type-list-plus-substitution-failure.cpp

#include <type_traits>
#include <iostream>

template<typename... T> struct type_list;

template<typename T, typename List> struct in;
template<typename T, typename Head, typename... Tail> struct in<T, type_list<Head, Tail...>> {
	static constexpr auto value = std::is_same<T, Head>::value || in<T, type_list<Tail...>>::value;
};
template<typename T> struct in<T, type_list<>> {
	static constexpr auto value = false;
};

template<typename T,
		 typename std::enable_if<in<T, type_list<float, double, long double>>::value>::type * = nullptr>
void foo(T) { std::cout << "floating overload" << std::endl; }

template<typename T,
		 typename std::enable_if<in<T, type_list<signed char, short, int, long, long long>>::value>::type * = nullptr>
void foo(T) { std::cout << "signed integer overload" << std::endl; }

template<typename T,
		 typename std::enable_if<in<T,
			type_list<unsigned char, unsigned short, unsigned int, unsigned long, unsigned long long>>::value>::type * = nullptr>
void foo(T) { std::cout << "unsigned integer overload" << std::endl; }

void foo(char) { std::cout << "char overload" << std::endl; }

int main() {
	foo('\0');
	foo(0);
	foo(1.0f);
	foo(0ULL);
}