class ActiveModel::Validations::ConfirmationValidator

def setup!(klass)
  klass.attr_reader(*attributes.filter_map do |attribute|
    :"#{attribute}_confirmation" unless klass.method_defined?(:"#{attribute}_confirmation")
  end)
  klass.attr_writer(*attributes.filter_map do |attribute|
    :"#{attribute}_confirmation" unless klass.method_defined?(:"#{attribute}_confirmation=")
  end)
end