    # File lib/active_support/cache.rb, line 20
        def self.expand_cache_key(key, namespace = nil)
          expanded_cache_key = namespace ? "#{namespace}/" : ""

          if ENV["RAILS_CACHE_ID"] || ENV["RAILS_APP_VERSION"]
            expanded_cache_key << "#{ENV["RAILS_CACHE_ID"] || ENV["RAILS_APP_VERSION"]}/"
          end

          expanded_cache_key << case
          when key.respond_to?(:cache_key)
            key.cache_key
          when key.is_a?(Array)
            key.collect { |element| expand_cache_key(element) }.to_param
          when key.respond_to?(:to_param)
            key.to_param
          end

          expanded_cache_key
        end