[Rust] The constructor of Rational class

impl Rational {
    pub fn new(p: i32, q: i32) -> Rational {
        if q == 0 {
            panic!("Denominator should not be zero.");
        }

        let d = Rational::gcd(p, q).abs();

        Rational{ num: p / d, denom: q / d }
    }
}

impl Rational {
    fn gcd(a: i32, b: i32) -> i32 {
        if b == 0 {
            a
        } else {
            Rational::gcd(b, a % b)
        }
    }
}