00898-easy-includes.ts

/*
  898 - Includes
  -------
  by null (@kynefuk) #easy #array
  
  ### Question
  
  Implement the JavaScript `Array.includes` function in the type system. A type takes the two arguments. The output should be a boolean `true` or `false`.
  
  For example
  
  ```ts
  type isPillarMen = Includes<['Kars', 'Esidisi', 'Wamuu', 'Santana'], 'Dio'> // expected to be `false`
  ```
  
  > View on GitHub: https://tsch.js.org/898
*/

/* _____________ Your Code Here _____________ */

type MyEqual<X, Y> =
    (<T>() => T extends X ? 1 : 2) extends
    <T>() => T extends Y ? 1 : 2
  ? true
  : false;
   
type Includes<T extends readonly unknown[], U> = T extends [infer A, ...infer R]
  ? MyEqual<A, U> extends true
    ? true
    : Includes<R, U>
  : false;

/* _____________ Test Cases _____________ */ 
import type { Equal, Expect } from "@type-challenges/utils";

type cases = [
  Expect<
    Equal<Includes<["Kars", "Esidisi", "Wamuu", "Santana"], "Kars">, true>
  >,
  Expect<
    Equal<Includes<["Kars", "Esidisi", "Wamuu", "Santana"], "Dio">, false>
  >,
  Expect<Equal<Includes<[1, 2, 3, 5, 6, 7], 7>, true>>,
  Expect<Equal<Includes<[1, 2, 3, 5, 6, 7], 4>, false>>,
  Expect<Equal<Includes<[1, 2, 3], 2>, true>>,
  Expect<Equal<Includes<[1, 2, 3], 1>, true>>,
  Expect<Equal<Includes<[{}], { a: "A" }>, false>>,
  Expect<Equal<Includes<[boolean, 2, 3, 5, 6, 7], false>, false>>,
  Expect<Equal<Includes<[true, 2, 3, 5, 6, 7], boolean>, false>>,
  Expect<Equal<Includes<[false, 2, 3, 5, 6, 7], false>, true>>,
  Expect<Equal<Includes<[{ a: "A" }], { readonly a: "A" }>, false>>,
  Expect<Equal<Includes<[{ readonly a: "A" }], { a: "A" }>, false>>,
  Expect<Equal<Includes<[1], 1 | 2>, false>>,
  Expect<Equal<Includes<[1 | 2], 1>, false>>,
  Expect<Equal<Includes<[null], undefined>, false>>,
  Expect<Equal<Includes<[undefined], null>, false>>
];

/* _____________ Further Steps _____________ */
/*
  > Share your solutions: https://tsch.js.org/898/answer
  > View solutions: https://tsch.js.org/898/solutions
  > More Challenges: https://tsch.js.org
*/