Implement a generic First<T> that takes an Array T and returns it's first element's type.
type arr1 = ['a', 'b', 'c']
type arr2 = [3, 2, 1]
type head1 = First<arr1> // expected to be 'a'
type head2 = First<arr2> // expected to be 3
/* _____________ Your Code Here _____________ */
type First<T extends any[]> = T extends [infer F, ...(infer RT)] ? F: never
/* _____________ 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' }>,
]标签：Typescript,_____________,expect,Challenges,Expect,Array,type,First From： https://www.cnblogs.com/Answer1215/p/16648387.html