From: Pat Maddox <pergesu@...>
Date: 2006-05-14T15:28:29+09:00
Subject: "Seeing Metaclasses Clearly"

I saw a link for why's article "Seeing Metaclasses Clearly" [1]
earlier this week.  Been looking at it, and honestly I can't say it's
making things more clear for me.  The final example is:

 class MailTruck
   def self.company( name )
     meta_def :company do; name; end
   end
 end

 class HappyTruck < MailTruck
   company "Happy's -- We Bring the Mail, and That's It!"
 end

I simply don't see how that's different from

class MailTruck
  def self.company(name)
    instance_eval do
      define_method(name) { name }
    end
  end
end

except for, um, my code doesn't work - wrong number of arguments (0 for 1)

I also don't understand why this doesn't work, I thought it was the
same thing as the first example, just without the helper methods that
why wrote:

class Truck
  def self.company(name)
    class << self
      instance_eval do
        define_method(name) { name }
      end
    end
  end
end

Now after reading this I don't even have a clue how/why all the evals
are supposed to be used.  Thought I had it down, but I'm just way more
confused after this article.  I know there's already a post on the
various evals, but can someone explain what's going on in this
metclass article?  Clearly, please.

Pat


[1] http://whytheluckystiff.net/articles/seeingMetaclassesClearly.html