.ts

type FruitTemplate<Type extends string, Props> ={ type: Type } & Props

type Fruit =
  | AppleFruit
  | BananaFruit

type AppleFruit = FruitTemplate<'Apple', {
  sliced: boolean;
  peeled: boolean;
}>

type BananaFruit = FruitTemplate<'Banana', {
  color: 'yellow' | 'green';
}>

function createFruitOf<T extends Fruit['type']>(type: T) {
  if (type === 'Apple') {
    const apple: AppleFruit = {
      peeled: false,
      sliced: false,
      type: 'Apple',
    };
    return apple;
  }

  if (type === 'Banana') {
    const banana: BananaFruit = {
      color: 'green',
      type: 'Banana',
    };
    return banana;
  }

  throw new Error(`Unknown type "${type}"`);
}

const apple = createFruitOf('Apple');