Proposal: DeepPartial about type-fest

[fabiospampinato]

I'm not sure what's about that patch function, but here there's an implementation of DeepPartial:

type DeepPartial<T> = {
  [P in keyof T]?: T[P] extends Array<infer U>
    ? Array<DeepPartial<U>>
    : T[P] extends ReadonlyArray<infer U>
      ? ReadonlyArray<DeepPartial<U>>
      : DeepPartial<T[P]>
};

[sindresorhus]

Alright. I'm gonna accept this. It seems it's quite common: https://github.com/search?l=TypeScript&q=DeepPartial&type=Code

It should be named PartialDeep since we already have ReadonlyDeep.

For anyone that wants to tackle this, please read guide for adding a type and also see how ReadonlyDeep was added: 22c3a99 (Note the extensive docs and comments).

[uyeong]

patch is just an example. I changed the name to fn. thanks for letting me know.

I actually opened this issue because I think type-fest should include the DeepPartial type.

[dylang]

@fabiospampinato Does that handle promises?

Seems like it should have

T[P] extends Promise<infer U>
 ? Promise<Partial<U>>
 : ...

[fabiospampinato]

@dylang Yeah I don't think it handles promises that way. I'm not sure if you'd necessarily want that though 🤔

[dylang]

@fabiospampinato Thanks for the feedback. It was useful for a deep partial ReturnValue<T> wrapper when mocking functions for our tests, but makes sense that it's not always what developers would expect.

[Psidium]

Does DeepPartial support arrays?

interface Inter {
	prop: string;
	children: string[];
}

turns into the equivalent of

interface Inter {
	prop?: string;
	children?: Array<string | undefined>;
}

[sindresorhus]

@uyeong Do you have any real-world uses of it that you can link to? It seems useful in theory, but I haven't encountered a situation where I would need it personally.

[fabiospampinato]

@sindresorhus I think it could be useful when merging a default settings object with another object, the second object would be a deep partial of the default object.

[sindresorhus]

@fabiospampinato Do you have any actual code using that pattern? I'm asking because it's easy to suggest things that look useful, but I'm trying very hard to only add things to type-fest that people would actually use, or are already using in production.

[fabiospampinato]

@sindresorhus Yes, I do that all the time, here there some examples: 1, 2, 3, 4.

Often though I try to keep the options object flat, in those cases I don't really need DeepPartial.

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