struct S; impl<T> std::ops::Add<T> for S { type Output = (); fn add(self, _: T) {} } fn main() { let _ = ..0; let _ = S + ..0; let _ = &..0; let _ = || ..0; let _ = *..0; }

With the exception of *..0, all of the above expressions parse successfully, so .. is definitely allowed to appear at the beginning of an expression — including an expression with higher precedence such as binary + and unary &. I think it is a bug that *..0 does not parse. Same for -..0 and !..0.

error: expected expression, found `..`  --> src/main.rs:12:14  | 12 | let _ = *..0;  | ^^ expected expression