Class::Autouse(3) User Contributed Perl Documentation Class::Autouse(3)
NAME
Class::Autouse - Run-time load a class the first time you call a method
in it.
SYNOPSIS
# Debugging (if you go that way) must be set before the first use
BEGIN {
$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};
DESCRIPTION
"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 CGI.pm 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.
mod_perl
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.
prefork
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/Bar.pm' )
Class::Autouse::load -> Loading in Foo/Bar.pm
Class::Autouse::load( 'Foo::More' )
etc...
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.
METHODS
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.
devel
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.
superloader
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.
SUPPORT
Bugs should be always be reported via the CPAN bug tracker at
<http://rt.cpan.org/NoAuth/ReportBug.html?Queue=Class-Autouse>
For other issues, or commercial enhancement or support, contact the
author.
AUTHORS
Adam Kennedy (Creator and Maintainer), <http://ali.as/>, cpan@ali.as
Rob Napier (No longer involved), rnapier@employees.org
SEE ALSO
autoload, autoclass
COPYRIGHT
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.
perl v5.10.0 2007-11-11 Class::Autouse(3)
Mac OS X 10.6 - Generated Thu Sep 17 20:11:13 CDT 2009