Boost variant recursive wrapper with non-copyable type

Question

I am trying to create a variant of non-copyable types possibly using the recursive wrapper, such as in the following code:

#include "boost/variant.hpp"

using namespace std;
using namespace boost;

struct A
{
  A() {}
  A(A &&) noexcept {}
  A& operator=(A &&) noexcept {}
  A(A const &) = delete;
  A& operator=(A const &) = delete;
};
struct B;
typedef variant<A, recursive_wrapper<B>> ABC;
struct B
{
  B() {}
  B(B &&) noexcept {}
  B& operator=(B &&) noexcept {}
  B(B const &) = delete;
  B& operator=(B const &) = delete;
};

int main(int argc, char** argv)
{
  ABC _a, _b;
  _b = std::move(_a);
}

The issue is that the recursive wrapper expects the objects to be copy constructible if I code a move assignment. This is the compilation error I get:

/usr/include/boost/variant/recursive_wrapper.hpp:116:32: error: use of deleted function 'B::B(const B&)'
     : p_(new T( operand.get() ))

Does anybody see where is the problem?