chuck-dispatcher

ChucK Dispatcher

A ChucK implementation of the Dispatcher in Facebook's Flux pattern.

Why Flux?

yes really, that flux

ChucK is garbage. It has poor documentation. It's inconsistent. It has such a bad type system it might as well not exist. Loading and managing source files and dependencies is a nightmare. It's asynchronous without a sane way to handle asyncronicity in the standard library. State is easily mismanaged.

It reminds me a lot of Javascript :troll:.

I messed around with the Flux pattern in actual JS and it seemed to handle the complexity of an event driven application pretty well. I liked how it consolidated the application state and had easily pluggable components. So I decided to try to adapt it to building a synth in the ChucK language. Unlike most of my crazy ideas I actually did it and it actually worked!

Usage

Note: This will probably make more sense if you are familiar with the JS pattern...

The Dispatcher

The heart of the Flux pattern. You can create one (usually in a singleton AppDispatcher) like this.

public class AppDispatcher
{
  static Dispatcher @ _dispatcher;
  new Dispatcher @=> _dispatcher;

  fun static Dispatcher Instance()
  {
    return _dispatcher;
  }
}
AppDispatcher appDispatcher;

Registering with the Dispatcher

The Dispatcher has a Register method. This takes an implementation of DispatchableBase and returns a DispatchToken. The DispatchToken is a thin wrapper around a string because ChucK cannot handle static strings; You can register a DispatchableBase like this:

public class DispatchableImplementation extends DispatchableBase { }
DispatchableImplementation dispatchable;

AppDispatcher.Instance()
  .Register(DispatchableImplementation)
  @=> DispatchToken token;

Dispatching Messages

Once you've registered with the Dispatcher you're ready to send and receive DispatchMessages. The DispatchMessage has two properties ActionType() and Payload(). You can send a DispatchMessage like this:

public class PayloadImplementation extends PayloadBase { }
PayloadImplementation payload;

AppDispatcher.Instance()
  .Dispatch(DispatchMessage.Create(123456, payload));

Just like in JS dispatching messages can be made cleaner by wrapping this behavior in an XxxActions static class and using a static Constants class to represent the ActionType. For example:

public class Constants
{
  123456 => static int SOMETHING_COOL;
}
Constants constants;

public class SampleActions
{
  fun static void SomethingCool()
  {
    SomeCoolPayload payload;

    AppDispatcher.Instance()
      .Dispatch(DispatchMessage.Create(
        Constants.SOMETHING_COOL,
        payload));
  }
}

SampleActions.SomethingCool();

In order to handle the DispatchMessage you must override the Handle method on the DispatchableBase, once you register a dispatchable the Handle method is going to be called for every DispatchMessage regardless of ActionType so you will need to filter based on ActionType(). Once you have confirmed the ActionType you can safely cast the Payload() to access it's data. For example:

public class SampleDispatchable extends DispatchableBase
{
  fun void Handle(DispatchMessage message)
  {
    if(message.ActionType() == Constants.SOMETHING_COOL)
    {
      (message.Payload() $ SomeCoolPayload) @=> SomeCoolPayload payload;
      payload.CoolThing();
    }
  }
}

In the Flux pattern you are usually going to be manipulating state in a Store based on data contained in the Payload.

Unregistering with the Dispatcher

Sometimes you may want to stop handling DispatchMessages that you previously Registered to handle. You can do this by using the Unregister method. For example:

DispatchToken token; // This will come from the Register method

AppDispatcher.Instance()
  .Unregister(token);

Waiting for other Dispatchables

Sometimes you want to have two separate DispatchableBase implementations Handle the same DispatchMessage. By default the Handle method will be called on both implementations in a non-deterministic order. If order matters, say if implementation A depends on a side-effect of implementation B you will have to WaitFor B to finish it's handling. For example:

public class SampleDispatchable extends DispatchableBase
{
  fun void Handle(DispatchMessage message)
  {
    if(message.ActionType() == Constants.SOMETHING_COOL)
    {
      AppDispatcher.Instance()
        .WaitFor(TheOtherDispatchable.Token());
      // This execution will block until TheOtherDispatchable has finished handling the current message.

      (message.Payload() $ SomeCoolPayload) @=> SomeCoolPayload payload;
      payload.CoolThing();
    }
  }
}

Note: you can pass an array of DispatchTokens and wait for multiple other DispatchableBase implementations.