packages/shared/util/Recoil_concatIterables.js

/**
 * Copyright (c) Facebook, Inc. and its affiliates.
 *
 * This source code is licensed under the MIT license found in the
 * LICENSE file in the root directory of this source tree.
 *
 * @emails oncall+recoil
 * @flow strict
 * @format
 */
'use strict';

/**
 * Combines multiple Iterables into a single Iterable.
 * Traverses the input Iterables in the order provided and maintains the order
 * of their elements.
 *
 * Example:
 * ```
 * const r = Array.from(concatIterables(['a', 'b'], ['c'], ['d', 'e', 'f']));
 * r == ['a', 'b', 'c', 'd', 'e', 'f'];
 * ```
 */
function* concatIterables<TValue>(
  iters: Iterable<Iterable<TValue>>,
): Iterable<TValue> {
  for (const iter of iters) {
    for (const val of iter) {
      yield val;
    }
  }
}

module.exports = concatIterables;