boost::variant; std::unique_ptr and copy

Question

This Question Determined That a Non-Copyable Type Can\'t Be Used With Boost Variant

Tree class

template 

        

Answer 1

using Mixed = boost::variant< 
  std::unique_ptr,
  std::unique_ptr,
  std::unique_ptr,
  std::unique_ptr
>;

int main() {    
  auto md = std::unique_ptr(new int(123));
  Mixed mixed = std::move(md);
  std::cout << *boost::get< std::unique_ptr >(mixed) << std::endl;
  return 0;
}

unique_ptr is move-only and can be used in variant. The above example can compile and work (C++11).