David Abrahams wrote:
What was wrong with my proposal?
You can't guarantee it will be right every time, but it's easy to correct when wrong, and that would only take a very few specializations.
Please note: The question is /not/ whether T has a custom swap. The question is whether default-construction + swap outperforms copy-construction for type T. Only in that case, it makes sense to activate "Swaptimization". Anyway, I agree, your approach provides a reasonable first guess:
std is an associated namespace of T ? has_member_swap<T> : has_nonmember_swap<T>
So for such a type T, _Move_operation_category<T>::_Move_cat should be set to "_Swap_move_tag", instead of "_Undefined_move_tag", by default. Do you know how we can technically overrule the default _Move_operation_category<T> provided by MSVC's STL? In ConceptC++, it would look a little bit like this: template <class T> where HasCustomSwap<T> // Pseudo ConceptC++ struct _Move_operation_category<T> { typedef _Swap_move_tag _Move_cat; }; But how to do that in C++03? Kind regards, Niels