How to test if a type T has a begin<T> defined

[JUANDENT]

I have a SFINAE context where I have the following:

	struct have_sort { char c; };
	struct have_range { char c[2]; };
	struct have_none { char c[3]; };

	template<typename T> have_sort test_sort(decltype(&T::sort), decltype(&T::sort));
	template<typename T> have_range test_sort(decltype(&T::begin), decltype(&T::end));
	template<typename T> have_none test_sort(...);

	template<typename T, size_t s> struct fast_sort_helper;

	// specialization 1
	template<typename T>
	struct fast_sort_helper<T, sizeof(have_sort)>
	{
		static void sort(T& x)
		{
			x.sort();
		}
	};

	// specialization 2
	template<typename T>
	struct fast_sort_helper<T, sizeof(have_range)>
	{
		static void sort(T& x)
		{
			std::sort(x.begin(), x.end());
		}
	};
	// specialization 3
	template<typename T>
	struct fast_sort_helper<T, sizeof(have_none)>
	{
		static void sort(T& x)
		{
			static_assert(sizeof(T)< 0, "No sort available");
		}
	};


	template<typename T>
	void fast_sort(T& t)
	{
		fast_sort_helper<T, sizeof(test_sort<T>(nullptr,nullptr))>::sort(t);
	}

How do I test for the presence of a free function begin, the one that works on containers?

I tried this:"

template<typename T> long test_sort(decltype(&begin<T>), decltype(&begin<T>));

but it does not compile...

Regards,
Juan