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) { // 结构体加上mutating
self.name = name
}
var name: String = "dog"
var birthPlace: String = "china"
func fed() {
print("fed me")
}
internal func playWith() {
print("play with me")
}
}
var dog:Dog = Dog() dog.birthPlace = "beijing" var pet:Pet = Dog() pet.birthPlace = "beijing"再看上面的代码，前两行声明一个Dog类型的实例，可以修改其birthPlace,后面两行声明的是一个Pet类型的实例，不能修改其birthPlace,因为在Pet协议里birthPlace是只读的
可以看出，虽然Dog类实现了Pet协议，但协议规定的只读属性发生了改变。
协议里声明构造函数：
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关键字 对应 父类animal,required 对应协议Pet
super.init(name: name)
}
internal func changeName(name: String) {
}
internal func fed() {
}
internal func playWith() {
}
internal var birthPlace: String = ""
}
