Clean up the implementation of AR::Dirty

This moves a bit more of the logic required for dirty checking into the
attribute objects. I had hoped to remove the `with_value_from_database`
stuff, but unfortunately just calling `dup` on the attribute objects
isn't enough, since the values might contain deeply nested data
structures. I think this can be cleaned up further.

This makes most dirty checking become lazy, and reduces the number of
object allocations and amount of CPU time when assigning a value. This
opens the door (but doesn't quite finish) to improving the performance
of writes to a place comparable to 4.1

2 files changed, 11 insertions, 0 deletions

diff --git a/activemodel/lib/active_model/type/helpers/accepts_multiparameter_time.rb b/activemodel/lib/active_model/type/helpers/accepts_multiparameter_time.rb
index fa1ccd057e..facea12704 100644
--- a/activemodel/lib/active_model/type/helpers/accepts_multiparameter_time.rb
+++ b/activemodel/lib/active_model/type/helpers/accepts_multiparameter_time.rb
@@ -11,6 +11,14 @@ module ActiveModel
             end
           end
 
+          define_method(:assert_valid_value) do |value|
+            if value.is_a?(Hash)
+              value_from_multiparameter_assignment(value)
+            else
+              super(value)
+            end
+          end
+
           define_method(:value_from_multiparameter_assignment) do |values_hash|
             defaults.each do |k, v|
               values_hash[k] ||= v
diff --git a/activemodel/lib/active_model/type/value.rb b/activemodel/lib/active_model/type/value.rb
index c7d1197d69..5fea0561a6 100644
--- a/activemodel/lib/active_model/type/value.rb
+++ b/activemodel/lib/active_model/type/value.rb
@@ -91,6 +91,9 @@ module ActiveModel
           limit == other.limit
       end
 
+      def assert_valid_value(*)
+      end
+
       private
 
       # Convenience method for types which do not need separate type casting