00012-medium-chainable-options.ts

// ============= Test Cases =============
import type { Alike, Expect } from "./test-utils";

declare const a: Chainable;

const result1 = a
  .option("foo", 123)
  .option("bar", { value: "Hello World" })
  .option("name", "type-challenges")
  .get();

const result2 = a
  .option("name", "another name")
  // @ts-expect-error
  .option("name", "last name")
  .get();

const result3 = a
  .option("name", "another name")
  // @ts-expect-error
  .option("name", 123)
  .get();

type cases = [
  Expect<Alike<typeof result1, Expected1>>,
  Expect<Alike<typeof result2, Expected2>>,
  Expect<Alike<typeof result3, Expected3>>
];

type Expected1 = {
  foo: number;
  bar: {
    value: string;
  };
  name: string;
};

type Expected2 = {
  name: string;
};

type Expected3 = {
  name: number;
};

// ============= Your Code Here =============
type Chainable<T extends object = {}> = {
  option<K extends string, V>(
    key: K extends keyof T ? never : K,
    value: V
  ): Chainable<Omit<T, K> & { [P in K]: V }>;
  get(): { [P in keyof T]: T[P] };
};