From: avi@...4.com (Avi Bryant)
Date: 2002-02-14T05:54:56+09:00
Subject: Re: qualms about respond_to? idiom

> All tags respond to tagStart? and tagEnd?  But not all events in my
> stream are tags.  So....
> 
>          if e.respond_to? :tagStart?
>            context.push(e.name) if e.tagStart?
>          end
> 
> is my way of testing, first, whether it's a tag (but without actually
> checking whether it's a tag), and, second, whether it's a start tag.
> This is a case where I wish I knew a way to avoid the duplication,
> which feels really clunky to me.

Ok, how about:

class Object
  def try_sending(msg, *args)
     if respond_to? msg
       yield send(msg, *args)
     end
  end
end

e.try_sending(:tagStart?) {|s| context.push(e.name) if s}