I am going through Deitel & Deitel's C++ book (section 8.8 of the
fourth edition), in which they construct an Array class and show how
to overload operators. The assignment operator is overloaded as
follows:

const Array &operator=(const Array &);

According to D&D, the const return is designed to avoid (a1 = a2) =
a3. My questions are:

1) Why is this necessary? After all, an assignment like (a1 = a2) = a3
works for ordinary variables.

2) What if you want to use this method on a non-constant Array object,
or if you want it to return a non-constant Array? I can see it still
works, but why don't the const declarations get in the way?

Thanks.