error: lifetime may not live long enough
  --> $DIR/ex3-both-anon-regions.rs:2:5
   |
LL | fn foo(x: &mut Vec<&u8>, y: &u8) {
   |                    -        - let's call the lifetime of this reference `'1`
   |                    |
   |                    let's call the lifetime of this reference `'2`
LL |     x.push(y);
   |     ^^^^^^^^^ argument requires that `'1` must outlive `'2`
   |
help: consider introducing a named lifetime parameter
   |
LL | fn foo<'a>(x: &mut Vec<&'a u8>, y: &'a u8) {
   |       ++++              ++          ++

error: aborting due to 1 previous error