The instructions for this challenge are:

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

Constructs a type with all properties of T set to readonly, meaning the properties of the constructed type cannot be reassigned.

Example code that should compile correctly is provided:

interface Todo {
    title: string
    description: string
}

const todo: MyReadonly<Todo> = {
    title: "Hey",
    description: "foobar"
}

The initial type is type MyReadonly<T> = any.

We’re back in the realm of the easy challenges. This one is particularly easy thanks to the built-in typescript mapping modifiers. We should follow the pattern of the earlier challenges where we used a mapped type but apply the mapping modifier to make it readonly. We can do this by adding +readonly in front of the mapped type statement. The rest of the statement is straightforward.

This results in an eventual solution of:

type MyReadonly<T> = { +readonly [P in keyof T]: T[P] }