From: Matt Greer <matt.e.greer@...>
Date: 2007-07-19T07:29:10+09:00
Subject: overriding nil?, curiosity

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Maybe this is a dumb question, but I'm gonna give it a shot.

I was showing my friends how Ruby classes are always open and I did some
dumb things like redefine Integer#+ to always return 5, and such. But trying
this:

NilClass.class_eval do
  def nil?
    false
  end
end

result in this:

irb(main):008:0> nil
/opt/local/lib/ruby/1.8/irb/slex.rb:235:in `match_io': undefined method
`call' for nil:NilClass (NoMethodError)
        from /opt/local/lib/ruby/1.8/irb/slex.rb:76:in `match'
        from /opt/local/lib/ruby/1.8/irb/ruby-lex.rb:287:in `token'
        from /opt/local/lib/ruby/1.8/irb/ruby-lex.rb:263:in `lex'
        from /opt/local/lib/ruby/1.8/irb/ruby-lex.rb:234:in
`each_top_level_statement'
        from /opt/local/lib/ruby/1.8/irb/ruby-lex.rb:230:in `loop'
        from /opt/local/lib/ruby/1.8/irb/ruby-lex.rb:230:in
`each_top_level_statement'
        from /opt/local/lib/ruby/1.8/irb/ruby-lex.rb:229:in `catch'
        from /opt/local/lib/ruby/1.8/irb/ruby-lex.rb:229:in
`each_top_level_statement'
        from /opt/local/lib/ruby/1.8/irb.rb:146:in `eval_input'
        from /opt/local/lib/ruby/1.8/irb.rb:70:in `start'
        from /opt/local/lib/ruby/1.8/irb.rb:69:in `catch'
        from /opt/local/lib/ruby/1.8/irb.rb:69:in `start'
        from /opt/local/bin/irb:13



Taking a look at the code and I'm completely lost. Obviously Ruby itself
depends on a usable definition of nil? I'm sure it depends on some key
methods in String, Array etc to be defined as expected too. So I guess there
are some exceptions where ruining a method ruins Ruby itself making it so
you never get a chance to ruin your own code :)

Like I said, dumb question and just a curiosity, my apologies if this isn't
very relevant.

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