make kv store return its type interface directly

kv_store.hpp

@@ -5,20 +5,29 @@
 #include <fstream>
 #include <optional>
 #include <string>
+#include <variant>
+#include <sstream>
 
 using std::string;
 
 class KeyValueStore {
 public:
-	void set(const string& key, const string& value) {
+	using Value = std::variant<int, double, string, bool>;
+
+	void set(const string& key, const Value& value) {
 		std::lock_guard<std::mutex> lock(mutex_);
 		data_[key] = value;
 	}
 
-	std::optional<string> get(const string& key) {
+	template<typename T>
+	std::optional<T> get(const string& key) {
 		std::lock_guard<std::mutex> lock(mutex_);
 		auto it = data_.find(key);
-		return it != data_.end() ? std::optional<string>{it->second} : std::nullopt;
+		if (it == data_.end()) return std::nullopt;
+		if (auto* ptr = std::get_if<T>(&it->second)) {
+			return *ptr;
+		}
+		return std::nullopt;
 	}
 
 	bool del(const string& key) {
@@ -43,8 +52,17 @@ public:
 		string line;
 		while (std::getline(file, line)) {
 			size_t eq = line.find('=');
-			if (eq != string::npos) {
-				data_[line.substr(0, eq)] = line.substr(eq + 1);
+			if (eq == string::npos || eq < 2) continue;
+
+			string key = line.substr(2, eq - 2);
+			string val_str = line.substr(eq + 1);
+			char type = line[0];
+
+			switch (type) {
+				case 'i': data_[key] = std::stoi(val_str); break;
+				case 'd': data_[key] = std::stod(val_str); break;
+				case 's': data_[key] = val_str; break;
+				case 'b': data_[key] = (val_str == "1"); break;
 			}
 		}
 	}
@@ -55,12 +73,27 @@ public:
 		if (!file.is_open()) return;
 
 		for (const auto& [key, value] : data_) {
-			file << key << "=" << value << "\n";
+			file << serialize_entry(key, value) << "\n";
 		}
 	}
 
 private:
-	std::unordered_map<string, string> data_;
+	string serialize_entry(const string& key, const Value& value) {
+		return std::visit([&key](const auto& val) -> string {
+			using T = std::decay_t<decltype(val)>;
+			if constexpr (std::is_same_v<T, int>) {
+				return "i:" + key + "=" + std::to_string(val);
+			} else if constexpr (std::is_same_v<T, double>) {
+				return "d:" + key + "=" + std::to_string(val);
+			} else if constexpr (std::is_same_v<T, string>) {
+				return "s:" + key + "=" + val;
+			} else if constexpr (std::is_same_v<T, bool>) {
+				return "b:" + key + "=" + (val ? "1" : "0");
+			}
+		}, value);
+	}
+
+	std::unordered_map<string, Value> data_;
 	mutable std::mutex mutex_;
 	string filename_ = "store.txt";
 };

main.cpp

@@ -61,9 +61,9 @@ int main() {
 	});
 
 	router.get("/admin/counter", [](const HttpRequest& req, HttpResponse& res) {
-		auto current = server->store.get("visit_count");
-		int count = current ? std::stoi(current.value()) : 0;
-		server->store.set("visit_count", std::to_string(count + 1));
+		auto current = server->store.get<int>("visit_count");
+		int count = current ? current.value() : 0;
+		server->store.set("visit_count", count + 1);
 
 		res.set_text("Counter: " + std::to_string(count + 1));
 	});