extern crate num;

use std::ops::AddAssign;
use num::Integer;

fn add_1<T: Integer + AddAssign<i32> + PartialEq<i32>>(v: &mut T) {
    if *v == 0 {
        *v += 1
    }
}

fn main() {
    let mut x = 0;
    println!("{}", x);
    add_1(&mut x);
    println!("{}", x);
}