Реализации на С++

Visitor

Общая реализация на языке С++

Visitor

class Circle;
class Rectangle;

class Visitor
{
public:
    virtual ~Visitor() = default;
    virtual void visit(Circle& ref) = 0;
    virtual void visit(Rectangle& ref) = 0;
};

Shape

class Shape
{
public:
    virtual ~Shape() = default;
    virtual void accept(shared_ptr<Visitor> visitor) = 0;
};

Circle

class Circle : public Shape
{
public:
    void accept(shared_ptr<Visitor> visitor) override 
    { 
        visitor->visit(*this); 
    }
};

Rectangle

class Rectangle : public Shape
{
public:
    void accept(shared_ptr<Visitor> visitor)  override 
    { 
        visitor->visit(*this); 
    }
};

ConcreteVisitor

class ConcreteVisitor : public Visitor
{
public:
    void visit(Circle& ref) override 
    { 
        cout << "Circle;" << endl; 
    }
    void visit(Rectangle& ref) override 
    { 
        cout << "Rectangle;" << endl; 
    }
};

Figure

class Figure : public Shape
{
    using Shapes = vector<shared_ptr<Shape>>;
private:
    Shapes shapes;
public:
    Figure(initializer_list<shared_ptr<Shape>> list)
    {
        for (auto&& elem : list)
            shapes.emplace_back(elem);
    }
    void accept(shared_ptr<Visitor> visitor)  override
    {
        for (auto& elem : shapes)
            elem->accept(visitor);
    }
};

# include <iostream>
# include <memory>
# include <vector>

using namespace std;

int main()
{
    shared_ptr<Shape> figure = make_shared<Figure>(
        initializer_list<shared_ptr<Shape>>(
            { make_shared<Circle>(), make_shared<Rectangle>(), make_shared<Circle>() }
        )
    );
    shared_ptr<Visitor> visitor = make_shared<ConVisitor>();
    figure->accept(visitor);
}