Function to_string

tutorials/external/catch.hpp:9302–9310

namespace Catch {
    template <typename T>
    std::string to_string(T const& t) {
#if defined(CATCH_CONFIG_CPP11_TO_STRING)
        return std::to_string(t);
#else
        ReusableStringStream rss;
        rss << t;
        return rss.str();
#endif
    }
} // end namespace Catch

// end catch_to_string.hpp