2757-partialbykeys.ts

/**
 * 2757 - PartialByKeys
 *
 * Implement a generic `PartialByKeys<T, K>` which takes two type argument `T` and `K`.
 *
 * `K` specify the set of properties of `T` that should set to be optional. When `K` is not provided, it should make all properties optional just like the normal `Partial<T>`.
 *
 * For example
 *
 * ```typescript
 * interface User {
 *   name: string
 *   age: number
 *   address: string
 * }
 *
 * type UserPartialName = PartialByKeys<User, 'name'> // { name?:string; age:number; address:string }
 * ```
 */

/* _____________ Your Code Here _____________ */

type PartialByKeysV1<T extends object, K extends keyof T = keyof T> =
  (Omit<T, K> & { [Key in K]?: T[Key] }) extends infer Intersection
    ? { [Key in keyof Intersection]: Intersection[Key] }
    : never;

type PartialByKeys<T extends object, K extends keyof T = keyof T> =
  Omit<(Omit<T, K> & { [Key in K]?: T[Key] }), never>

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

interface User {
  name: string
  age: number
  address: string
}

interface UserPartialName {
  name?: string
  age: number
  address: string
}

interface UserPartialNameAndAge {
  name?: string
  age?: number
  address: string
}

type cases = [
  Expect<Equal<PartialByKeys<User, 'name'>, UserPartialName>>,
  Expect<Equal<PartialByKeys<User, 'name' | 'age'>, UserPartialNameAndAge>>,
  Expect<Equal<PartialByKeys<User>, Partial<User>>>,
  // @ts-expect-error
  Expect<Equal<PartialByKeys<User, 'name' | 'unknown'>, UserPartialName>>,
]