class TypeSchemaMapper implements SchemaMapper {

	private static Collection<ColumnPair<?>> create(Iterable<Column<?>> columns1,
		Iterable<Column<?>> columns2) {
		return StreamUtils.seq(columns1).crossJoin(columns2)
			.map(t -> t.map(SchemaMapperHelper::toPair))
			.flatMap(Optionals::stream)
			.collect(Collectors.toList());
	}

}