus (presumably) defining the needed subroutine. AUTOLOAD will then
	C<goto> the newly defined subroutine.

	Once this process completes for a given function, it is defined, so
	future calls to the subroutine will bypass the AUTOLOAD mechanism.

	=head2 Subroutine Stubs

	In order for object method lookup and/or prototype checking to operate
	correctly even when methods have not yet been defined it is necessary to
	"forward declare" each subroutine (as in C<sub NAME;>). See
	L<perlsub/"SYNOPSIS">. Such forward declaration creates "subroutine
	stubs", which are place holders with no code.

	The AutoSplit and B<AutoLoader> modules automate the creation of forward
	declarations. The AutoSplit module creates an 'index' file containing
	forward declarations of all the AutoSplit subroutines. When the
	AutoLoader module is 'use'd it loads these declarations into its callers
	package.

	Because of this mechanism it is important that B<AutoLoader> is always
	C<use>d and not C<require>d.

	=head2 Using B<AutoLoader>'s AUTOLOAD Subroutine

	In order to use B<AutoLoader>'s AUTOLOAD subroutine you I<must>
	explicitly import it:

	use AutoLoader 'AUTOLOAD';

	=head2 Overriding B<AutoLoader>'s AUTOLOAD Subroutine

	Some modules, mainly extensions, provide their own AUTOLOAD subroutines.
	They typically need to check for some special cases (such as constants)
	and then fallback to B<AutoLoader>'s AUTOLOAD for the rest.

	Such modules should I<not> import B<AutoLoader>'s AUTOLOAD subroutine.
	Instead, they should define their own AUTOLOAD subroutines along these
	lines:

	use AutoLoader;
	use Carp;

	sub AUTOLOAD {
	my $sub = $AUTOLOAD;
	(my $constname = $sub) =~ s/.*:://;
	my $val = constant($constname, @_ ? $_[0] : 0);
	if ($! != 0) {
	if ($! =~ /Invalid/ \|\| $!{EINVAL}) {
	$AutoLoader::AUTOLOAD = $sub;
	goto &AutoLoader::AUTOLOAD;
	}
	else {
	croak "Your vendor has not defined constant $constname";
	}
	}
	*$sub = sub { $val }; # same as: eval "sub $sub { $val }";
	goto &$sub;
	}

	If any module's own AUTOLOAD subroutine has no need to fallback to the
	AutoLoader's AUTOLOAD subroutine (because it doesn't have any AutoSplit
	subroutines), then that module should not use B<AutoLoader> at all.

	=head2 Package Lexicals

	Package lexicals declared with C<my> in the main block of a package
	using B<AutoLoader> will not be visible to auto-loaded subroutines, due to
	the fact that the given scope ends at the C<__END__> marker. A module
	using such variables as package globals will not work properly under the
	B<AutoLoader>.

	The C<vars> pragma (see L<perlmod/"vars">) may be used in such
	situations as an alternative to explicitly qualifying all globals with
	the package namespace. Variables pre-declared with this pragma will be
	visible to any autoloaded routines (but will not be invisible outside
	the package, unfortunately).

	=head2 Not Using AutoLoader

	You can stop using AutoLoader by simply

	no AutoLoader;

	=head2 B<AutoLoader> vs. B<SelfLoader>

	The B<AutoLoader> is similar in purpose to B<SelfLoader>: both delay the
	loading of subroutines.

	B<SelfLoader> uses the C<__DATA__> marker rather than C<__END__>.
	While this avoids the use of a hierarchy of disk files and the
	associated open/close for each routine loaded, B<SelfLoader> suffers a
	startup speed disadvantage in the one-time parsing of the lines after
	C<__DATA__>, after which routines are cached. B<SelfLoader> can also
	handle multiple packages in a file.

	B<AutoLoader> only reads code as it is requested, and in many cases
	should be faster, but requires a mechanism like B<AutoSplit> be used to
	create the individual files. L<ExtUtils::MakeMaker> will invoke
	B<AutoSplit> automatically if B<AutoLoader> is used in a module source
	file.

	=head1 CAVEATS

	AutoLoaders prior to Perl 5.002 had a slightly different interface. Any
	old modules which use B<AutoLoader> should be changed to the new calling
	style. Typically this just means changing a require to a use, adding
	the explicit C<'AUTOLOAD'> import if needed, and removing B<AutoLoader>
	from C<@ISA>.

	On systems with restrictions on file name length, the file corresponding
	to a subroutine may have a shorter name that the routine itself. This
	can lead to conflicting file names. The I<AutoSplit> package warns of
	these potential conflicts when used to split a module.

	AutoLoader may fail to find the autosplit files (or even find the wrong
	ones) in cases where C<@INC> contains relative paths, B<and> the program
	does C<chdir>.

	=head1 SEE ALSO

	L<SelfLoader> - an autoloader that doesn't use external files.

	=head1 AUTHOR

	C<AutoLoader> is maintained by the perl5-porters. Please direct
	any questions to the canonical mailing list. Anything that
	is applicable to the CPAN release can be sent to its maintainer,
	though.

	Author and Maintainer: The Perl5-Porters <perl5-porters@perl.org>

	Maintainer of the CPAN release: Steffen Mueller <smueller@cpan.org>

	=head1 COPYRIGHT AND LICENSE

	This package has been part of the perl core since the first release
	of perl5. It has been released separately to CPAN so older installations
	can benefit from bug fixes.

	This package has the same copyright and license as the perl core:

	Copyright (C) 1993, 1994, 1995, 1996, 1997, 1998, 1999,
	2000, 2001, 2002, 2003, 2004, 2005, 2006, 2007, 2008, 2009, 2011
	by Larry Wall and others

	All rights reserved.

	This program is free software; you can redistribute it and/or modify
	it under the terms of either:

	a) the GNU General Public License as published by the Free
	Software Foundation; either version 1, or (at your option) any
	later version, or

	b) the "Artistic License" which comes with this Kit.

	This program is distributed in the hope that it will be useful,
	but WITHOUT ANY WARRANTY; without even the implied warranty of
	MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See either
	the GNU General Public License or the Artistic License for more details.

	You should have received a copy of the Artistic License with this
	Kit, in the file named "Artistic". If not, I'll be glad to provide one.

	You should also have received a copy of the GNU General Public License
	along with this program in the file named "Copying". If not, write to the
	Free Software Foundation, Inc., 51 Franklin St, Fifth Floor, Boston,
	MA 02110-1301, USA or visit their web page on the internet at
	http://www.gnu.org/copyleft/gpl.html.

	For those of you that choose to use the GNU General Public License,
	my interpretation of the GNU General Public License is that no Perl
	script falls under the terms of the GPL unless you explicitly put
	said script under the terms of the GPL yourself. Furthermore, any
	object code linked with perl does not automatically fall under the
	terms of the GPL, provided such object code only adds definitions
	of subroutines and variables, and does not otherwise impair the
	resulting interpreter from executing any standard Perl script. I
	consider linking in C subroutines in this manner to be the moral
	equivalent of defining subroutines in the Perl language itself. You
	may sell such an object file as proprietary provided that you provide
	or offer to provide the Perl source, as specified by the GNU General
	Public License. (This is merely an alternate way of specifying input
	to the program.) You may also sell a binary produced by the dumping of
	a running Perl script that belongs to you, provided that you provide or
	offer to provide the Perl source as specified by the GPL. (The
	fact that a Perl interpreter and your code are in the same binary file
	is, in this case, a form of mere aggregation.) This is my interpretation
	of the GPL. If you still have concerns or difficulties understanding
	my intent, feel free to contact me. Of course, the Artistic License
	spells all this out for your protection, so you may prefer to use that.

	=cut