Supplier<T> delegate, long duration, TimeUnit unit) {
    checkNotNull(delegate);
    checkArgument(duration > 0, "duration (%s %s) must be > 0", duration, unit);
    return new ExpiringMemoizingSupplier<>(delegate, unit.toNanos(duration));
  }

  /**
   * Returns a supplier that caches the instance supplied by the delegate and removes the cached
   * value after the specified time has passed. Subsequent calls to {@code get()} return the cached

      Supplier<T> delegate, long duration, TimeUnit unit) {
    checkNotNull(delegate);
    checkArgument(duration > 0, "duration (%s %s) must be > 0", duration, unit);
    return new ExpiringMemoizingSupplier<>(delegate, unit.toNanos(duration));
  }

  /**
   * Returns a supplier that caches the instance supplied by the delegate and removes the cached
   * value after the specified time has passed. Subsequent calls to {@code get()} return the cached

   * nanos to match CacheBuilder implementation.
   */
  private static @Nullable Long durationInNanos(long duration, @Nullable TimeUnit unit) {
    return (unit == null) ? null : unit.toNanos(duration);
  }

  /** Base class for parsing integers. */
  private abstract static class IntegerParser implements ValueParser {
    abstract void parseInteger(CacheBuilderSpec spec, int value);

    @Override

   * nanos to match CacheBuilder implementation.
   */
  private static @Nullable Long durationInNanos(long duration, @Nullable TimeUnit unit) {
    return (unit == null) ? null : unit.toNanos(duration);
  }

  /** Base class for parsing integers. */
  private abstract static class IntegerParser implements ValueParser {
    abstract void parseInteger(CacheBuilderSpec spec, int value);

    @Override