[SOLVED] Swift error: Initializer for conditional binding must have Optional type, not '()'

Swift error: Initializer for conditional binding must have Optional type, not '()'

I'm doing the course of iTunes University called "Developing iOS 8 Apps with Swift". On the third video I encountered with a problem that did not happen in the video, even though it was the same code, that is as follows:

class ViewController: UIViewController{

…

@IBAction func operate(sender: UIButton) {
        if userIsInTheMiddleOfTypingANumber{
            enter()
        }
        if let operation = sender.currentTitle {
            if let result = brain.performOperation(operation) { > ERROR HERE
                displayValue = result
            } else {
                displayValue = 0
            }
        }
    } 
…
}

After reading many explanations of this error I suppose the problem comes from here:

class CalculatorBrain
{

…
func performOperation(symbol: String) {
        if let operation = knownOps[symbol] {            opStack.append(operation)
        }
    }
}

Thank you if you can help me!

Solution

performOperation doesn't return anything and needs to return an optional type so that it can be used in your if let statement (to check if it did indeed return a value) and that's what it could be moaning about.

Try:

func performOperation(symbol: String) -> Int? {

which means it could return an Int, and then your if let statement should be happy.