diff --git a/05-type-mapping/main.ts b/05-type-mapping/main.ts
new file mode 100644
index 0000000..c1ac3cd
--- /dev/null
+++ b/05-type-mapping/main.ts
@@ -0,0 +1,34 @@
+enum OpCode {
+    PING,
+    HELLO,
+    MOVE,
+}
+
+type HelloEvent = {
+    name: string;
+};
+
+type MoveEvent = {
+    x: number;
+    y: number;
+};
+
+type OpArgsMapping = {
+    [OpCode.PING]: null;
+    [OpCode.HELLO]: HelloEvent;
+    [OpCode.MOVE]: MoveEvent;
+};
+
+class WebSocketClient {
+    public op<TOp extends OpCode, TArgs extends OpArgsMapping[TOp]>(
+        op: TOp,
+        args: TArgs,
+    ) {
+        // ...
+    }
+}
+
+function main() {
+    const client = new WebSocketClient();
+    client.op(OpCode.HELLO, { name: "foo" });
+}