gistfile1.rs

trait TypeFoldable {
  fn fold_with(&self) -> Self;
}

impl<'a> TypeFoldable for &'a uint {
  fn fold_with(&self) -> &'a uint { *self }
}

trait Subst {
  fn subst(&self) -> Self;
}

impl<T: TypeFoldable> Subst for T {
  fn subst(&self) -> T {
      (*self).fold_with()
  }
}

fn main() {
  let a = &5u;
  println!("{}", a.subst());
}

gistfile2.txt

test.rs:21:18: 21:27 error: the trait `TypeFoldable` is not implemented for the type `uint`
test.rs:21   println!("{}", a.subst());
                            ^~~~~~~~~
note: in expansion of format_args!
<std macros>:2:23: 2:77 note: expansion site
<std macros>:1:1: 3:2 note: in expansion of println!
test.rs:21:3: 21:29 note: expansion site
error: aborting due to previous error