状态在 Swift 中的实现
State is a behavioral design pattern that allows an object to change the behavior when its internal state changes.
The pattern extracts state-related behaviors into separate state classes and forces the original object to delegate the work to an instance of these classes, instead of acting on its own.
在 Swift 中使用模式
Usage examples: The State pattern is commonly used in Swift to convert massive
switch-base state machines into the objects.
Identification: State pattern can be recognized by methods that change their behavior depending on the objects' state, controlled externally.