counting the number of lines in rust

use std::os;
use std::io;

fn main() {
    let args = os::args();
    if args.len() != 2 {
        println!("Usage: {:s} <file>", args[0].as_slice());
        return;
    }
    let p = Path::new(args[1].as_slice());
    match io::File::open(&p) {
        Ok(f) => {
            let cnt = count_lines(f);
            println!("{}", cnt);
        }
        Err(e) => fail!("{}", e),
    }
}

fn count_lines(mut f: io::File) -> uint {
    let mut lines = 0u;

    // // ~ 1) slow
    // let mut r = io::BufferedReader::new(f);
    // loop {
    //     match r.read_byte() {
    //         Ok(c)  => if c == b'\n' {lines += 1;},
    //         Err(_) => break,
    //     }
    // }

    // // ~ 2) slow as well
    // lines += io::BufferedReader::new(f).chars().filter(|c| match c {
    //     &Ok(c) if c == '\n' => true,
    //     _ => false,
    // }).count();

    // // ~ 3) faster by still slow
    // lines += io::BufferedReader::new(f).lines().count();

    // ~ 4) as fast as i could get it so far
    let mut buf = [0u8, ..64*1024];
    loop {
        match f.read(buf) {
            Ok(n) => {
                for i in range(0, n) {
                    if buf[i] == b'\n' {
                        lines += 1;
                    }
                }
            }
            Err(_) => {
                break;
            }
        }
    }

    return lines;
}