返回元组从

Question

我已经定义了一个协议与方法委托（可选类型没有解开的值）返回一个元组：

protocol SMCalculatorDelegate { 

    func numbersToAdd() -> (Int, Int) 

} 

当我尝试在我的课像这样来调用这个对委托方法：

class SMCalculator: NSObject { 

    var delegate : SMCalculatorDelegate? 

    func add() { 

     let myTuple : (n1: Int, n2: Int) = delegate?.numbersToAdd() 

    } 

} 

我得到首发let myTuple...行引用该行代码的.numbersToAdd()部分下面的错误。

"Value of optional type '(Int, Int)?' not unwrapped; did you mean to use '!' or '?'?" 

为什么不能这样工作时，我可以提取元组没有像这样的错误？

let tuple = delegate?.numbersToAdd() 

println(tuple) //Prints (5,5) 

Answer 1

我仍然试图抓住一切，但它似乎是正确的行为。

应该delegate是零，你将会分配到零myTuple，因此你需要myTuple可选，以及...

class SMCalculator: NSObject { 

    var delegate : SMCalculatorDelegate? 

    func add() { 

     let myTuple : (n1: Int, n2: Int)? = delegate?.numbersToAdd() 

     // this works, because we're saying that myTuple definitely isn't nil 
     println(myTuple!.n1) 

     // this works because we check the optional value 
     if let n1 = myTuple?.n1 { 
      println(n1) 
     } else { 
      println("damn, it's nil!") 
     } 

     // doesn't work because you're trying to access the value of an optional structure 
     println(myTuple.n1) 

    } 

} 

作品对我来说