Conditionally readonly object type in TypeScript

We already solved the challenge with readonly (see Readonly under the hood). Today we want to apply readonly modifier only to the specified keys (Readonly 2).

Combination of 2 challenges

Again, as for previous challenge Omit under the hood, we have a combination of challenges that we already did:

1. We already learnt how to apply readonly modifier to the keys:

2. We also need to pick specified keys:

3. And we need to have excluded keys without readonly modifier:

The algorithm is:

1. Pick keys we want to make readonly
2. Make picked keys readonly
3. Add the rest (or excluded) keys without changes

If you check the current solution, you see that you cannot use Pick and Omit if K is not part of keyof T. Let's fix that:

But still we expect to have all keys by default if we don't specify K. So the final solution is:

As usual, the solution is in Playground 💻

Have a nice weekend 🌤