Swift 常用标准库协议

struct Size: Equatable, Comparable, CustomStringConvertible { // 相等的协议
    var width: Double
    var height: Double
    
    var description: String {
        return "witth:" + "\(self.width)" + " " + "height" + "\(self.height)"
    }
}

// 相等协议的实现
func ==(left: Size, right: Size) -> Bool {
    return left.height == right.height && left.width == right.height
}

// 比较协议的实现
func <(left: Size, right: Size) ->Bool {
    if left.width * left.height != right.height * right.width {
        return left.width * left.height < right.height * right.width
    }
    
    return left.width * left.height > right.height * right.width
}

扩展协议

protocol student:CustomStringConvertible {
    var name: String{get}
    var height: Double {get}
    
}

// 扩展协议，在协议扩展中可以