A simple C++11 detection idiom presented.

test.cpp

#include <type_traits>
#include <iostream>
#include <utility>

namespace mystd {

namespace detail {

template <typename...>
using void_t = void;

template <typename T, typename Void = void>
struct has_swap : std::false_type {};

template <typename T>
struct has_swap<T, void_t<decltype(std::declval<T>().swap(std::declval<T&>()))>> : std::true_type {};

template <typename T>
static inline auto constexpr has_swap_v = has_swap<T>::value;

}

template <typename T>
auto swap(T& a, T& b) -> typename std::enable_if<detail::has_swap_v<T>>::type {
	std::cout << "Member swap.\n";
}

template <typename T>
auto swap(T& a, T& b) -> typename std::enable_if<not detail::has_swap_v<T>>::type  {
	std::cout << "Free swap.\n";
}

}

auto main() -> int {
	struct HasMemberSwap {
		void swap(HasMemberSwap&) {}
	};

	struct DoesntHaveMemberSwap {};

	{
		HasMemberSwap a, b;
		mystd::swap(a, b);
	}
	{
		DoesntHaveMemberSwap a, b;
		mystd::swap(a, b);
	}
}