1 files changed, 56 insertions, 0 deletions
diff --git a/activerecord/lib/active_record/attribute.rb b/activerecord/lib/active_record/attribute.rb
new file mode 100644
index 0000000000..f78cde23c5
--- /dev/null
+++ b/activerecord/lib/active_record/attribute.rb
@@ -0,0 +1,56 @@
+module ActiveRecord
+  class Attribute # :nodoc:
+    class << self
+      def from_database(value, type)
+        FromDatabase.new(value, type)
+      end
+
+      def from_user(value, type)
+        FromUser.new(value, type)
+      end
+    end
+
+    attr_reader :value_before_type_cast, :type
+
+    # This method should not be called directly.
+    # Use #from_database or #from_user
+    def initialize(value_before_type_cast, type)
+      @value_before_type_cast = value_before_type_cast
+      @type = type
+    end
+
+    def value
+      # `defined?` is cheaper than `||=` when we get back falsy values
+      @value = type_cast(value_before_type_cast) unless defined?(@value)
+      @value
+    end
+
+    def value_for_database
+      type.type_cast_for_database(value)
+    end
+
+    def type_cast
+      raise NotImplementedError
+    end
+
+    protected
+
+    def initialize_dup(other)
+      if defined?(@value) && @value.duplicable?
+        @value = @value.dup
+      end
+    end
+
+    class FromDatabase < Attribute
+      def type_cast(value)
+        type.type_cast_from_database(value)
+      end
+    end
+
+    class FromUser < Attribute
+      def type_cast(value)
+        type.type_cast_from_user(value)
+      end
+    end
+  end
+end