How to map Union type to Tuple of the same length?

Question

I want to turn this:

type UnionType = Variant1 | Variant2

into this:

type ResultingType = [UnionType, UnionType]

If the union has 3 member types, the tuple should have 3 elements.

Answer 1

Do you mean "permutation"?

type UnionType = 'a' | 'b'

type UnionPermutation<U, K = U> =
  [U] extends [never]
  ? []
  : U extends any
  ? [U, ...UnionPermutation<Exclude<K, U>>]
  : never

// ['a', 'b'] | ['b', 'a']
type test = UnionPermutation<UnionType>

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