Template::Plugin(3) User Contributed Perl Documentation Template::Plugin(3)NAMETemplate::Plugin - Base class for Template Toolkit plugins
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;
}
DESCRIPTION
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 $template = Template->new({
PLUGIN_BASE => 'MyOrg::Template::Plugin',
});
METHODS
The following methods form the basic interface between the Template
Toolkit and plugin modules.
load($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
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 $class; # returns 'MyPlugin'
}
new($context, @params)
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,
}, $class; # returns blessed MyPlugin object
}
error($error)
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";
DEEPER MAGIC
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".
AUTHOR
Andy Wardley <abw@wardley.org> <http://wardley.org/>
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.
SEE ALSO
Template, Template::Plugins, Template::Context
perl v5.14.3 2011-12-20 Template::Plugin(3)
