gistfile1.rb

class CreditCardController < ApplicationController
  def create
    respond_with CreditCardCreator.new(params)
  end
end

class Grouper::Responder
  delegate :errors, to: :resource

  def resource
    raise NotImplementedError
  end

  def to_json
    call
    resource
  end
end

class CreditCardCreator < Grouper::Responder
  def initialize(params)
    @params = params
  end

  def resource
    @resource ||= CreditCard.new(@params)
  end

  def call
    resource.save
    ...
    response = Stripe.create_card(resource)

    unless response.success?
      errors << response.error_message
    end
  end
end