[Typescript] 72. Medium - IndexOf

Implement the type version of Array.indexOf, indexOf<T, U> takes an Array T, any U and returns the index of the first U in Array T.

type Res = IndexOf<[1, 2, 3], 2>; // expected to be 1
type Res1 = IndexOf<[2,6, 3,8,4,1,7, 3,9], 3>; // expected to be 2
type Res2 = IndexOf<[0, 0, 0], 2>; // expected to be -1

 

/* _____________ Your Code Here _____________ */
export type Equal<T, U> = 
  (<P>(x: P) => P extends T ? 1: 2) extends 
  (<P>(x: P) => P extends U ? 1: 2) 
    ? true
    : false;
export type IndexOf<T extends any[], U, ACC extends unknown[] = []> = T extends [infer F, ...infer RT]
  ? Equal<F, U> extends true
    ? ACC['length']
    : IndexOf<RT, U, [...ACC, unknown]>
  : -1;


/* _____________ Test Cases _____________ */
import type { Expect } from '@type-challenges/utils'

type cases = [
  Expect<Equal<IndexOf<[1, 2, 3], 2>, 1>>,
  Expect<Equal<IndexOf<[2, 6, 3, 8, 4, 1, 7, 3, 9], 3>, 2>>,
  Expect<Equal<IndexOf<[0, 0, 0], 2>, -1>>,
  Expect<Equal<IndexOf<[string, 1, number, 'a'], number>, 2>>,
  Expect<Equal<IndexOf<[string, 1, number, 'a', any], any>, 4>>,
  Expect<Equal<IndexOf<[string, 'a'], 'a'>, 1>>,
  Expect<Equal<IndexOf<[any, 1], 1>, 1>>,
]