/**
 * Copyright 2017-2020 Plexus Interop Deutsche Bank AG
 * SPDX-License-Identifier: Apache-2.0
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *     http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */
/**
 * Call source fn only once, even if source promise is rejected
 */
export declare const once: <Req, Res>(fn: (req?: Req | undefined) => Promise<Res>) => (req?: Req | undefined) => Promise<Res>;
export declare function onceVoid(fn: () => void): () => void;