protocol Pet {
    
    var name: String {get set}
    var birthPlace: String {get}
    func playWith()
    func fed()
    
    mutating func changeName(name: String)
}

struct Dog: Pet {
    
    internal mutating func changeName(name: String) { // 結構體加上mutating
        self.name = name
    }

    
    var name: String = "dog"
    var birthPlace: String = "china"
    
    func fed() {
        print("fed me")
    }

    internal func playWith() {
        print("play with me")
    }
}
 

協議裡定義的方法和屬性要全部實現

var dog:Dog = Dog()
dog.birthPlace = "beijing"

var pet:Pet = Dog()
pet.birthPlace = "beijing"

協議裡宣告建構函式：

protocol Pet {
    
    var name: String {get set}
    var birthPlace: String {get}
    func playWith()
    func fed()
    init(name: String)
    mutating func changeName(name: String)
}

class Animal {
    var legs: Int = 4
    var name: String = "i am a animal"
    init(name: String) {
        self.name = name
    }
}

class Bird: Animal, Pet {
    override required init(name: String) { // override關鍵字 對應 父類animal, required 對應協議Pet
        super.init(name: name)
    }

    internal func changeName(name: String) {
        
    }

    internal func fed() {
        
    }

    internal func playWith() {
        
    }

    internal var birthPlace: String = ""
}