----- Mensaje original ----- De: Jonathan Turkanis <technews@kangaroologic.com> Fecha: Jueves, Septiembre 9, 2004 6:44 pm Asunto: [boost] Re: Empty member optimization [...]

Second, I don't have time to look into the details of your implementation, but I wan't to make sure you're aware of the EBO problems Dave Held ran into with his policy_ptr, based on the loki SmartPtr. Basically, compilers will apply EBO once or twice for a given class, and that's it. The exception seems to be recent versions of gcc (I don't remember if its 3.3 or 3.4).

Maybe the implementation can be changed so that compressed_member can inherit from another compressed_member, so as to make this syntax feasible: template <typename T0, typename T1> struct A : private compressed_member<T0> ::and<T1, 1>::type ::and<T2, 2>::type { } or something similar, resolving to a linear hierarchy of compressed_member's. AFAICS, EBO applicability limitations would be solved that way. An sketch of copmresed_member implementation would be as follows: struct dummy{}; template <typename T, size_t Index = 0, typename Base=dummy> struct compresed_member: public Base { // utility metafunc for adding members template <typename Q, size_t AnotherIndex = Index+1> struct and { typedef compressed_member< Q, AnotherIndex, compressed_member<T, Index, Base> > type; }; // rest of the implementation } Get the idea? Joaquín M López Muñoz Telefónica, Investigación y Desarrollo