lecture 3 stuff

lectures/03/shapes2.rs

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+// how to put different shapes in a container?
+// solution 2: use a trait object; late dispatch
+
+struct Point(f64, f64);
+struct Circle(Point, f64);
+struct Rectangle(Point, Point);
+
+trait Shape {
+    fn area(&self) -> f64;
+}
+
+impl Shape for Circle {
+    fn area(&self) -> f64 { std::f64::consts::PI * self.1 * self.1 }
+}
+
+impl Shape for Rectangle {
+    fn area(&self) -> f64 { ((self.1.0 - self.0.0) * (self.1.1 - self.0.1)).abs() }
+}
+
+fn total_area(shapes: &[Box<dyn Shape>]) -> f64 {
+    let mut total = 0.0;
+
+    for s in shapes {
+        total += s.area();
+    }
+    total
+}
+
+fn main() {
+    // let x = Box::new(42);
+
+    let v: Vec<Box<dyn Shape>> = vec![
+        Box::new(Circle(Point(0.0, 0.0), 1.0)),
+        Box::new(Rectangle(Point(1.0, 1.0), Point(2.0, 3.0))),
+    ];
+
+    println!("{}", total_area(&v));
+    println!("{}", total_area(&v));
+}