/**
 * Copyright 2019 The AMP HTML Authors. All Rights Reserved.
 *
 * 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.
 */
/**
 * FastStringArray acts like a `Set` (allowing only one occurrence of a string
 * `key`), but provides the index of the `key` in the backing array.
 *
 * This is designed to allow synchronizing a second array with the contents of
 * the backing array, like how `sourcesContent[i]` is the source content
 * associated with `source[i]`, and there are never duplicates.
 */
export default class FastStringArray {
    private indexes;
    array: ReadonlyArray<string>;
    constructor();
    /**
     * Puts `key` into the backing array, if it is not already present. Returns
     * the index of the `key` in the backing array.
     */
    put(key: string): number;
}