feat: Add enums exercises

exercises/enums/enums3.rs

@@ -0,0 +1,63 @@
+// enums3.rs
+// Address all the TODOs to make the tests pass!
+
+enum Message {
+    // TODO: implement the message variant types based on their usage below
+}
+
+struct Point {
+    x: u8,
+    y: u8
+}
+
+struct State {
+    color: (u8, u8, u8),
+    position: Point,
+    quit: bool
+}
+
+impl State {
+    fn change_color(&mut self, color: (u8, u8, u8)) {
+        self.color = color;
+    }
+
+    fn quit(&mut self) {
+        self.quit = true;
+    }
+
+    fn echo(&self, s: String) {
+        println!("{}", s);
+    }
+
+    fn move_position(&mut self, p: Point) {
+        self.position = p;
+    }
+
+    fn process(&mut self, message: Message) {
+        // TODO: create a match expression to process the different message variants
+    }
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+
+    #[test]
+    fn test_match_message_call() {
+        let mut state = State{
+            quit: false,
+            position: Point{ x: 0, y: 0 },
+            color: (0, 0, 0)
+        };
+        state.process(Message::ChangeColor(255, 0, 255));
+        state.process(Message::Echo(String::from("hello world")));
+        state.process(Message::Move{ x: 10, y: 15 });
+        state.process(Message::Quit);
+
+        assert_eq!(state.color, (255, 0, 255));
+        assert_eq!(state.position.x, 10);
+        assert_eq!(state.position.y, 15);
+        assert_eq!(state.quit, true);
+    }
+
+}