swift - 如何在 Swift 中通过实际类型限制 switch case

Question

我想将 Swift 枚举中的情况与基于协议(protocol)的关联值进行匹配。具体来说，我想将情况限制为关联值的实际类型，但我不确定这是否可能。

protocol MyProtocol {}

extension Int:MyProtocol {}
extension Double:MyProtocol {}

enum MyEnum {
   case something(MyProtocol)
   case nothing
}

let somethingInt = .something(10)
let somethingDouble = .something(10.0)

switch somethingInt {
   case .something(let aValueInt):
   !!! I want to figure out how to limit this case to a double or an int
   case .something(let aValueDouble):
   !!! I want to figure out how to limit this case to a double or an int
   case .nothing:
   break
}

Answer 1

下面是一个可以正确编译并运行的示例:

    protocol MyProtocol {}

    extension Int:MyProtocol {}
    extension Double:MyProtocol {}

    enum MyEnum {
        case something(MyProtocol)
        case nothing
    }

    let somethingInt = MyEnum.something(10)
    let somethingDouble = MyEnum.something(11.0)

    switch somethingInt { // and try it with somethingDouble instead
    case .something(let aValueInt as Int): print(aValueInt)
    case .something(let aValueDouble as Double): print(aValueDouble)
    case .something(_): break
    case .nothing: break
    }