From: Mathieu Bouchard <matju@...>
Date: 2002-01-11T01:00:26+09:00
Subject: Re: instance variables automatically accessible?


On Thu, 10 Jan 2002 cmlr@math.rochester.edu wrote:

> Does anyone know the best way to make instance variables in a class
> automatically accessible?  In other words, how do you avoid writing
> attr_accessor :a, :b, :c
> I came up with the following way, but I don't like it, since it
> uses "eval".
>       eval "attr_accessor :#{v[1..-1]}"

that line can be written:

attr_accessor v[1..-1].intern

because attr_accessor is a method of the Class class with a Symbol
argument. (but note that "alias" and "undef" are not class methods)

however your code does not work with attributes that are not created in
#initialize; maybe this is not a problem for you; otherwise you'd have to
override #method_missing to detect them and create attributes on-the-fly.

I also notice that you recreate the same attributes over and over. If
every call to #initialize creates the same attributes, then you can
optimise things this way:

class Class
  alias oldNew new
  private :oldNew
  def new(*args)
    o = oldNew(*args)
    unless @attribs_created
      for v in o.instance_variables
        attr_accessor v[1..-1].intern
      end
      @attribs_created=true
    end
    o
  end
end

note: @-vars in Class objects are per class; @@-vars are per class-tree,
and can be accessed from instances of the classes of that tree.

note2: attribute accessors will be duplicated when creating
subclasses. it mostly just means a little wasted memory, as attributes of
base classes will have redundant accessors which hide each other. the
wasted memory is per-class, not per-object, so this is probably not a
problem.

________________________________________________________________
Mathieu Bouchard                   http://hostname.2y.net/~matju