collection_by_cache_keys

# File actionview/lib/action_view/renderer/partial_renderer/collection_caching.rb, line 32
      def collection_by_cache_keys
        seed = callable_cache_key? ? @options[:cached] : ->(i) { i }

        @collection.each_with_object({}) do |item, hash|
          hash[expanded_cache_key(seed.call(item))] = item
        end
      end