protocol Record {
var wins: Int {get}
var losses: Int {get}
func winningpercent() -> Double
}
可以在拓展中实现协议
extension Record {
var description: String {
return String(format: "WINS:%d,LOSSES:%d",arguments:[wins,losses])
}
var gamePlayed: Int {
retrun wins + losses
}
}
可以定义另外一个协议，然后限定同时实现两个协议的实现，继承这个拓展
protocol Tieable{
var ties: Int {get set}
}
extension Record where Self: Tieable {
var gamePlayed: Int {
retrun gane: {
return wins + losses + ties
}
}
}
struct FootballRecord : Record,Tieable {
var wins: Int
var losses: Int
var ties: Int
}
可以限定方法传入的参数必须符合bc两种（或其他）协议
func a (one:protocol<b,c>) {
......
}
struct aa: b,c {
.....
}
a(aa)
