Using rustc 1.13.0-nightly (923bac459 2016-09-06) x86-64/linux

01-bench

#

test clone_str                  ... bench:     370,601 ns/iter (+/- 14,692) = 2829 MB/s
test clone_vec_from_fn          ... bench:     372,835 ns/iter (+/- 38,525) = 2812 MB/s
test clone_vec_from_incremental ... bench:     369,055 ns/iter (+/- 8,690) = 2841 MB/s
test fast_clone_vec             ... bench:     374,947 ns/iter (+/- 11,168) = 2796 MB/s

benchmark.rs

#![feature(test)]
extern crate test;

use test::{Bencher, black_box};

static SIZE: usize = 1024*1024;

#[bench]
fn clone_str(bh: &mut Bencher) {
    let mut x = String::with_capacity(SIZE);
    for _ in 0..SIZE {
        x.push('x');
    }
    bh.iter(|| x.clone());
    bh.bytes = x.len() as u64;
}

#[bench]
fn clone_vec_from_incremental(bh: &mut Bencher) {
    let mut x: Vec<u8> = Vec::with_capacity(SIZE);
    for _ in 0..SIZE {
        x.push(0x78);
    }
    bh.iter(|| x.clone());
    bh.bytes = x.len() as u64;
}

#[bench]
fn clone_vec_from_fn(bh: &mut Bencher) {
    let x = black_box(vec![0x78u8; SIZE]);
    bh.iter(|| x.clone());
    bh.bytes = x.len() as u64;
}

#[bench]
fn fast_clone_vec(bh: &mut Bencher) {
    let x = black_box(vec![0x78u8; SIZE]);
    bh.iter(|| {
        let mut copy = Vec::<u8>::with_capacity(SIZE);
        unsafe {
            std::ptr::copy_nonoverlapping(x.as_ptr(), copy.as_mut_ptr(), x.len());
            copy.set_len(SIZE);
        }
        copy
    });
    bh.bytes = x.len() as u64;
}