Expert to Expert: Brian Beckman and Erik Meijer - Inside the .NET Reactive Framework (Rx)

Great video! Really fascinating. I can't wait to see the code - just push it to me

A question: The scope of the  IDisposable object returned by Subscribe() was unclear to me. Erik implies you can put it in a using statement, like a normal IDisposable. But the lexical scope of the IDisposable returned seems much different than the lifetime ("runtime scope"?) of the IObserver you pass in. For example, the using statemetn with IDisposable for files is pretty obvious:

  using(fs = new Stream("somefile.txt"))   
  {     
    // ... do work on fs ...   
  } // fs is closed and disposed. 

But in the IObserver case, I don't think the using statement's scope is appropriate for indicating you don't care about events anymore. Using the autocomplete example above:

using(q.Subscribe(suggestions => ... ))
{
  // ???
} 

What happens in the body of the using statement? All the work seems to occur in the lambda passed to Subscribe. If I understood correctly, as soon as we leave the scope of the using statement, my lambda stops receiving events. Hmm, I bet the object implementing IDisposable has the secret sauce for the reactive framework. Maybe it has a method for testing for conditions and will "yield" until the condition is met? For example if I had another observer which looked for ENTER or TAB on the textbox and indicated that a selection was made, maybe it would let me write this code:

class KeyObserver :  IObserver<...>
 {
    publi c bool SelectionMade()
 }

KeyObserver key = ...;

using(cntrl = q.Subscribe(suggestions => ... ))
{
   if(! key.SelectionMade())
     sleep;
} 
// selection has been made and we stop listening to suggest events

Hopefully that makes some sense. It looks like the beginnings of a way to do reasonable event based programming. Apologies for answering my own question but glad to hear if I'm on track ...

Two other notes:

• Check out the AsyncEnumerator library from Jeffrey Richter. He leveraged enumerators and iterators to do something similar, but I think his solution still has an "inversion of control" problem where you need to write the code to drive the enumerator. A recent article can be found at http://msdn.microsoft.com/en-us/magazine/cc721613.aspx
• Erik mentioned a paper by Phillip Wadler called "The essence of monads" or similar. I think he meant "The essence of functional programming" (http://citeseerx.ist.psu.edu/viewdoc/summary?doi=10.1.1.38.9516).

Great stuff, get me this code!

Justin