Adds Perl's XOR-able strings to Ruby, except that an argument longer than the receiver will be cycled as needed and a Fixnum argument frobnicates (see memfrob(3)) the receiver, though not necessarily with 42. Also, non-alphanumeric XOR pairs for gits and shiggles.

string_xor.rb

module XOR
  def ^ other
    case other
    when Fixnum
      chars.map { |c| (c.ord ^ other).chr }.join
    when String
      chars.zip(other.chars.cycle).map { |a, b| (a.ord ^ b.ord).chr }.join
    else
      raise ArgumentError, "must be String or Fixnum"
    end
  end

  def non_alphanumeric_xor_pair
    syms = '`~!@#$%^&*()_+{}|[]\\\'";:,./<>?'
    ords = syms.chars.map &:ord
    pair = ['', '']

    chars.map(&:ord).each do |o|
      candidates = []
      ords.each do |a|
        ords.each do |b|
          candidates << [a, b] if a ^ b == o
        end
      end

      return [] if candidates.empty?

      winner = candidates.sample
      pair[0] << winner.pop
      pair[1] << winner.pop
    end

    pair
  end
end

class String
  include XOR
end

if $0 == __FILE__
  eval DATA.read, nil, $0, __LINE__ + 4
end

__END__

require 'test/unit'

class TestXOR < Test::Unit::TestCase
  def test_with_fixnum
    assert_equal 'abc' ^ 5, 'dgf'
  end

  def test_with_string
    assert_equal 'Just another Ruby hacker',
                 '*+.]@:./[@;)].*<]](_<+>^' ^ '`^])`[@@/(^[}|_^$}@>_@[,'
  end

  def test_with_cycled_string
    assert_equal 'RubyRuby' ^ '<3', 'nF^JnF^J'
  end

  def test_with_invalid_argument
    assert_raise(ArgumentError) { 'abc' ^ [] }
  end

  def test_xor_pair
    a, b = 'Ruby'.non_alphanumeric_xor_pair
    assert_equal a ^ b, 'Ruby'
  end

  def test_unpairable_string
    assert_empty '<3'.non_alphanumeric_xor_pair
  end
end