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From Mike Stanley <>
Subject sandbox proposal. Events
Date Mon, 04 Oct 2004 15:19:15 GMT
I've implemented a pattern, somewhat based off the .NET event and
delegate pattern, however the pattern is also commonly seen in
frameworks (to some extent).  

At a high level, the pattern is made up of two objects:
- Event
- DelegateMethod

The Event is a container for DelegateMethods.  Delegate Methods are
registered with the Event (added to the container).  The first delegate
method added to the container determines the contract for that event. 
I.e. each method added must have similar signatures (take the same
number and types of parameters and return the same type).  At any time
the event can be fired.  When an event is fired it invokes the delegate
methods in the order they were added.  The event can be configured to
fail on first exception, or continue without failing.  If the delegate
methods return a value, the last value would be returned (this is the
behavior of the .NET approach.  I'm open to other suggestions).  

A Delegate Method gets created with an instance of an object and the
name of the method (optionally when instantiating the Delegate Method
you may specify the signature - or actual Method, in the case that there
are multiple methods with the same name but different signatures).  This
method will be invoked using reflection (delegateMethod.invoke(args))
when the event is fired.  

At it's core this is the basic idea.  Above this, there are (*plans*) to
create Asynchronous Delegate Methods and events, providing simple
support for multi-threaded events.  This will use the same concepts from
.NET (callbacks, begin invokes, end invokes, async results, etc).  

I'm also investigating migrating the pattern to utilize "commons-chain".

Currently this does not exist as a stand-alone library.  However, if
there is interest, I will begin to pull it out and contribute it to the

- Mike

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