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/**
* @license
* Copyright (c) 2016 The Polymer Project Authors. All rights reserved.
* This code may only be used under the BSD style license found at http://polymer.github.io/LICENSE.txt
* The complete set of authors may be found at http://polymer.github.io/AUTHORS.txt
* The complete set of contributors may be found at http://polymer.github.io/CONTRIBUTORS.txt
* Code distributed by Google as part of the polymer project is also
* subject to an additional IP rights grant found at http://polymer.github.io/PATENTS.txt
*/
/**
* @template T
*/
export default class Deferred {
constructor() {
/**
* @private
* @type {T|undefined}
*/
this._value = undefined;
/**
* @private
* @type {Function|undefined}
*/
this._resolve = undefined;
/**
* @private
* @type {!Promise<T>}
*/
this._promise = new Promise(resolve => {
this._resolve = resolve;
if (this._value) {
resolve(this._value);
}
});
}
/**
* @param {T} value
*/
resolve(value) {
if (this._value) {
throw new Error('Already resolved.');
}
this._value = value;
if (this._resolve) {
this._resolve(value);
}
}
/**
* @return {!Promise<T>}
*/
toPromise() {
return this._promise;
}
}