error[E0623]: lifetime mismatch
  --> $DIR/ex3-both-anon-regions-both-are-structs.rs:15:12
   |
14 | fn foo(mut x: Vec<Ref>, y: Ref) {
   |                   ---      --- these two types are declared with different lifetimes...
15 |     x.push(y); //~ ERROR lifetime mismatch
   |            ^ ...but data from `y` flows into `x` here

error: aborting due to previous error