1 error[E0308]: mismatched types
2 --> $DIR/retslot-cast.rs:13:5
5 | ^^^^^^^^ expected trait `std::iter::Iterator<Item = ()>`, found trait `std::iter::Iterator<Item = ()> + std::marker::Send`
7 = note: expected type `std::option::Option<&dyn std::iter::Iterator<Item = ()>>`
8 found type `std::option::Option<&dyn std::iter::Iterator<Item = ()> + std::marker::Send>`
10 error: aborting due to previous error
12 For more information about this error, try `rustc --explain E0308`.