Abstract class and unique pointer

Question

I have the following error in my code:

error: allocating an object of abstract class type \'Material\'

I don\'t know how to handle this case.

Answer 1

You can use a templated constructor to arrange for constructing the right types without needing a clone method:

#include 
#include 

struct Material {
    Material() = default;
    virtual int get_color() const = 0;
};

struct Basic : Material {
    Basic() = default;
    int get_color() const override {
        return 1;
    }
};

struct Mix : Material {
    template
    Mix(const M1& mat1, const M2& mat2)
        : mat1_{std::make_unique(std::move(mat1))}
        , mat2_{std::make_unique(std::move(mat2))}
    {} 

    int get_color() const override {
        return mat1_->get_color() + mat2_->get_color();
    }

private:
    std::unique_ptr mat1_;
    std::unique_ptr mat2_;
};

int main() {
    auto mix = Mix(Basic(), Basic());
    std::cout << mix.get_color() << '\n';
}

Note that this works only if you send instance of a material with a known type.