easy plugin

#include <string.h>
#include <iostream>
#include <list>
#include <memory>
class polygon {
public:
    polygon() = default;
    virtual ~polygon() = default;
    virtual double area() const = 0;
};
class triangle : public polygon {
public:
    virtual double area() const override {
        std::cerr << "triangle." << std::endl;
        return 0;
    }
};
class polygon_plugin {
public:
    void add_plugin(const char *name) {
        if (0 == strcasecmp(name, "triangle")) {
            plugin_list.push_front(std::unique_ptr<polygon>(new triangle));
        }
    }
    void run_plugin() {
        for (auto &plugin : plugin_list) {
            plugin->area();
        }
    }
private:
    std::list<std::unique_ptr<polygon>>plugin_list;
};
int main() {
    polygon_plugin pp;
    pp.add_plugin("triangle");
    pp.run_plugin();
    
    return 0;
}