使用

  let newPromise = Promise<Result<Bool>> { resolver in

        resolver.fulfill(Result<Bool>.fulfilled(true))
        print("in resolve1")
    }.then(on: nil) { result -> Promise<Bool> in
        switch result {
        case .fulfilled: print("fulfilled")
        case .rejected: print("rejected")
        }
        return Promise { seal in
            // next promise
            print("in resolve2")
            seal.resolve(Result<Bool>.fulfilled(true))
        }
    }