[perl5.git] / lib / AutoLoader.pm

package AutoLoader;

use 5.006_001;
our(@EXPORT, @EXPORT_OK, $VERSION);

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

BEGIN {
    require Exporter;
    @EXPORT = @EXPORT = ();
    @EXPORT_OK = @EXPORT_OK = qw(AUTOLOAD);
    $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 = '5.59';
}

AUTOLOAD {
    my $sub = $AUTOLOAD;
    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#/#:#;
		$filename =~ s#^(.*)$pkg\.pm\z#$1auto:$pkg:$func.al#s;
	    } else {
		$filename =~ s#^(.*)$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 (-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;
	}
    }
    my $save = $@;
    local $!; # Do not munge the value. 
    eval { local $SIG{__DIE__}; require $filename };
    if ($@) {
	if (substr($sub,-9) eq '::DESTROY') {
	    *$sub = sub {};
	} else {
	    # 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 succesfully 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 import {
    my $pkg = shift;
    my $callpkg = caller;

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

    if ($pkg eq 'AutoLoader') {
      local $Exporter::ExportLevel = 1;
      Exporter::import $pkg, @_;
    }

    #
    # 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($path)) {
	# Try absolute path name.
	if ($is_macos) {
	    (my $malldir = $calldir) =~ tr#/#:#;
	    $path =~ s#^(.*)$malldir\.pm\z#$1auto:$malldir:autosplit.ix#s;
	} else {
	    $path =~ s#^(.*)$calldir\.pm\z#$1auto/$calldir/autosplit.ix#;
	}

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

sub unimport {
  my $callpkg = caller;
  eval "package $callpkg; sub AUTOLOAD;";
}

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.

=cut
Commit	Line	Data
8990e307	1	package AutoLoader;
21c92a1d	2
3b825e41	3	use 5.006_001;
17f410f9	4	our(@EXPORT, @EXPORT_OK, $VERSION);
f06db76b	5
adaafad2	6	my $is_dosish;
ed79a026	7	my $is_epoc;
adaafad2	8	my $is_vms;
084592ab	9	my $is_macos;
adaafad2	10
1be0b951 CS	11	BEGIN {
1be0b951 CS	12	require Exporter;
e3d0cac0 IZ	13	@EXPORT = @EXPORT = ();
e3d0cac0 IZ	14	@EXPORT_OK = @EXPORT_OK = qw(AUTOLOAD);
2986a63f	15	$is_dosish = $^O eq 'dos' \|\| $^O eq 'os2' \|\| $^O eq 'MSWin32' \|\| $^O eq 'NetWare';
ed79a026	16	$is_epoc = $^O eq 'epoc';
adaafad2	17	$is_vms = $^O eq 'VMS';
084592ab	18	$is_macos = $^O eq 'MacOS';
88d01e8d	19	$VERSION = '5.59';
1be0b951	20	}
f06db76b	21
8990e307	22	AUTOLOAD {
7d4fbd98 GS	23	my $sub = $AUTOLOAD;
7d4fbd98 GS	24	my $filename;
5a556d17 NIS	25	# Braces used to preserve $1 et al.
5a556d17 NIS	26	{
adaafad2 GS	27	# Try to find the autoloaded file from the package-qualified
	28	# name of the sub. e.g., if the sub needed is
	29	# Getopt::Long::GetOptions(), then $INC{Getopt/Long.pm} is
	30	# something like '/usr/lib/perl5/Getopt/Long.pm', and the
	31	# autoload file is '/usr/lib/perl5/auto/Getopt/Long/GetOptions.al'.
	32	#
	33	# However, if @INC is a relative path, this might not work. If,
	34	# for example, @INC = ('lib'), then $INC{Getopt/Long.pm} is
	35	# 'lib/Getopt/Long.pm', and we want to require
	36	# 'auto/Getopt/Long/GetOptions.al' (without the leading 'lib').
	37	# In this case, we simple prepend the 'auto/' and let the
	38	# C<require> take care of the searching for us.
	39
7d4fbd98	40	my ($pkg,$func) = ($sub =~ /(.*)::([^:]+)$/);
adaafad2	41	$pkg =~ s#::#/#g;
7d4fbd98	42	if (defined($filename = $INC{"$pkg.pm"})) {
084592ab CN	43	if ($is_macos) {
	44	$pkg =~ tr#/#:#;
	45	$filename =~ s#^(.*)$pkg\.pm\z#$1auto:$pkg:$func.al#s;
	46	} else {
	47	$filename =~ s#^(.*)$pkg\.pm\z#$1auto/$pkg/$func.al#s;
	48	}
adaafad2 GS	49
	50	# if the file exists, then make sure that it is a
	51	# a fully anchored path (i.e either '/usr/lib/auto/foo/bar.al',
	52	# or './lib/auto/foo/bar.al'. This avoids C<require> searching
	53	# (and failing) to find the 'lib/auto/foo/bar.al' because it
	54	# looked for 'lib/lib/auto/foo/bar.al', given @INC = ('lib').
	55
7d4fbd98	56	if (-r $filename) {
14a089c5	57	unless ($filename =~ m\|^/\|s) {
adaafad2	58	if ($is_dosish) {
14a089c5	59	unless ($filename =~ m{^([a-z]:)?[\\/]}is) {
2986a63f JH	60	if ($^O ne 'NetWare') {
	61	$filename = "./$filename";
	62	} else {
	63	$filename = "$filename";
	64	}
adaafad2 GS	65	}
adaafad2 GS	66	}
ed79a026 OF	67	elsif ($is_epoc) {
	68	unless ($filename =~ m{^([a-z?]:)?[\\/]}is) {
	69	$filename = "./$filename";
	70	}
4d6b4052 JH	71	}
4d6b4052 JH	72	elsif ($is_vms) {
7d4fbd98 GS	73	# XXX todo by VMSmiths
7d4fbd98 GS	74	$filename = "./$filename";
adaafad2	75	}
084592ab	76	elsif (!$is_macos) {
7d4fbd98	77	$filename = "./$filename";
adaafad2 GS	78	}
	79	}
	80	}
	81	else {
7d4fbd98	82	$filename = undef;
adaafad2 GS	83	}
adaafad2 GS	84	}
7d4fbd98	85	unless (defined $filename) {
adaafad2	86	# let C<require> do the searching
7d4fbd98 GS	87	$filename = "auto/$sub.al";
7d4fbd98 GS	88	$filename =~ s#::#/#g;
adaafad2	89	}
5a556d17	90	}
e14baed2	91	my $save = $@;
212caf55	92	local $!; # Do not munge the value.
7d4fbd98	93	eval { local $SIG{__DIE__}; require $filename };
8990e307	94	if ($@) {
7d4fbd98 GS	95	if (substr($sub,-9) eq '::DESTROY') {
7d4fbd98 GS	96	*$sub = sub {};
e14baed2	97	} else {
	98	# The load might just have failed because the filename was too
	99	# long for some old SVR3 systems which treat long names as errors.
	100	# If we can succesfully truncate a long name then it's worth a go.
	101	# There is a slight risk that we could pick up the wrong file here
	102	# but autosplit should have warned about that when splitting.
7d4fbd98 GS	103	if ($filename =~ s/(\w{12,})\.al$/substr($1,0,11).".al"/e){
7d4fbd98 GS	104	eval { local $SIG{__DIE__}; require $filename };
e14baed2	105	}
	106	if ($@){
	107	$@ =~ s/ at .*\n//;
fb73857a	108	my $error = $@;
	109	require Carp;
	110	Carp::croak($error);
e14baed2	111	}
a0d0e21e	112	}
8990e307	113	}
e14baed2	114	$@ = $save;
7d4fbd98	115	goto &$sub;
8990e307	116	}
1be0b951	117
c2960299	118	sub import {
1be0b951 CS	119	my $pkg = shift;
	120	my $callpkg = caller;
	121
	122	#
	123	# Export symbols, but not by accident of inheritance.
	124	#
	125
e3d0cac0 IZ	126	if ($pkg eq 'AutoLoader') {
	127	local $Exporter::ExportLevel = 1;
	128	Exporter::import $pkg, @_;
	129	}
1be0b951 CS	130
1be0b951 CS	131	#
c2960299 AD	132	# Try to find the autosplit index file. Eg., if the call package
	133	# is POSIX, then $INC{POSIX.pm} is something like
	134	# '/usr/local/lib/perl5/POSIX.pm', and the autosplit index file is in
	135	# '/usr/local/lib/perl5/auto/POSIX/autosplit.ix', so we require that.
	136	#
	137	# However, if @INC is a relative path, this might not work. If,
	138	# for example, @INC = ('lib'), then
	139	# $INC{POSIX.pm} is 'lib/POSIX.pm', and we want to require
	140	# 'auto/POSIX/autosplit.ix' (without the leading 'lib').
	141	#
1be0b951	142
1c1c7f20	143	(my $calldir = $callpkg) =~ s#::#/#g;
1be0b951 CS	144	my $path = $INC{$calldir . '.pm'};
1be0b951 CS	145	if (defined($path)) {
c2960299	146	# Try absolute path name.
4d6b4052 JH	147	if ($is_macos) {
	148	(my $malldir = $calldir) =~ tr#/#:#;
	149	$path =~ s#^(.*)$malldir\.pm\z#$1auto:$malldir:autosplit.ix#s;
	150	} else {
	151	$path =~ s#^(.*)$calldir\.pm\z#$1auto/$calldir/autosplit.ix#;
	152	}
	153
c2960299 AD	154	eval { require $path; };
	155	# If that failed, try relative path with normal @INC searching.
	156	if ($@) {
1be0b951	157	$path ="auto/$calldir/autosplit.ix";
c2960299 AD	158	eval { require $path; };
c2960299 AD	159	}
fb73857a	160	if ($@) {
	161	my $error = $@;
	162	require Carp;
	163	Carp::carp($error);
	164	}
f06db76b	165	}
f06db76b	166	}
8990e307	167
cb0cff20 JH	168	sub unimport {
	169	my $callpkg = caller;
	170	eval "package $callpkg; sub AUTOLOAD;";
	171	}
	172
8990e307	173	1;
1be0b951 CS	174
	175	__END__
	176
	177	=head1 NAME
	178
	179	AutoLoader - load subroutines only on demand
	180
	181	=head1 SYNOPSIS
	182
	183	package Foo;
	184	use AutoLoader 'AUTOLOAD'; # import the default AUTOLOAD subroutine
	185
	186	package Bar;
	187	use AutoLoader; # don't import AUTOLOAD, define our own
	188	sub AUTOLOAD {
	189	...
	190	$AutoLoader::AUTOLOAD = "...";
	191	goto &AutoLoader::AUTOLOAD;
	192	}
	193
	194	=head1 DESCRIPTION
	195
	196	The B<AutoLoader> module works with the B<AutoSplit> module and the
	197	C<__END__> token to defer the loading of some subroutines until they are
	198	used rather than loading them all at once.
	199
	200	To use B<AutoLoader>, the author of a module has to place the
	201	definitions of subroutines to be autoloaded after an C<__END__> token.
	202	(See L<perldata>.) The B<AutoSplit> module can then be run manually to
	203	extract the definitions into individual files F<auto/funcname.al>.
	204
	205	B<AutoLoader> implements an AUTOLOAD subroutine. When an undefined
	206	subroutine in is called in a client module of B<AutoLoader>,
	207	B<AutoLoader>'s AUTOLOAD subroutine attempts to locate the subroutine in a
	208	file with a name related to the location of the file from which the
	209	client module was read. As an example, if F<POSIX.pm> is located in
	210	F</usr/local/lib/perl5/POSIX.pm>, B<AutoLoader> will look for perl
	211	subroutines B<POSIX> in F</usr/local/lib/perl5/auto/POSIX/*.al>, where
	212	the C<.al> file has the same name as the subroutine, sans package. If
	213	such a file exists, AUTOLOAD will read and evaluate it,
	214	thus (presumably) defining the needed subroutine. AUTOLOAD will then
	215	C<goto> the newly defined subroutine.
	216
f610777f	217	Once this process completes for a given function, it is defined, so
1be0b951 CS	218	future calls to the subroutine will bypass the AUTOLOAD mechanism.
	219
	220	=head2 Subroutine Stubs
	221
	222	In order for object method lookup and/or prototype checking to operate
	223	correctly even when methods have not yet been defined it is necessary to
	224	"forward declare" each subroutine (as in C<sub NAME;>). See
	225	L<perlsub/"SYNOPSIS">. Such forward declaration creates "subroutine
	226	stubs", which are place holders with no code.
	227
	228	The AutoSplit and B<AutoLoader> modules automate the creation of forward
	229	declarations. The AutoSplit module creates an 'index' file containing
	230	forward declarations of all the AutoSplit subroutines. When the
	231	AutoLoader module is 'use'd it loads these declarations into its callers
	232	package.
	233
	234	Because of this mechanism it is important that B<AutoLoader> is always
	235	C<use>d and not C<require>d.
	236
	237	=head2 Using B<AutoLoader>'s AUTOLOAD Subroutine
	238
	239	In order to use B<AutoLoader>'s AUTOLOAD subroutine you I<must>
	240	explicitly import it:
	241
	242	use AutoLoader 'AUTOLOAD';
	243
	244	=head2 Overriding B<AutoLoader>'s AUTOLOAD Subroutine
	245
	246	Some modules, mainly extensions, provide their own AUTOLOAD subroutines.
	247	They typically need to check for some special cases (such as constants)
	248	and then fallback to B<AutoLoader>'s AUTOLOAD for the rest.
	249
	250	Such modules should I<not> import B<AutoLoader>'s AUTOLOAD subroutine.
	251	Instead, they should define their own AUTOLOAD subroutines along these
	252	lines:
	253
	254	use AutoLoader;
fb73857a	255	use Carp;
1be0b951 CS	256
1be0b951 CS	257	sub AUTOLOAD {
7d4fbd98 GS	258	my $sub = $AUTOLOAD;
7d4fbd98 GS	259	(my $constname = $sub) =~ s/.*:://;
1be0b951 CS	260	my $val = constant($constname, @_ ? $_[0] : 0);
1be0b951 CS	261	if ($! != 0) {
265f5c4a	262	if ($! =~ /Invalid/ \|\| $!{EINVAL}) {
7d4fbd98	263	$AutoLoader::AUTOLOAD = $sub;
1be0b951 CS	264	goto &AutoLoader::AUTOLOAD;
	265	}
	266	else {
	267	croak "Your vendor has not defined constant $constname";
	268	}
	269	}
7d4fbd98 GS	270	*$sub = sub { $val }; # same as: eval "sub $sub { $val }";
7d4fbd98 GS	271	goto &$sub;
1be0b951 CS	272	}
	273
	274	If any module's own AUTOLOAD subroutine has no need to fallback to the
	275	AutoLoader's AUTOLOAD subroutine (because it doesn't have any AutoSplit
	276	subroutines), then that module should not use B<AutoLoader> at all.
	277
	278	=head2 Package Lexicals
	279
	280	Package lexicals declared with C<my> in the main block of a package
	281	using B<AutoLoader> will not be visible to auto-loaded subroutines, due to
	282	the fact that the given scope ends at the C<__END__> marker. A module
	283	using such variables as package globals will not work properly under the
	284	B<AutoLoader>.
	285
	286	The C<vars> pragma (see L<perlmod/"vars">) may be used in such
	287	situations as an alternative to explicitly qualifying all globals with
	288	the package namespace. Variables pre-declared with this pragma will be
	289	visible to any autoloaded routines (but will not be invisible outside
	290	the package, unfortunately).
	291
cb0cff20 JH	292	=head2 Not Using AutoLoader
	293
	294	You can stop using AutoLoader by simply
	295
	296	no AutoLoader;
	297
1be0b951 CS	298	=head2 B<AutoLoader> vs. B<SelfLoader>
	299
	300	The B<AutoLoader> is similar in purpose to B<SelfLoader>: both delay the
	301	loading of subroutines.
	302
	303	B<SelfLoader> uses the C<__DATA__> marker rather than C<__END__>.
	304	While this avoids the use of a hierarchy of disk files and the
	305	associated open/close for each routine loaded, B<SelfLoader> suffers a
	306	startup speed disadvantage in the one-time parsing of the lines after
	307	C<__DATA__>, after which routines are cached. B<SelfLoader> can also
	308	handle multiple packages in a file.
	309
	310	B<AutoLoader> only reads code as it is requested, and in many cases
f610777f	311	should be faster, but requires a mechanism like B<AutoSplit> be used to
1be0b951 CS	312	create the individual files. L<ExtUtils::MakeMaker> will invoke
	313	B<AutoSplit> automatically if B<AutoLoader> is used in a module source
	314	file.
	315
	316	=head1 CAVEATS
	317
	318	AutoLoaders prior to Perl 5.002 had a slightly different interface. Any
	319	old modules which use B<AutoLoader> should be changed to the new calling
	320	style. Typically this just means changing a require to a use, adding
	321	the explicit C<'AUTOLOAD'> import if needed, and removing B<AutoLoader>
	322	from C<@ISA>.
	323
	324	On systems with restrictions on file name length, the file corresponding
	325	to a subroutine may have a shorter name that the routine itself. This
	326	can lead to conflicting file names. The I<AutoSplit> package warns of
	327	these potential conflicts when used to split a module.
	328
adaafad2 GS	329	AutoLoader may fail to find the autosplit files (or even find the wrong
	330	ones) in cases where C<@INC> contains relative paths, B<and> the program
	331	does C<chdir>.
	332
1be0b951 CS	333	=head1 SEE ALSO
	334
	335	L<SelfLoader> - an autoloader that doesn't use external files.
	336
	337	=cut