From: Roland Swingler <roland.swingler@...>
Date: 2007-01-07T01:15:14+09:00
Subject: Getting existing context when defining a singleton method (class << obj)

Hi

I'm fairly new to this "meta-programming" thing, so excuse me if I get
my terminology wrong. Is there any way of getting access to the
exisiting context when using class << obj or otherwise creating a
singleton method?

For example of what I mean - I have a method that returns a Proc:

def foo()
  local_var = "Bar"
  Proc.new { local_var }
end

x = foo()
x.call --> returns "Bar", 'remembering' the local context

and I want to something similar with methods defined using class <<
obj:

class MyObject
end

def foo(my_object_instance)
  local_var = "Bar"
  class << my_object_instance
    define_method(:a_method) { local_var }
  end
end

o = MyObject.new
foo(o)
o.a_method --> throws an error, complaining about missing local
variable

If I just wanted to assign this method to the class then I think I
could do the following in foo:

my_object_instance.class.send(:define_method, :a_method) { local_var }

But I want to define a singleton method, and I don't think you can get
access to an object instance's virtual class in a similar way?

Any help with this much appreciated,

TIA
Roland