28143-optionalundefined.ts

/**
 * 28143 - OptionalUndefined
 *
 * Implement the util type `OptionalUndefined<T, Props>` that turns all the properties of `T` that can be `undefined`, into optional properties. In addition, a second -optional- generic `Props` can be passed to restrict the properties that can be altered.
 * 
 * ```ts
 * OptionalUndefined<{ value: string | undefined, description: string }>
 * // { value?: string | undefined; description: string }
 * 
 * OptionalUndefined<{ value: string | undefined, description: string | undefined, author: string | undefined }, 'description' | 'author'>
 * // { value: string | undefined; description?: string | undefined, author?: string | undefined }
 * ```
 *
 *
 */

/* _____________ Your Code Here _____________ */

type OptionalUndefined<T, Props extends keyof T = keyof T> = {
  [
    Key in keyof T as Key extends Props
      ? undefined extends T[Key]
        ? Key
        : never
      : never
  ]?: T[Key]
} extends infer OptionalObj extends object
  ? Omit<Omit<T, keyof OptionalObj> & OptionalObj, never>
  : never

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

type cases = [
  Expect<Equal<OptionalUndefined<{ value: string | undefined }, 'value'>, { value?: string | undefined }>>,
  Expect<Equal<OptionalUndefined<{ value: string, desc: string }, 'value'>, { value: string, desc: string }>>,
  Expect<Equal<OptionalUndefined<{ value: string | undefined, desc: string }, 'value'>, { value?: string, desc: string }>>,
  Expect<Equal<OptionalUndefined<{ value: string | undefined, desc: string | undefined }, 'value'>, { value?: string | undefined, desc: string | undefined }>>,
  Expect<Equal<OptionalUndefined<{ value: string | undefined, desc: string }, 'value' | 'desc'>, { value?: string, desc: string }>>,
  Expect<Equal<OptionalUndefined<{ value: string | undefined, desc: string | undefined }>, { value?: string, desc?: string }>>,
  Expect<Equal<OptionalUndefined<{ value?: string }, 'value'>, { value?: string }>>,
  Expect<Equal<OptionalUndefined<{ value?: string }>, { value?: string }>>,
]