From: "Mauricio Fernández" <batsman.geo@...>
Date: 2002-10-17T00:24:26+09:00
Subject: Re: Hooking on method invocation

On Wed, Oct 16, 2002 at 11:17:58PM +0900, Mauricio Fern�ndez wrote:
> On Wed, Oct 16, 2002 at 10:43:05PM +0900, Eugene Zaikonnikov wrote:
> > Hello,
> > 
> > Is there a way to hook on invocation of *any* instance method of an
> > object?
> > 
> > My first attempt was to override the send method:
> > 
> > class Foo
> >     #just ban them
> >     def send(symbol, *args)
> > 	puts "blocked"
> >     end
> > end
> > 
> > It works when I do:
> > 
> > foo = Foo.new
> > foo.send :something
> > 
> > But it has no effect on "conventional" method invocations. It seems
> > that send is not a part of the built-in method dispatch procedure.
> > 
> > I want such functionality to implement 'write barriers' for certain
> > objects. The idea was to track invocation of writer methods and notify
> > object's observer of changes. If this is achievable by other means,
> > any hints will be greatly appreciated.
> 
> Delegation maybe?

Code follows:

module Observable
# pretty lame and useless, but I didn't feel like removing it after all this
# typing; it could probably automate the generation of the list in a
# sensible way
def get_method_list
 [ ]
end
end

class BarrierKeeper
def initialize(obj)
 @theobj = obj
end

def method_missing(sym,*args) 
 h = @theobj.get_method_list
 ret = true
 ret = h[sym].call if h[sym]
 @theobj.send(sym, *args) if ret
end

end



class AnObject 
include Observable

def initialize
 @block_proc = proc { puts "ACTION: Blocked!"; false } 
 @notify_proc = proc do 
 	puts "ACTION: notify the observers; w/ 'require \"observer\"'"
	true
 end
end

def amethod
 puts "METH: You won't see this"
end

def another
 puts "METH: This one is not blocked."
end

def get_method_list
 { :amethod => @block_proc, :another => @notify_proc }
end

end


a = AnObject.new
theproxy = BarrierKeeper.new a
theproxy.amethod
theproxy.another



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