Ensure objects cached with MemoryStore are immutable

activesupport/lib/active_support/cache/memory_store.rb

@@ -22,7 +22,7 @@ module ActiveSupport
       def write(name, value, options = nil)
         @guard.synchronize do
           super
-          @data[name] = value
+          @data[name] = value.freeze
         end
       end
 

activesupport/test/caching_test.rb

@@ -120,4 +120,10 @@ class MemoryStoreTest < Test::Unit::TestCase
   def test_fetch_with_forced_cache_miss
     @cache.fetch('foo', :force => true) { 'bar' }
   end
+
+  def test_store_objects_should_be_immutable
+    @cache.write('foo', 'bar')
+    assert_raise(ActiveSupport::FrozenObjectError) { @cache.read('foo').gsub!(/.*/, 'baz') }
+    assert_equal 'bar', @cache.read('foo')
+  end
 end