@Override
  public boolean retainAll(Collection c) {
    if (c instanceof StructSet) {
      return retainAll((StructSet) c);
    }
    return super.retainAll(c);
  }
Remove the field values from a struct of the correct type
geode-core/src/main/java/org/apache/geode/cache/query/internal/SortedStructSet.java