On 01/11/13 08:59, Peter Dimov wrote:
Larry Evans wrote:
Are you suggesting that move is enabled only if the current tag (the variant<*>::which() result) indicates the current type is default constructable?
No, I'm suggesting that move (in the presence of recursive_wrappers) can be enabled only when there is at least one type that is nothrow-default-constructible, regardless of whether it's current.
typedef variant<int, recursive_wrapper<foo>> V;
V v1( std::move(v2) );
This move-constructs v1 from v2 and leaves int() into v2.
Thanks for the clarification. However, that seems to involve a lot of checking because you'd have to check possibly all the bounded types to find one that is nothrow-default-constructible. Wouldn't it be simpler to define variant to have, implicitly, a nothrow-default-constructible type something like the special_type<nothing_id> I mentioned in my previous post or like the boost::blank which Andrey just mentioned in his post? -regards, Larry