Current implementation of recursive_wrapper move constructor is not optimal: recursive_wrapper<T>::recursive_wrapper(recursive_wrapper&& operand) : p_(new T(std::move(operand.get()) )) { } During descussion were made following proposals: I: Leave it as is - bad performance - can not provide noexcept guarantee II: Set operand.p_ to NULL, add BOOST_ASSERT in get operations + good performance + provides noexcept guarantee for move constructor + optimization will be used even if varinat has no type with trivial default constructor + easy to implement - triggers an assert when user tries to reuse moved object - adds an empty state to the recursive_wrapper III: Make recursive_wrapper and variant cooperate, enable move for varinat in the presence of recursive_wrappers only when there is at least one type that is nothrow-default-constructible, regardless of whether it's current. It is easyer to understand by example: typedef variant<int, recursive_wrapper<foo>> V; V v1( std::move(v2) ); This move-constructs v1 from v2 and leaves int() into v2. + good performance + provides noexcept guarantee for rcursive_wrapper + does not adds an empty state - optimization won't trigger if varinat has no type with trivial default constructor - hard to implement - user may be obscured by the fact, that v2 from the example now contains int IV: After move away, delay construction of type held by recursive_wrapper till it will be be required. +/- good performance? but more checks + provides noexcept guarantee for rcursive_wrapper + does not adds an explicit empty state + optimization will be used even if varinat has no type with trivial default constructor +/- not hard to implement --- additional requirement for type T of recursive_wrapper: it must be default constructible - less obvious behavior for user (for example get() function would construct values, allocate memory and can possibly throw) Please, vote for solution or propose a better one. P.S.: As I know Joel de Guzman votes for solution II (and totally agains solution I, because it is too slow). I wanted to leave as is (solution I) or use solution IV, but Joel talked me to solution II. P.P.S.: More info can be obtained from ticket #7718 https://svn.boost.org/trac/boost/ticket/7718 and previous series of letters. -- Best regards, Antony Polukhin