Decorators, Addons, and Extensions

[JSideris]

Overview

Extensions are the newest way to extend the functionality of a GameObject. The other supported ways are using decorators and augmentations (addons).

Extensions differ from addons and decorators. Decorators permanently update the class hierarchy of a class. This is useful for adding functionality that will exist on both client and server for all instances of the class. For instance, the @ownable decorator contains everything it means to be owned and controlled by a Controller. In general, a single decorator is designed to be generic as to be able to add functionality to different types of GameObjects. Decorators modify the definition of a class, and therefore apply to both client and server.

Addons augment a specific instance of a class with new behavior. This is useful for adding functionality at runtime. For instance, a player could pick up a powerup that grants some ability (e.g. night vision). In general, addons are designed for specific inherited types of GameObject. Addons augment objects on the client and the server.

An extension provides functionality that overlaps greatly with decorators, but rather than changing the definition of a class, it augments each instance of the class with new behavior. To that end, extensions combine some of the functionality of decorators and addons. The advantage over decorators is in modding, or in situations where the behavior of an object is different on the client from the server (for instance, drawing and sound effects). The advantage of using extensions over addons is in the fact that they are completely managed by the game engine. For instance, to add a draw method to an Alien class client-side, using addons it would be possible to intercept an onAddGameObject event, augment the new object, and manage the lifecycle of the drawing for each Alien. But with extensions, the extension for drawing an Alien is registered once in the client-side version of the code and the extension is automatically instantiated for each Alien GameObject that is created. Cleanup is also automatic.

Detailed Comparison

	Decorator	Extension	Addon
Modifies	Class	All Instances	Individual Instance
Form	TypeScript Decorator	Attached Game Object	Attached Game Object
Affects	Client and Server	Client and/or Server	Client and/or Server
Applied	On Compilation	On Compilation or Runtime	At Runtime
Managed	By TypeScript	By Engine	By Game
Master	Game Object	Extension	Addon or Game Object
Slave	Decorator	Game Object	Addon or Game Object
Generic	Yes	No	Maybe
Uses	Abstraction / Code Reuse / Plugins	Mods / Client/Server-Only	Buffs / Debuffs / Weapons / Abilities
Actions	Polymorphism	Event-Driven	Event-Driven
Example	Teamable	Drawable	Shield Augmentation