Swift 4 switch 语句比较多个值，使用大于或小于

Question

我知道在 Swift 中我可以做一个简单的 Swift switch 语句来将计算值与单个变量进行比较：

let distanceTravelled = -145.1
switch distanceTravelled {
case _ where distanceTravelled < 15:
    print("You travelled the right distance")
default:
    print("Sad face")
}

但我希望能够使用元组设置比较矩阵，如下所示：

let distanceTravelled = -145.1,
    origin = 2

switch (origin, distanceTravelled) {
case (2, _ where distanceTravelled < 15):
    print("You travelled the right distance")
default:
    print("Sad face")
}

但这不能编译，抱怨expected ',' separator和expected expression in list of expressions。

显然这在语法上是不正确的，但是考虑到它是有效的，它不应该有效吗？

switch (2, -145.1) {
case (2, _):
    print("You travelled the right distance")
default:
    print("Sad face")
}

Answer 1

啊哈！在优秀的Swift 文档中找到了答案。我并没有从元组的条件来考虑这一点。

switch (origin, distanceTravelled) {
case let (_, d) where d < 15:
    print("You travelled the right distance")
default:
    print("Sad face")
}

对于我的实际用例，这有点奇怪，因为我正在比较enum属性的来源，但结果是：

let absOriginDistanceFromDefault = abs(defaultDividerPosition - viewDividerOrigin)

switch (splitViewOrigin, distanceTravelled) {
case let (.defaultPosition, d) where d < -100:
    return .shouldMoveToTopView
case let (.defaultPosition, d) where d > 100:
    return .shouldMoveToBottomView
case (.topView, _) where currentDividerPosition - defaultDividerPosition < -100:
    return .shouldMoveToBottomView
case (.topView, _) where abs(distanceTravelled) > absOriginDistanceFromDefault * 0.5 && currentDividerPosition < self.view.bounds.height:
    return .shouldMoveToDefaultPosition
case (.bottomView, _) where currentDividerPosition - defaultDividerPosition > 100:
    return .shouldMoveToTopView
case (.bottomView, _) where abs(distanceTravelled) > absOriginDistanceFromDefault * 0.3 && currentDividerPosition > 0:
    return .shouldMoveToDefaultPosition
default:
    return .shouldReturnToOrigin
}

奇怪的是，在进一步简化过程中，我什至不需要在前两次检查中声明变量：

let absOriginDistanceFromDefault = abs(defaultDividerPosition - viewDividerOrigin)

switch (splitViewOrigin, distanceTravelled) {
case (.defaultPosition, _) where distanceTravelled < -100,
     (.bottomView, _) where currentDividerPosition - defaultDividerPosition > 100:
    return .shouldMoveToTopView
case (.defaultPosition, _) where distanceTravelled > 100,
     (.topView, _) where currentDividerPosition - defaultDividerPosition < -100:
    return .shouldMoveToBottomView
case (.topView, _) where abs(distanceTravelled) > absOriginDistanceFromDefault * 0.5 && currentDividerPosition < maxHeight,
     (.bottomView, _) where abs(distanceTravelled) > absOriginDistanceFromDefault * 0.3 && currentDividerPosition > 0:
    return .shouldMoveToDefaultPosition
default:
    return .shouldReturnToOrigin
}