Creates a stream that constructs a Map with the latest value of the inner stream of each key.
keys$: Stream of the list of keys to subscribe to.
getInner$: Function that returns the stream for each key.
A stream with a map containing the latest value from the stream of each key.
You're typically going to call this after
Here it is in action, picking up from the
example. You have a stream representing the list of pets, you have a function
that returns the stream associated with each pet, and now combineKeys() gives
you a stream that emits a map of this whole data structure whenever any of it
changes. If you're careful about where you bind these you can save a lot of