Firebase2.swift

public extension DatabaseQuery {
    func observeSingleEvent<T>(of type: DataEventType,
                               with block: @escaping (DecodeResult<T>) -> Void)
        where T: Decodable {
            observeSingleEvent(of: type) { snap in
                block(snap.decoded())
            }
    }

    func observe<T>(eventType: DataEventType,
                    with block:  @escaping (DecodeResult<T>) -> Void) -> UInt
        where T: Decodable {
            return observe(eventType, with: { snap in
                block(snap.decoded())
            })
    }
}