Interactor

create_mailgun_domain.rb

# Finally, all comes together in an interactor
class CreateMailgunDomain
  include Interactor
  include MailgunApi

  pattr_initialize :domain

  def call
    response = post('/domains', name: domain, smtp_password: random_password)
    if response.code == 200
      response
    else
      fail!(response)
    end
  end

  private

  def random_password
    SecureRandom.hex
  end
end

failure.rb

# Defines the failure object, which (optionally) takes an object and a message.
class Failure < StandardError
  attr_reader :object

  def initialize(object = nil, message = nil)
    super(message)
    @object = object
  end
end

interactor.rb

# Offers the #fail! method and implicitely returns a successful `Result` with the return value.
module Interactor
  def self.included(base)
    base.extend(ClassMethods)
  end

  def fail!(object = nil)
    self.class.fail!(object)
  end

  module ClassMethods
    def call(*args)
      object = new(*args).call
      Result.new(true, object)
    rescue Failure => failure
      Result.new(false, failure.object)
    end

    def fail!(object = nil)
      fail Failure, object
    end
  end
end

result.rb

# Reponds to success? and failure?. Also uses `SimpleDelegator` to make accessing the underyling object a bit nicer.
class Result < SimpleDelegator
  def initialize(success, object = nil)
    @success = success
    super(object)
  end

  def success?
    @success
  end

  def failure?
    !@success
  end
end