generic type erasure mechanism demo

type_erasure_generic.cpp

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

template <typename Common>
class I {
public:
    template <typename T>
    I(const T& x) : mptr{new Model<T>(x)} {}
    I(const I& x) : mptr{x.mptr->clone()} {}

    void common()
    {
        mptr->virtual_impl();
    }

private:
    struct Concept {
        virtual ~Concept() = default;
        virtual void virtual_impl() const = 0;
        virtual std::unique_ptr<Concept> clone() const = 0;
    };

    template <typename T>
    struct Model final : Concept {
        Model(const T& x) : mx{x} {}
        std::unique_ptr<Concept> clone() const override
        {
            return std::make_unique<Model>(*this);
        }

        void virtual_impl() const override
        {
            Common::impl(mx);
        }

        T mx;
    };

    std::unique_ptr<Concept> mptr;
};

struct A {
    int ival;
    void print()
    {
        std::cout << ival << " ";
    }
};

struct B {
    double dval;
    void print()
    {
        std::cout << dval << " ";
    }
};

struct Printable
{
    template <typename T>
    static void impl(T t)
    {
        t.print();
    }
};

int main() {
    std::vector<I<Printable>> vec;

    vec.push_back(A{56});
    vec.push_back(B{1.2});

    for( auto a : vec)
    {
        a.common();
    }
}