Metaprogramming

• 5

  SEP
  2009

  eval() Isn't Quite Pure Evil

  I was explaining method lookup to the Lone Star Ruby Conference attendees and needed to show some trivial code like this:

  module B
    def call
      puts "B"
      super
    end
  end
  
  module C
    def call
      puts "C"
      super
    end
  end
  
  module D
    def call
      puts "D"
      super
    end
  end
  

  Unfortunately, my space was limited due to the code being on slides and me needing to show more than just what you see above. I cracked under the pressure and committed two major programming sins. First, I collapsed the code with eval():

  %w[B C D].each do |name|
    eval <<-END_RUBY
    module #{name}
      def call
        puts "#{name}"
        super
      end
    end
    END_RUBY
  end
  

  Then I really blew it when I jokingly apologized to the audience for using eval().

  I got the first email with corrected code before I even finished the speech. OK, the email was from a friend and he wasn't mean, but he still instantly needed to set me straight. I had clearly turned from the light.

  Only, his corrected code didn't quite work. It got close, but it had bugs. Still the approach was sound and it could be made to work. Let me fix the bugs and show you what was recommended:

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  In: Ruby Tutorials | Tags: Metaprogramming | 24 Comments

• 9

  DEC
  2008

  XMPP and Metaprogramming Screencasts

  I've mentioned some nice screencasts I've found in the past. Well, I've been watching quite a few more lately and I've uncovered some more hits.

  First, PeepCode has another excellent screencast on using XMPP with Ruby. This video explains what XMPP is and isn't, why it's important, and shows a good deal of information about how you can work with the protocol to accomplish some real world server to server or human communication tasks. You don't need any prior XMPP knowledge going into this one.

  It's hard to overstate exactly how much PeepCode got right with this video. For example, I've seen quite a few screencasts now that byte off more than they can chew for a short video. That's not the case here. XMPP turns out to be perfectly bite sized in that a one hour video can serve as a strong introduction to pretty much all you need to know when using it. This has other advantages too. Since the creator isn't trying to squeeze too much content into too short of time, he can afford to drop some truly stellar related tips. In the case of the XMPP video these are what IM client to use when debugging, because it allows you to see the underlying protocol, and how to easily combine XMPP with DRb for fire-and-forget messaging. These extras really push this screencast over the top.

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  In: Screencasts | Tags: XMPP & Metaprogramming | 0 Comments