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 <typename T>
class shared_ptr_helper
{
protected:
	typedef typename std::remove_const<T>::type TNoConst;

	template <typename TAlloc>
	struct Deleter
	{
		void operator()(typename TAlloc::value_type * ptr)
		{
			using AllocTraits = std::allocator_traits<TAlloc>;
			ptr->~TNoConst();
			AllocTraits::deallocate(alloc, ptr, 1);
		}

		TAlloc alloc;
	};

	/// see std::allocate_shared
	template <typename TAlloc, typename ... TArgs>
	static std::shared_ptr<T> allocate_shared(const TAlloc & alloc, TArgs &&... args)
	{
		using AllocTraits = std::allocator_traits<TAlloc>;
		TAlloc alloc_copy(alloc);

		auto ptr = AllocTraits::allocate(alloc_copy, 1);

		try
		{
			new (ptr) TNoConst(std::forward<TArgs>(args)...);
		}
		catch (...)
		{
			AllocTraits::deallocate(alloc_copy, ptr, 1);
			throw;
		}

		return std::shared_ptr<TNoConst>(
			ptr,
			Deleter<TAlloc>(),
			alloc_copy);
	}

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

}