! is not a valid ty token in macros

[alexcrichton]

This program:

macro_rules! foo(($t:ty) => ()) 

foo!(!)                         

fn main() {}                    

fails with

foo.rs:3:5: 3:6 error: expected type, found token NOT
foo.rs:3 foo!(!)
              ^

I ran into this when creating a condition which returned ! (not sure if that's even the right use of conditions...)

[alexcrichton]

Oh it appears you also can't do

type Bot = !;

Now seeing that, is this intentional?

[brson]

Yes, ! is not a type, just a special token that says a function doesn't return.

[alexcrichton]

Oh, ok, that makes sense to me.