map for http get

get.cpp

#include <exception>
#include <fmt/format.h>
#include <map>
#include <source_location>
#include <string>

std::string locationFull(const std::source_location location = std::source_location::current()) {
	return fmt::format("{}:{} in {}", location.file_name(), location.line(), location.function_name());
}

template <typename K>
class NotFoundMixin {

      public:
	using Funtor = void (*)(const K& key);

	NotFoundMixin() = default;
	NotFoundMixin(Funtor f)
	    : notFoundCallback(f){};

	Funtor notFoundCallback = nullptr;

	void callNotFoundCallback(const K& key, const std::string location) const {
		(void)location;
		if (notFoundCallback) {
			(*notFoundCallback)(key);
			return;
		}
		throw std::runtime_error(fmt::format("key >>>{}<<< not found in {}", key, location));
	}
};

template <typename K, typename V, typename Compare = std::less<K>>
class mapV2 : public std::map<K, V, Compare>, public NotFoundMixin<K> {
      public:
	using value_type   = std::pair<const K, V>;
	using map_parent   = std::map<K, V, Compare>;
	using mixin_parent = NotFoundMixin<K>;

	mapV2() = default;

	mapV2(std::initializer_list<value_type> map_init)
	    : map_parent(map_init) {
	}

	mapV2(std::initializer_list<value_type> map_init, typename mixin_parent::Funtor f)
	    : map_parent(map_init), mixin_parent(f) {
	}

	[[nodiscard]] V rq(const K& k) const {
		if (auto iter = this->find(k); iter != this->end()) {
			return iter->second;
		}
		this->callNotFoundCallback(k, locationFull());
		return {};
	}
};

class HttpException : public std::exception {
      public:
	unsigned statusCode = 400;
	// what to print to the user
	std::string forceErrMsg;

	static void HttpParamErrorHandler1(const std::string& key);
};

void HttpException::HttpParamErrorHandler1(const std::string& key) {
	std::string   msg = key + " is not set and is required!";
	HttpException e;
	e.forceErrMsg = msg;
	e.statusCode  = 200;
	throw e;
}

int main() {
	try {
		mapV2<int, int> x{{1, 2}, {2, 3}};
		x.rq(4);
	} catch (...) {
	}

	try {
		mapV2<std::string, int> getParameter({{"param1", 1}, {"param2", 2}}, HttpException::HttpParamErrorHandler1);
		getParameter.rq("param3");
	} catch (HttpException& e) {
		//print on user
		int y = 0;
	} catch (std::exception& e) {
		//print internally
	}
}