How to model your entities - 13

Message.ts

export type $TextMessage = {
  text: string;
}

const { toOpaque, fromOpaque, isOpaque } = createOpaqueAPI<
  'TextMessage',
  $TextMessage,
>('TextMessage’);

export type TextMessage = ReturnType<typeof toOpaque>;

export function createText(text: string): TextMessage {
  return toOpaque({ text });
}

export function text(message: TextMessage): string {
  const $message = fromOpaque(message);
  return $message.text;
}

// We can use the isOpaque type guard without needing the `messageType` tag,
// free of charge!
export function isText(message: Message): message is TextMessage {
  return isOpaque(message);
}