实现的目的；提高 C/C++ 编译速度，fmt 库模板嵌套过多编译速度非常慢，且编译后程序体积也过大，函数步入的栈帧过多！
只支持格式；{}
不支持格式；{:02x}
class fmt
{
public:template <typename S, typename ...T>static std::string format(const S& fmt, T ... args) noexcept{std::string str;if constexpr (std::is_same<S, std::string>::value){str = fmt;}else if constexpr (std::is_same<S, std::string_view>::value){str = std::string(fmt.data(), fmt.size());}else{str = fmt;}(..., format_string(str, args));return str;}template <typename OutputIt, typename ...T>static void format_to(OutputIt&& out, const std::string& fmt, T ... args){std::string result = format(fmt, std::forward<T&&>(args)...);for (char ch : result){*out = ch;}}private:template <typename T>static std::string to_string(const T& value) noexcept{if constexpr (std::is_same<T, bool>::value){return value ? "true" : "false";}else if constexpr (std::is_pointer<T>::value){using DECAY_T = typename std::decay<T>::type;if constexpr (std::is_same<char*, DECAY_T>::value || std::is_same<const char*, DECAY_T>::value){return value ? value : "";}else {if (value){char buf[sizeof(value) << 2];snprintf(buf, sizeof(buf), "%p", reinterpret_cast<const void*>(value));return buf;}return "null";}}else if constexpr (std::is_same<T, std::string>::value){return value;}else if constexpr (std::is_same<T, std::string_view>::value){return std::string(value.data(), value.size());}else{return std::to_string(value);}}template <typename T>static std::string to_string(const std::shared_ptr<T>& value) noexcept{return fmt::to_string(value.get());}template <typename T>static void format_string(std::string& out, const T& value) noexcept{replace_string(out, "{}"sv, fmt::to_string(value));}public:static bool replace_string(std::string& str, const std::string_view& old_string, const std::string_view& new_string) noexcept;
};inline bool fmt::replace_string(std::string& str, const std::string_view& old_string, const std::string_view& new_string) noexcept
{size_t pos = str.find(old_string);if (pos == std::string::npos){return false;}str.replace(pos, old_string.length(), new_string);return true;
}
)
