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08-type-mapping/README.md

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+# Type Mapping in TypeScript
+
+This example demonstrates how to use TypeScript's mapped types and generics to create a type-safe mapping between an operation code (enum) and the expected arguments for that operation.
+
+```typescript
+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,
+  ) {
+    // ...
+  }
+}
+```
+
+When calling `send`, TypeScript automatically infers the correct type for `args` based on the value passed for `op`.
+
+```typescript
+client.send(OpCode.MOVE, { x: 10, y: 20 }); // Correct
+client.send(OpCode.MOVE, { name: "foo" }); // -> 💥 Compiler Error
+```