Reinterpreting a union to a different union

Question

I have a standard-layout union that has a whole bunch of types in it:

union Big {
    Hdr h;

    A a;
    B b;
    C c;
    D d;
    E e;
    F f;
};
         


        

Answer 1

I can find no wording in n4296 (draft C++14 standard) which would make this legal. What is more, I cannot even find any wording that given:

union Big2 {
    Hdr h;

    A a;
    B b;
    C c;
    D d;
    E e;
    F f;
};

we can reinterpret_cast a reference to Big into a reference to Big2 and then use the reference. (Note that Big and Big2 are layout-compatible.)