Benchmarking iterator creation ( http://stackoverflow.com/questions/35402244/whats-the-most-efficient-way-to-reuse-an-iterator-in-rust )

bench_iterators.rs

// [build] rustc -O bench_iterators.rs --test
// [build] ./bench_iterators.exe --bench

#![feature(test)]
extern crate test;
use test::{Bencher, black_box};

#[bench]
fn construction_only(b: &mut Bencher) {
    let foo = String::from("foo");
    b.iter(|| {
        let i1 = foo.chars().flat_map(|c| c.to_uppercase());
        black_box(i1);
    })
}

#[bench]
fn inplace_construction(b: &mut Bencher) {
    let foo = String::from("foo");
    b.iter(|| {
        let s1: String = foo.chars().flat_map(|c| c.to_uppercase()).collect();
        black_box(s1);
        let s2: String = foo.chars().flat_map(|c| c.to_uppercase()).collect();
        black_box(s2);
    })
}

#[bench]
fn closure(b: &mut Bencher) {
    let foo = String::from("foo");
    let iter = || foo.chars().flat_map(|c| c.to_uppercase());
    b.iter(|| {
        let s1: String = iter().collect();
        black_box(s1);
        let s2: String = iter().collect();
        black_box(s2);
    })
}

#[bench]
fn vec_inplace_iter(b: &mut Bencher) {
    let v = vec![1, 2, 3, 4, 5, 6, 7, 8, 9];
    b.iter(|| {
        let i = v.iter().skip(2);
        black_box(i);
    })
}

#[bench]
fn vec_clone_iter(b: &mut Bencher) {
    let v = vec![1, 2, 3, 4, 5, 6, 7, 8, 9];
    let i = v.iter().skip(2);
    b.iter(|| {
        let i = i.clone();
        black_box(i);
    })
}