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 $template = Template->new({
PLUGIN_BASE => 'MyOrg::Template::Plugin',
});
The following methods form the basic interface between the Template
Toolkit and plugin modules.
This method is called by the Template Toolkit when the plugin module
is first loaded. It is called as a package method and thus implicitly
receives the package name as the first parameter. A reference to the
the Template::Context manpage object loading the plugin is also passed. The
default behaviour for the load() method is to simply return the class
name. The calling context then uses this class name to call the new()
package method.
package MyPlugin;
sub load { # called as MyPlugin->load($context)
my ($class, $context) = @_;
return $class; # returns 'MyPlugin'
}
This method is called to instantiate a new plugin object for the USE
directive. It is called as a package method against the class name returned by
load(). A reference to the the Template::Context manpage object creating the plugin
is passed, along with any additional parameters specified in the USE
directive.
sub new { # called as MyPlugin->new($context)
my ($class, $context, @params) = @_;
bless {
_CONTEXT => $context,
}, $class; # returns blessed MyPlugin object
}
This method, inherited from the the Template::Base manpage module, is used for
reporting and returning errors. It can be called as a package method
to set/return the $ERROR package variable, or as an object method to
set/return the object _ERROR member. When called with an argument, it
sets the relevant variable and returns undef. When called without an
argument, it returns the value of the variable.
package MyPlugin;
use base 'Template::Plugin';
sub new {
my ($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";
The the Template::Context manpage 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 looks something like this:
$class = MyPlugin->load($context); # returns 'MyPlugin'
$object = $class->new($context, @params) # MyPlugin->new(...)
|| die $class->error(); # MyPlugin->error()
The load() method may alternately return a blessed reference to an
object instance. In this case, new() and error() are then called as
object methods against that prototype instance.
package YourPlugin;
sub load {
my ($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.
Andy Wardley <abw@wardley.org> http://wardley.org/
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.
Template, the Template::Plugins manpage, the Template::Context manpage
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