00730-hard-union-to-tuple.ts

// ============= Test Cases =============
import type { Equal, Expect } from './test-utils'

type ExtractValuesOfTuple<T extends any[]> = T[keyof T & number]

type cases = [
  Expect<Equal<UnionToTuple<'a' | 'b'>['length'], 2>>,
  Expect<Equal<ExtractValuesOfTuple<UnionToTuple<'a' | 'b'>>, 'a' | 'b'>>,
  Expect<Equal<ExtractValuesOfTuple<UnionToTuple<'a'>>, 'a'>>,
  Expect<Equal<ExtractValuesOfTuple<UnionToTuple<any>>, any>>,
  Expect<
    Equal<ExtractValuesOfTuple<UnionToTuple<undefined | void | 1>>, void | 1>
  >,
  Expect<Equal<ExtractValuesOfTuple<UnionToTuple<any | 1>>, any | 1>>,
  Expect<Equal<ExtractValuesOfTuple<UnionToTuple<any | 1>>, any>>,
  Expect<
    Equal<
      ExtractValuesOfTuple<UnionToTuple<'d' | 'f' | 1 | never>>,
      'f' | 'd' | 1
    >
  >,
  Expect<
    Equal<ExtractValuesOfTuple<UnionToTuple<[{ a: 1 }] | 1>>, [{ a: 1 }] | 1>
  >,
  Expect<Equal<ExtractValuesOfTuple<UnionToTuple<never>>, never>>,
  Expect<
    Equal<
      ExtractValuesOfTuple<
        UnionToTuple<'a' | 'b' | 'c' | 1 | 2 | 'd' | 'e' | 'f' | 'g'>
      >,
      'f' | 'e' | 1 | 2 | 'g' | 'c' | 'd' | 'a' | 'b'
    >
  >
]

// ============= Your Code Here =============
type UnionToIntersection<T> = (
  T extends unknown ? (arg: T) => unknown : never
) extends (arg: infer R) => unknown
  ? R
  : never

type LastInUnion<T> = UnionToIntersection<
  T extends unknown ? (arg: T) => unknown : never
> extends (arg: infer R) => unknown
  ? R
  : never

type UnionToTuple<T, U = LastInUnion<T>> = [T] extends [never]
  ? []
  : [...UnionToTuple<Exclude<T, U>>, U]

type Test = UnionToTuple<'a' | 'b'>