Child observable should call this method on its parents when it is started. This observable calls onStart if this action has given it its first observer (internal or external).

Subscribe an external observer to this observable

Total number of internal and external observers

When starting an observable, this is called recursively on every one of its parents that are not started. This whole chain happens before onStart callback is called. This chain serves to prepare the internal states of observables that are about to start, e.g. you should update the signal's value to match its parent signal's value in this callback, if applicable.

Default implementation, for observables that don't need anything, should be to call parent.maybeWillStart() for every parent observable.

If custom behaviour is required, you should generally call parent.maybeWillStart() BEFORE your custom logic. Then your logic will be able to make use of parent's updated value.

Note: THIS METHOD MUST NOT CREATE TRANSACTIONS OR FIRE ANY EVENTS! DO IT IN ONSTART IF NEEDED.

Child observable should call removeInternalObserver(parent, childInternalObserver) when it is stopped. This observable calls onStop if this action has removed its last observer (internal or external).

Note: Use Protected.topoRank(observable) to read another observable's topoRank if needed

Apply pf to event and emit the resulting value, or emit nothing if pf is not defined for that event.

Apply fn to parent stream event, and emit resulting x if it returns Some(x)

See also debug convenience method in BaseObservable

This is the method that subclasses override to preserve the user's ability to set custom display names.

Make a stream that emits this stream's values but waits for after stream to emit first in a given transaction. You can use this for Signals too with Signal.composeChanges (see docs for more details)

Distinct events (but keep all errors) by == (equals) comparison

Distinct events (but keep all errors) by matching key Note: key(event) might be evaluated more than once for each event

Distinct events (but keep all errors) using a comparison function

Distinct events (but keep all errors) by reference equality (eq)

Distinct errors only (but keep all events) using a comparison function

Distinct all values (both events and errors) using a comparison function

Drop (skip) the first numEvents events from this stream. Note: errors are NOT dropped.

Drop (skip) events from this stream as long as they do NOT pass the test (as soon as they start passing, stop dropping) Note: errors are NOT dropped.

Drop (skip) events from this stream as long as they pass the test (as soon as they stop passing, stop dropping) Note: errors are NOT dropped.

Airstream may internally use Scala library functions which use == or hashCode for equality, for example List.contains. Comparing observables by structural equality pretty much never makes sense, yet it's not that hard to run into that, all you need is to create a case class subclass, and the Scala compiler will generate a structural-equality equals and hashCode methods for you behind the scenes.

To prevent that, we make equals and hashCode methods final, using the default implementation (which is reference equality).

Create an external observer from a function and subscribe it to this observable.

Note: since you won't have a reference to the observer, you will need to call Subscription.kill() to unsubscribe

Force reference equality checks. See comment for equals.

value is passed by name, so it will be evaluated whenever the Observable fires. Use it to sample mutable values (e.g. myInput.ref.value in Laminar).

See also: mapToStrict

value is evaluated strictly, only once, when this method is called.

See also: mapTo

This name should identify the instance (observable or observer) uniquely enough for your purposes. You can read / write it to simplify debugging. Airstream uses this in debugLog* methods. In the future, we will expand on this. #TODO[Debug] We don't use this to its full potential yet.

Observer removals scheduled to run as soon as this observable's event propagation finishes. Only put calls to removeInternalObserverNow and removeExternalObserverNow here, no custom logic.

Returns a stream that emits events from this stream AND all off the streams, interleaved. Note: For other types of combination, see combineWith, withCurrentValueOf, sample etc.

This is used in Signal-s. It's a no-op for Streams.

This method is fired when this observable starts working (listening for parent events and/or firing its own events), that is, when it gets its first Observer (internal or external).

onStart can potentially be called multiple times, the second time being after it has stopped (see onStop).

This method is fired when this observable stops working (listening for parent events and/or firing its own events), that is, when it loses its last Observer (internal or external).

onStop can potentially be called multiple times, the second time being after it has started again (see onStart).

See docs for MapStream

Convert this to an observable that emits Failure(err) instead of erroring

Note: do not expose this to end users. See https://github.com/raquo/Airstream/issues/10

Removal still happens synchronously, just after we're done iterating over this observable's observers, to avoid interference with that logic.

Note: The delay is necessary not just because of interference with actual while(index < observers.length) iteration, but also because on a high level it is too risky to remove observers from arbitrary observables while the propagation is running. This would mean that some graphs would not propagate fully, which would break very basic expectations of end users.

UPDATE: In 15.0.0 we made the observable removal delay more fine grained – previously we would wait until the whole transaction completed before removing observers, now we only wait until this observable's iteration is done. This helped us fix https://github.com/raquo/Airstream/issues/95

Note: To completely unsubscribe an Observer from this Observable, you need to remove it as many times as you added it to this Observable.

Safely remove internal observer (such that it doesn't interfere with iteration over the list of observers). Removal still happens synchronously, just after we're done iterating over this observable's observers.

Child observable should call this method on its parents when it is stopped.

A signal that emits the accumulated value every time that the parent stream emits.

A signal that emits the accumulated value every time that the parent stream emits.

Set the display name for this instance (observable or observer). - This method modifies the instance and returns this. It does not create a new instance. - New name you set will override the previous name, if any. This might change in the future. For the sake of sanity, don't call this more than once for the same instance. - If display name is set, toString will output it instead of the standard type@hashcode string

Take the first numEvents events from this stream, ignore the rest. Note: As long as events are being taken, ALL errors are also taken

Imitate parent stream as long as events to NOT pass the test; stop emitting after that.

Imitate parent stream as long as events pass the test; stop emitting after that.

Unwrap Try to "undo" recoverToTry – Encode Failure(err) as observable errors, and Success(v) as events

Override defaultDisplayName instead of this, if you need to.

Convert this observable to a signal of Option[A]. If it is a stream, set initial value to None.