Why is std::array< T> not empty?

Question

Given any std::array< T, 0 >, why is it not empty? I mean \"empty\" as in:

 std::is_empty< std::array< int, 0 > >::value


        

Answer 1

The standard doesn't say anything about whether tuple or array should be empty, what you're seeing are implementation details, but there's no reason to make tuple<> non-empty, whereas there is a good reason for array<T, 0> being non-empty, consider:

std::array<int, sizeof...(values)> = { { values... } };

When the parameter pack is empty you'd get:

std::array<int, 0> = { { } };

For the initializer to be valid the object needs a member, which cannot be int[0] because you can't have zero-sized arrays as members, so a possible implementation is int[1]

An implementation doesn't have to special case the whole array, it can just do:

T m_data[N == 0 ? 1 : N];

and all other members work exactly the same way (assuming end() is defined as begin()+N)