OpenHash is a hash with a #method_missing that routes to [] and []=.

openhash.rb

# OpenHash is a hash with a #method_missing method
# that routes to [] and []=.
class OpenHash < Hash
  def method_missing(s, *a)
    case s
    when /\?$/
      self.key?(s.chomp('?'))
    when /\=$/
      self[s] = a[0]
    else
      a.empty? ? self[s] : super
    end
  end
end