fn process_samples(
    samples: &[i32],
    scale: &[i32],
    upper_limit: i32
) {
    let mut sum = 0;
    let mut min = None;
    let mut max = None;
    for (sample, scale) in samples.iter().zip(scale) {
        let scaled = sample * scale;
        if scaled <= upper_limit {
            continue;
        }
        sum += scaled;
        min = Some(match min {
            Some(min) => scaled.min(min),
            None => scaled,
        });
        max = Some(match max {
            Some(max) => scaled.max(max),
            None => scaled,
        });
    }
    // ...
}

use reductor::{Reduce, Reductors, Sum, Min, Max};
fn process_samples(
    samples: &[i32],
    scale: &[i32],
    upper_limit: i32
) {
    let Reductors((Sum::<i32>(sum), Min::<Option<i32>>(min), Max::<Option<i32>>(max))) = samples
        .iter()
        .zip(scale)
        .map(|(sample, scale)| sample * scale)
        .filter(|&scaled| scaled > upper_limit)
        .reduce_with();
    // ...
}