int compare(const charT* low1, const charT* high1,
const charT* low2, const charT* high2) const;
Returns: do_compare(low1, high1, low2, high2).
string_type transform(const charT* low, const charT* high) const;
Returns: do_transform(low, high).
long hash(const charT* low, const charT* high) const;
Returns: do_hash(low, high).