Object oriented (OO) implementation of the Visitor pattern.

Visitor-Pattern-variant.cpp

#include <variant>
#include <vector>

using namespace std;

class Circle;
class Square;

class DrawVisitor {
public:
    void operator()(const Circle&) const { cout << "draw circle\n"; }
    void operator()(const Square&) const { cout << "draw square\n"; }
};

class Circle {
public:
    explicit Circle(double radius) : radius_(radius) {}
private:
    double radius_;
};

class Square {
public:
    explicit Square(double side) : side_(side) {}
private:
    double side_;
};

int main()
{
    using Shape = variant<Circle, Square>;
    using Shapes = vector<Shape>;
    Shapes shapes;

    shapes.emplace_back(Circle{1.0});
    shapes.emplace_back(Square{1.0});

    for (const auto& shape : shapes)  {
        std::visit(DrawVisitor{}, shape);
    }
}