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 $template = Template->new({
PLUGIN_BASE => 'MyOrg::Template::Plugin',
});
The following methods form the basic interface between the Template Toolkit and plugin modules.
This method is called by the Template Toolkit when the plugin module is
first loaded. It is called as a package method and thus implicitly
receives the package name as the first parameter. A reference to the Template::Context
object loading the plugin is also passed. The default behaviour for the
load() method is to simply return the class name. The
calling context then uses this class name to call the new()
package method.
package MyPlugin;
sub load { # called as MyPlugin->load($context)
my ($class, $context) = @_;
return $class; # returns 'MyPlugin'
}
This method is called to instantiate a new plugin object for the
USE directive. It is called as a package method against the
class name returned by load(). A reference to
the Template::Context object creating the plugin is passed, along
with any additional parameters specified in the USE
directive.
sub new { # called as MyPlugin->new($context)
my ($class, $context, @params) = @_;
bless {
_CONTEXT => $context,
}, $class; # returns blessed MyPlugin object
}
This method, inherited from the Template::Base 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 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 looks something like this:
$class = MyPlugin->load($context); # returns 'MyPlugin'
$object = $class->new($context, @params) # MyPlugin->new(...)
|| die $class->error(); # MyPlugin->error()
The load() method may alterately return a blessed reference to an object instance. In this case, new() and error() are then called as object methods against that prototype instance.
package YourPlugin;
sub load {
my ($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.
Andy Wardley <abw@wardley.org> https://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.