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Refer: Easy - Includes
Describe
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
code snippetCopytypescripttype isPillarMen = Includes<['Kars', 'Esidisi', 'Wamuu', 'Santana'], 'Dio'> // expected to be `false`
Test Cases
code snippetCopytypescriptimport { 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>>,
]
Solution
Recursive operation used.
code snippetCopytypescripttype Includes<T extends readonly any[], U> = T extends [infer P, ...infer K]
? Equal<U, P> extends true
? true
: Includes<K, U>
: false