コンストラクタでもshared_from_thisが使えるenable_shared_from_thisの製作

gistfile1.cpp

#include <iostream>
#include <memory>
#include <boost/optional.hpp>
#include <boost/utility/in_place_factory.hpp>

template<typename T>
class x_enable_shared_from_this
{
public:
	std::shared_ptr<T> shared_from_this()
	{
		return std::shared_ptr<T>(pWeakThis);
	}
	std::shared_ptr<T const> shared_from_this() const
	{
		return std::shared_ptr<T const>(pWeakThis);
	}
protected:
	x_enable_shared_from_this() {}
	explicit x_enable_shared_from_this(std::shared_ptr<T> const& pThis)
	: pWeakThis(pThis)
	{
	}
	x_enable_shared_from_this(x_enable_shared_from_this const&) {}
	x_enable_shared_from_this& operator =(x_enable_shared_from_this const&)
	{
		return *this;
	}
	~x_enable_shared_from_this() = default;
private:
	std::weak_ptr<T> pWeakThis;
};

template<typename T>
class x_enable_shared_from_this_impl : public T
{
public:
	template<typename... Args>
	x_enable_shared_from_this_impl(std::shared_ptr<void> pThis, Args&&... args)
		: x_enable_shared_from_this<T>(std::shared_ptr<T>(pThis, this))
		, T(std::forward<Args>(args)...)
	{
	}
	~x_enable_shared_from_this_impl() = default;
	x_enable_shared_from_this_impl(x_enable_shared_from_this_impl const&) = delete;
	x_enable_shared_from_this_impl& operator =(x_enable_shared_from_this_impl const&) = delete;
};

template<typename T, typename... Args>
std::shared_ptr<T> x_make_shared(Args&&... args)
{
	auto tmp = std::make_shared<boost::optional<x_enable_shared_from_this_impl<T>>>();
	*tmp = boost::in_place(tmp, std::forward<Args>(args)...);
	return {tmp, tmp->get_ptr()};
}

class Hoge : public virtual x_enable_shared_from_this<Hoge>
{
public:
	Hoge(int x, int y, int z)
	{
		auto p = shared_from_this();
		std::cout << p << '\n';
		std::cout << this << '\n';
		std::cout << x << ' ' << y << ' ' << z << std::endl;
	}
	~Hoge() {}
};

int main()
{
	auto p = x_make_shared<Hoge>(1, 2, 3);
}