Protocol associated types and generics

Question

My code looks like this:

protocol Remotable {
    init?(dict: Dictionary<String, String>)
}

protocol SearchResultable {
    associatedtype TRS: Remotable
    static func myFunction(remote: TRS)
}

struct MySearchResult<T:SearchResultable, TR: Remotable> {
    typealias TRS = TR
    let items: Array<T>
    let limit: Int

    func testMethod() {
        let dict = [["id": "asd123"],["id":"asd456"]]
        let a = dict.flatMap(TRS.init)
        let b = a[0] //has type TR
        let c = T.myFunction(... //expects an argument of type T.TRS
    }
}

And I cannot get to call myFunction because it expects a T.TRS type of argument. I was expecting that I can call myFunction with the b parameter that is of type TR. Do you have any idea of what am I doing wrong?

Answer 1

I also found an answer to my own question. I don't know which one is better, I would be grateful if someone would explain which is better and why.

struct MySearchResult<T:SearchResultable, TR where T.TRS == TR > {
    let items: Array<T>
    let limit: Int

    func testMethod() {
        let dict = [["id": "asd123"],["id":"asd456"]]
        let a = dict.flatMap(TR.init)
        let b = a[0]
        let c = T.myFunction(b)
    }
}

So I just had to tell the compiler that T.TRS is the same as TR.

Answer 2

Try to force unwrap a[0] as the function expects an argument of type T.TRS , you are sure that a[0] will conform to protocol Remotable .

let c = a[0] as! T.TRS
T.myFunction(c)