code from CS193P: Developing iOS 8 Applications with Swift that longer compiles with the solution

sc193p_example.swift

    // bad code
    func performOperationWith(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()
        }
    }
   
   // good code
    func performOperationWithTwoOperands(operation: (Double, Double) -> Double) {
        if operandStack.count >= 2 {
            displayValue = operation(operandStack.removeLast(), operandStack.removeLast())
            enter()
        }
    }
    
    func performOperationWithOneOperand(operation: Double -> Double) {
        if operandStack.count >= 1 {
            displayValue = operation(operandStack.removeLast())
            enter()
        }
    }