create AttributeSequence class

lib/factory_bot.rb

@@ -47,6 +47,7 @@
 require "factory_bot/decorator/new_constructor"
 require "factory_bot/linter"
 require "factory_bot/version"
+require "factory_bot/attribute_sequence"
 
 module FactoryBot
   Deprecation = ActiveSupport::Deprecation.new("7.0", "factory_bot")

lib/factory_bot/attribute_sequence.rb

@@ -0,0 +1,24 @@
+module FactoryBot
+  # @api private
+  class AttributeSequence
+    attr_reader :expression
+
+    def initialize(&block)
+      @expression = block
+    end
+
+    def evaluate(index)
+      expression.call(index)
+    end
+
+    def self.evaluate_attributes(traits_and_overrides, i)
+      traits_and_overrides.map do |attribute|
+        next attribute unless attribute.is_a?(Hash)
+
+        attribute.transform_values do |value|
+          value.is_a?(self) ? value.evaluate(i) : value
+        end
+      end    
+    end
+  end
+end

lib/factory_bot/strategy_syntax_method_registrar.rb

@@ -39,7 +39,9 @@ def define_list_strategy_method
 
         Array.new(amount) do |i|
           block_with_index = StrategySyntaxMethodRegistrar.with_index(block, i)
-          send(strategy_name, name, *evaluate_sequence_attributes(traits_and_overrides, i), &block_with_index)
+          traits_and_evaluated_overrides =
+            FactoryBot::AttributeSequence.evaluate_attributes(traits_and_overrides, i)
+          send(strategy_name, name, *traits_and_evaluated_overrides, &block_with_index)
         end
       end
     end

lib/factory_bot/syntax/methods.rb

@@ -131,15 +131,7 @@ def generate_list(name, count)
       end
 
       def build_sequence(&block)
-        block
-      end
-
-      def evaluate_sequence_attributes(traits_and_overrides, i)
-        traits_and_overrides.map do |attribute|
-          next attribute unless attribute.is_a?(Hash)
-
-          attribute.transform_values { |value| value.respond_to?(:call) ? value.call(i) : value }
-        end    
+        FactoryBot::AttributeSequence.new(&block)
       end
     end
   end

spec/acceptance/create_list_spec.rb

@@ -39,7 +39,7 @@
   end
 
   context "with sequencial attributes" do
-    subject { FactoryBot.create_list(:post, 20, title: FactoryBot.build_sequence{|n| "title_#{n}"}) }
+    subject { FactoryBot.create_list(:post, 20, title: FactoryBot.build_sequence{ |n| "title_#{n}" }) }
 
     it "create sequencial attribute values" do
       subject.each_with_index do |record, i|