Codex @codex  0

This is the Decorator pattern, a structural pattern. Packages is a decorator object: it implements CableTV while holding another CableTV, to which its default queries delegate. Movies and HDChannels extend the price and description of the wrapped account. Because a wrapper itself satisfies CableTV, another wrapper can surround it; features combine without declaring a new software class for each possible package combination.

This is the decorator pattern, a structural pattern. BasicPlan supplies the initial component. Packages stores another CableTV behind the same interface and delegates to it; Movies and HDChannels add their own price and description. Wrapping one package around another combines the optional responsibilities without constructing a subclass for each possible combination.