From: Christoph <chr_news@...>
Date: 2002-09-23T21:19:51+09:00
Subject: Re: self as method argument revisited

dblack wrote
....
> A while ago transami brought up the question of an object needing
> access to the object that created it, and there was discussion of
> techniques including sending self as an argument.  I've been working
> on a case of the underlying problem he was talking about, and I
> thought I'd share my (current) solution.  Comments welcome.
>
> The big object is a (simple) database image.  It creates Row objects
> from arguments to an #insert method, and populates itself hash-wise
> with the values.
>
> There are also field names.  A Row object needs to know its own field
> names, so that one can do things like:
>
>   r = db["Black"]   # r is a Row object
>   r["first_name"]   # => David
>
> Originally I had been creating an array of field names for every row,
> but that seemed very clunky.  Then I got an idea....
>
> When the database object is created, it creates a new class, which
> inherits from an existing Row class (DBDBD::Row).  That new class has
> an instance variable (i.e., its virtual class defines an accessor
> method) called @row_class.  The new database object assigns itself to
> @db in that Row class's virtual class:

While I am still marveling what problem your are trying to solve -
I am sort of wandering why you are creating a Row constant in
the scope of the meta  (virtual) class of every DBDB instance?
I doubt hat you woould ever make use of this constant, unless
your are planning on peppering every DBDB instance with a
barrage of singleton methods.

---
 class DBDB # The 1.6 object model is inferior
    def initialize(...)
      ...
      @row_class = Class.new (DBDBD::Row)
      class << @row_class
         attr_accessor :db
      end
      @row_class.db = self
    end
    ...
 end


class DBDB  # 1.7 version
   class Row
      ...
      @row_class = self
       class << self
          attr_accessor :db
       end
   end
   def initialize(...)
      ...
      @row_class = Class.new (DBDBD::Row)
      @row_class.db = self
   end
    ...
 end
---


/Christoph