ClickHouse/libs/libcommon/include/ext/shared_ptr_helper.hpp

#pragma once

#include <memory>

namespace ext
{

/**
 * Class AllocateShared allow to make std::shared_ptr<T> from T with private constructor.
 * Derive your T class from shared_ptr_helper<T>, define him as friend and call allocate_shared()/make_shared() method.
**/
template <class T>
class shared_ptr_helper
{
protected:
	typedef typename std::remove_const<T>::type TNoConst;

	template <class TAlloc>
	struct Deleter
	{
		void operator()(typename TAlloc::value_type * ptr)
		{
			std::allocator_traits<TAlloc>::destroy(alloc, ptr);
		}
		TAlloc alloc;
	};

	///see std::allocate_shared
	template <class TAlloc, class ... TArgs>
	static std::shared_ptr<T> allocate_shared(const TAlloc & alloc, TArgs && ... args)
	{
		TAlloc alloc_copy(alloc);
		return std::shared_ptr<TNoConst>(new (std::allocator_traits<TAlloc>::allocate(alloc_copy, 1)) TNoConst(std::forward<TArgs>(args)...), Deleter<TAlloc>(), alloc_copy);
	}

	template <class ... TArgs>
	static std::shared_ptr<T> make_shared(TArgs && ... args)
	{
		return allocate_shared(std::allocator<TNoConst>(), std::forward<TArgs>(args)...);
	}
};

}