----- Mensaje original ----- De: "vicente.botet" <vicente.botet@wanadoo.fr> Fecha: Domingo, Enero 27, 2008 7:10 pm Asunto: Re: [boost] [review] Review of Flyweight library started January 21and still running!: equality semantic Para: boost@lists.boost.org
Hi all, equality semantic bool b=(&(fw1.get())==&(fw2.get())); versus bool b=((fw1.get())==(fw2.get())); Why not delegate this responsability to the factory, the factory knows better when the two handles are equal, isn't it?
friend bool operator==(const flyweight& x,const flyweight& y) { return core:are_equals(x.h==y.h); }
The factories provided by the library could define this are_equals function as return (&x==&y); Regards---------------------------
Umm, this approach is interesting! Better yet, instead of relying on an explicit are_equals function, we can just require that Factory::handle_type is EqualityComparable and use that: friend bool operator==(const flyweight& x,const flyweight& y) { return x.h==y.h; } As a matter of fact, all the current factories have EqualityComparable handles that precisely implement reference equality semantics, so it looks all very natural. This approach would solve the second problem of the list I presented at the review notes: * The resulting equality semantics might not coincide with that of the underlying T; the possibility of this hapenning and making a real difference is probably small, though. * The assumption that equal flyweight objects always share their value interfere with potential extensions to the library, like the no-factory proposal by Throsten Ottosen. but would not address the first point. Thanks for your suggestion, Joaquín M López Muñoz Telefónica, Investigación y Desarrollo