private final Set<Object> delegate;

    JdkBackedSetBuilderImpl(SetBuilderImpl<E> toCopy) {
      super(toCopy); // initializes dedupedElements and distinct
      delegate = Sets.newHashSetWithExpectedSize(distinct);
      for (int i = 0; i < distinct; i++) {
        /*
         * requireNonNull is safe because we ensure that the first `distinct` elements have been
         * populated.
         */

      try {
        return super.retainAll(checkNotNull(c));
      } catch (UnsupportedOperationException e) {
        // if the iterators don't support remove
        Set<@Nullable Object> keys = Sets.newHashSetWithExpectedSize(c.size());
        for (Object o : c) {
          /*
           * `o instanceof Entry` is guaranteed by `contains`, but we check it here to satisfy our
           * nullness checker.
           */

      try {
        return super.retainAll(checkNotNull(c));
      } catch (UnsupportedOperationException e) {
        // if the iterators don't support remove
        Set<@Nullable Object> keys = Sets.newHashSetWithExpectedSize(c.size());
        for (Object o : c) {
          /*
           * `o instanceof Entry` is guaranteed by `contains`, but we check it here to satisfy our
           * nullness checker.
           */