refactor(types/actions): allow type-setting args on ActionCreator

[zanona]

Following up #3541 (comment)

We are allowing Action creators to be typed by declaring their return type as well as the argument type so function calls keep the expected parameter types.

---

name: "allow type-setting args on ActionCreator"
about: improving type declarations on Redux

PR Type

Does this PR add a new feature, or fix a bug?

It sort of adds a new feature, but it's opt-in for the type usage defaulting to the same as the previous behaviour.

Why should this PR be included?

Allow developers to use Redux provided typings in order to implement ActionCreators

Checklist

• Have you added an explanation of what your changes do and why you'd like us to include them?
• Is there an existing issue for this PR?
  • link issue here
• Have the files been linted and formatted?
• Have the docs been updated to match the changes in the PR?
• Have the tests been updated to match the changes in the PR?
• Have you run the tests locally to confirm they pass?

New Features

What new capabilities does this PR add?

What docs changes are needed to explain this?

Bug Fixes

What is the current behavior, and the steps to reproduce the issue?

What is the expected behavior?

How does this PR fix the problem?

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[zanona]

I'm not quite sure if there are tests for TS typings. Please let me know if I can add those in, if necessary. Thanks

[timdorr]

Because it's a rest parameter, this is enforcing a uniform type for every argument. However, it would be possible to support non-uniform types like so:

interface ActionCreator<A, P extends any[] = any[]> {
  (...args: P): A
}

That would allow you to separately type each argument.

The counter-point would be that you must pass an array type, such as ActionCreator<MyAction, string[]>. But I think that's OK to get more fine-grained control there.

[zanona]

The counter-point would be that you must pass an array type, such as ActionCreator<MyAction, string[]>. But I think that's OK to get more fine-grained control there.

👏 That's a very nice idea! I'd guess it could look easier to the eye, having it declared as ActionCreator<MyAction, [string]>?

So we could even have ActionCreator<MyAction, [string, number, string[]]> 😎

Thanks for the review.

[timdorr]

OK, I'm cool with this as-is. Thanks!