feat: Add enums exercises

exercises/enums/README.md

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+### Enums
+
+Rust allows you to define a type called `enums` which allow you to enumerate possible values. In combination with enums, we have the concept of `pattern matching` in Rust, which makes it easy to run different code for different values of an enumeration. Enums, while available in many languages, Rust's enums are most similar to `algebraic data types` in functional languages, such as F#, OCaml, and Haskell.
+
+#### Book Sections
+
+- [Enums](https://doc.rust-lang.org/book/ch06-00-enums.html)

exercises/enums/enums1.rs

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+// enums1.rs
+// Make me compile! Scroll down for hints!
+
+#[derive(Debug)]
+enum Message {
+    // TODO: define a few types of messages as used below
+}
+
+fn main() {
+    println!("{:?}", Message::Quit);
+    println!("{:?}", Message::Echo);
+    println!("{:?}", Message::Move);
+    println!("{:?}", Message::ChangeColor);
+}
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+// Hint: The declaration of the enumeration type has not been defined yet.

exercises/enums/enums2.rs

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+// enums2.rs
+// Make me compile! Scroll down for hints
+
+#[derive(Debug)]
+enum Message {
+    // TODO: define the different variants used below
+}
+
+impl Message {
+    fn call(&self) {
+        println!("{:?}", &self);
+    }
+}
+
+fn main() {
+    let messages = [
+        Message::Move{ x: 10, y: 30 },
+        Message::Echo(String::from("hello world")),
+        Message::ChangeColor(200, 255, 255),
+        Message::Quit
+    ];
+
+    for message in &messages {
+        message.call();
+    }
+}
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+// Hint: you can create enumerations that have different variants with different types
+// such as no data, anonymous structs, a single string, tuples, ...etc

exercises/enums/enums3.rs

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+// 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);
+    }
+
+}

info.toml

@@ -86,6 +86,20 @@ mode = "test"
 path = "exercises/structs/structs2.rs"
 mode = "test"
 
+# ENUMS
+
+[[exercises]]
+path = "exercises/enums/enums1.rs"
+mode = "compile"
+
+[[exercises]]
+path = "exercises/enums/enums2.rs"
+mode = "compile"
+
+[[exercises]]
+path = "exercises/enums/enums3.rs"
+mode = "test"
+
 # TESTS
 
 [[exercises]]