计算型属性用法

class People {
    
    //普通属性
    var firstName:String = ""
    var lastName:String  = ""
    var nickName:String  = ""
    
    /// 计算属性
    var fullName: String {
        get{
            return "1" + "2" + "3"
        }
    }
    /// //带属性监视器的普通属性
    
    var age:Int = 0 {
        //我们需要在age属性变化前做点什么
        willSet {
            print("Will set an new value \(newValue) to age")
        }
        // //我们需要在age属性发生变化后，更新一下nickName这个属性
        didSet {
             print("age filed changed form \(oldValue) to \(age)")
            if age<10
            {
                nickName = "Little"
            }else
            {
                nickName = "Big"
            }
        }
    }
    func toString() -> String {
        return "Full Name: \(fullName) " + ", Age: \(age) "
    }
}

let me = People()
me.firstName = "Li"
me.lastName  = "Lei"
me.age = 30

print(me.toString())