Detect whether a type is an zero-element array?

Question

Consider the following function :

template <typename Type>
void f(const Type& x)

I would like to do something special (without specialization) in it whether the passed type is an empty std::tuple or an empty std::array. For a tuple of nu elements, I can use std::is_same<Type, std::tuple<>>::value but what trick can I use to detect an zero-element array ?

(I am searching for a solution that do not require the creation of another function or class, ...)

Answer 1

You can use std::tuple_size, as it will also work for std::array! See here. Simply use:

std::tuple_size<Type>::value == 0

to check if Type is an empty std::tuple<> or an empty std::array<T,0>.

---

With the above, the question remains what happens if Type is neither a std::tuple not a std::array. The general approach I see is this:

constexpr bool IsNotTupleOrArray =
  !std::is_class<Type>::value ||
  std::is_same<Type,ExcludeThisClass>::value ||
  sizeof(Type)>1 || // non-portable, works for GCC 4.8+
  ...;

std::conditional< IsNotTupleOrArray,
                  std::false_type,
                  std::tuple_size<Type> >::type::value;

which basically means that you have to explicitly exclude other types. For example is_class<Type> excludes all fundamental types like int, pointers, etc.