enum MyResult<D, E> {
    case data(D)
    case error(E)
}


enum MyError {
    case invalidRequest
}


typealias MyErrorResult<D> = MyResult<D, MyError>


extension MyErrorResult where D == Int {
    func update(with value: Int) -> MyErrorResult<Int> {
        return self // error: Cannot convert return expression of type 'MyResult<Int, E>' to return type 'MyErrorResult<Int>' (aka 'MyResult<Int, MyError>')
    }
}

extension MyErrorResult where D == Int, E == MyError {
    func update(with value: Int) -> MyErrorResult<Int> {
        return self
    }
}