playground.rs

type RenderData = u32;

struct Manager {
    render_data: Vec<Option<RenderData>>
}

pub fn main() {

    let mut entity_manager = Manager {
        render_data: vec![None, Some(5), None, Some(2), None]
    };

    for (data, i) in entity_manager.render_data.iter_mut().zip(0..)
            .filter_map(|(x, i)| x.as_mut().map(|x| (x, i))) {
        *data += 1;
        println!("{:?}: {:?}", i, data);
    }
}