time_it macro in Rust

time_it.rs

macro_rules! time_it {
    ($msg:expr, $code:block) => ({
        let start = SystemTime::now();
        let res = { $code };
        let end = SystemTime::now();
        println!("{:?} duration: {:?}", $msg, end.duration_since(start).ok().unwrap());
        res
    })
}

...

time_it!(format!("Iteration: {}", _idx), {
    let new_matches = Match::coalesce(&inputs,
                                      templates,
                                      references,
                                      &excluded_datums,
                                      n,
                                      results,
                                      s_distance,
                                      strategy);
    if new_matches.is_empty() {
        return found_matches;
    } else {
        for m in new_matches.iter() {
            if !excluded_datums.contains(&m.output) {
                excluded_datums.insert(m.output.clone());
                inputs.push(m.clone());
                found_matches.push(m.clone())
            }
        }
    }
})