NAME

Class::Loader - Load modules and create objects on demand.

VERSION

$Revision: 1.6 $
$Date: 2001/04/27 15:53:24 $

SYNOPSIS

package Web::Server;
use Class::Loader; 
@ISA = qw(Class::Loader);

$self->_load( 'Content_Handler', { 
                         Module => "Filter::URL",
                    Constructor => "new",
                           Args => [ ],
                     } 
            );

DESCRIPTION

Certain applications like to defer the decision to use a particular module till runtime. This is possible in perl, and is a useful trick in situations where the type of data is not known at compile time and the application doesn't wish to pre-compile modules to handle all types of data it can work with. Loading modules at runtime can also provide flexible interfaces for perl modules. Modules can let the programmer decide what modules will be used by it instead of hard-coding their names.

Class::Loader is an inheritable class that provides a method, _load(), to load a module from disk and construct an object by calling its constructor. It also provides a way to map modules names and associated metadata with symbolic names that can be used in place of module names at _load().

METHODS

_load()

_load() loads a module and calls its constructor. It returns the newly constructed object on success or a non-true value on failure. The first argument to load can be the name of the key in which the returned object is stored. This argument is optional. The second (or the first) argument is a hash which can take the following keys:

Module

This is name of the class to load. (It is not the module's filename.)

Name

Symbolic name of the module defined with _storemap(). Either one of Module or Name keys must be present in a call to _load().

Constructor

Name of the constructor. Defaults to "new".

Args

A reference to the list of arguments for the constructor. _load() calls the constructor with this list. If no Args are present, _load() will call the constructor without any arguments.

_storemap()

Class::Loader maintains a class table that maps symbolic names to parameters accepted by _load(). It takes a hash as argument whose keys are symbolic names and value are hash references that contain a set of _load() arguments. Here's an example:

$self->_storemap ( "URL" => { Module => "Filter::URL", 
                              Constructor => "foo", 
                              Args => [qw(bar baz)], 
                            }
                 );

# time passes...

$self->{handler} = $self->_load ( Name => 'URL' );

_retrmap()

_retrmap() returns the entire map stored with Class::Loader. Class::Loader maintains separate maps for different classes, and _retrmap() returns the map valid in the caller class.

AUTHOR

Vipul Ved Prakash, <mail@vipul.net>

LICENSE

Copyright (c) 2000-2001, Vipul Ved Prakash. All rights reserved. This code is free software; you can redistribute it and/or modify it under the same terms as Perl itself.