Swift开关模式与数组匹配

Question

好奇如果有办法在Swift中执行以下操作.

let foo = [1, 2, 3]
let bar = [4, 5, 6]

let value = 5

switch value {
case in foo
    print("5 is in foo")
case in bar
    print("5 is in bar")
default:
    break
}

我理解还有其他方法可以使这个人为的例子工作,比如case 4, 5, 6:使用或不使用开关而是使用,bar.contains(value)但我正在寻找一个专门涉及到数组的开关模式匹配的解决方案.谢谢!

Answer 1

怎么样:

let foo = [1, 2, 3]
let bar = [4, 5, 6]

let value = 5

switch value {
case _ where foo.contains(value):
    print("\(value) is in foo")
case _ where bar.contains(value):
    print("\(value) is in bar")
default:
    print("\(value) is not in foo or bar")
}

Answer 2

您可以定义一个自定义模式匹配运算符 ~=,它将数组作为"模式"和值:

func ~=<T : Equatable>(array: [T], value: T) -> Bool {
    return array.contains(value)
}

let foo = [1, 2, 3]
let bar = [4, 5, 6]

let value = 5

switch value {
case foo:
    print("\(value) is in foo")
case bar:
    print("\(value) is in bar")
default:
    break
}

类似的运算符已存在,例如间隔:

public func ~=<I : IntervalType>(pattern: I, value: I.Bound) -> Bool