abstract static class IteratorBasedImmutableMap<K, V> extends ImmutableMap<K, V> {
    abstract UnmodifiableIterator<Entry<K, V>> entryIterator();

    @Override
    ImmutableSet<Entry<K, V>> createEntrySet() {
      return new ImmutableMapEntrySet<K, V>() {
        @Override
        ImmutableMap<K, V> map() {
          return IteratorBasedImmutableMap.this;
        }

        @Override

        @Override
        ImmutableMap<K, V> map() {
          return IteratorBasedImmutableMap.this;
        }

        @Override
        public UnmodifiableIterator<Entry<K, V>> iterator() {
          return entryIterator();
        }

        @Override
        public Spliterator<Entry<K, V>> spliterator() {
          return IteratorBasedImmutableMap.this.entrySpliterator();
        }

    builder.putAll(entries);
    return builder.build();
  }

  static final Entry<?, ?>[] EMPTY_ENTRY_ARRAY = new Entry<?, ?>[0];

  abstract static class IteratorBasedImmutableMap<K, V> extends ImmutableMap<K, V> {
    abstract UnmodifiableIterator<Entry<K, V>> entryIterator();

    @Override
    ImmutableSet<K> createKeySet() {
      return new ImmutableMapKeySet<>(this);
    }