error[E0308]: mismatched types
--> $DIR/retslot-cast.rs:13:5
|
+LL | -> Option<&Iterator<Item=()>> {
+ | -------------------------- expected `Option<&dyn Iterator<Item = ()>>` because of return type
+...
LL | inner(x)
| ^^^^^^^^ expected trait `Iterator<Item = ()>`, found trait `Iterator<Item = ()> + Send`
|