Refer: Easy - If

Describe

Implement a utils If which accepts condition C, a truthy return type T, and a falsy return type F. C is expected to be either true or false while T and F can be any type.

For example:

code snippetCopytypescript
type A = If<true, 'a', 'b'> // expected to be 'a'
type B = If<false, 'a', 'b'> // expected to be 'b'

Test Cases

code snippetCopytypescript
import { Equal, Expect } from '@type-challenges/utils'

type cases = [Expect<Equal<If<true, 'a', 'b'>, 'a'>>, Expect<Equal<If<false, 'a', 2>, 2>>]

// @ts-expect-error
type error = If<null, 'a', 'b'>

Solution

code snippetCopytypescript
type If<C, T, F> = C extends true ? T : F