Hidden index key interface class.
- Author
- Stuart G. Mentzer (Stuar.nosp@m.t_Me.nosp@m.ntzer.nosp@m.@obj.nosp@m.exx.c.nosp@m.om)
- Note
- Interface provides common base class for covariant return in hierarchies
- Derived classes specify the friend class(es) that can access the index
- Index can be ignored if not used as key/index into a container
- Can safely derive from concrete Key types as long as fields aren't added
- Can derive privately from an Key to share the index set of another Key type without allowing convertibility (for type safety)