关于ios8斯坦福公开课第二课

    @IBAction func oprate(sender: UIButton) {
        let opration = sender.currentTitle!
        if userIsOnInput {
            enter()
        }
        switch opration {
        case "+": performOperation{ $0+$1 }
            
        case "−": performOperation{ $1-$0 }
        case "×": performOperation{ $0*$1 }
        case "÷": performOperation{ $1/$0 }
//        case "√": performOperation{ sqrt($0) }
        default: break
        }
        
        
    }
    func performOperation(opretion:(Double,Double) -> Double) {
        if operandStack.count >= 2 {
            displayValue = opretion(operandStack.removeLast(), operandStack.removeLast())
            enter()
        }
    }
    
    /** 并不能闭包参数的重载  */
//    func performOperation(opretion: Double -> Double) {
//        if operandStack.count >= 1 {
//            displayValue = opretion(operandStack.removeLast())
//            enter()
//        }
//    }