C++实现简单DI容器方法解析

class container {
private:
    std::map> registry;
public:
template 
void register_type() {
registry[std::type_index(typeid(Interface))] = []() -> void* {
return new Implementation();
};
}
template <typename T>
T* resolve() {
    auto it = registry.find(std::type_index(typeid(T)));
    if (it == registry.end()) return nullptr;
    return static_cast<T*>(it->second());
}
};

template 
T* create_instance() {
    return new T(resolve()...);
}

template 
void register_type_with_deps() {
    registry[std::type_index(typeid(Interface))] = [this]() -> void* {
        return create_instance();
    };
}

template 
void register_singleton() {
    Implementation* instance = nullptr;
    registry[std::type_index(typeid(Interface))] = [this, &instance]() -> void* {
        if (!instance) {
            instance = create_instance();
        }
        return instance;
    };
}

struct ILogger {
    virtual void log(const std::string& msg) = 0;
    virtual ~ILogger() = default;
};
struct ConsoleLogger : ILogger {
void log(const std::string& msg) override {
std::cout << "[LOG] " << msg << std::endl;
}
};
struct UserService {
ILogger logger;
UserService(ILogger l) : logger(l) {}
void do_work() { logger->log("work done"); }
};

container c;
c.register_singleton();
c.register_type_with_deps();
auto user_service = c.resolve();
user_service->do_work(); // 输出: [LOG] work done