Comment by Animats

Yes. I once wanted C unions limited to fully mapped type conversions, where any bit pattern in either type is a valid bit pattern in the other. Then you can map two "char" to "int". Even "float". But pointer types must match exactly.

If you want disjoint types, something like Pascal's discriminated variants or Rust's enums is the way to go. It's embarrassing that C never had this.

Many bad design decision in C come from the fact that originally, separate compilation was really dumb, so the compiler would fit in small machines.