example_controller.rb

## example_controller.rb
class UserController < ActionController::Base

  def new
    @user = User.new
  end

  def create
    result = SignupUser.call(params[:user])
    if result.successful?
      redirect_to root_url, notice: "A welcome e-mail is on it's way!"
    else
      @user = result.user
      render
    end
  end

end

## example_service.rb
class SignupUser < Service::Call

  attribute :name, String
  attribute :email, String
  attribute :wants_email, Boolean, default: ->(signup_user, attribute) { true }

  class Result < Service::Result
    attribute :user, User
  end

  def call
    user = User.new(name: name, email: email, accepts_email: wants_email)
    result.user = user

    if user.save
      UserMailer.welcome_email(user.email).deliver
      result.successful!
    else
      result.add_errors(user)
    end

    result
  end
end


## service_call.rb
class Service::Call
  include Virtus.model

  attribute :result, Service::Result, default: ->(service,_) { service.build_result }

  def self.call(*args)
    new(*args).call
  end

  protected

  def build_result
    klass = self.class.const_get("Result") rescue Service::Result
    klass.new
  end

  def with_exception_catching
    begin
      yield
    rescue StandardError => exception
      result.exception = exception
      result.add_errors(exception.record) if exception.respond_to?(:record)
    end
  end

end

## service_result.rb
class Service::Result
  include Virtus.model

  attribute :status, String, default: Status::ERROR
  attribute :errors, Object, default: ->(sr,_) { ActiveModel::Errors.new(sr) }
  attribute :exception, StandardError

  module Status
    SUCCESSFUL = 'successful'
    ERROR = 'error'
  end

  def successful!; self.status = Status::SUCCESSFUL; self; end
  def successful?; self.status == Status::SUCCESSFUL; end
  def error!;      self.status = Status::ERROR; self; end
  def error?;      self.status == Status::ERROR; end

  def add_error_message(message)
    errors.add(:base, message)
  end

  def add_errors(obj_with_errors)
    Array(obj_with_errors).each do |obj|
      self.errors.messages.merge!(obj.errors) unless obj.errors.empty?
    end
  end

  def add_errors_or_be_successful!(obj_with_errors)
    add_errors(obj_with_errors)
    successful! if errors.empty?
    self
  end
end