From: Robert Klemme <bob.news@...>
Date: 2005-04-01T20:29:44+09:00
Subject: Re: how to simulate self-style delegation


"itsme213" <itsme213@hotmail.com> schrieb im Newsbeitrag
news:y463e.17923$1H3.10469@tornado.texas.rr.com...
> I have classes A and B.
>
> class A
>   def x
>     "A::x "
>   end
>   def xy
>     self.x + "A::y"
>   end
> end
>
> class B
>   def initialize a
>     @a = a
>   end
>   def x
>     "B::x "
>   end
>   def method_missing ???
>     ?? SELF-style delegate to @a
>   end
> end
>
> I want true SELF-style delegation from objects of class B to A. i.e.
self
> calls on an A are in the context of the delegating B (if any).
>
> a = A.new
> a.xy #=> "A::x A::y"
>
> b = B.new a
>
> b.xy #=> "B::x A::y"
>     # calls b.method missing
>     # calls a.xy
>     # calls b.x #=> "B::x"
>     # calls a.y #=> "A::y"
>     # return "B::x A::y"
>
> How can I do this?

From all that I know you can't because you cannot do any of these:

 - bind an instance method of A to B (unless B is a superclass of A)

 - convert a method to a proc that is usable with instance_eval.

The question is: does it make sense to do that?

Kind regards

    robert


Below's my test code.

class A
  def x
    "A::x "
  end
  def xy
    self.x + "A::y"
  end
end

class B
  def initialize a
    @a = a
  end
  def x
    "B::x "
  end
  # def respond_to?(*x) true end
  def method_missing(sym, *args, &bl)
    ppp = @a.method(sym).to_proc
    # p ppp.arity
    class<<self; self; end.class_eval { define_method(sym){ instance_eval
&ppp } }
    # class<<self; self; end.class_eval { define_method(sym){ p self } }
    # p respond_to?( sym )
    send(sym,args)
    # self.instance_eval &ppp
    # instance_eval { ppp.call(*args) }
  end
end

b=B.new A.new
# set_trace_func lambda {|*a| p a}
p b.xy