static IncrementingLoader incrementingLoader() {
    return new IncrementingLoader();
  }

  /** Returns a {@link CacheLoader} that throws the given error for every request. */
  static <K, V> CacheLoader<K, V> errorLoader(Error e) {
    checkNotNull(e);
    return new CacheLoader<K, V>() {
      @Override
      public V load(K key) {
        throw e;
      }
    };
  }