Why does structured binding fails with empty base class?

I saw following example here,

#include <iostream>

struct B 
{ 

};
struct D : B 
{ 
    int i;
};

int main() 
{
    auto [i] = D{};
    return 0;
}

I have compiled this program with GCC 7.2.0 (C++1Z), and I got following error:

error: cannot decompose class type 'D': both it and its base class 'D' have non-static data members
     auto [i] = D{};
          ^~~

So, Why does structured binding fails with empty base class?