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21220-medium-permutations-of-tuple
Medium
union
tuple
conditional type
recursion

Challenge Source: type-challenges/21220-medium-permutations-of-tuple

Given a generic tuple type T extends unknown[], write a type which produces all permutations of T as a union.

For example:

PermutationsOfTuple<[1, number, unknown]>
// Should return:
// | [1, number, unknown]
// | [1, unknown, number]
// | [number, 1, unknown]
// | [unknown, 1, number]
// | [number, unknown, 1]
// | [unknown, number ,1]

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Test cases from: type-challenges/21220-medium-permutations-of-tuple/test-cases.ts
import type { Equal, Expect, ExpectFalse } from '@type-challenges/utils'

type cases = [
  Expect<Equal<PermutationsOfTuple<[]>, []>>,
  Expect<Equal<PermutationsOfTuple<[any]>, [any]>>,
  Expect<Equal<PermutationsOfTuple<[any, unknown]>, [any, unknown] | [unknown, any]>>,
  Expect<Equal<
    PermutationsOfTuple<[any, unknown, never]>,
    | [any, unknown, never]
    | [unknown, any, never]
    | [unknown, never, any]
    | [any, never, unknown]
    | [never, any, unknown]
    | [never, unknown, any]
  >>,
  Expect<Equal<
    PermutationsOfTuple<[1, number, unknown]>,
    | [1, number, unknown]
    | [1, unknown, number]
    | [number, 1, unknown]
    | [unknown, 1, number]
    | [number, unknown, 1]
    | [unknown, number, 1]
  >>,
  ExpectFalse<Equal<PermutationsOfTuple<[ 1, number, unknown ]>, [unknown]>>,
]