*this contains a value | *this does not contain a value | |||

rhs contains a value | calls swap(*(*this), *rhs) | initializes the contained value of *this as if
direct-non-list-initializing an object of type T with the expression std::move(*rhs),
followed by rhs.val->T::~T();
postcondition is that *this contains a value and rhs does not contain a value | ||

rhs does not contain a value | initializes the contained value of rhs as if
direct-non-list-initializing an object of type T with the expression std::move(*(*this)),
followed by val->T::~T();
postcondition is that *this does not contain a value and rhs contains a value | no effect |