Optional Values of Type about type-fest

[sindresorhus]

Since this seems to be a valid use-case, how would we feel about PRing OptionalKeys in separately to #56?

Sure, but if we add OptionalKeys, we should probably also add RequiredKeys.

[sindresorhus]

What problem are you trying to solve? Why do you need to get the optionals?

[WORMSS]

Specifying what the optional defaults should be.

[resynth1943]

@WORMSS You're probably looking for OptionalKeys, as discussed here #56 (comment)

@sindresorhus Since this seems to be a valid use-case, how would we feel about PRing OptionalKeys in separately to #56?

[resynth1943]

Also, as for specifying the defaults, if they're all the same, you can do this.

type AWithDefaults = Omit<A, OptionalKeys<A>> & Record<OptionalKeys<A>, Default>;

[dcousens]

+1 for OptionalKeys and RequiredKeys.
I didn't mind the learning exercise before I found this ticket, but it would have been nice to have it in the library!

My solution was

type OptionalKeys <T> = {
  [K in keyof T]: Pick<Partial<T>, K> extends Pick<T, K> ? K : never
}[keyof T]

Happy to PR, but maybe @resynth1943's answer from #56: {} extends Pick<T, K> ? K : never is nicer.