You might already be thinking that one potential use for std::variant would be to represent the notion of "Maybe I have an object, and maybe I don't." For example, we could represent the "maybe I don't" state using the standard tag type std::monostate:
std::map<std::string, int> g_limits = { { "memory", 655360 } }; std::variant<std::monostate, int> get_resource_limit(const std::string& key) { if (auto it = g_limits.find(key); it != g_limits.end()) { return it->second; } return std::monostate{}; } void test() { auto limit = get_resource_limit("memory"); if (std::holds_alternative<int>(limit)) { use( std::get<int>(limit) ); } else { use( some_default ); } }
You'll be pleased to know that this is ...
