Mirrored observable collections

[Mike Hearn]

Thanks Tomas! I'm a big fan of your work and blog.

I learned about ReactFX after I started writing my current project, seems
like a very useful abstraction indeed, although so far I've found the basic
JFX stuff to be nearly sufficient (a few more transformers and mirrored
observables were so far all I needed).

Actually I didn't realise ReactFX could do this. I learned about what it
can do by reading the github page which covers many features but doesn't
mention threading anywhere, so I figured it didn't have any support for it.
I should have dug deeper! Maybe you could add a discussion of threading and
how to manage asynchronous state using ReactFX?

Additionally a discussion of debugging would be helpful. My experience so
far is that reactive/streaming code is fun to write and painful to debug
compared to traditional imperative code.

In my UI I use content bindings, so I'd need to (I think) use
EventStreams.merge() to merge the event stream back into a copy of the set,
and at that point the API would be more verbose than
MirroredObservableSet/List. Still ReactFX is clearly a lot more general and
I might well switch to it at some point.

Incidentally the lack of a uni-directional string binding utility in JavaFX
is really annoying: converting a read only observable value into a string
is a really common thing to want to do!