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.\" ========================================================================
.\"
.IX Title "Class::Loader 3pm"
.TH Class::Loader 3pm "2005-04-27" "perl v5.34.0" "User Contributed Perl Documentation"
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.SH "NAME"
Class::Loader \- Load modules and create objects on demand.
.SH "VERSION"
.IX Header "VERSION"
.Vb 2
\&    $Revision: 2.2 $
\&    $Date: 2001/07/18 20:21:39 $
.Ve
.SH "SYNOPSIS"
.IX Header "SYNOPSIS"
.Vb 3
\&    package Web::Server;
\&    use Class::Loader; 
\&    @ISA = qw(Class::Loader);
\&    
\&    $self\->_load( \*(AqContent_Handler\*(Aq, { 
\&                             Module => "Filter::URL",
\&                        Constructor => "new",
\&                               Args => [ ],
\&                         } 
\&                );
.Ve
.SH "DESCRIPTION"
.IX Header "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.
.PP
Class::Loader is an inheritable class that provides a method, \fB_load()\fR,
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 \fB_load()\fR.
.SH "METHODS"
.IX Header "METHODS"
.IP "\fB\fBnew()\fB\fR" 4
.IX Item "new()"
A basic constructor. You can use this to create an object of
Class::Loader, in case you don't want to inherit Class::Loader.
.IP "\fB\fB_load()\fB\fR" 4
.IX Item "_load()"
\&\fB_load()\fR 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 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:
.RS 4
.IP "\fBModule\fR" 4
.IX Item "Module"
This is name of the class to load. (It is not the module's filename.)
.IP "\fBName\fR" 4
.IX Item "Name"
Symbolic name of the module defined with \fB_storemap()\fR. Either one of Module
or Name keys must be present in a call to \fB_load()\fR.
.IP "\fBConstructor\fR" 4
.IX Item "Constructor"
Name of the Module constructor. Defaults to \*(L"new\*(R".
.IP "\fBArgs\fR" 4
.IX Item "Args"
A reference to the list of arguments for the constructor. \fB_load()\fR calls
the constructor with this list. If no Args are present, \fB_load()\fR will call
the constructor without any arguments.
.IP "\fB\s-1CPAN\s0\fR" 4
.IX Item "CPAN"
If the Module is not installed on the local system, \fB_load()\fR can fetch &
install it from \s-1CPAN\s0 provided the \s-1CPAN\s0 key is present. This functionality
assumes availability of a pre-configured \s-1CPAN\s0 shell.
.RE
.RS 4
.RE
.IP "\fB\fB_storemap()\fB\fR" 4
.IX Item "_storemap()"
Class::Loader maintains a class table that maps symbolic names to
parameters accepted by \fB_load()\fR. It takes a hash as argument whose keys are
symbolic names and value are hash references that contain a set of \fB_load()\fR
arguments. Here's an example:
.Sp
.Vb 5
\&    $self\->_storemap ( "URL" => { Module => "Filter::URL", 
\&                                  Constructor => "foo", 
\&                                  Args => [qw(bar baz)], 
\&                                }
\&                     );
\&
\&    # time passes...
\&
\&    $self\->{handler} = $self\->_load ( Name => \*(AqURL\*(Aq );
.Ve
.IP "\fB\fB_retrmap()\fB\fR" 4
.IX Item "_retrmap()"
\&\fB_retrmap()\fR returns the entire map stored with Class::Loader. Class::Loader
maintains separate maps for different classes, and \fB_retrmap()\fR returns the
map valid in the caller class.
.SH "SEE ALSO"
.IX Header "SEE ALSO"
\&\fBAnyLoader\fR\|(3)
.SH "AUTHOR"
.IX Header "AUTHOR"
Vipul Ved Prakash, <mail@vipul.net>
.SH "LICENSE"
.IX Header "LICENSE"
Copyright (c) 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.