# The Mixin

An extremely important piece of the Framework is the Mixin. Before PHP 5.4, the language had no concept of Traits. These are class-like structures that, when ‘used’ by an object, provide some type of functionality (similar to Multiple Inheritance). But still, these Traits can't be introduced into an object at runtime.

Nooku has been solving these problems for years (since PHP 5.2) with the Mixin.

The Mixin not only lets you compose objects together, but it also adds each mixed object’s methods to the composite object’s interface. The object using the mixin seems to ‘inherit’ the mixed in object’s methods.

Almost all objects in the Framework have this ability because they extend the base class KObject that defines the mixin() method.

Let's look at Nooku's Controller Architecture to see how this works

The major classes in Nooku’s controller architecture are also descended from KObject. The abstract controller is the KControllerAbstract class and by inspection you can see that it takes advantage of the Mixing ability right away. Whenever an instance of this class is constructed, the KCommandMixin and KBehaviorMixin functionality is immediately added to its interface. Consequently, each controller in Nooku is composed with Command Chain and Behavior management functionality through the respective objects.

The KBehaviorMixin class holds all the pieces to give KControllerAbstract the ability to load specific Behaviors at runtime. Behavioral strategies are classes that describe a process or logic that can be separated out and used by other classes (e.g., editable, executable). KBehaviorMixin is fairly simple and has only four 'interface' methods: getBehavior, hasBehavior, addBehavior and getBehaviors. That's all we need to give an object the ability to handle and encapsulate different behavioral strategies.

Similarly, KCommandMixin has more methods, but if you hadn’t guessed, they provide a KControllerAbstract based object with the ability to implement a command chain (or Chain of Responsibility design pattern), but also lets it do so at runtime.

With that, you can think of this Mixing as a simple arithmetic addition as it adds all the methods from KCommandMixin and KBehaviorMixin to the KControllerAbstract base object's interface.

By definition Abstract classes are meant to be extended and so by the magic of inheritance all objects that are children or instances of KControllerAbstract also gain the ability to add behaviors and commands to a command chain at runtime.

### Great...But what does all that actually mean?

In short, Nooku provides componentized functionality; that is, Nooku allows you to modularize your functionality and compose functionalities across modules at runtime.

These two examples serve to demonstrate composition. They also serve to demonstrate the Framework’s support for further composition at its core. This is an important advantage. The methods added to KControllerAbstract above support the “Strategy Design Pattern” by giving developers the tools to encapsulate what varies before one line of code has been written. The fact that the mixin() method is part of every extension of KObject means that you can readily define and add other behavioral management interfaces to most objects at runtime.