From: Ralph Shnelvar <ralphs@...32.com>
Date: 2009-11-28T22:00:57+09:00
Subject: Re: Class variables, instance variables, singleton; Ruby v. C++

DAB> And of course this is one of the (many) problems with class variables:
DAB> they make obscure the otherwise rather simple notion that classes can
DAB> have instance variables because classes are objects and any object can
DAB> have instance variables.

David ... this may be the higher-level gestalt that I was missing.  It
sure sounds like it.

Let me flesh out my questions/comments about this paragraph so that you and
others have something specific to answer.  Let's call the classed  F &
G.

(1) OK, classes are (i) objects; (ii) are executable code.


(2) If I do the following
      class F
      end
      f = F.new
      F.class  # class
      f.class  # F
this makes sense to me.

What (relevant and important conceptually) messages (other than "new")
can I send to a class?  But see (3), below.



(3)
    class F
      def sub1
        @@x = 1
      end
    end

    class G
      self.sub1
        @@x=2
      end
    end

    # Why?  Didn't the interpreter "see" @@x in class F?
    F.class_variables  # []

    # makes sense
    G.class_variables  # ["@@x"]

    f = F.new

    # Why?  Shouldn't the method inherit from the class?
    f.class_variables  # undefined method

    f.sub1  # 1

    # makes sense.  class variable now explicitly executed
    F.class_variables # ["@@x"]

    # How to use class_variable_get if the method is private???
    F.class_variable_get(:@@x)  # error private method!



OK, that should do it for now.