type_erasure.cpp

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



struct knight
{
    void attack() { std::cout << "draw sword\n"; }
};

struct mage
{
    void attack() { std::cout << "spell magic curse\n"; }
};

struct unit
{
    template <typename T>
    unit(T&& obj) : unit_(std::make_shared<unit_model<T>>(std::forward<T>(obj))) {}

    void attack()
    {
        unit_->attack();
    }

    struct unit_concept
    {
        virtual void attack() = 0;
        virtual ~unit_concept() = default;
    };

    template <typename T>
    struct unit_model : public unit_concept
    {
        unit_model(T& unit) : t(unit) {}

        void attack() override { t.attack(); }
    private:
        T& t;
    };

private:
    std::shared_ptr<unit_concept> unit_;
};

void fight(std::vector<unit>& units)
{
    for (auto& u : units)
        u.attack();
}

int main()
{
      knight k;
      mage m;

      std::vector<unit> v{ unit(k), unit(m) };
      
      fight(v);
    return 0;
}