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MyReadonly<T>

EasyP1Coding

Implement the built-in Readonly<T> generic without using it.

MyReadonly<T> builds a type with every property of T marked readonly, so assigning to any property is a compile error.

Tests your type must pass

interface Todo1 {
  title: string
  description: string
  completed: boolean
  meta: {
    author: string
  }
}

declare const todo: MyReadonly<Todo1>

type cases = [
  Expect<Equal<MyReadonly<Todo1>, Readonly<Todo1>>>,
  Expect<Equal<keyof MyReadonly<Todo1>, 'title' | 'description' | 'completed' | 'meta'>>,
]

// @ts-expect-error title is readonly
todo.title = 'Hello'
// @ts-expect-error description is readonly
todo.description = 'barFoo'
// @ts-expect-error completed is readonly
todo.completed = true

Hints

TypeScript
Run and Submit type-check your solution against the tests.