add typestate typescript example

08-type-mapping/main.ts

@@ -0,0 +1,36 @@
+enum OpCode {
+  PING,
+  HELLO,
+  MOVE,
+}
+
+type PingEvent = Record<string, never>;
+
+type HelloEvent = {
+  name: string;
+};
+
+type MoveEvent = {
+  x: number;
+  y: number;
+};
+
+type OpArgsMapping = {
+  [OpCode.PING]: PingEvent;
+  [OpCode.HELLO]: HelloEvent;
+  [OpCode.MOVE]: MoveEvent;
+};
+
+class WebSocketClient {
+  public send<TOp extends OpCode, TArgs extends OpArgsMapping[TOp]>(
+    op: TOp,
+    args: TArgs,
+  ) {
+    // ...
+  }
+}
+
+function main1() {
+  const client = new WebSocketClient();
+  client.send(OpCode.PING, {});
+}