items.filter(|(i)| cond(i)).map(Pointer::idx).collect()

you can probably get away with this if you implement a Trait, not sure how but I know for a fact this is possible, idk why there's an enumerate there when you aren't even using it.

items is already an iteratible so you can do direct .filter on it as well

tl;dr if the code looks ugly you're probably not taking advantage of a language feature that allows it to look pretty.