chained_comparisons.rb

# Always wanted to chain comparisons the snaky way?
#
#   puts 'Right there!' if 5 < x <= 15
#
# There you go.

# May be used under the terms of the MIT License
# Contributors: Tero Tilus <[email protected]>, Jan Steffens

class FalseClass
  ['<', '>', '<=', '>='].each do |op|
    eval "def #{op}(other) false end"
  end
end

module ChainedComparisons
  def self.included(klass)
    [['<',  '',  -1],
     ['>',  '',   1],
     ['<=', '!',  1],
     ['>=', '!', -1]].each do |op, neg, cmp|
      klass.class_eval <<-EOS
        def #{op}(other)
          #{neg}(self<=>other).equal?(#{cmp}) ? other : false
        end
      EOS
    end
  end
end

[Comparable, Fixnum, Float].each do |chainable|
  chainable.send :include, ChainedComparisons
end

if $0 == __FILE__

  require 'test/unit'

  class TC_ChainedComparisons < Test::Unit::TestCase
    def test_pairs
      assert 1<2
      assert !(2<2)
      assert 3>2
      assert !(1>2)
      assert 1<=2
      assert 2<=2
      assert !(3<=2)
      assert 3>=2
      assert 2>=2
      assert !(1>=2)
    end

    def test_chains
      # < only
      assert 1<2<3
      assert 1<2<3<4
      assert !(1<2<2)
      assert !(3<2<3<4)
      # > only
      assert 3>2>1
      assert 4>3>2>1
      assert !(3>2>2)
      assert !(2>3>2>1)
      # mixed
      assert 1<=2>=1
      assert 2<=2>=2
      assert 1<2<=2>=2>1
      assert !(2<=2<2)
      assert !(2>2<2)
      assert !(1>=2>=1<0>1)
    end

    def test_coercion
      assert 1.0<2<30000000000000000000000000000000
      assert !(1.0>2<30000000000000000000000000000000)
    end
  end

end