swift - 我想在扩展中使用开关

Question

protocol Sound { func makeSound() }

extension Sound {  
   func makeSound() { 
     print("Wow") 
   } 
}

protocol Flyable {
   func fly()
}

extension Flyable { 
    func fly() {
        print("✈️") 
    }
}

class Airplane: Flyable { }

class Pigeon: Sound, Flyable { }

class Penguin: Sound { }

let pigeon = Pigeon()
pigeon.fly()  // prints ✈️
pigeon.makeSound() // prints Wow

上面的代码工作正常，但我需要打印不同类型的声音 (I.E)。如果我调用 airplane.fly() 它应该打印 me ("something different") 。企鹅也一样

Answer 1

为 Airplane 类提供 fly():

class Airplane: Flyable {
    func fly() {
        print("something different")
    }
}

let airBus: Airplane = Airplane()
airBus.fly()
//prints "something different"

你可以为企鹅类做同样的事情:

class Penguin: Sound {
    func makeSound() {
        print("squawk")
    }
}

let 🐧 = Penguin()
🐧.makeSound()
//prints "squawk"

您提供的功能是协议(protocol)的默认实现。如果一个类型没有覆盖函数，它将采用默认实现。您可以在 docs 中找到更多信息:

You can use protocol extensions to provide a default implementation to any method or computed property requirement of that protocol. If a conforming type provides its own implementation of a required method or property, that implementation will be used instead of the one provided by the extension.