error: unsatisfied lifetime constraints
  --> $DIR/dyn-trait-underscore.rs:18:5
   |
LL | fn a<T>(items: &[T]) -> Box<dyn Iterator<Item=&T>> {
   |                - let's call the lifetime of this reference `'1`
LL |     //                      ^^^^^^^^^^^^^^^^^^^^^ bound *here* defaults to `'static`
LL |     Box::new(items.iter()) //~ ERROR cannot infer an appropriate lifetime
   |     ^^^^^^^^^^^^^^^^^^^^^^ returning this value requires that `'1` must outlive `'static`

error: aborting due to previous error