［iOS-Swift编程］Method '...' with Objective-C selector '...' 错误的解决方法

我的Xcode版本是Version 6.4 (6E35b)

描述（写了2个一样的func）：    

    func performOperation(operation: (Double, Double) -> Double) {

        if operandStack.count >= 2 {

            displayValue = operation(operandStack.removeLast(), operandStack.removeLast())

            enter()

        }

    }

    func performOperation(operation: Double -> Double) {

        if operandStack.count >= 1 {

            displayValue = operation(operandStack.removeLast())

            enter()

        }

报错信息如下：

Method 'performOperation' with Objective-C selector 'performOperation:' conflicts with previous declaration with the same Objective-C selector

解决方法：

1. 对第二个performOperation进行改名;

2. 在第二个performOperation的定义前添加privtate