#============================================================= -*-Perl-*-
#
# Template::Plugin
#
# DESCRIPTION
#
# Module defining a base class for a plugin object which can be loaded
# and instantiated via the USE directive.
#
# AUTHOR
# Andy Wardley <abw@wardley.org>
#
# COPYRIGHT
# Copyright (C) 1996-2007 Andy Wardley. All Rights Reserved.
#
# This module is free software; you can redistribute it an/or
# modify it under the same terms as Perl itself.
#
#============================================================================
package Template::Plugin;
use strict;
use warnings;
use base 'Template::Base';
our $VERSION = 2.70;
our $DEBUG = 0 unless defined $DEBUG;
our $ERROR = '';
our $AUTOLOAD;
#========================================================================
# ----- CLASS METHODS -----
#========================================================================
#------------------------------------------------------------------------
# load()
#
# Class method called when the plugin module is first loaded. It
# returns the name of a class (by default, its own class) or a prototype
# object which will be used to instantiate new objects. The new()
# method is then called against the class name (class method) or
# prototype object (object method) to create a new instances of the
# object.
#------------------------------------------------------------------------
sub load {
return $_[0];
}
#------------------------------------------------------------------------
# new($context, $delegate, @params)
#
# Object constructor which is called by the Template::Context to
# instantiate a new Plugin object. This base class constructor is
# used as a general mechanism to load and delegate to other Perl
# modules. The context is passed as the first parameter, followed by
# a reference to a delegate object or the name of the module which
# should be loaded and instantiated. Any additional parameters passed
# to the USE directive are forwarded to the new() constructor.
#
# A plugin object is returned which has an AUTOLOAD method to delegate
# requests to the underlying object.
#------------------------------------------------------------------------
sub new {
my $class = shift;
bless {
}, $class;
}
sub old_new {
my ($class, $context, $delclass, @params) = @_;
my ($delegate, $delmod);
return $class->error("no context passed to $class constructor\n")
unless defined $context;
if (ref $delclass) {
# $delclass contains a reference to a delegate object
$delegate = $delclass;
}
else {
# delclass is the name of a module to load and instantiate
($delmod = $delclass) =~ s|::|/|g;
eval {
require "$delmod.pm";
$delegate = $delclass->new(@params)
|| die "failed to instantiate $delclass object\n";
};
return $class->error($@) if $@;
}
bless {
_CONTEXT => $context,
_DELEGATE => $delegate,
_PARAMS => \@params,
}, $class;
}
#------------------------------------------------------------------------
# fail($error)
#
# Version 1 error reporting function, now replaced by error() inherited
# from Template::Base. Raises a "deprecated function" warning and then
# calls error().
#------------------------------------------------------------------------
sub fail {
my $class = shift;
my ($pkg, $file, $line) = caller();
warn "Template::Plugin::fail() is deprecated at $file line $line. Please use error()\n";
$class->error(@_);
}
#========================================================================
# ----- OBJECT METHODS -----
#========================================================================
#------------------------------------------------------------------------
# AUTOLOAD
#
# General catch-all method which delegates all calls to the _DELEGATE
# object.
#------------------------------------------------------------------------
sub OLD_AUTOLOAD {
my $self = shift;
my $method = $AUTOLOAD;
$method =~ s/.*:://;
return if $method eq 'DESTROY';
if (ref $self eq 'HASH') {
my $delegate = $self->{ _DELEGATE } || return;
return $delegate->$method(@_);
}
my ($pkg, $file, $line) = caller();
# warn "no such '$method' method called on $self at $file line $line\n";
return undef;
}
1;
__END__
=head1 NAME
Template::Plugin - Base class for Template Toolkit plugins
=head1 SYNOPSIS
package MyOrg::Template::Plugin::MyPlugin;
use base qw( Template::Plugin );
use Template::Plugin;
use MyModule;
sub new {
my $class = shift;
my $context = shift;
bless {
...
}, $class;
}
=head1 DESCRIPTION
A "plugin" for the Template Toolkit is simply a Perl module which
exists in a known package location (e.g. C<Template::Plugin::*>) and
conforms to a regular standard, allowing it to be loaded and used
automatically.
The C<Template::Plugin> module defines a base class from which other
plugin modules can be derived. A plugin does not have to be derived
from Template::Plugin but should at least conform to its object-oriented
interface.
It is recommended that you create plugins in your own package namespace
to avoid conflict with toolkit plugins. e.g.
package MyOrg::Template::Plugin::FooBar;
Use the L<PLUGIN_BASE|Template::Manual::Config#PLUGIN_BASE> option to specify
the namespace that you use. e.g.
use Template;
my $template = Template->new({
PLUGIN_BASE => 'MyOrg::Template::Plugin',
});
=head1 METHODS
The following methods form the basic interface between the Template
Toolkit and plugin modules.
=head2 load($context)
This method is called by the Template Toolkit when the plugin module
is first loaded. It is called as a package method and thus implicitly
receives the package name as the first parameter. A reference to the
L<Template::Context> object loading the plugin is also passed. The
default behaviour for the C<load()> method is to simply return the class
name. The calling context then uses this class name to call the C<new()>
package method.
package MyPlugin;
sub load { # called as MyPlugin->load($context)
my ($class, $context) = @_;
return $class; # returns 'MyPlugin'
}
=head2 new($context, @params)
This method is called to instantiate a new plugin object for the C<USE>
directive. It is called as a package method against the class name returned by
L<load()>. A reference to the L<Template::Context> object creating the plugin
is passed, along with any additional parameters specified in the C<USE>
directive.
sub new { # called as MyPlugin->new($context)
my ($class, $context, @params) = @_;
bless {
_CONTEXT => $context,
}, $class; # returns blessed MyPlugin object
}
=head2 error($error)
This method, inherited from the L<Template::Base> module, is used for
reporting and returning errors. It can be called as a package method
to set/return the C<$ERROR> package variable, or as an object method to
set/return the object C<_ERROR> member. When called with an argument, it
sets the relevant variable and returns C<undef.> When called without an
argument, it returns the value of the variable.
package MyPlugin;
use base 'Template::Plugin';
sub new {
my ($class, $context, $dsn) = @_;
return $class->error('No data source specified')
unless $dsn;
bless {
_DSN => $dsn,
}, $class;
}
package main;
my $something = MyPlugin->new()
|| die MyPlugin->error(), "\n";
$something->do_something()
|| die $something->error(), "\n";
=head1 DEEPER MAGIC
The L<Template::Context> object that handles the loading and use of plugins
calls the L<new()> and L<error()> methods against the package name returned by
the L<load()> method. In pseudo-code terms looks something like this:
$class = MyPlugin->load($context); # returns 'MyPlugin'
$object = $class->new($context, @params) # MyPlugin->new(...)
|| die $class->error(); # MyPlugin->error()
The L<load()> method may alterately return a blessed reference to an
object instance. In this case, L<new()> and L<error()> are then called as
I<object> methods against that prototype instance.
package YourPlugin;
sub load {
my ($class, $context) = @_;
bless {
_CONTEXT => $context,
}, $class;
}
sub new {
my ($self, $context, @params) = @_;
return $self;
}
In this example, we have implemented a 'Singleton' plugin. One object
gets created when L<load()> is called and this simply returns itself for
each call to L<new().>
Another implementation might require individual objects to be created
for every call to L<new(),> but with each object sharing a reference to
some other object to maintain cached data, database handles, etc.
This pseudo-code example demonstrates the principle.
package MyServer;
sub load {
my ($class, $context) = @_;
bless {
_CONTEXT => $context,
_CACHE => { },
}, $class;
}
sub new {
my ($self, $context, @params) = @_;
MyClient->new($self, @params);
}
sub add_to_cache { ... }
sub get_from_cache { ... }
package MyClient;
sub new {
my ($class, $server, $blah) = @_;
bless {
_SERVER => $server,
_BLAH => $blah,
}, $class;
}
sub get {
my $self = shift;
$self->{ _SERVER }->get_from_cache(@_);
}
sub put {
my $self = shift;
$self->{ _SERVER }->add_to_cache(@_);
}
When the plugin is loaded, a C<MyServer> instance is created. The L<new()>
method is called against this object which instantiates and returns a C<MyClient>
object, primed to communicate with the creating C<MyServer>.
=head1 AUTHOR
Andy Wardley E<lt>abw@wardley.orgE<gt> L<http://wardley.org/>
=head1 COPYRIGHT
Copyright (C) 1996-2007 Andy Wardley. All Rights Reserved.
This module is free software; you can redistribute it and/or
modify it under the same terms as Perl itself.
=head1 SEE ALSO
L<Template>, L<Template::Plugins>, L<Template::Context>
=cut
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