Permutation

Challenge

Implement permutation type that transforms union types into the array that includes permutations of unions.

type perm = Permutation<"A" | "B" | "C">; // ['A', 'B', 'C'] | ['A', 'C', 'B'] | ['B', 'A', 'C'] | ['B', 'C', 'A'] | ['C', 'A', 'B'] | ['C', 'B', 'A']

Solution

Um das distribute Verhalten zu verhindern, packt man die Typen in einen Array:

type ToArrayNonDist<Type> = [Type] extends [any] ? Type[] : never;

type Permutation<T, U = T> = [T] extends [never]
  ? []
  : T extends U
  ? [T, ...Permutation<Exclude<U, T>>]
  : never;

References