#include <string>       // std::string
#include <iostream>     // std::cout
#include <sstream>      // std::stringstream

int main () {

  std::stringstream stream("1234");
  
  //stream = std::move(std::stringstream("5678"));
  
  stream.operator=(std::move(std::stringstream("5678")));
  
  //stream.operator=(std::stringstream("5678"));
  
  return 0;
}