+ void add_signal(Signal &);
+ const std::set<Signal *> &get_signals() const { return signals; }
+ Signal *pick_signal(const Ray &);
+ void remove_signal(Signal &);
+
+ Object *pick_object(const Ray &);
+
+private:
+ template<typename T>
+ static T *pick(const std::set<T *> &, const Ray &);
+
+public: