type-challenges-solutions/en/medium-readonly-2 about type-challenges-solutions HOT 8 OPEN

Very well explained! I did not know that we can assign default value to a type.
I was trying to create a ternary condition (and I failed), instead of using extend via intersect.

from type-challenges-solutions.

@ghaiklor solution fails all checks on TS versions >= 4.5.5 at the time of writing. I didn't see a obvious reason in the v4.5 release blog. From what I can tell intersections in v4.5+ don't overwrite the optionality(?) or readonly specifiers when that key already exists in the first type.

Something like this TS playground seems necessary now.

from type-challenges-solutions.

@dvlden thanks! I'm trying to explain as much as I can, but sure, there are some explanations that can be improved (I'm referring to variadic tuple types and Pop, Last).

from type-challenges-solutions.

Please double check that this solution passes the cases.

from type-challenges-solutions.

@michaeljsalo cases can be added later after I made the explanation. You can leave the updated solution in the comments if you wish.

from type-challenges-solutions.

@RileyMShea @martisss has updated the solution with a comment in regard to your issue. Looks like an explanation for the bug. The post is already updated and published.

from type-challenges-solutions.

Great explanation, Idk "= keyof T" makes it assign all the keys of T in case not provided. Thanks

from type-challenges-solutions.

My solution that works with the updated tests.

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

from type-challenges-solutions.