Merge pull request #173 from dojoengine/enums

add enum section

src/SUMMARY.md

@@ -28,6 +28,7 @@
   - [Events](./cairo/events.md)
   - [Authorization](./cairo/authorization.md)
   - [Metadata](./cairo/metadata.md)
+  - [Enum](./cairo/enum.md)
 - [Migration](./cairo/migration.md)
   - [0.2.0 -> 0.3.0](./cairo/migration/0.3.0.md)
 - [ECS in 15 minutes](./cairo/hello-dojo.md)

src/cairo/enum.md

@@ -0,0 +1,55 @@
+## Enum
+
+Enums are very useful in game design, as they simplify the creation of clean, complex logic.
+
+You can define an enum as follows:
+
+```rust,ignore
+
+// This enum simply defines the states of a game.
+#[derive(Serde, Copy, Drop, Introspect, PartialEq, Print)]
+enum GameStatus {
+    NotStarted: (),
+    Lobby: (),
+    InProgress: (),
+    Finished: (),
+}
+
+// We define an into trait
+impl GameStatusFelt252 of Into<GameStatus, felt252> {
+    fn into(self: GameStatus) -> felt252 {
+        match self {
+            GameStatus::NotStarted => 0,
+            GameStatus::Lobby => 1,
+            GameStatus::InProgress => 2,
+            GameStatus::Finished => 3,
+        }
+    }
+}
+```
+
+Then within a trait you can create something like this:
+
+```rust,ignore
+#[derive(Model, Copy, Drop, Serde)]
+struct Game {
+    #[key]
+    game_id: u32,
+    status: GameStatus,
+}
+
+#[generate_trait]
+impl GameImpl of GameTrait {
+    fn assert_in_progress(self: Game) {
+        assert(self.status == GameStatus::InProgress, "Game not started");
+    }
+    fn assert_lobby(self: Game) {
+        assert(self.status == GameStatus::Lobby, "Game not in lobby");
+    }
+    fn assert_not_started(self: Game) {
+        assert(self.status == GameStatus::NotStarted, "Game already started");
+    }
+}
+```
+
+> Read more about Cairo enums [here](https://book.cairo-lang.org/ch06-00-enums-and-pattern-matching.html)