1 A return statement with an expression shall not appear in a function whose return type is void.
It's a constraint violation. It doesn't matter what the type of the expression is.
It looks as if C++ made a small improvement here.
Yes, the bottom type is at the bottom of the type derivation hierarchy. That's why the word bottom is there; that's what it's at the bottom of. It's also why it can't have any instances. Since every other type is a supertype, then if the bottom type contained some value V, that value would be imposed into every other type! V would be a valid String, Widget, Integer, Stream, Array ... what have you.
To clarify, it could be that the bottom type is not the base of all types, if the language has a split between some types which participate in that sort of thing and others that don't (e.g. class versus basic types or whatever).
But void is not the base of anything in C and C++.
You could argue that void is in some category of types where it is at the bottom; but no other types are in that category.
There is another problem: a bottom type should be the subtype of all types in that category. That includes being its own subtype. There we have a problem: C and C++ void is not a subtype of void in any sense.
6.8.7.5 The return statement
Constraints
1 A return statement with an expression shall not appear in a function whose return type is void.
It's a constraint violation. It doesn't matter what the type of the expression is.
It looks as if C++ made a small improvement here.
Yes, the bottom type is at the bottom of the type derivation hierarchy. That's why the word bottom is there; that's what it's at the bottom of. It's also why it can't have any instances. Since every other type is a supertype, then if the bottom type contained some value V, that value would be imposed into every other type! V would be a valid String, Widget, Integer, Stream, Array ... what have you.