Будь проклят тот день...[С++ template hell]

struct CDestroyer
{
...
    template <typename T>
    struct CHelper4
    {
        template <bool a>
        static void delete_data(T& data)
        {
            CHelper2<T>::delete_data<object_type_traits::is_pointer<T>::value>(data);
        }
    };

    template <typename T> 
    static void delete_data(T& data)
    {
        CHelper4<T>::delete_data<object_type_traits::is_stl_container<T>::value>(data);
    }
};

template <typename T>
template <>
void CDestroyer::CHelper4<T>::delete_data<true>(T& data)
{
    CHelper3::delete_data(data);
}

#include <cstdio>
#include <cstdint>
#include <string>
#include <iostream>
#include <type_traits>

template <typename T>
struct CHelper4
{
	template <bool a>
	static void delete_data(std::enable_if_t<a, T&> data)
	{
		std::cout << 1 << std::endl;
	}

	template <bool a>
	static void delete_data(std::enable_if_t<!a, T&> data)

	{
		std::cout << 2 << std::endl;
	}
};

int main()
{
	int a = 1;
	CHelper4<int>::delete_data<true>(a);
	CHelper4<int>::delete_data<false>(a);
	return 0;
}

    template <typename T>
    struct CHelper4
    {
        template <bool a>
        static void delete_data(T& data)
        {
            CHelper2<T>::delete_data<object_type_traits::is_pointer<T>::value>(data);
        }
    };

    template <typename T>
    static void delete_data(T& data)
    {
        CHelper4<T>::delete_data<object_type_traits::is_stl_container<T>::value>(data);
    }
};

template <typename T>
template <> // error: enclosing class templates are not explicitly specialized
static void CDestroyer::CHelper4<T>::delete_data<true>(T& data)
{
    CHelper3::delete_data(data);
}

template<typename T>
void foo()
{
    if constexpr (object_type_traits::is_stl_container<T>::value)
    {
        CHelper3::delete_data(data);
    }
    else
    {
        CHelper2<T>::delete_data<object_type_traits::is_pointer<T>::value>(data);
    }
}

template <>
template <>

// либо так

template <>
template <bool a>

// обратный порядок нельзя

template <>
template <bool a>
void CHelper4<int>::delete_data(int& data)
{
}

class MyCls
{
public:
    int sum(int a, int b);
};

int MyCls::sum(int a, int b)
{
    return a + b;
}