12    template<
typename FmtStr, 
typename... Args>
 
   13    Error(FmtStr&& format, Args&&... args) :
 
   14        m_message(fmt::format(format, std::forward<Args>(args)...)) {}
 
   16    std::string_view message()
 const {
 
   20    operator std::string()
 const {
 
   25    std::string m_message;