macro_rules! borrow { ($x:expr) => { &$x } //~ ERROR mismatched types } fn foo(_: String) {} fn foo2(s: &String) { foo(s); //~^ ERROR mismatched types } fn foo3(_: u32) {} fn foo4(u: &u32) { foo3(u); //~^ ERROR mismatched types } fn main() { let s = String::new(); let r_s = &s; foo2(r_s); foo(&"aaa".to_owned()); //~^ ERROR mismatched types foo(&mut "aaa".to_owned()); //~^ ERROR mismatched types foo3(borrow!(0)); foo4(&0); assert_eq!(3i32, &3i32); //~^ ERROR mismatched types }