1 files changed, 5 insertions, 4 deletions
diff --git a/actionpack/lib/action_dispatch/http/cache.rb b/actionpack/lib/action_dispatch/http/cache.rb
index f9b278349e..747d295261 100644
--- a/actionpack/lib/action_dispatch/http/cache.rb
+++ b/actionpack/lib/action_dispatch/http/cache.rb
@@ -69,17 +69,17 @@ module ActionDispatch
         end
 
         def date
-          if date_header = headers['Date']
+          if date_header = headers[DATE]
             Time.httpdate(date_header)
           end
         end
 
         def date?
-          headers.include?('Date')
+          headers.include?(DATE)
         end
 
         def date=(utc_time)
-          headers['Date'] = utc_time.httpdate
+          headers[DATE] = utc_time.httpdate
         end
 
         def etag=(etag)
@@ -89,10 +89,11 @@ module ActionDispatch
 
       private
 
+        DATE          = 'Date'.freeze
         LAST_MODIFIED = "Last-Modified".freeze
         ETAG          = "ETag".freeze
         CACHE_CONTROL = "Cache-Control".freeze
-        SPECIAL_KEYS  = %w[extras no-cache max-age public must-revalidate]
+        SPECIAL_KEYS  = Set.new(%w[extras no-cache max-age public must-revalidate])
 
         def cache_control_segments
           if cache_control = self[CACHE_CONTROL]