users_controller_service.rb

class UsersController < ApplicationController 
  def create 
    CreateUserService.new.call(
      params[:user], 
      on_success: public_method(:create_successful), 
      on_failure: public_method(:create_failure)
    )
  end
  
  def create_successful(user)
    flash[:notice] ="The user was created successfully" 
    redirect_to :index
  end
  
  def create_failure(invalid_user)
    render 'new', locals: { user: invalid_user }
  end
end

class CreateUserService
  attr_reader :user_factory
    
  def initialize(user_factory: User.public_method(:new))
    @user_factory = user_factory
  end
   
  def call(attributes: {}, on_success: proc{}, on_failure: proc{})
    user = user_factory.call attributes
      
    user.save ? on_success[user] : on_faiulre[user]
  end
end