Super Primitive, header-only (almost), no-dependency, C++ JSON output "thing"

simple_json.hpp

#pragma once

#include <variant>
#include <string>
#include <vector>
#include <unordered_map>

namespace json {

	inline std::string util_replace(std::string haystack, const std::string_view& needle, const std::string_view& replaced_data) {
		std::string::size_type pos = 0;
		while ((pos = haystack.find(needle, pos)) != std::string::npos) {
			haystack.replace(pos, needle.length(), replaced_data);
			pos += replaced_data.length();
		}
		return haystack;
	}

	class Value;
	using Object = std::unordered_map<std::string, Value>;
	using Array = std::vector<Value>;

	class Null {
	public:
		static Null value; ///Remember to implement this somewhere!
	};

	class Undefined {
	public:
		static Undefined value; //Remember to implement this somewhere!
	};

	class Value : public std::variant<std::string, double, bool, Null, Undefined, Object, Array> { 
	public:
		template<typename T>
		Value(T t) : std::variant<std::string, double, bool, Null, Undefined, Object, Array>(t) {

		}

		Value() : std::variant<std::string, double, bool, Null, Undefined, Object, Array>(Undefined::value) {

		}
	};

	template<typename T>
	inline void write(const Value& val, T& stream) {
		auto idx = val.index();
		if (idx == 0) {
			const auto& str = std::get<std::string>(val);
			auto final_str = util_replace(str, "\"", "\\\""); 
			stream << "\"" << final_str << "\""; 
		} else if (idx == 1) {
			stream << std::get<double>(val);
		} else if (idx == 2) {
			stream << (std::get<bool>(val) ? "true" : "false");
		} else if (idx == 3) {
			stream << "null";
		} else if (idx == 4) {
			stream << "undefined";
		} else if (idx == 5) {
			stream << "{ ";
			const auto& map = std::get<Object>(val);
			for (auto it = map.cbegin(); it != map.cend(); it++) {
				if (it != map.cbegin()) {
					stream << ", ";
				}
				auto final_label = util_replace(it->first, "\"", "\\\"");
				stream << "\"" << final_label << "\": ";
				write(it->second, stream);
			}
			stream << " }";
		} else if (idx == 6) {
			stream << "[ ";
			const auto& vec = std::get<Array>(val);
			for(auto it = vec.cbegin(); it != vec.cend(); it++) {
				if (it != vec.cbegin()) {
					stream << ", ";
				}
				write(*it, stream);
			}
			stream << " ]";
		}	
	}
}