func (idx *Index) HasField(fieldName string) bool {
	_, ok := idx.fields[fieldName]
	return ok
}
func (idx *Index) HasField(fieldName string) bool {
	_, ok := idx.fields[fieldName]
	return ok
}
func ( idx * Index ) HasField ( fieldName string ) bool { _ , ok := idx . fields [ fieldName ] return ok }
// HasFields returns true if the given field exists in the index.
HasFields returns true if the given field exists in the index .