application_presenter.rb

class ApplicationPresenter

  # Override this in your presenter
  def to_hash
    {}
  end
  
  def to_json
    to_hash.to_json
  end

  class << self

    def render
      JSON.parse(retrieve, object_class: OpenStruct)
    rescue TypeError => error
      if saved?
        raise error
      else
        save
        render
      end
    end
    
    def retrieve
      if perform_caching?
        redis.get(redis_key)
      else
        instance.to_json
      end
    end

    def save
      redis.set(redis_key, instance.to_json)
    end

    def saved?
      redis.exists(redis_key)
    end

    private
    
    def instance
      @instance ||= new
    end

    def perform_caching?
      ENV["CACHE_PRESENTERS"] || Rails.application.config.action_controller.perform_caching
    end

    def redis
      REDIS
    end

    def redis_key
      self.to_s.split("::").map(&:underscore).join(":")
    end

  end
end

sample_presenter.rb

class SamplePresenter < ApplicationPresenter
  
  def to_hash
    {
      data: really_expensive_computation!
    }
  end
  
  private
  
  def really_expensive_computation!
    sleep 10
  end
  
end