[Typescript] 100. Hard IsAny

Sometimes it's useful to detect if you have a value with any type. This is especially helpful while working with third-party Typescript modules, which can export any values in the module API. It's also good to know about any when you're suppressing implicitAny checks.

So, let's write a utility type IsAny<T>, which takes input type T. If T is any, return true, otherwise, return false.

type Equal<T, U> = 
  (<P>(x: P) => P extends T ? 1: 2) extends
  (<P>(x: P) => P extends U ? 1: 2 )
    ? true: false
type IsAny<T> = Equal<any, T>

import type { Expect } from '@type-challenges/utils'

type cases = [
  Expect<Equal<IsAny<any>, true>>,

  Expect<Equal<IsAny<undefined>, false>>,
  Expect<Equal<IsAny<unknown>, false>>,
  Expect<Equal<IsAny<never>, false>>,
  Expect<Equal<IsAny<string>, false>>,
]