# 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
```