Adam Kennedy > Class-Autouse-1.29 > Class::Autouse



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Module Version: 1.29   Source   Latest Release: Class-Autouse-2.01


Class::Autouse - Run-time load a class the first time you call a method in it.


  # Debugging (if you go that way) must be set before the first use
      $Class::Autouse::DEBUG = 1;
  # Load a class on method call
  use Class::Autouse;
  Class::Autouse->autouse( 'CGI' );
  print CGI->b('Wow!');

  # Use as a pragma
  use Class::Autouse qw{CGI};

  # Turn on developer mode
  use Class::Autouse qw{:devel};

  # Turn on the Super Loader
  use Class::Autouse qw{:superloader};
  # Disable module-existance check, and thus one additional 'stat'
  # per module, at autouse-time if loading modules off a remote
  # network drive such as NFS or SMB.
  use Class::Autouse qw{:nostat};


Class::Autouse allows you to specify a class the will only load when a method of that class is called. For large classes that might not be used during the running of a program, such as Date::Manip, this can save you large amounts of memory, and decrease the script load time a great deal.

Class, not Module

The terminology "class loading" instead of "module loading" is used intentionally. Modules will only be loaded if they are acting as a class.

That is, they will only be loaded during a Class->method call. If you try to use a subroutine directly, say with Class::method(), the class will not be loaded and a fatal error will mostly likely occur.

This limitation is made to allow more powerfull features in other areas, because the module can focus on just loading the modules, and not have to deal with importing.

And really, if you are doing OO Perl, you should be avoiding importing wherever possible.

Use as a pragma

Class::Autouse can be used as a pragma, specifying a list of classes to load as the arguments. For example

   use Class::Autouse qw{CGI Data::Manip This::That};

is equivalent to

   use Class::Autouse;
   Class::Autouse->autouse( 'CGI'         );
   Class::Autouse->autouse( 'Data::Manip' );
   Class::Autouse->autouse( 'This::That'  );

Developer Mode

Class::Autouse features a developer mode. In developer mode, classes are loaded immediately, just like they would be with a normal 'use' statement (although the import sub isn't called).

This allows error checking to be done while developing, at the expense of a larger memory overhead. Developer mode is turned on either with the devel method, or using :devel in any of the pragma arguments. For example, this would load immediately

    use Class::Autouse qw{:devel CGI};

While developer mode is roughly equivalent to just using a normal use command, for a large number of modules it lets you use autoloading notation, and just comment or uncomment a single line to turn developer mode on or off. You can leave it on during development, and turn it off for speed reasons when deploying.

No-Stat Mode

For situations where a module exists on a remote disk or another relatively expensive location, you can call Class::Autouse with the :nostat param to disable initial file existance checking at hook time.

  # Disable autoload-time file existance checking
  use Class::Autouse qw{:nostat};

Super Loader Mode

Turning on the Class::Autouse super loader allows you to automatically load ANY class without specifying it first. Thus, the following will work and is completely legal.

    use Class::Autouse qw{:superloader};

    print CGI->b('Wow!');

The super loader can be turned on with either the Class::Autouse->superloader> method, or the :superloader pragma argument.

Please note that unlike the normal one-at-a-time autoloading, the super-loader makes global changes, and so is not completely self-contained.

It has the potential to cause unintended effects at a distance. If you encounter unusual behaviour, revert to autousing one-at-a-time, or use the recursive loading.

Use of the Super Loader is highly discouraged for widely distributed public applications or modules unless unavoidable. Do not use just to be lazy and save a few lines of code.

Recursive Loading

As an alternative to the super loader, the autouse_recursive and load_recursive methods can be used to autouse or load an entire tree of classes.

For example, the following would give you access to all the URI related classes installed on the machine.

    Class::Autouse->autouse_recursive( 'URI' );

Please note that the loadings will only occur down a single branch of the include path, whichever the top class is located in.


The mechanism that Class::Autouse uses is not compatible with mod_perl. In particular with reloader modules like Apache::Reload. Class::Autouse detects the presence of mod_perl and acts as normal, but will always load all classes immediately, equivalent to having developer mode enabled.

This is actually beneficial, as under mod_perl classes should be preloaded in the parent mod_perl process anyway, to prevent them having to be loaded by the Apache child classes. It also saves HUGE amounts of memory.


As for mod_perl, Class::Autouse is compatible with the prefork module, and all modules autoloaded will be loaded before forking correctly, when requested by prefork.

The Internal Debugger

Class::Autouse provides an internal debugger, which can be used to debug any weird edge cases you might encounter when using it.

If the $Class::Autouse::DEBUG variable is true when Class::Autouse is first loaded, debugging will be compiled in. This debugging prints output like the following to STDOUT.

 Class::Autouse::autouse_recursive( 'Foo' )
  Class::Autouse::_recursive( 'Foo', 'load' )
   Class::Autouse::load( 'Foo' )
   Class::Autouse::_child_classes( 'Foo' )
   Class::Autouse::load( 'Foo::Bar' )
    Class::Autouse::_file_exists( 'Foo/' )
    Class::Autouse::load -> Loading in Foo/
   Class::Autouse::load( 'Foo::More' )

Please note that because this is optimised out if not used, you can no longer (since 1.20) enable debugging at run-time. This decision was made to remove a large number of unneeded branching and speed up loading.


autouse $class, ...

The autouse method sets one or more classes to be loaded as required.

load $class

The load method loads one or more classes into memory. This is functionally equivalent to using require to load the class list in, except that load will detect and remove the autoloading hook from a previously autoused class, whereas as use effectively ignore the class, and not load it.


The devel method sets development mode on (argument of 1) or off (argument of 0).

If any classes have previously been autouse'd and not loaded when this method is called, they will be loaded immediately.


The superloader method turns on the super loader.

Please note that once you have turned the superloader on, it cannot be turned off. This is due to code that might be relying on it being there not being able to autoload its classes when another piece of code decides they don't want it any more, and turns the superloader off.

class_exists $class

Handy method when doing the sort of jobs that Class::Autouse does. Given a class name, it will return true if the class can be loaded ( i.e. in @INC ), false if the class can't be loaded, and undef if the class name is invalid.

Note that this does not actually load the class, just tests to see if it can be loaded. Loading can still fail. For a more comprehensive set of methods of this nature, see Class::Inspector.

autouse_recursive $class

The same as the autouse method, but autouses recursively.

load_recursive $class

The same as the load method, but loads recursively. Great for checking that a large class tree that might not always be loaded will load correctly.


Bugs should be always be reported via the CPAN bug tracker at

For other issues, or commercial enhancement or support, contact the author.


Adam Kennedy (Creator and Maintainer),,

Rob Napier (No longer involved),


autoload, autoclass


Copyright (c) 2002 - 2006 Adam Kennedy.

This program is free software; you can redistribute it and/or modify it under the same terms as Perl itself.

The full text of the license can be found in the LICENSE file included with this module.

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