[Typescript] Using Extract type until to get the value from Union type

import { Equal, Expect } from '../helpers/type-utils';
import { F } from 'ts-toolbelt';

interface Fruit {
  name: string;
  price: number;
}

export const wrapFruit = <TFruits extends Fruit[]>(
  fruits: F.Narrow<TFruits>
) => {
  const getFruit = <
    TName extends TFruits[number]['name']
  >(
    name: TName
  ): RT => {
    return fruits.find((fruit) => fruit.name === name) as Extract<TFruits[number], { name: TName }>;
  };

  return {
    getFruit,
  };
};

const fruits = wrapFruit([
  {
    name: 'apple',
    price: 1,
  },
  {
    name: 'banana',
    price: 2,
  },
]);

const banana = fruits.getFruit('banana');
const apple = fruits.getFruit('apple');
// @ts-expect-error
const notAllowed = fruits.getFruit('not-allowed');

type tests = [
  Expect<Equal<typeof apple, { name: 'apple'; price: 1 }>>,
  Expect<Equal<typeof banana, { name: 'banana'; price: 2 }>>
];

 

See how to extract: as Extract<TFruits[number], { name: TName }>;