Code shared from the Rust Playground

playground.rs

use criterion::black_box;
fn using_flat_map(big: i32) {
    for (a, b) in (1..big).flat_map(|a| (0..a).map(move |b| (a, b))) {
        black_box((a, b));
    }
}

fn using_for_loops(big: i32) {
    for a in 1..big {
        for b in 0..a {
            black_box((a, b));
        }
    }
}