Swift 泛型。 如何指定输出类型？

Question

I have, for example, enum and what I want to archive is that each enum case can give me some different output type for, let's say a function. Code example:

protocol MyType: Codable {
    var id: String {get set}
}

struct Type1: MyType {
    var id: String
    var name:String
}


struct Type2: MyType {
    var id: String
    var amount: Int
}


enum ReturnType {
    case first, second
    //Option 1
    func getElement() -> MyType {
        switch self {
        case .first:
            return Type1(id: "1", name: "Name")
        case .second:
            return Type2(id: "2", amount: 10)
        }
    }

    //Some crap is here - don't pay attention
    func test<T:MyType>(data: T) -> T {
        return data
    }
}

//Option 2
func getElement(ofType type: ReturnType) -> MyType {
    switch type {
    case .first:
        return Type1(id: "1", name: "Name")
    case .second:
        return Type2(id: "2", amount: 10)
    }
}




let test1 = ReturnType.first.getElement() as! Type1
let test2 = ReturnType.second.getElement()
let test3 = getElement(ofType: .first)

So currently only test1 is Type1 but test2 and test3 is MyType I want to archive strong typing without forcing that with as!

I was trying to do it with generics but didn't get any success.. Any thoughts? Much appreciated! Thanks!

Answer 1

you can do the following:

enum ReturnType {
    case first, second
    //Option 1
    func getElement<T: MyType>() -> T {
        switch self {
        case .first:
            return Type1(id: "1", name: "Name") as! T
        case .second:
            return Type2(id: "2", amount: 10) as! T
        }
    }

}

//Option 2
func getElement<T: MyType>(ofType type: ReturnType) -> T {
    switch type {
    case .first:
        return Type1(id: "1", name: "Name") as! T
    case .second:
        return Type2(id: "2", amount: 10) as! T
    }
}

after that when you call the func you just need to declare what type you want the variable as:

let test1: Type1 = ReturnType.first.getElement()
let test2: Type2 = ReturnType.second.getElement()
let test3: Type1 = getElement(ofType: .first)

hope it helped