03312-easy-parameters.ts

/*
  3312 - Parameters
  -------
  by midorizemi (@midorizemi) #easy #infer #tuple #built-in
  
  ### Question
  
  Implement the built-in Parameters<T> generic without using it.
  
  > View on GitHub: https://tsch.js.org/3312
*/

/* _____________ Your Code Here _____________ */

type MyParameters<T extends (...args: any[]) => any> = T extends (...args: infer A) => any ? A : never;

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

const foo = (arg1: string, arg2: number): void => {};
const bar = (arg1: boolean, arg2: { a: "A" }): void => {};
const baz = (): void => {};

type cases = [
  Expect<Equal<MyParameters<typeof foo>, [string, number]>>,
  Expect<Equal<MyParameters<typeof bar>, [boolean, { a: "A" }]>>,
  Expect<Equal<MyParameters<typeof baz>, []>>
];

/* _____________ Further Steps _____________ */
/*
  > Share your solutions: https://tsch.js.org/3312/answer
  > View solutions: https://tsch.js.org/3312/solutions
  > More Challenges: https://tsch.js.org
*/