Subscribe an external observer to this observable

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

This should only be called when all inputs are ready. It will throw if the required parent values are missing.

See also debug methods in com.raquo.airstream.debug.DebuggableObservable

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

Note: Observer can be added more than once to an Observable. If so, it will observe each event as many times as it was added.

Signal propagates only if its value has changed

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

Evaluate initial value of this Signal. This method must only be called once, when this value is first needed. You should override this method as def (no val or lazy val) to avoid holding a reference to the initial value beyond the duration of its relevance.

Check whether inputs (parent observables' values) are all available to be combined.

Note: This is enforced to be a Set outside of the type system #performance

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.

Get the signal's current value

Total number of internal and external observers

Add a noop observer to this signal to ensure that it's started. This lets you access .now and .tryNow on the resulting StrictSignal.

You can use myStream.toWeakSignal.observe.tryNow() to read the last emitted value from event streams just as well.

Implementations should call this instead of .fireValue() / .fireTry() Transaction will call syncFire when it's time, and that in turn will evaluate maybeCombinedValue and call .fireTry()

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).

Parent observers are not immediately active. onStart/onStop regulates that.

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

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

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

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.

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

Note: Initial value is only evaluated if/when needed (when there are observers)