Add ActionCreator#match method for single-argument type guard

[AlexanderOtavka]

This is invaluable when using redux-observable since RxJS is written in typescript and has super solid type checking when the Observable.prototype.filter function gets a valid one-arg type guard.

I am open to changing the function name, I considered createTypeGuard or maybe something else.

[aikoven]

This is cool, thanks!

How about createTypePredicate? Or maybe even just typePredicate, short enough to just inline it

const epic = (actions$: Observable<Action>) =>
  actions$.filter(typePredicate(myAction))

Another idea is to add some method to the action creator itself, like test or match:

const epic = (actions$: Observable<Action>) =>
  actions$.filter(myAction.match)

The latter would be handy in reducers as well as an alternative to isType:

// before
if (isType(action, myAction)) {
  // ...
}

// after
if (myAction.match(action)) {
  // ...
}

What do you think?

[AlexanderOtavka]

I love the match method idea. I hadn't considered that. I'll make the changes.

[NicholasBoll]

👍 @AlexanderOtavka Found this PR looking for a solution for your exact use-case (redux-observable epics)

[aikoven]

Looks good!

Could you please also add a regular test, apart from typings test?

[AlexanderOtavka]

@aikoven Done!

[aikoven]

Thanks! I'll make a release very soon.

[AlexanderOtavka]

You are welcome! I look forward to upgrading my project.

[aikoven]

Just released v2.5.0