From: Robert Dober <robert.dober@...>
Date: 2008-03-15T00:53:40+09:00
Subject: [RRR] Robert's Ruby Riddle: Methodical Digits

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Hi list

I was just bitten very recently by a subtlety of Ruby I had completely
forgotten about.
I thought it might be a challenge to use this subtlety in order to
make the following test (the attached file contains the same code of
course) work:

----------------------------------- 8< -----------------------------------
require 'test/unit'

$user_params = ARGV[0..1]
class RRR_002_Methods < Test::Unit::TestCase
  def test_params_without_digits
    assert /^\D+$/ === $user_params.first, $user_params.first
    assert /^\D+$/ === $user_params.last, $user_params.last
  end

  def test_rrr002
    class << the_answer = Class::new
      def answer base=10
        42.to_s base
      end
    end
    assert_equal "42", the_answer.answer
    assert_equal "22", the_answer.answer( 20 )

    #
    # And now a little challange ;)
    #
    class << first_answer = Class::new( the_answer )
      def answer base = 2
        "[" << eval( $user_params.first ) << "]"
      end
    end

    class << second_answer = Class::new( the_answer )
      def answer base = 2
        "[" << eval( $user_params.last ) << "]"
      end
    end

    assert_equal "[101010]", first_answer.answer
    assert_equal "[42]", second_answer.answer
  end
end
----------------------------------- 8< -----------------------------------

As you can see digits are not allowed as parameters of the program.

Apart from the solution I would like to show, there is a completely
different one (not really very interesting but maybe a challange for
newbies), I could have blocked it easily enough by restricting the
length of the parameters but why spoil the fun ;).

Take the hint, the solution is a short one, much less than the 132
characters of the second solution.

But maybe there are even more solutions than these two.

Have fun
Robert
The following whitespace is intentional of course





































-- 
http://ruby-smalltalk.blogspot.com/

---
Whereof one cannot speak, thereof one must be silent.
Ludwig Wittgenstein

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