error[E0046]: not all trait items implemented, missing: `Item`
  --> $DIR/issue-23729.rs:20:9
   |
LL |         impl Iterator for Recurrence {
   |         ^^^^^^^^^^^^^^^^^^^^^^^^^^^^ missing `Item` in implementation
   |
   = note: `Item` from trait: `type Item;`

error: aborting due to previous error

If you want more information on this error, try using "rustc --explain E0046"