extension扩展Int，必包作为参数，好巧妙
extension Int{
func times(closure:(() -> ())?){ //必包作为参数，巧用self
if self >= 0 {
for _ in 0 ..< self {
closure?()
}
}
}
}
10.times{
print(“something”)
}// 打印十次
extension CustomStringConvertible{ //扩展协议
var upperDescription:String{
return self.description.uppercaseString
}
}
[“key”:”value”].upperDescription