C++接口自动注册

#include <iostream>
#include <memory>

template <typename T> class Interface
{
  public:
    using SharedPtr = std::shared_ptr<T>;
    using WeakPtr = std::weak_ptr<T>;

    static WeakPtr reg(SharedPtr impl)
    {
        instance().m_impl = impl;
        return impl;
    }
    static void unreg() { instance().m_impl.reset(); }
    static SharedPtr interface() { return instance().m_impl; }

  private:
    SharedPtr m_impl;

    static Interface &instance()
    {
        static Interface inst;
        return inst;
    }
};

class AbscractConfig
{
  public:
    virtual void set(int value) = 0;
    virtual int get() = 0;
};

class Impl : public AbscractConfig
{
  public:
    Impl() { std::cout << "Impl" << std::endl; }
    ~Impl() { std::cout << "~Impl" << std::endl; }
    void set(int value) override { m_value = value; }
    int get() override { return m_value; }

  private:
    int m_value = 222;
};

static auto configInstance =
    Interface<AbscractConfig>::reg(std::make_shared<Impl>());

int main(int argc, char const *argv[])
{
    auto config = Interface<AbscractConfig>::interface();
    std::cout << "hello: " << config << std::endl;
    config->set(456);
    std::cout << "value: " << config->get() << std::endl;
    config.reset();
    Interface<AbscractConfig>::unreg();
    std::cout << "--------------------" << std::endl;
    return 0;
}