class ActiveModel::Validations::ConfirmationValidator

def setup(klass)
  klass.send(:attr_accessor, *attributes.map do |attribute|
    :"#{attribute}_confirmation" unless klass.method_defined?(:"#{attribute}_confirmation")
  end.compact)
end

def validate_each(record, attribute, value)
  confirmed = record.send(:"#{attribute}_confirmation")
  return if confirmed.nil? || value == confirmed
  record.errors.add(attribute, :confirmation, options)
end