struct Rectangle {
    width: f64,
    height: f64,
}

impl Rectangle {
    fn new(width: f64, height: f64) -> Self {
        Rectangle { width, height }
    }

    fn area(&self) -> f64 {
        self.width * self.height
    }

    fn is_square(&self) -> bool {
        (self.width - self.height).abs() < f64::EPSILON
    }
}

fn main() {
    let rect = Rectangle::new(10.0, 5.0);
    println!("area: {}", rect.area());
    println!("square: {}", rect.is_square());

    let sq = Rectangle::new(4.0, 4.0);
    println!("square: {}", sq.is_square());
}