From: Thomas Counsell <tamc2@...>
Date: 2004-12-16T05:45:59+09:00
Subject: Re: Can I make a new function like attr_accessor?

Hi Paul

Not tested, but something like this should do the trick:

class Class
	def attr_emitter( *syms )
		syms.each do |sym|
			class_eval( "def #{sym}; @#{sym} end" )
			class_eval( "def #{sym}=(x)
							old, @#{sym} = @#{sym}, x
							emit(:#{sym}, old)
						end" )
		end
	end
end

Note that I think you also need to define @listeners in your Emitter 
module .....  (@listeners ||= [] ).push( listener) or some such.

Regards

Tom

On 15 Dec 2004, at 20:08, Jack, Paul wrote:

> I'm writing a program that has a bunch of components I'd like
> to link together using Java-style property change events.
>
> So I created a mixin module:
>
>   module Emitter
>
>     def addListener(listener)
>       @listeners.push(listener)
>     end
>
>     def removeLister(listener)
>       @listeners.delete(listener)
>     end
>
>     def emit(sym, oldValue)
>       @listeners.each { |x| x.propertyChanged(self, sym, oldValue) }
>     end
>
>   end
>
> In my component objects, I just make them include Emitter and invoke
> "emit" on any mutator:
>
>   class ExampleComponent
>
>     include Emitter
>
>     def foo
>       @foo
>     end
>
>     def foo=(x)
>       old = @foo
>       @foo = x
>       emit(:foo, old)
>     end
>
>   end
>
> I'd like to automate the creation of emitter properties, though.  Just
> like I can use attr_accessor to quickly create readable/writeable
> attributes, I'd like a new attr_emitter function to quickly create
> readable/writeable/emitable attributes.
>
> But I can't figure out how to do that. :(  Is it possible?  It would
> save me a LOT of redundant typing...
>
> Thanks all,
>
> -Paul
>
>