简易的 format

format.hpp

namespace details {

template <size_t fmt_len, typename... Args>
struct format_to_h;
template <size_t fmt_len, typename Arg, typename... Args>
struct format_to_h<fmt_len, Arg, Args...> {
    auto operator()(std::ostream & out, char const (&fmt)[fmt_len], size_t fmt_start, Arg && arg, Args && ... args) -> void {
        auto const braces = std::strstr(&fmt[fmt_start], "{}");
        if (braces == nullptr) {
            format_to_h<fmt_len>()(out, fmt, fmt_start);
            return;
        }

        out.write(&fmt[fmt_start], braces - &fmt[fmt_start]);
        out << std::forward<Arg>(arg);
        format_to_h<fmt_len, Args...>()(out, fmt, (braces + 2) - fmt, std::forward<Args>(args)...);
    }
};
template <size_t fmt_len>
struct format_to_h<fmt_len> {
    auto operator()(std::ostream & out, char const (&fmt)[fmt_len], size_t fmt_start) -> void {
        out.write(&fmt[fmt_start], (fmt_len - 1) - fmt_start);
    }
};

}   // namespace details

template <size_t fmt_len, typename... Args>
auto format_to(std::ostream & out, char const (&fmt)[fmt_len], Args && ... args) -> void {
    details::format_to_h<fmt_len, Args...>()(
        out, fmt, 0, std::forward<Args>(args)...);
}

template <size_t fmt_len, typename... Args>
auto format(char const (&fmt)[fmt_len], Args && ... args) -> std::string {
    auto oss = std::ostringstream();
    format_to(oss, fmt, std::forward<Args>(args)...);
    return oss.str();
}

template <size_t fmt_len, typename... Args>
auto print(char const (&fmt)[fmt_len], Args && ... args) -> void {
    format_to(std::cout, fmt, std::forward<Args>(args)...);
}