cpp_trait/main.cpp

#include "trait.h"
#include "circle.h"
#include "rectangle.h"
#include "circle_shape.h"
#include "rectangle_shape.h"
#include "shape.h"
#include <vector>

using namespace std;

int main()
{
    vector<Shape> geometries;
    geometries.emplace_back(Circle());
    geometries.emplace_back(Rectangle());

    for (const auto &shape : geometries)
    {
        cout << shape.area() << endl;
    }
    return 0;
}