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

fn add_1<T>(ref mut v: T)
    where T: Integer + AddAssign<i32> + PartialEq<i32> + std::fmt::Display
{
    println!("Inside observed {}", *v);
    if *v == 0 {
        *v += 1
    }
}

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