* might strip UnsafeComparator entirely. (TODO(cpovirk): Are we confident that optimizers
         * aren't stripping UnsafeComparator today? Should we have Proguard configuration for it?)
         *
         * - if Unsafe is removed entirely from JDKs (or already absent in some unusual environment
         * today). TODO: b/392974826 - Check for the existence of Unsafe and its methods

    return (result == null) ? keySet = createKeySet() : result;
  }

  /*
   * This could have a good default implementation of `return new ImmutableKeySet<K, V>(this)`, but
   * ProGuard can't figure out how to eliminate that default when RegularImmutableMap overrides it.
   */
  abstract ImmutableSet<K> createKeySet();

  UnmodifiableIterator<K> keyIterator() {