type-challenges-judge

Type Challenges Judge

Problems

Progress

First of Array

提出詳細

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

提出日時	2022-10-06 14:14:43
問題	First of Array
ユーザー	yotarotsukada
ステータス	Accepted

テストケース

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' }>,
]