C++: What is type erasure in C++?

1// Simple type erasure example
2class Drawable {
3    struct Concept {
4        virtual void draw() const = 0;
5        virtual ~Concept() = default;
6    };
7
8    template<typename T>
9    struct Model : Concept {
10        T obj;
11        Model(T o) : obj(std::move(o)) {}
12        void draw() const override { obj.draw(); }
13    };
14
15    std::unique_ptr<Concept> impl;
16
17public:
18    template<typename T>
19    Drawable(T obj) : impl(new Model<T>(std::move(obj))) {}
20
21    void draw() const { impl->draw(); }
22};
23
24class Circle { public: void draw() const {} };
25class Square { public: void draw() const {} };
26
27std::vector<Drawable> shapes;
28shapes.emplace_back(Circle{});
29shapes.emplace_back(Square{});
30for (const auto& s : shapes) s.draw();