On Fri, Jan 25, 2013 at 10:21 AM, Dave Abrahams <dave@boostpro.com> wrote:
Yes. IIUC the question here is whether the invariant of variant [;-)] shall be weakened to accommodate efficient move semantics, thereby breaking some code, or not, at some cost (the specific costs to be incurred by various strategies presently under discussion).
I'm new to this list, so I won't be offended if you correct me on any rookie mistakes. Concerning the invariant of variant: Why not provide a specialization of boost::optional for variant, which supports move Semantics? Users who don't want their invariant harmed, can use boost::variant as is. Users who need to squeeze out performance could use an optional<variant> and would be explicitly aware of the new null state they introduced for this. Markus www.clean-cpp.org