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Manual Reference Pages  -  CLASS::ADAPTER (3)

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Class::Adapter - Perl implementation of the "Adapter" Design Pattern



The Class::Adapter class is intended as an abstract base class for creating any sort of class or object that follows the Adapter pattern.

    What is an Adapter?

The term Adapter refers to a Design Pattern of the same name, from the famous Gang of Four book Design Patterns. Although their original implementation was designed for Java and similar single-inheritance strictly-typed langauge, the situation for which it applies is still valid.

An Adapter in this Perl sense of the term is when a class is created to achieve by composition (objects containing other object) something that can’t be achieved by inheritance (sub-classing).

This is similar to the Decorator pattern, but is intended to be applied on a class-by-class basis, as opposed to being able to be applied one object at a time, as is the case with the Decorator pattern.

The Class::Adapter object holds a parent object that it wraps, and when a method is called on the Class::Adapter, it manually calls the same (or different) method with the same (or different) parameters on the parent object contained within it.

Instead of these custom methods being hooked in on an object-by-object basis, they are defined at the class level.

Basically, a Class::Adapter is one of your fall-back positions when Perl’s inheritance model fails you, or is no longer good enough, and you need to do something twisty in order to make several APIs play nicely with each other.

    What can I do with the actual Class::Adapter class

Well... nothing really. It exist to provide some extremely low level fundamental methods, and to provide a common base for inheritance of Adapter classes.

The base Class::Adapter class doesn’t even implement a way to push method calls through to the underlying object, since the way in which <B>thatB> happens is the bit that changes from case to case.

To actually DO something, you probably want to go take a look at Class::Adapter::Builder, which makes the creation of Adapter classes relatively quick and easy.


The Class::Adapter class itself supplies only the two most common methods, a default constructor and a private method to access the underlying object.

new CW$object

The default new constructor takes a single object as argument and creates a new object which holds the passed object.

Returns a new Class::Adapter object, or undef if you do not pass in an object.


The _OBJECT_ method is provided primarily as a convenience, and a tool for people implementing sub-classes, and allows the Class::Adapter interface to provide a guarenteed correct way of getting to the underlying object, should you need to do so.


Bugs should be reported via the CPAN bug tracker at


For other issues, contact the author.


- Write more comprehensive tests


Adam Kennedy <>


Class::Adapter::Clear, Class::Adapter::Builder, Class::Decorator


Copyright 2005 - 2011 Adam Kennedy.

This program is free software; you can redistribute it and/or modify it under the same terms as Perl itself.

The full text of the license can be found in the LICENSE file included with this module.

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perl v5.20.3 CLASS::ADAPTER (3) 2011-03-24

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