Factor out ancestor class Field of Attribute and Reflection.

lib/active_model/serializer/attribute.rb

@@ -1,40 +1,25 @@
+require 'active_model/serializer/field'
+
 module ActiveModel
   class Serializer
-    Attribute = Struct.new(:name, :options, :block) do
-      def value(serializer)
-        if block
-          serializer.instance_eval(&block)
-        else
-          serializer.read_attribute_for_serialization(name)
-        end
-      end
-
-      def included?(serializer)
-        case condition
-        when :if
-          serializer.public_send(condition)
-        when :unless
-          !serializer.public_send(condition)
-        else
-          true
-        end
-      end
-
-      private
-
-      def condition_type
-        if options.key?(:if)
-          :if
-        elsif options.key?(:unless)
-          :unless
-        else
-          :none
-        end
-      end
-
-      def condition
-        options[condition_type]
-      end
+    # Holds all the meta-data about an attribute as it was specified in the
+    # ActiveModel::Serializer class.
+    #
+    # @example
+    #   class PostSerializer < ActiveModel::Serializer
+    #     attribute :content
+    #     attribute :name, key: :title
+    #     attribute :email, key: :author_email, if: :user_logged_in?
+    #     attribute :preview do
+    #       truncate(object.content)
+    #     end
+    #
+    #     def user_logged_in?
+    #       current_user.logged_in?
+    #     end
+    #   end
+    #
+    class Attribute < Field
     end
   end
 end

lib/active_model/serializer/field.rb

@@ -0,0 +1,55 @@
+module ActiveModel
+  class Serializer
+    # Holds all the meta-data about a field (i.e. attribute or association) as it was
+    # specified in the ActiveModel::Serializer class.
+    # Notice that the field block is evaluated in the context of the serializer.
+    Field = Struct.new(:name, :options, :block) do
+      # Compute the actual value of a field for a given serializer instance.
+      # @param [Serializer] The serializer instance for which the value is computed.
+      # @return [Object] value
+      #
+      # @api private
+      #
+      def value(serializer)
+        if block
+          serializer.instance_eval(&block)
+        else
+          serializer.read_attribute_for_serialization(name)
+        end
+      end
+
+      # Decide whether the field should be serialized by the given serializer instance.
+      # @param [Serializer] The serializer instance
+      # @return [Bool]
+      #
+      # @api private
+      #
+      def included?(serializer)
+        case condition
+        when :if
+          serializer.public_send(condition)
+        when :unless
+          !serializer.public_send(condition)
+        else
+          true
+        end
+      end
+
+      private
+
+      def condition_type
+        if options.key?(:if)
+          :if
+        elsif options.key?(:unless)
+          :unless
+        else
+          :none
+        end
+      end
+
+      def condition
+        options[condition_type]
+      end
+    end
+  end
+end

lib/active_model/serializer/reflection.rb

@@ -1,3 +1,5 @@
+require 'active_model/serializer/field'
+
 module ActiveModel
   class Serializer
     # Holds all the meta-data about an association as it was specified in the
@@ -12,7 +14,6 @@ class Serializer
     #     end
     #  end
     #
-    #  Notice that the association block is evaluated in the context of the serializer.
     #  Specifically, the association 'comments' is evaluated two different ways:
     #  1) as 'comments' and named 'comments'.
     #  2) as 'object.comments.last(1)' and named 'last_comments'.
@@ -25,28 +26,7 @@ class Serializer
     #
     # So you can inspect reflections in your Adapters.
     #
-    Reflection = Struct.new(:name, :options, :block) do
-      # @api private
-      def value(instance)
-        if block
-          instance.instance_eval(&block)
-        else
-          instance.read_attribute_for_serialization(name)
-        end
-      end
-
-      # @api private
-      def included?(serializer)
-        case condition_type
-        when :if
-          serializer.public_send(condition)
-        when :unless
-          !serializer.public_send(condition)
-        else
-          true
-        end
-      end
-
+    class Reflection < Field
       # Build association. This method is used internally to
       # build serializer's association by its reflection.
       #
@@ -91,20 +71,6 @@ def build_association(subject, parent_serializer_options)
 
       private
 
-      def condition_type
-        if options.key?(:if)
-          :if
-        elsif options.key?(:unless)
-          :unless
-        else
-          :none
-        end
-      end
-
-      def condition
-        options[condition_type]
-      end
-
       def serializer_options(subject, parent_serializer_options, reflection_options)
         serializer = reflection_options.fetch(:serializer, nil)