registration_service.rb

class RegistrationService
  
  def self.register attributes
    user    = User.create attributes[:user]
    success = user && user.errors.empty?
    
    {
      user:     user,
      success:  success
    }
  end

  # def self.unregister attributes
  #   ...
  # end

end

registrations_controller.rb

class RegistrationsController < BaseController

  def new
    @registration = {}
    @registration[:user] = User.new
  end
  
  def create
    @registration = RegistrationService.register params[:registration]

    if @registration[:success]
      redirect_to registrations_path, success: "Hoorraa"
    else
      render action: :new
    end
  end
  
end