Initial commit

exercises/19_smart_pointers/rc1.rs

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+// In this exercise, we want to express the concept of multiple owners via the
+// `Rc<T>` type. This is a model of our solar system - there is a `Sun` type and
+// multiple `Planet`s. The planets take ownership of the sun, indicating that
+// they revolve around the sun.
+
+use std::rc::Rc;
+
+#[derive(Debug)]
+struct Sun;
+
+#[derive(Debug)]
+enum Planet {
+    Mercury(Rc<Sun>),
+    Venus(Rc<Sun>),
+    Earth(Rc<Sun>),
+    Mars(Rc<Sun>),
+    Jupiter(Rc<Sun>),
+    Saturn(Rc<Sun>),
+    Uranus(Rc<Sun>),
+    Neptune(Rc<Sun>),
+}
+
+impl Planet {
+    fn details(&self) {
+        println!("Hi from {self:?}!");
+    }
+}
+
+fn main() {
+    // You can optionally experiment here.
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+
+    #[test]
+    fn rc1() {
+        let sun = Rc::new(Sun);
+        println!("reference count = {}", Rc::strong_count(&sun)); // 1 reference
+
+        let mercury = Planet::Mercury(Rc::clone(&sun));
+        println!("reference count = {}", Rc::strong_count(&sun)); // 2 references
+        mercury.details();
+
+        let venus = Planet::Venus(Rc::clone(&sun));
+        println!("reference count = {}", Rc::strong_count(&sun)); // 3 references
+        venus.details();
+
+        let earth = Planet::Earth(Rc::clone(&sun));
+        println!("reference count = {}", Rc::strong_count(&sun)); // 4 references
+        earth.details();
+
+        let mars = Planet::Mars(Rc::clone(&sun));
+        println!("reference count = {}", Rc::strong_count(&sun)); // 5 references
+        mars.details();
+
+        let jupiter = Planet::Jupiter(Rc::clone(&sun));
+        println!("reference count = {}", Rc::strong_count(&sun)); // 6 references
+        jupiter.details();
+
+        // TODO
+        let saturn = Planet::Saturn(Rc::clone(&sun));
+        println!("reference count = {}", Rc::strong_count(&sun)); // 7 references
+        saturn.details();
+
+        // TODO
+        let uranus = Planet::Uranus(Rc::clone(&sun));
+        println!("reference count = {}", Rc::strong_count(&sun)); // 8 references
+        uranus.details();
+
+        // TODO
+        let neptune = Planet::Neptune(Rc::clone(&sun));
+        println!("reference count = {}", Rc::strong_count(&sun)); // 9 references
+        neptune.details();
+
+        assert_eq!(Rc::strong_count(&sun), 9);
+
+        drop(neptune);
+        println!("reference count = {}", Rc::strong_count(&sun)); // 8 references
+
+        drop(uranus);
+        println!("reference count = {}", Rc::strong_count(&sun)); // 7 references
+
+        drop(saturn);
+        println!("reference count = {}", Rc::strong_count(&sun)); // 6 references
+
+        drop(jupiter);
+        println!("reference count = {}", Rc::strong_count(&sun)); // 5 references
+
+        drop(mars);
+        println!("reference count = {}", Rc::strong_count(&sun)); // 4 references
+
+        // TODO
+        drop(earth);
+        println!("reference count = {}", Rc::strong_count(&sun)); // 3 references
+
+        // TODO
+        drop(venus);
+        println!("reference count = {}", Rc::strong_count(&sun)); // 2 references
+
+        // TODO
+        drop(mercury);
+        println!("reference count = {}", Rc::strong_count(&sun)); // 1 reference
+
+        assert_eq!(Rc::strong_count(&sun), 1);
+    }
+}