solid-mvc.rb

# data trait
module Option
  def list
    all.sort.unshift(default)
  end
  def default
    'all'
  end
end

# data object
class Tag
  include Option
  def all
    [1, 2, 3]
  end
end

# handle cache service
class CacheService
  def initialize tag_model
    @tag_model = tag_model
  end
  def handle(tag)
    if tag == tag_model.default
      Rails.cache.clear
    elsif tag_model.list.include? tag
      Rails.cache.delete_matched("#{tag}*")
    end
  end
end

# view controller
class Controller

  # ex 1: display the view
  def index
    @tags = tag_model.list
  end

  # ex 2: handle an action
  def action
    service.handle params[:action]
    redirect_to index_page
  end

  protected

  def service
    @service ||= CacheService.new tag_model
  end

  def tag_model
    @tag_model ||= Tag.new
  end

end

puts Controller.new.index