Either make hlines and id const (loosing default copy and move ctors and operators), or make every method const.
Ctor does not check the hlines sortedness: make the only HLine accepting ctor private, and the builder classes friends. (Maybe the Blob2Builder could use the StortedBuilder internally, so that only one friend is needed.)
Either make hlines and id const (loosing default copy and move ctors and operators), or make every method const. Ctor does not check the hlines sortedness: make the only HLine accepting ctor private, and the builder classes friends. (Maybe the Blob2Builder could use the StortedBuilder internally, so that only one friend is needed.)