Code shared from the Rust Playground

playground.rs

#![feature(test)]
mod bench {
    extern crate test;

    #[bench]
    fn chain(b: &mut Bencher) {
        b.iter(|| {
            let a = (0..500000).map(|x| x * 2);
            let b = (0..500000).map(|x| x * 3);
            let _c: Vec<_> = a.chain(b).collect();
        })
    }

    #[bench]
    fn extend(b: &mut Bencher) {
        b.iter(|| {
            let a = (0..500000).map(|x| x * 2);
            let b = (0..500000).map(|x| x * 3);
            let mut c = Vec::with_capacity(a.size_hint().1.unwrap() + b.size_hint().1.unwrap());
            c.extend(a);
            c.extend(b);
        })
    }
}