chained_comparisons.rb

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

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

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