1097. Isunion

<题目描述>

::: playground#ts 1097. Isunion

@file index.ts

// ============= Test Cases =============
import type { Equal, Expect } from '@type-challenges/utils'

type cases = [
  Expect<Equal<IsUnion<string>, false>>,
  Expect<Equal<IsUnion<string | number>, true>>,
  Expect<Equal<IsUnion<'a' | 'b' | 'c' | 'd'>, true>>,
  Expect<Equal<IsUnion<undefined | null | void | ''>, true>>,
  Expect<Equal<IsUnion<{ a: string } | { a: number }>, true>>,
  Expect<Equal<IsUnion<{ a: string | number }>, false>>,
  Expect<Equal<IsUnion<[string | number]>, false>>,
  // Cases where T resolves to a non-union type.
  Expect<Equal<IsUnion<string | never>, false>>,
  Expect<Equal<IsUnion<string | unknown>, false>>,
  Expect<Equal<IsUnion<string | any>, false>>,
  Expect<Equal<IsUnion<string | 'a'>, false>>,
  Expect<Equal<IsUnion<never>, false>>,
]

// ============= Your Code Here =============
type UnionToInterSection<T> = (T extends any ? (arg: T) => any : never) extends (arg : infer R) => any ? R : never
type IsUnion<T> = [T] extends [UnionToInterSection<T>] ? false : true

:::

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