From: avi@...4.com (Avi Bryant)
Date: 2001-11-15T10:38:39+09:00
Subject: [ruby-talk:25234] Re: attr_accessor question

Michael Sullivan <mps@discomsys.com> wrote:
> I was wondering if when one has defined "attr_accessor" for their
> instance variables if there was any way to determine when one of the
> variables changes.

We really need a more generic attr framework, so that I can write something like

class Foo
  attr [:read, :write, :initialize, :notify] :x, :y
end

(and while we're at it, we need to be able to do the same thing for methods
and classes...)

But for now, how about:

def Module.attr_notify(*vars)
  vars.each do |var|
    module_eval %{
      def #{var}() @#{var} end
      def #{var}=(_#{var})
         @#{var} = _#{var}
         changed(:#{var})
      end
    }
  end
end


This is untested, but it should allow:

class Foo
   attr_notify :x, :y

   def changed(var)
     puts "#{var} was changed!"
   end
end