相关疑难解决方法(0)

我使用可变参数模板来实现访问者模式:

template<typename... Types>
class Visitor;

template<typename Type>
class Visitor<Type> {
    public:
        virtual void visit(Type &visitable) = 0;
};

template<typename Type, typename... Types>
class Visitor<Type, Types...>: public Visitor<Types...> {
    public:
        using Visitor<Types...>::visit;

        virtual void visit(Type &visitable) = 0;
};


template<typename... Types>
class VisitableInterface {
    public:
        virtual void accept(Visitor<Types...> &visitor) = 0;
};

template<typename Derived, typename... Types>
class Visitable : public VisitableInterface<Types...> {
    public:
        virtual void accept(Visitor<Types...> &visitor) {
            visitor.visit(static_cast<Derived&>(*this));
        }
};

class IntegerElement;
class StringElement;
class BoxElement;
class ImageElement;

class IntegerElement: …