Includes

introduction#

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`

ts
type isPillarMen = Includes<['Kars', 'Esidisi', 'Wamuu', 'Santana'], 'Dio'>; // expected to be `false`

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start point#

ts
/* _____________ Your Code Here _____________ */
type Includes<T extends readonly any[], U> = any;
 
/* _____________ Test Cases _____________ */
type cases = [
  Expect<Equal<Includes<['Kars', 'Esidisi', 'Wamuu', 'Santana'], 'Kars'>, true>>,
Type 'false' does not satisfy the constraint 'true'.2344Type 'false' does not satisfy the constraint 'true'.  Expect<Equal<Includes<['Kars', 'Esidisi', 'Wamuu', 'Santana'], 'Dio'>, false>>,
Type 'false' does not satisfy the constraint 'true'.2344Type 'false' does not satisfy the constraint 'true'.  Expect<Equal<Includes<[1, 2, 3, 5, 6, 7], 7>, true>>,
Type 'false' does not satisfy the constraint 'true'.2344Type 'false' does not satisfy the constraint 'true'.  Expect<Equal<Includes<[1, 2, 3, 5, 6, 7], 4>, false>>,
Type 'false' does not satisfy the constraint 'true'.2344Type 'false' does not satisfy the constraint 'true'.  Expect<Equal<Includes<[1, 2, 3], 2>, true>>,
Type 'false' does not satisfy the constraint 'true'.2344Type 'false' does not satisfy the constraint 'true'.  Expect<Equal<Includes<[1, 2, 3], 1>, true>>,
Type 'false' does not satisfy the constraint 'true'.2344Type 'false' does not satisfy the constraint 'true'.  Expect<Equal<Includes<[{}], { a: 'A' }>, false>>,
Type 'false' does not satisfy the constraint 'true'.2344Type 'false' does not satisfy the constraint 'true'.  Expect<Equal<Includes<[boolean, 2, 3, 5, 6, 7], false>, false>>,
Type 'false' does not satisfy the constraint 'true'.2344Type 'false' does not satisfy the constraint 'true'.  Expect<Equal<Includes<[true, 2, 3, 5, 6, 7], boolean>, false>>,
Type 'false' does not satisfy the constraint 'true'.2344Type 'false' does not satisfy the constraint 'true'.  Expect<Equal<Includes<[false, 2, 3, 5, 6, 7], false>, true>>,
Type 'false' does not satisfy the constraint 'true'.2344Type 'false' does not satisfy the constraint 'true'.  Expect<Equal<Includes<[{ a: 'A' }], { readonly a: 'A' }>, false>>,
Type 'false' does not satisfy the constraint 'true'.2344Type 'false' does not satisfy the constraint 'true'.  Expect<Equal<Includes<[{ readonly a: 'A' }], { a: 'A' }>, false>>
Type 'false' does not satisfy the constraint 'true'.2344Type 'false' does not satisfy the constraint 'true'.];Try

ts
/* _____________ Your Code Here _____________ */
type Includes<T extends readonly any[], U> = any;
 
/* _____________ Test Cases _____________ */
type cases = [
  Expect<Equal<Includes<['Kars', 'Esidisi', 'Wamuu', 'Santana'], 'Kars'>, true>>,
Type 'false' does not satisfy the constraint 'true'.2344Type 'false' does not satisfy the constraint 'true'.  Expect<Equal<Includes<['Kars', 'Esidisi', 'Wamuu', 'Santana'], 'Dio'>, false>>,
Type 'false' does not satisfy the constraint 'true'.2344Type 'false' does not satisfy the constraint 'true'.  Expect<Equal<Includes<[1, 2, 3, 5, 6, 7], 7>, true>>,
Type 'false' does not satisfy the constraint 'true'.2344Type 'false' does not satisfy the constraint 'true'.  Expect<Equal<Includes<[1, 2, 3, 5, 6, 7], 4>, false>>,
Type 'false' does not satisfy the constraint 'true'.2344Type 'false' does not satisfy the constraint 'true'.  Expect<Equal<Includes<[1, 2, 3], 2>, true>>,
Type 'false' does not satisfy the constraint 'true'.2344Type 'false' does not satisfy the constraint 'true'.  Expect<Equal<Includes<[1, 2, 3], 1>, true>>,
Type 'false' does not satisfy the constraint 'true'.2344Type 'false' does not satisfy the constraint 'true'.  Expect<Equal<Includes<[{}], { a: 'A' }>, false>>,
Type 'false' does not satisfy the constraint 'true'.2344Type 'false' does not satisfy the constraint 'true'.  Expect<Equal<Includes<[boolean, 2, 3, 5, 6, 7], false>, false>>,
Type 'false' does not satisfy the constraint 'true'.2344Type 'false' does not satisfy the constraint 'true'.  Expect<Equal<Includes<[true, 2, 3, 5, 6, 7], boolean>, false>>,
Type 'false' does not satisfy the constraint 'true'.2344Type 'false' does not satisfy the constraint 'true'.  Expect<Equal<Includes<[false, 2, 3, 5, 6, 7], false>, true>>,
Type 'false' does not satisfy the constraint 'true'.2344Type 'false' does not satisfy the constraint 'true'.  Expect<Equal<Includes<[{ a: 'A' }], { readonly a: 'A' }>, false>>,
Type 'false' does not satisfy the constraint 'true'.2344Type 'false' does not satisfy the constraint 'true'.  Expect<Equal<Includes<[{ readonly a: 'A' }], { a: 'A' }>, false>>
Type 'false' does not satisfy the constraint 'true'.2344Type 'false' does not satisfy the constraint 'true'.];Try

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my solution#

Spoiler warning // Click to reveal answer

ts
type isEqual<X, Y> = (<T>() => T extends X ? 1 : 2) extends <T>() => T extends Y ? 1 : 2
  ? true
  : false;
type Includes<T, U> = T extends [infer F, ...infer Rest]
  ? isEqual<F, U> extends true
    ? true
    : Rest extends []
    ? false
    : Includes<Rest, U>
  : false;Try

ts
type isEqual<X, Y> = (<T>() => T extends X ? 1 : 2) extends <T>() => T extends Y ? 1 : 2
  ? true
  : false;
type Includes<T, U> = T extends [infer F, ...infer Rest]
  ? isEqual<F, U> extends true
    ? true
    : Rest extends []
    ? false
    : Includes<Rest, U>
  : false;Try

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