14 - First of Array

[lxxmnmn]

First of Array

배열(튜플) T를 받아 첫 원소의 타입을 반환하는 제네릭 First<T>를 구현하세요.

/* _____________ Your Code Here _____________ */

type First<T extends any[]> = T extends [] ? never : T[0];

/* _____________ Test Cases _____________ */

import type { Equal, Expect } from '@type-challenges/utils'

type cases = [
  Expect<Equal<First<[3, 2, 1]>, 3>>,
  Expect<Equal<First<[() => 123, { a: string }]>, () => 123>>,
  Expect<Equal<First<[]>, never>>,
  Expect<Equal<First<[undefined]>, undefined>>,
]

type errors = [
  // @ts-expect-error
  First<'notArray'>,
  // @ts-expect-error
  First<{ 0: 'arrayLike' }>,
]