Frank Mori Hess wrote:
On Thursday 26 June 2008 10:51 am, David Abrahams wrote:
Don't you think it /always/ makes sense to provide a custom swap overload for a Swappable type, as long as it outperforms the default std::swap, in one way or the other? That's the whole question. I'm not 100% sure.
I'd say if the default std::swap compiles for the type, then there is no reason not to provide a more efficient swap specialization. The only question for me would be in a case where the type is not assignable/copy constructible. Then you might want to have a compile error instead of a non O(1) swap. But given that the default std::swap can in reality already have arbitrary complexity, depending on the complexity of a type's assignment/copy constructor, I don't see much value in producing a compile error.
That's an argument by implementation, not design. Who's to say that the default std::swap wasn't just there to conveniently provide swap for PODs? Well, I guess *I* can say that: the original sort implementations used swap(), and the sort implementations only required CopyConstructible and Assignable. Okay, I'm satisfied :-) -- Dave Abrahams BoostPro Computing http://www.boostpro.com