def [](url)
      interpret case
        when store.respond_to?(:[])
          store[key_for(url)]
        when store.respond_to?(:get)
          store.get key_for(url)
        when store.respond_to?(:read)
          store.read key_for(url)
      end
    end
def [](url)
      interpret case
        when store.respond_to?(:[])
          store[key_for(url)]
        when store.respond_to?(:get)
          store.get key_for(url)
        when store.respond_to?(:read)
          store.read key_for(url)
      end
    end
Read from the Cache.