error[E0261]: use of undeclared lifetime name `'a`
  --> $DIR/box-pattern-type-mismatch.rs:7:31
   |
LL | struct X(dyn Iterator<Item = &'a ()>);
   |                               ^^ undeclared lifetime
   |
   = note: for more information on higher-ranked polymorphism, visit https://doc.rust-lang.org/nomicon/hrtb.html
help: consider making the bound lifetime-generic with a new `'a` lifetime
   |
LL | struct X(dyn for<'a> Iterator<Item = &'a ()>);
   |              +++++++
help: consider introducing lifetime `'a` here
   |
LL | struct X<'a>(dyn Iterator<Item = &'a ()>);
   |         ++++

error: aborting due to 1 previous error

For more information about this error, try `rustc --explain E0261`.