Implicit Deref

gistfile1.txt

mod implicit_deref {
    use std::ops::Deref;

    struct T(i32);
    struct S<'a>(&'a T);

    impl<'a> Deref for S<'a> {
        type Target = T;
        fn deref(&self) -> &T { &self.0; }
    }

    fn f(t: T, n: i32) { assert_eq!(n, t.0); }

    #[test]
    fn test() {
        let t = T(42);
        let s = S(&t);
        f(s, 42);
    }
}

Dies with:

cd ~/rust/play2 && cargo test
   Compiling play2 v0.0.1 (file:///home/jimb/rust/play2)
src/main.rs:193:11: 193:12 error: mismatched types:
 expected `implicit_deref::T`,
    found `implicit_deref::S<'_>`
(expected struct `implicit_deref::T`,
    found struct `implicit_deref::S`) [E0308]
src/main.rs:193         f(s, 42);
                          ^
error: aborting due to previous error
Could not compile `play2`.