type-samurai/src/includes.d.ts

Advanced utility types for Typescript

import { IsEmptyArray } from "./array";
import { IfEqual } from "./equal";
import { Shift } from "./shift";

/**
 * Returns a boolean whether the second argument is in the first array argument
 * @example
 * ```ts
 * // true
 * type Case1 = Includes<[1, 2, 3], 1>
 * // false
 * type Case1 = Includes<[1, 2, 3], 4>
 * ```
 */
export type Includes<
  T extends readonly unknown[],
  Pivot
> = IsEmptyArray<T> extends true
  ? false
  : Shift<T, { includeRemoved: true }> extends [
      infer Rest extends readonly unknown[],
      infer Removed
    ]
  ? IfEqual<Pivot, Removed, true, Includes<Rest, Pivot>>
  : false;