Source: lib/util/lazy.js

  1. /** @license
  2.  * Copyright 2016 Google LLC
  3.  * SPDX-License-Identifier: Apache-2.0
  4.  */
  6. goog.provide('shaka.util.Lazy');
  8. goog.require('goog.asserts');
  11. /**
  12.  * @summary
  13.  * This contains a single value that is lazily generated when it is first
  14.  * requested.  This can store any value except "undefined".
  15.  *
  16.  * @template T
  17.  */
  18. shaka.util.Lazy = class {
  19.   /** @param {function():T} gen */
  20.   constructor(gen) {
  21.     /** @private {function():T} */
  22.     this.gen_ = gen;
  24.     /** @private {T|undefined} */
  25.     this.value_ = undefined;
  26.   }
  28.   /** @return {T} */
  29.   value() {
  30.     if (this.value_ == undefined) {
  31.       // Compiler complains about unknown fields without this cast.
  32.       this.value_ = /** @type {*} */ (this.gen_());
  33.       goog.asserts.assert(
  34.           this.value_ != undefined, 'Unable to create lazy value');
  35.     }
  36.     return this.value_;
  37.   }
  39.   /** Resets the value of the lazy function, so it has to be remade. */
  40.   reset() {
  41.     this.value_ = undefined;
  42.   }
  43. };