NAME
   AutoLoader - load subroutines only on demand

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;
       }

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

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

   AutoLoader implements an AUTOLOAD subroutine. When an undefined
   subroutine in is called in a client module of AutoLoader, 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 POSIX.pm is located in
   /usr/local/lib/perl5/POSIX.pm, AutoLoader will look for perl subroutines
   POSIX in /usr/local/lib/perl5/auto/POSIX/*.al, where the ".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 "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.

 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 "sub NAME;"). See "SYNOPSIS" in
   perlsub. Such forward declaration creates "subroutine stubs", which are
   place holders with no code.

   The AutoSplit and 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 AutoLoader is always
   "use"d and not "require"d.

 Using AutoLoader's AUTOLOAD Subroutine
   In order to use AutoLoader's AUTOLOAD subroutine you *must* explicitly
   import it:

       use AutoLoader 'AUTOLOAD';

 Overriding 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 AutoLoader's AUTOLOAD for the rest.

   Such modules should *not* import 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 AutoLoader at all.

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

   The "vars" pragma (see "vars" in perlmod) 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).

 Not Using AutoLoader
   You can stop using AutoLoader by simply

           no AutoLoader;

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

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

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

CAVEATS
   AutoLoaders prior to Perl 5.002 had a slightly different interface. Any
   old modules which use AutoLoader should be changed to the new calling
   style. Typically this just means changing a require to a use, adding the
   explicit 'AUTOLOAD' import if needed, and removing AutoLoader from @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 *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 @INC contains relative paths, and the program does
   "chdir".

SEE ALSO
   SelfLoader - an autoloader that doesn't use external files.

AUTHOR
   "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 <[email protected]>

   Maintainer of the CPAN release: Steffen Mueller <[email protected]>

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.

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