feat: add isNothing()

[unional]

fix#988

I can add tests, but want to know which file should I add it to. Type guard is TS stuff so maybe I create a new file __tests__/common.ts?

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[unional]

Another thing is, should the Nothing type be exposed?

Right now I have to access it through typeof nothing

[mweststrate]

Sorry for the late response! Feature looks good time, as does the test proposal. Would you mind to add the test file indeed, testing both the type inference and runtime behavior of the utility? Thanks!

[unional]

Would you mind to add the test file indeed, testing both the type inference and runtime behavior of the utility?

Sure, do you mind I add type-plus to the dev dependency so that I can easily test the types?

[unional]

Also, looking at the PR again, it turns out the type is actually not exported. Will need to fix that.

The circular dependency is also an issue. Maybe I can create a different PR to fix all circular dependency issue first, as that would lead to many problems.

[mweststrate]

Sure, do you mind I add type-plus to the dev dependency so that I can easily test the types?

We already use spec.ts (see e.g. produce.ts), or using // @ts-expected-error might suffice?

[unional]

I'll check that out. Thx

[mweststrate]

@unional were you able to set up some tests?

[unional]

Hi, yes I just get back to this.

I have tried the spec.ts and // @ts-expected-error and saw how you use it:

// @ts-expect-errorassert(value,_asNothing)// vsisType.equal<false,typeofvalue,Nothing>()

It works either way. Didn't know about @ts-expect-error. Thanks!.

I do found one issue from this PR.
The function isNothing() depends on the Nothing type, but immer implement this mechanism using the a dummy class Nothing.

I looked up the code and found that it is actually needed by one of the public types already:

/** Converts `nothing` into `undefined` */typeFromNothing<T>=TextendsNothing ? undefined : T/** The inferred return type of `produce` */exporttypeProduced<Base,Return>=Returnextendsvoid
? Base
: ReturnextendsPromise<infer Result>
? Promise<Resultextendsvoid ? Base : FromNothing<Result>>
: FromNothing<Return>

Produced -> FromNothing -> Nothing.

So exposing the type should be needed in the first place and that may be an existing bug.
But testing and proving that could be difficult.

However, exposing this Nothing class is not good because it is not used as a class but a type.
One way to fix this is replace the mechanism with a branded type, e.g. https://github.com/unional/type-plus/blob/main/ts/nominal-types/Brand.ts#L11

But that will need some investigation.

[unional]

Updated branch and code. Added directly to immer.ts as it is exporting NOTHING as nothing there.

[coveralls]

Pull Request Test Coverage Report for Build 20424962423

Details

• 1 of 3(33.33%) changed or added relevant lines in 1 file are covered.
• No unchanged relevant lines lost coverage.
• Overall coverage decreased (-0.02%) to 42.86%

---

Changes Missing Coverage	Covered Lines	Changed/Added Lines	%
src/immer.ts	1	3	33.33%

Totals
Change from base Build 20394930238:	-0.02%
Covered Lines:	1679
Relevant Lines:	4774

---

💛 - Coveralls

[unional]

Want to share that since v10 of using symbol, it has a drawback of not able to distribute the union type with Promise.
i.e.:

typeUpdater=(s: any)=>number|typeofNOTHING|Promise<number|typeofNOTHING>// error hereconstu: Updater=async()=>NOTHING

Type 'Promise<symbol>' is not assignable to type 'number | unique symbol | Promise<number | unique symbol>'.
Type 'Promise<symbol>' is not assignable to type 'Promise<number | unique symbol>'.
Type 'symbol' is not assignable to type 'number | unique symbol'.ts(2322)

An explicit type declaration is needed:

constu: Updater=async(): Promise<typeofNOTHING>=>NOTHING

I believe this is a limitation on TypeScript.