// TODO: Test blocking to re-enter monitor after being signaled.
  // TODO: Test interrupts with both interruptible and uninterruptible monitor.
  // TODO: Test multiple waiters: If guard is still satisfied, signal next waiter.
  // TODO: Test multiple waiters: If guard is no longer satisfied, do not signal next waiter.

   * @param interfaceType the interface you wish the returned proxy to implement
   * @param timeoutDuration with timeoutUnit, the maximum length of time that callers are willing to
   *     wait on each method call to the proxy
   * @param timeoutUnit with timeoutDuration, the maximum length of time that callers are willing to
   *     wait on each method call to the proxy
   * @return a time-limiting proxy

   * code would be responsible for populating a "real" {@code T} (which might still be the value
   * {@code null}!) before returning it to callers. Depending on how the code is structured, a
   * nullness analysis might not understand that the field has been populated. To avoid that problem
   * without having to add {@code @SuppressWarnings}, the code can call this method.

  /**
   * Creates a TimeLimiter instance using the given executor service to execute method calls.
   *
   * <p><b>Warning:</b> using a bounded executor may be counterproductive! If the thread pool fills
   * up, any time callers spend waiting for a thread may count toward their time limit, and in this
   * case the call may even time out before the target method is ever invoked.
   *

  /**
   * Wrapper for {@link Map#get(Object)} that forces the caller to pass in a key of the same type as
   * the map. Besides being slightly shorter than code that uses {@link #getMap()}, it also ensures
   * that callers don't pass an {@link Entry} by mistake.
   */
  protected V get(K key) {
    return getMap().get(key);
  }

  protected final K k0() {
    return e0().getKey();
  }

  protected final V v0() {

  // TODO: Test blocking to re-enter monitor after being signaled.
  // TODO: Test interrupts with both interruptible and uninterruptible monitor.
  // TODO: Test multiple waiters: If guard is still satisfied, signal next waiter.
  // TODO: Test multiple waiters: If guard is no longer satisfied, do not signal next waiter.

    int result = hashCode;
    return (result == 0) ? hashCode = delegate.hashCode() : result;
  }

  @Override
  public String toString() {
    return delegate.toString();
  }

  // All callers of the constructor are restricted to <E extends Enum<E>>.
  @Override
  @J2ktIncompatible // serialization
  Object writeReplace() {
    return new EnumSerializedForm<E>(delegate);
  }

   * code would be responsible for populating a "real" {@code T} (which might still be the value
   * {@code null}!) before returning it to callers. Depending on how the code is structured, a
   * nullness analysis might not understand that the field has been populated. To avoid that problem
   * without having to add {@code @SuppressWarnings}, the code can call this method.

    return seq.length() - pos;
  }

  /*
   * To avoid the need to call requireNonNull so much, we could consider more clever approaches,
   * such as:
   *
   * - Make checkOpen return the non-null `seq`. Then callers can assign that to a local variable or
   *   even back to `this.seq`. However, that may suggest that we're defending against concurrent
   *   mutation, which is not an actual risk because we use `synchronized`.

  }

  /** Returns an {@link EndpointPair} representing the endpoints of an undirected edge. */
  public static <N> EndpointPair<N> unordered(N nodeU, N nodeV) {
    // Swap nodes on purpose to prevent callers from relying on the "ordering" of an unordered pair.
    return new Unordered<>(nodeV, nodeU);
  }

  /** Returns an {@link EndpointPair} representing the endpoints of an edge in {@code graph}. */