From: Niklas Frykholm <r2d2@...>
Date: 2002-02-02T02:54:58+09:00
Subject: Re: [GUI] Signal/slot pattern in ruby

[nobu.nokada@softhome.net]:
>> I think the signal/slot mechanism in Qt is the most elegant basic
>> mechanism. (The other options are AFAIK: callbacks, observers and
>> subclassing.) In a ruby GUI, signals and slots should be ordinary ruby
>> functions. It should also be possible to use Proc's as slots. Like
>> this:
> 
> It looks cool, but Signal is used as POSIX signal.

(snip)

I like most of your changes. Neat trick using append_features. But I like to
have the option to write 

	a.connect(:new_value, b, :x=)

As well as

	a.connect(:new_value, b.method(:x=))

since the former is more symmetric. Here is an implementation that
allows both: 

	module SignalSlot
	  def connect(signal, *args, &pr)
		((@_signals ||= {})[signal] ||= []) << (pr ? [pr] : args)
	  end

	  def disconnect(signal, *args)
		@_signals[signal].delete(args) if @_signals
	  end

	  def activate_signal(signal, *args, &pr)
		@_signals[signal].each {|obj, *meth|
			obj.send(*((meth[0] ? meth : [:call])+args), &pr)
		} if @_signals
	  end

	  def self.append_features(klass)
		super
		class << klass
		  def signal(*args)
			args.each {|a|
			  module_eval %Q{def #{a}(*args, &pr)
					activate_signal(:#{a}, *args, &pr)
				end}
			}
		  end
		end
	  end
	end

It also lets you add arguments to the methods, like this:

	def print_value(name, v)
		puts "#{name} value set to #{v}"
	end

	a.connect(:new_value, self, :print_value, 'a')

I'm not sure what to do with this module. Should I put it in the RAA?
Seems a bit silly for such a short module. I guess that is the problem
with ruby. Something that requires umpteen lines of code and a special
preprocessor (moc) in C++ can be done in 28 lines of ruby. Oh well...

// Niklas