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First of Array

提出詳細

type First<T extends any[]> = T extends [infer Head, ...any[]] ? Head : never
提出日時2024-10-28 01:59:34
問題First of Array
ユーザーbalckowl
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' }>,
]