From: "David A. Black" <dblack@...>
Date: 2005-07-12T20:25:55+09:00
Subject: adding attributes (attr_*-style) to single objects

Hi --

Having a special method to add attributes to Class objects has come up
a lot over the years, and several times recently.  As I've said
probably too often, it seems to me to make a special case where there
shouldn't be one.  There's really no more reason to have
class_attr_accessor than string_attr_accessor, hash_attr_accessor, or
myclass_attr_accessor.

I'd like to suggest a reformulation of the problem, starting by taking
it down to its roots.  The root of the problem is that people want to
add attributes to an object, but don't want to have to open up the
object's singleton class with the "class" keyword.

It seems to me that the best solution, therefore, would be a method
that allows you do exactly that: to add attributes to an object
without having to open up the object's singleton class.  What I have
in mind (here using the full "accessor" as an example) is this:

   class Object
     def add_attr_accessor(syms)
       (class << self; self; end).class_eval { attr_accessor(syms) }
     end
   end

(I assume the naming would be hotly debated, so I'll ignore that for
now :-)

Here's what it allows you to do:

   o = Object.new
   o.add_attr_accessor(:x)
   o.x = 100
   # etc.

and it seamlessly, consistently allows you to do exactly the same
thing for a class object:

   class C
     add_attr_accessor(:x)
   end

   C.x = 100
   # etc.

I think this is a much more useful and scaleable approach than a set
of purpose-written methods exclusively for the use of Class objects.


David

-- 
David A. Black
dblack@wobblini.net