From: "Pedro Côrte-Real" <pedro@...>
Date: 2006-08-01T00:29:06+09:00
Subject: Weird elusive bug using Comparable

I have this class:

class SimpleDate
  include Comparable

  VALS = [:year, :month, :day]
  attr_accessor *VALS

  def initialize(year, month, day)
    @year = year
    @month = month
    @day = day
  end

  #ideas on making this much shorter are welcome
  def <=>(other)
    VALS.each do |key|
      v1 = self.send(key)
      v2 = other.send(key)

      result = (v1 <=> v2)
      if result != 0
        return result
      end
    end
    0
  end
end

that represents a date that might have any of the three parts not
existant. For some reason date1 == date2 returns nil when done like
this:

class SimpleDateTest < Test::Unit::TestCase
  def test_comparison_with_nils
    date1 = SimpleDate.new(1,nil,nil)
    date2 = SimpleDate.new(1,nil,nil)

    assert_not_equal date1.object_id, date2.object_id
    assert date1 == date2
  end
end

The code shouldn't even work because nil doesn't implement <=>. What
the hell is comparable doing behind my back?

I thought date1 == date2 was the same as (date1 <=> date2> == 0 but
apparently not.

Pedro.