swift - 小于或大于 Swift switch 语句

Question

我熟悉 Swift 中的 switch 语句，但想知道如何用 switch 替换这段代码:

if someVar < 0 {
    // do something
} else if someVar == 0 {
    // do something else
} else if someVar > 0 {
    // etc
}

Answer 1

这是一种方法。假设 someVar 是一个 Int 或其他 Comparable，您可以选择将操作数分配给一个新变量。这使您可以使用 where 关键字来限制范围:

var someVar = 3

switch someVar {
case let x where x < 0:
    print("x is \(x)")
case let x where x == 0:
    print("x is \(x)")
case let x where x > 0:
    print("x is \(x)")
default:
    print("this is impossible")
}

这可以稍微简化一下:

switch someVar {
case _ where someVar < 0:
    print("someVar is \(someVar)")
case 0:
    print("someVar is 0")
case _ where someVar > 0:
    print("someVar is \(someVar)")
default:
    print("this is impossible")
}

您还可以通过范围匹配完全避免 where 关键字:

switch someVar {
case Int.min..<0:
    print("someVar is \(someVar)")
case 0:
    print("someVar is 0")
default:
    print("someVar is \(someVar)")
}