how std::type_traits work

#include <string>

namespace op {

template<typename T>
struct remove_const {
    typedef T type;
};

template<typename T>
struct remove_const<T const> {
    typedef T type;
};
}

int main()
{
    using T = op::remove_const<const std::string>::type;

    T str = "Das";
    str += " ist ein Test!";

    return 0;
}