The State pattern is a way to allow a game object to change its behavior and functionality in response to different stimuli within the game, especially when a variable or a condition within that object changes, as those changes may trigger a change in state. The state of an object is managed by some context (commonly referred to in the game industry as a machine), but the states tell the machine when to change states and thereby functionality. The State pattern contains two parts: the state and the context. The context object holds the current state and can be used by the state class to change what state should be run, whereas the state object holds the actual functionality:

In the Mach5 Engine, there is a class that already uses the State pattern (M5StateMachine) but, before we dive into a completed version, let's actually build one from scratch.

There are multiple ways to implement the State pattern or to get a State-like behavior. We'll go over some of the commonly seen versions and the pros and cons of using them before moving to our final version.