interface Promise<T> {
    as<T, B>(b: B): Promise<B>;
    tap<T>(f: (t: T) => void): Promise<T>;
    flatTap<T>(f: (t: T) => Promise<void>): Promise<T>;
    tapError<T>(e: (e: any) => void): Promise<T>;
    flatTapError<T>(e: (e: any) => Promise<void>): Promise<T>;
}