ruby error with extra field

attachable-error.rb

# error class:
class AttachableError < StandardError
  attr_reader :data

  def initialize(message = nil, data = nil)
    @message = message
    @data = data
  end

  def to_s
    @message || 'Default error message'
  end
end

# usage:
raise AttachableError.new('my message', data)