00008-medium-readonly-2.ts

/*
  8 - Readonly 2
  -------
  by Anthony Fu (@antfu) #medium #readonly #object-keys
  
  ### Question
  
  Implement a generic `MyReadonly2<T, K>` which takes two type argument `T` and `K`.
  
  `K` specify the set of properties of `T` that should set to Readonly. When `K` is not provided, it should make all properties readonly just like the normal `Readonly<T>`.
  
  For example
  
  ```ts
  interface Todo {
    title: string
    description: string
    completed: boolean
  }
  
  const todo: MyReadonly2<Todo, 'title' | 'description'> = {
    title: "Hey",
    description: "foobar",
    completed: false,
  }
  
  todo.title = "Hello" // Error: cannot reassign a readonly property
  todo.description = "barFoo" // Error: cannot reassign a readonly property
  todo.completed = true // OK
  ```
  
  > View on GitHub: https://tsch.js.org/8
*/

/* _____________ Your Code Here _____________ */

type MyReadonly2<T, K extends keyof T = keyof T> = {
  readonly [k in K]: T[k];
} & Omit<T, K>;

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

type cases = [
  Expect<Alike<MyReadonly2<Todo1>, Readonly<Todo1>>>,
  Expect<Alike<MyReadonly2<Todo1, "title" | "description">, Expected>>,
  Expect<Alike<MyReadonly2<Todo2, "title" | "description">, Expected>>
];

interface Todo1 {
  title: string;
  description?: string;
  completed: boolean;
}
 
interface Todo2 {
  readonly title: string;
  description?: string;
  completed: boolean;
}

interface Expected {
  readonly title: string;
  readonly description?: string;
  completed: boolean;
}

/* _____________ Further Steps _____________ */
/*
  > Share your solutions: https://tsch.js.org/8/answer
  > View solutions: https://tsch.js.org/8/solutions
  > More Challenges: https://tsch.js.org
*/