I don't know. I find this:

    fn get_ids(data: Vec<Widget>) -> Vec<Id> {
        let mut result = Vec::new();
    
        for widget in &data {
            if widget.alive {
                result.push(widget.id);
            }
        }
    
        result
    }

more readable than this:

    fn get_ids(data: Vec<Widget>) -> Vec<Id> {
        data.iter()
            .filter(|w| w.alive)
            .map(|w| w.id)
            .collect()
    }

and I also dislike Rust requiring you to write "mut" for function mutable values. It's mostly just busywork and dogma.