02757-medium-partialbykeys.ts

// ============= Test Cases =============
import type { Equal, Expect } from "./test-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>>
];

// ============= Your Code Here =============
type FlatObject<T> = {
  [P in keyof T]: T[P];
};
type R = PartialByKeys<User, "name">;
type PartialByKeys<T, K extends keyof T = keyof T> = FlatObject<
  Omit<T, K> & {
    [P in K]?: T[P];
  }
>;