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    <p>You've generally got the right idea here, actually. You just need to do the actual dispatch. For this, SelectMany will help:</p> <pre><code>class Bus { Subject&lt;Command&gt; commands; Subject&lt;Invocation&gt; invocations; // TODO: Instantiate me List&lt;Func&lt;Command, bool&gt;&gt; handlerList; public Bus() { this.commands = new Subject&lt;Command&gt;(); this.invocations = new Subject&lt;Invocation&gt;(); commands.SelectMany(x =&gt; { // This FirstOrDefault() is just good ol' LINQ var passedHandler = handlerList.FirstOrDefault(handler =&gt; handler(x) == true); return passedHandler != null ? Observable.Return(new Invocation() { Command = x, Handled = true}) : Observable.Throw&lt;Invocation&gt;(new Exception("Unhandled!")); }).Multicast(invocations).Connect(); } /* ... snip ... */ } </code></pre> <p>But, to be honest, this doesn't really demonstrate the power of Rx, because it's executing the handler list synchronously. Let's make this more compelling by making this completely non-blocking.</p> <p>First, we'll change our Func prototype to be <code>Func&lt;Command, IObservable&lt;Invocation&gt;&gt;</code>. This means, a method that takes a command and produces a Future Invocation result (a-la <code>Task&lt;T&gt;</code>). Then, we can get identical behavior yet have our handlers be async via this selector (coding via TextArea ahead):</p> <pre><code>commands.SelectMany(x =&gt; handlerList.ToObservable() .Select(h =&gt; Observable.Defer(() =&gt; h(x))) .Concat() .SkipWhile(x =&gt; x.Handled == false) .TakeLast(1)) .Multicast(invocations).Connect(); </code></pre> <p>This is a pretty graduate-level use of Rx, but the idea is, for each Command, we're going to initially create a Stream of handlers and run them in order (that's what Defer + Concat does), until we find one whose Handled is true, then take the last one. </p> <p>The outer SelectMany selects a stream of Commands into a Stream of Future Results (i.e. the type is <code>IO&lt;IO&lt;Invocation&gt;&gt;</code> then flattens it, so it becomes a stream of results. </p> <p>No blocking ever, very concise, 100% testable, type-safe code that just expressed a pretty complicated idea that would've been really ugly to write imperatively. This is why Rx is cool.</p>
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    1. POComposing a command bus using RX
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    1. USAnderson Imes
    1. USPaul Betts
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    1. COThanks Paul. This will take a little time to get my head properly around but is showing the compositional power I was hoping to see. Will study it closely. I note that the point @Gideon made about ALL observers being notified has also shaped your solution. Essentially that IO<Invocation> subscriptions cannot be the mechanism for handlers to tegister themselves with the bus.
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      1. USPhil Degenhardt
    2. CO.TakeWhile(x => x.Handled == false) .TakeLast(1) I didn't try this, but won't I get the final Observable with the last unhandled, instead of the first handled? I would do .SkipWhile(x => x.Handled == false).Take(1). Is this true, or am I thinking it wrong?
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    3. COI think you're right actually
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