ReactiveX/rxdart

stanislasdrg

@stanislasdrg

.startWith() throws a type error in my case.

ReplaySubject is in a Shared Service as such :
ReplaySubject<bool> userProvidesLiquidity = ReplaySubject<bool>(maxSize: 1);

And is called within one of my app's template :
<div *ngIf="(sharedService.userProvidesLiquidity | async)">

I am trying to init with a false value.

If I call .add(false) in OnInit it works, I am just curious whether this is the best way to do it

Frank Pepermans

@frankpepermans

startWith would be your best option

Stream<bool> _userProvidesLiquidityWithStart;
  Stream<bool> get userProvidesLiquidityWithStart =>
      _userProvidesLiquidityWithStart ??=
          userProvidesLiquidity.startWith(false);

stanislasdrg

@stanislasdrg

Unfortunately the same code throws TypeError: Instance of 'minified:iV<bool>': type 'minified:iV<bool>' is not a subtype of type 'minified:oD<bool>' if I initialise my ReplaySubject the following way :
ReplaySubject<bool> userProvidesLiquidity = ReplaySubject<bool>(maxSize: 1).startWith(false);

Ah ok I see

It is a lot more verbose though.

Thanks @frankpepermans

Frank Pepermans

@frankpepermans

The getter is just a workaround so that Angular doesn't go into an update loop. On each update cycle, it will invoke your subject.startWith(), this will yield a new Stream instance on every call, causing overflow. If you store the Stream as a refernce, as with that getter, you can overcome that issue.

Frank Pepermans

@frankpepermans

PS a ReplaySubject with maxSize: 1 is really a BehaviorSubject (which effectively only replays the last value on subscribe)

stanislasdrg

@stanislasdrg

@frankpepermans

The getter is just a workaround so that Angular doesn't go into an update loop. On each update cycle, it will invoke your subject.startWith(), this will yield a new Stream instance on every call, causing overflow. If you store the Stream as a reference, as with that getter, you can overcome that issue.

Is it the startWith() that is responsible for such a behaviour ? I kind of expected the same instance to be returned each time as you have noticed.

Frank Pepermans

@frankpepermans

No, it will yield a new Stream. The original Stream cannot be altered, as it might be consumed by other Subscribers. So startWith does return a new, transformed Stream.

Think List.map, which returns an Iterable, leaving the original List untouched

stanislasdrg

@stanislasdrg

@frankpepermans Thank you very much for the straightforward explanation, appreciate it.

Byron Ferguson

@byronferguson

Evening all

Dusting off a Flutter project and updating pubs

_login
        .map<Request>(_formRequest)
        .doOnData((_) {
          _attemptLogin.sink.add(true);
        })
        .asyncMap(Auth.login)
        .doOnData((_) {
          _attemptLogin.sink.add(false);
        })
        .listen(_userAuth.sink.add);

I can’t seem to get the latest version to execute the asyncMap()

Frank Pepermans

@frankpepermans

Did the first doOnData trigger? Is Auth.login triggered?

Frank Pepermans

@frankpepermans

New dev release: https://pub.dev/packages/rxdart

Wheater

@Wheater

Not much going on in here. I'm a huge fan of RxJS and am moving over to dart to learn Flutter. I'd like to contribute in some way, is the doc a good place to start?

Frank Pepermans

@frankpepermans

We can always use help :) rxdart is pretty stable currently, this channel is pretty quiet, so I assume most folks are just happy using it

Wheater

@Wheater

Glad to pitch in when needed.

Frank Pepermans

@frankpepermans

We're gearing up for a 1.0 release, there's a few issues on git regarding docs, or other ones

Wheater

@Wheater

Awesome, I'll take a look tomorrow or Sunday hopefully.

Frank Pepermans

@frankpepermans

See the current dev release, which is almost 1 to 1 with the master branch

Wheater

@Wheater

What's the process to follow for PRs, fork then PR?

Frank Pepermans

@frankpepermans

Yeah that's fine

Usually @brianegan and myself review before merging, nothing special

I guess our biggest focus is correctly informing newcomers about the differences between dart streams and observables. That remains a point of confusion for many

Wheater

@Wheater

Sounds good. I am a professional dev, but new to open source, so it will take some getting used to.

Frank Pepermans

@frankpepermans

No worries, we're here if you need help :)

Wheater

@Wheater

Awesome! Thanks for the intro. I'll start out with docs to get familiar then move on wherever else needed :)

Wheater

@Wheater

@frankpepermans which branch is the dev branch I should fork from?

Wheater

@Wheater

Submitted a couple of PRs from the getting started issue set. One is a simple link change, the other is the interval operator.

Frank Pepermans

@frankpepermans

Thanks! Master is the main branch

Wheater

@Wheater

@frankpepermans build is passing now for the interval PR

Wheater

@Wheater

@frankpepermans given my failure on the previous PR I submitted, where is a good place to get started with the next?

Frank Pepermans

@frankpepermans

Not sure, we mostly act on incoming issues atm, is there anything from rxjs that you currently miss?

Wheater

@Wheater

Nothing that I can tell of so far. Y'all have done a great job.

Wheater

@Wheater

I will find another issue that looks interesting and work on it. I was curious about the combineLatest operator that was mentioned in: ReactiveX/rxdart#388

If you think there is value in taking a look at that, I will work on it. It does seem nice to be able to chain combineLatest instead of using the static operators.

Frank Pepermans

@frankpepermans

@Wheater sounds good, but keep in mind that the proposed extension in that issue is not good enough.

Wheater

@Wheater

I will look more in-depth later. What are the known issues with it at the moment?

Frank Pepermans

@frankpepermans

A stream can be single or broadcast, if we return combineLatest2 inside, then that specificity will be lost.

...so we need it as a transformer, I can help out tomorrow

Wheater

@Wheater

I think the issue was referring to using it as an operator/transformer IIRC. I will check again later this evening.

If I get a chance, I hope to have something out to review for tomorrow, but more likely later this week.

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