swift - 在多参数函数中解包可选

Question

这个问题可能看起来很基础，但我正在尝试解开下面代码中的 middleName 可选参数。我已经在这里成功解包了可选的返回，但我仍然得到了一个 Matthew Optional("Matt") Stevenson 记录。如何打开“Matt”并删除可选的返回？

func returnFullName (name: (firstName: String, middleName: String?,
                    lastName: String)) -> String? 
    {
    return ("\(name.firstName) \(name.middleName) \(name.lastName)")
}

var fullName = returnFullName(("Matthew", middleName: "Matt", lastName: "Stevenson"))

if let printFullName = fullName {
    print (printFullName)
}

Answer 1

您可以使用 nil coalescing operator对于可选的 middleName属性(property)。如果值为 nil , 默认 ""将被打印，而如果该值包含非零字符串，它将被解包。

return ("\(name.firstName) \(name.middleName ?? "") \(name.lastName)")

但是请注意，您不需要让 returnFullName(..) 的返回类型函数是可选的，因为该值永远不会为零。

func returnFullName (name: (firstName: String, middleName: String?,
    lastName: String)) -> String {
    return ("\(name.firstName) \(name.middleName ?? "") \(name.lastName)")
}

print(returnFullName(("Matthew", middleName: "Matt", lastName: "Stevenson"))) 
    // Matthew Matt Stevenson
print(returnFullName(("Matthew", middleName: nil, lastName: "Stevenson")))    
    // Matthew  Stevenson   <-- extra unwanted space 

此外，我没有看到任何明显的理由在函数签名中使用元组，而不是为不同的名称组件使用单独的参数。因此，替代方案如下:

func returnFullName (firstName: String, middleName: String?,
    lastName: String) -> String {
    return "\(firstName) \(middleName ?? "") \(lastName)"
}

print(returnFullName("Matthew", middleName: "Matt", lastName: "Stevenson")) 
    // Matthew Matt Stevenson
print(returnFullName("Matthew", middleName: nil, lastName: "Stevenson"))    
    // Matthew  Stevenson   <-- extra unwanted space

最后，为了避免 nil 的额外空间-值middleName ，我建议保留单行返回，而是使用带有 if let - else 的可选绑定(bind)子句:

func returnFullName(firstName: String, middleName: String?, lastName: String) -> String {
    if let middleName = middleName {
        return ("\(firstName) \(middleName) \(lastName)")
    }
    else {
        return ("\(firstName) \(lastName)")
    }
}

print(returnFullName("Matthew", middleName: "Matt", lastName: "Stevenson"))
    // Matthew Matt Stevenson
print(returnFullName("Matthew", middleName: nil, lastName: "Stevenson"))
    // Matthew Stevenson

---

现在，问题涉及为给定示例展开一个可选变量，现在上面已经很好地涵盖了这一点。不过，我想我会提到，您可以使用闭包和 Swifts 内置的函数式方法来压缩您的解决方案，如下所示:

// instead of a function: make use of a closure
let returnFullName : (String, String?, String) -> String = {
    [$0, $1, $2].flatMap{ $0 }.joinWithSeparator(" ") }

print(returnFullName("Matthew", "Matt", "Stevenson"))
    // Matthew Matt Stevenson
print(returnFullName("Matthew", nil, "Stevenson"))
    // Matthew Stevenson