AutoLoader AutoLoader is a Perl module that can load subroutines only on demand.
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Perl module load subroutines load subroutines on demand loading AutoLoader

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AutoLoader is a Perl module that can load subroutines only on demand. AutoLoader is a Perl module that can 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; }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 StubsIn 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 used and not required.Using AutoLoader's AUTOLOAD SubroutineIn order to use AutoLoader's AUTOLOAD subroutine you must explicitly import it: use AutoLoader 'AUTOLOAD';Overriding AutoLoader's AUTOLOAD SubroutineSome 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, @_ ? $_ : 0); if ($! != 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 LexicalsPackage 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 AutoLoaderYou can stop using AutoLoader by simply no AutoLoader;AutoLoader vs. SelfLoaderThe 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. Requirements: · Perl

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