// Define data structure
#[derive(Debug)]
enum Shape {
    Circle { radius: f64 },
    Rectangle { width: f64, height: f64 },
    Triangle { base: f64, height: f64 },
}

// Add methods
impl Shape {
    // "&self" = immutably borrow self - can't mutate values
    fn compute_area(&self) -> f64 {
        match self {
            Shape::Circle{ radius } => radius * 3.14159,
            Shape::Rectangle{ width, height } => width * height,
            Shape::Triangle{ base, height } => 0.5 * base * height,
            // No default required because compiler knows we hit every case!
            // If we add another variant to Shape, this match will no longer
            // compile. (Try it!)
        }
    }
}

fn main() {
    // shortcut macro to make an array literal
    // statically typed, but type inference lets you omit them for most local
    // vars
    let shapes = vec![
        Shape::Circle{ radius: 2.0 },
        Shape::Rectangle{ width: 3.0, height: 4.0 },
        Shape::Triangle{ base: 2.0, height: 3.0 },
    ];
    // awesome iterator syntax
    for shape in shapes.iter() {
        // weird printf style syntax... yeah we're still in a systems language
        println!("shape = {:?}, area = {:?}", shape, shape.compute_area());
    }
}