Template::Plugin - Base class for Template Toolkit plugins |
Template::Plugin - Base class for Template Toolkit plugins
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; }
A ``plugin'' for the Template Toolkit is simply a Perl module which exists in a known package location (e.g. Template::Plugin::*) and conforms to a regular standard, allowing it to be loaded and used automatically.
The 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 PLUGIN_BASE option to specify the namespace that you use. e.g.
use Template; my $template = Template->new({ PLUGIN_BASE => 'MyOrg::Template::Plugin', });
The following methods form the basic interface between the Template Toolkit and plugin modules.
load($context)
load()
method is to simply return the class
name. The calling context then uses this class name to call the new()
package method.
package MyPlugin;
sub load { # called as MyPlugin->load($context) my ($class, $context) = @_; return $class; # returns 'MyPlugin' }
sub new { # called as MyPlugin->new($context) my ($class, $context, @params) = @_; bless { _CONTEXT => $context, }, $class; # returns blessed MyPlugin object }
error($error)
sub new { my ($class, $context, $dsn) = @_;
return $class->error('No data source specified') unless $dsn;
bless { _DSN => $dsn, }, $class; }
...
my $something = MyModule->new() || die MyModule->error(), "\n";
$something->do_something() || die $something->error(), "\n";
The Template::Context object that handles the loading and use of
plugins calls the new()
and error()
methods against the package name
returned by the load()
method. In pseudo-code terms, it might look
something like this:
$class = MyPlugin->load($context); # returns 'MyPlugin'
$object = $class->new($context, @params) # MyPlugin->new(...) || die $class->error(); # MyPlugin->error()
The load()
method may alterately return a blessed reference to an
object instance. In this case, new()
and error()
are then called as
object methods against that prototype instance.
package YourPlugin;
sub load { my ($class, $context) = @_; bless { _CONTEXT => $context, }, $class; }
sub new { my ($self, $context, @params) = @_; return $self; }
In this example, we have implemented a 'Singleton' plugin. One object
gets created when load()
is called and this simply returns itself for
each call to new().
Another implementation might require individual objects to be created for every call to new(), but with each object sharing a reference to some other object to maintain cached data, database handles, etc. This pseudo-code example demonstrates the principle.
package MyServer;
sub load { my ($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 MyServer instance is created. The new()
method is called against this object which instantiates and returns a
MyClient object, primed to communicate with the creating MyServer.
As of version 2.01, the Template::Plugin module no longer provides an AUTOLOAD method to delegate to other objects or classes. This was a badly designed feature that caused more trouble than good. You can easily add your own AUTOLOAD method to perform delegation if you require this kind of functionality.
Andy Wardley <abw@andywardley.com>
http://www.andywardley.com/|http://www.andywardley.com/
2.60, distributed as part of the Template Toolkit version 2.10, released on 24 July 2003.
Copyright (C) 1996-2003 Andy Wardley. All Rights Reserved. Copyright (C) 1998-2002 Canon Research Centre Europe Ltd.
This module is free software; you can redistribute it and/or modify it under the same terms as Perl itself.
Template, Template::Plugins, Template::Context
Template::Plugin - Base class for Template Toolkit plugins |