baseless polymorphism in C++11

baseless_polymorphism.cpp

// http://channel9.msdn.com/Events/GoingNative/2013/Inheritance-Is-The-Base-Class-of-Evil

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

// ===== library ====

class Document
{
public:
    class Object
    {
    private:
        class Concept
        {
        public:
            virtual ~Concept() = default;
            virtual void draw_(std::ostream&, std::size_t) const = 0;
        };

        template <typename T>
        class Model
            : public Concept
        {
        private:
            T data_;

        public:
            Model(T x)
                : data_(std::move(x))
            {}

            void draw_(std::ostream& out, std::size_t position) const override
            {
                data_.draw(out, position);
            }
        };

        std::shared_ptr<const Concept> self_;

    public:
        template <typename T>
        Object(T x)
            : self_{std::make_shared<Model<T>>(std::move(x))}
        {}

        void draw(std::ostream& out, std::size_t position) const
        {
            self_->draw_(out, position);
        }
    };

    std::vector<Object> objects;

    void draw(std::ostream& out, std::size_t position) const
    {
        out << std::string(position, ' ') << "<document>" << std::endl;
        for (const auto& e : objects)
            e.draw(out, position + 2);
        out << std::string(position, ' ') << "</document>" << std::endl;
    }
};

// ====== user ======

class MyClass
{
public:
    int i;

    void draw(std::ostream& out, std::size_t position) const
    {
        out << std::string(position, ' ') << "MyClass " << i << std::endl;
    }
};

int main()
{
    Document document;
    document.objects.emplace_back(MyClass{1});
    document.objects.emplace_back(document);
    document.objects.emplace_back(MyClass{2});
    document.draw(std::cout, 0);
}