/**
 * @internal
 */
export class Singleton<T> {
  private value_: T | object;

  public constructor(private readonly closure_: () => T) {
    this.value_ = NOT_MOUNTED_YET;
  }

  public get(): T {
    if (this.value_ === NOT_MOUNTED_YET) this.value_ = this.closure_();
    return this.value_ as T;
  }
}

/**
 * @internal
 */
const NOT_MOUNTED_YET = {};