From: Christoph <chr_mail@...>
Date: 2004-05-29T00:51:40+09:00
Subject: Re: Visitor Pattern in Ruby

Charles Comstock wrote:

>module Visitable
>  def accept(visitor,&block)
>    for klass in self.class.ancestors do
>      break if (v = visitor.methods.include?("visit_#{klass}"))
>    end
>    if v
>      visitor.__send__("visit_#{klass}",self,&block)
>    else
>      visitor.default_visit(self,&block)
>    end
>  end
>  
>
The following "included" redefinition is superfluous since any
child of a "Visitable" class  is already "Visitable" - for example

---
module Visitable
  def accept(visitor,&block)
    for klass in self.class.ancestors do
      break if (v = visitor.methods.include?("visit_#{klass}"))
    end
    if v
      visitor.__send__("visit_#{klass}",self,&block)
    else
      visitor.default_visit(self,&block)
    end
  end
end

class A
    include Visitable
end

class B < A
end

p A < Visitable # true
p B < Visitable # true
---

>  def Visitable.included(kls)
>    kls.module_eval <<-"end_eval"
>    def self.inherited(child)
>      child.module_eval "include Visitable"
>    end
>    end_eval
>  end
>end
>
>  
>
/Christoph