Move Attribute and AttributeSet to ActiveModel

Use these to back the attributes API.  Stop automatically including
ActiveModel::Dirty in ActiveModel::Attributes, and make it optional.

1 files changed, 30 insertions, 0 deletions

diff --git a/activemodel/lib/active_model/attribute/user_provided_default.rb b/activemodel/lib/active_model/attribute/user_provided_default.rb
new file mode 100644
index 0000000000..f274b687d4
--- /dev/null
+++ b/activemodel/lib/active_model/attribute/user_provided_default.rb
@@ -0,0 +1,30 @@
+# frozen_string_literal: true
+
+require "active_model/attribute"
+
+module ActiveModel
+  class Attribute # :nodoc:
+    class UserProvidedDefault < FromUser # :nodoc:
+      def initialize(name, value, type, database_default)
+        @user_provided_value = value
+        super(name, value, type, database_default)
+      end
+
+      def value_before_type_cast
+        if user_provided_value.is_a?(Proc)
+          @memoized_value_before_type_cast ||= user_provided_value.call
+        else
+          @user_provided_value
+        end
+      end
+
+      def with_type(type)
+        self.class.new(name, user_provided_value, type, original_attribute)
+      end
+
+      protected
+
+        attr_reader :user_provided_value
+    end
+  end
+end