Question

在Swift中，有一个常见的if let模式用于解包选项：

if let value = optional {
    print("value is now unwrapped: \(value)")
}

我目前正在进行这种模式匹配，但在切换案例中使用元组，其中两个参数都是可选项：

//url is optional here
switch (year, url) {
    case (1990...2015, let unwrappedUrl):
        print("Current year is \(year), go to: \(unwrappedUrl)")
}

然而，这会打印出来：

"Current year is 2000, go to Optional(www.google.com)"

有没有办法可以解开我的可选和模式匹配，只有它不是零？目前我的解决方法是：

switch (year, url) {
    case (1990...2015, let unwrappedUrl) where unwrappedUrl != nil:
        print("Current year is \(year), go to: \(unwrappedUrl!)")
}

Answer 1

您可以使用x?模式：

case (1990...2015, let unwrappedUrl?):
    print("Current year is \(year), go to: \(unwrappedUrl)")

x?只是.some(x)的快捷方式，因此相当于

case (1990...2015, let .some(unwrappedUrl)):
    print("Current year is \(year), go to: \(unwrappedUrl)")

Answer 2

使用开关盒，您可以打开（在需要时）并在同一情况下评估未包装的值（通过使用where）。

像这样：

let a: Bool? = nil
let b: Bool? = true

switch (a, b) {
case let (unwrappedA?, unwrappedB?) where unwrappedA || unwrappedB:
  print ("A and B are not nil, either A or B is true")
case let (unwrappedA?, nil) where unwrappedA:
  print ("A is True, B is nil")
case let (nil, unwrappedB?) where unwrappedB:
  print ("A is nil, B is True")
default:
  print("default case")
}

Answer 3

你可以这样做：

switch(year, x) {
    case (1990...2015,.Some):
    print("Current year is \(year), go to: \(x!)")
}

你也可以

 switch(year, x) {
    case (1990...2015, let .Some(unwrappedUrl)):
    print("Current year is \(year), go to: \(unwrappedUrl)")
}

在Swift模式匹配元组时如何解包Optional？

3 个答案: