Philippe Mori wrote:
I think that the best thing would be that std::swap would only compile for a given type T if the resulting function cannot throws (because copy constructor and assigment would not throws) and thus having a type trait would not be as much usefull.
This implies that swap() would only be possible to implement in a non-throwing fashion if 1. the cctor and the copy assignment operator are accessible and 2. cctor and copy assignment operator do not throw. This requirement is way too strong. E.g. the cctor of boost::array can throw, because it allocates memory. However, the swap() function can guarantee non-throwing operation when swap() for the value_type operates non-throwing, too. Even accessibility of a copy-ctor or a copy-assignment operator aren't required. Classes like {i/o}stream aren't copyable. However, you could imagine to swap objects of types which implement similar concepts.
Also the compiler should be able to detect throw () specification and provide the type trait itself.
Are throw specifications used for anything other then the dtors of classes derived from std::exception? Many libraries don't use them and they have reasons to avoid them. Regards, m