From: Robert Klemme <shortcutter@...>
Date: 2005-08-26T21:13:52+09:00
Subject: Re: Circular dependecy on classes

2005/8/26, Anatol Pomozov <anatol.pomozov@gmail.com>:
> I have several classes that have circular dependencies on each other.
> See following example.
> 
> class Solder
>   @can_upgrade_to = [Knight]
>   #or use constant from Knight class
> 
>   def upgrade!(to)
>     raise "Unable to upgrade" unless @can_upgrade_to.contain(to)
>   end
> end
> 
> class Knight < Solder
> end
> 
> I cant use Knight constant (class name) before Solder and can't use
> Solder before Knight.
> 
> I am just come from Java lang and for Java circular class deps is not
> a problem.
> But ruby is a dynamic language and it creates classes just on script
> executing. (right?)
> 
> So my questions is: how to solve this problem? What is the best way to
> deal with it.

The easiest soltuion: Reopen class Solder after you defined class
Knight and put all the
code there.

But you can as well use #inherited to track all sub classes of Solder.
Thus making sub class registration automatic. Something along the
lines of (untested):

class Solder
  def self.inherited(sub_class)
    def sub_class.inherited(cl) superclass.inherited(cl) end
    (@sub_classes ||= []) << sub_class
  end

  def upgrade_to?(cl)
    raise "error" unless cl.ancestors.include? cl
    ...
  end
end

Btw, did you mean "Soldier"?

Kind regards

robert