error: implementation of `FnOnce` is not general enough --> $DIR/issue-67830.rs:23:5 | LL | Wrap(|a| Some(a).into_iter()) | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ implementation of `FnOnce` is not general enough | = note: closure with signature `fn(&'2 A) -> std::option::IntoIter<&A>` must implement `FnOnce<(&'1 A,)>`, for any lifetime `'1`... = note: ...but it actually implements `FnOnce<(&'2 A,)>`, for some specific lifetime `'2` error: implementation of `FnOnce` is not general enough --> $DIR/issue-67830.rs:23:5 | LL | Wrap(|a| Some(a).into_iter()) | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ implementation of `FnOnce` is not general enough | = note: closure with signature `fn(&'2 A) -> std::option::IntoIter<&A>` must implement `FnOnce<(&'1 A,)>`, for any lifetime `'1`... = note: ...but it actually implements `FnOnce<(&'2 A,)>`, for some specific lifetime `'2` error: aborting due to 2 previous errors