Strategy Design Pattern in PHP

This small project demonstrates the usage of the strategy design using two behaviors of a dog: walking and speaking.

The abstract Dog class is composed of two behaviors, both of which are interfaces:

1. Speaking - SpeakBehavior.php
2. Walking - WalkBehavior.php

Because the Dog class is composed of these behaviors, we define the behavior implementation within the children of Dog. However, if we choose to diverge from this behavior at runtime, the child dog object need only call the inherited setter methods for the behaviors.

Modifying the behavior of the Toy Labrador at runtime can be found in app/Demo.php.

##Advantages ###Favors composition over inheritance This design patterns brings several advantages. For one, it favors composition over inheritance (Dog is composed of behaviors). With inheritance, it's possibly that new implementations of Dog could inherit unexpected Speaking or Walking behaviors. For example, a hot dog doesn't speak or walk.

###Favors Code Reuse If each dog implementation were to implement their behaviors, then it creates a maintenance issue. Example:

class Labrador implements Walkable, Speakable { ... }

With this, each implementation of Dog would need to implement a version of walk() and speak() (no code reuse). Also, when a modification to a generic speak or walk behavior occurs, it will need to be changed across all classes.

##Output

In Demo 
I'm a real Labrador. | Speaking: Woof! Woof! | Walking: I'm walking on all four.
I'm a Toy Labrador. | Speaking: I don't speak! | Walking: I can't walk!
Changing ToyLabrador behavior at runtime
I'm a Toy Labrador. | Speaking: Woof! Woof! | Walking: I'm walking on all four.

This project was based off of the Duck example given in the Head First Design Patterns book by Eric Freeman and Elisabeth Robson