stanford 2 more xcode and swift mvc

calculator code

class ViewController: UIViewController {

    @IBOutlet weak var display: UILabel!
    
    var isTyping = false

    @IBAction func appendDigit(sender: UIButton) {
        let digit = sender.currentTitle!
        if isTyping{
            display.text = display.text! + digit
        } else {
            display.text = digit
            isTyping = true
        }
    }
    
    @IBAction func operate(sender: UIButton) {
        let operation = sender.currentTitle!
        if isTyping{
            enter()
        }
        switch operation {
        case "×": performOperation { $0 * $1 }
        case "÷": performOperation { $1 / $0 }
        case "+": performOperation { $0 + $1 }
        case "−": performOperation { $1 - $0 }
        case "√": performOperation { sqrt($0) }
        default: break
        }
    }
    
    func performOperation(operation:(Double, Double) -> Double) {
        if 2 <= operandStack.count{
            displayValue = operation(operandStack.removeLast(), operandStack.removeLast())
            enter()
        }
    }
    
    func performOperation(operation:(Double) -> Double) {
        if 1 <= operandStack.count{
            displayValue = operation(operandStack.removeLast())
            enter()
        }
    }
    
    var operandStack = [Double]()
    
    @IBAction func enter() {
        isTyping = false
        operandStack.append(displayValue)
        println("operandStack = \(operandStack)")
    }
    
    var displayValue: Double {
        get {
            return NSNumberFormatter().numberFromString(display.text!)!.doubleValue
        }
        
        set {
            display.text = "\(newValue)"
            isTyping = false
        }
    }
}

calculator code analysis

define a func

 func performOperation(operation:(Double, Double) -> Double) {
     if 2 <= operandStack.count{
         displayValue = operation(operandStack.removeLast(), operandStack.removeLast())
         enter()
     }
 }

you can call this func

 performOperation({ (op1: Double, op2: Double) -> Double in return op1 * op2 })

get rid of the type declaration

 performOperation({ (op1, op2) in return op1 * op2 })

get rid of the return

 performOperation({ (op1, op2) in op1 * op2 })

do not need to name arguments
```
 performOperation({ $0 * $1 })
```
this is the last argument you can move this outside the parentheses
```
 performOperation() { $0 * $1 }
```
there are no other arguments you can get rid of the parentheses
```
 performOperation { $0 * $1 }
```