tribool.hpp

template<typename CharT, typename Traits>
inline auto operator>>(std::basic_istream<CharT, Traits>& in, tribool& tri) -> decltype(in) {
    if(in.flags() & std::ios_base::boolalpha) {
        typename std::basic_istream<CharT, Traits>::sentry sentry(in);
        if(sentry) {
            auto&& loc = in.getloc();
            auto&& numpunct_facet = std::use_facet<std::numpunct<CharT>>(loc);
            auto&& false_name = numpunct_facet.falsename();
            auto&& true_name = numpunct_facet.truename();

            using other_facet = indeterminate_name<CharT>;
            std::basic_string<CharT> other_name = get_default_indeterminate_name<CharT>();
            if(std::has_facet<other_facet>(loc)) {
                auto&& facet = std::use_facet<other_facet>(loc);
                other_name = facet.name();
            }

            std::basic_string<CharT> str;
            if(in >> str) {
                if(str == false_name) {
                    tri = false;
                }
                else if(str == true_name) {
                    tri = true;
                }
                else if(str == other_name) {
                    tri = indeterminate;
                }
                else {
                    in.setstate(std::ios_base::failbit);
                }
            }
            return in;
        }
    }
    else {
        int x;
        if(in >> x) {
            switch(x) {
            case 0: tri = false;         break;
            case 1: tri = true;          break;
            case 2: tri = indeterminate; break;
            default:
                in.setstate(std::ios_base::failbit);
                break;
            }
        }
    }
    return in;
}