构造器及属性监视器

//默认构造器
class Student{
    var name : String = ""
    var number : Int = 0
}
//自定义构造函数
class Person{
    //雷属性
    var name:String
    var age:Int
    //类构造函数
    init(newName:String,newAge:Int) {
        self.name = newName
        self.age = newAge
    }
    //实例函数
    func say() -> String {
        return "我叫MT\(name)"
    }
}

class People {
    //普通属性
    var firstName:String = ""
    var lastName:String = ""
    var nickName:String = ""
    
    //计算属性
    var fullName:String {
        get {
            return nickName + " " + firstName + " " + lastName
        }
    }
    //带属性监视器普通属性
    var age:Int = 0 {
        //属性变化前
        willSet{
            print("will set an new value\(age) to age")
        }
        didSet{
            print("age file change form \(oldValue) to \(age)")
            if age < 10 {
                nickName = "Little"
            }else{
                nickName = "Big"
            }
        }
    }
    func toString() ->String{
        return "Full name \(fullName) +_ age\(age)"
    }
}