Convert concrete type having generic in class signature swift

Question

I have a struct like this

struct ApiResponse<T: Codable>: Codable {
 let result: T?
 let statusCode: String?
}

Somewhere in my code I need statusCode. I am not interested in result but Swift is not allowing me to use following:

let apiResponse = value as? ApiResponse

it shows following error:

Generic parameter 'T' could not be inferred in cast to 'ApiResponse'

which is quite obvious since struct definition ask some struct conforming to Codable but at same time i can not use one type as it will fail for other types.

e.g.

let apiResponse = value as? ApiResponse<ApiResult>

would be true for one type of response but if i have ApiResponse<ApiOtherResult> it will fail.

        NetworkLayer.requestObject(router: router) { (result: NetworkResult<T>) in

        switch result {
        case .success(let value):
            if let apiResponse = value as? ApiResponse {
                }
        case .failure: break
        }

    }

Check [Swift generic coercion misunderstanding](https://stackoverflow.com/questions/41976844/swift-generic-coercion-misunderstanding). There's no such type as `ApiResponse` and `ApiResponse and `ApiResponse` are completely unrelated types even if `A` and `B` are related. — Dávid Pásztor, Jun 09 '20 at 15:09

score 1 · Accepted Answer · answered Jun 09 '20 at 15:35

I'd suggest adding a new protocol

protocol StatusCodeProvider {
    var statusCode: String? { get }
}

Add it as a requirement in your function making sure that T in NetworkResult<T> conforms to StatusCodeProvider and add conformance for every T you want to request.

Convert concrete type having generic in class signature swift

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