type RenderData = u32;

struct Manager {
    num_entities: usize,
    render_data: Vec<Option<RenderData>>
}

pub fn main() {

    let mut entity_manager = Manager {
        num_entities: 3,
        render_data: vec![Some(5), Some(2), None]
    };

    // Inside my game loop...
    for i in 0..entity_manager.num_entities {
        match &mut entity_manager.render_data[i] { // render_data is Option<RenderData>, where RenderData is a struct containing my data...
             &mut Some(ref mut data) => { // I really don't want to copy this data everywhere.
                 // Render the entity using my data. The data kind of needs to be modified a bit. (Make sure the Uniforms are up to date, for those interested in why)
                 *data += 1;
             },
             &mut None => (),
         }
         println!("{:?}", &entity_manager.render_data[i]);
    }
}