INTERFACE:

#include <sstream>
#include <string>

class Sstring
{
    std::ostringstream out;
    
 public:
  operator std::string ()
    {
      return out.str();
    }

  std::string str () const
    {
      return out.str();
    }

  template <typename T>
  Sstring&
  operator << (const T& value)
    {
      out << value;
      return *this;
    }
};

IMPLEMENTATION: