From 5090a64aa3b9c08339c7aa370bfd6c08557ff8e7 Mon Sep 17 00:00:00 2001
From: Ryuta Kamizono <kamipo@gmail.com>
Date: Sun, 14 Jun 2020 13:50:07 +0900
Subject: [PATCH] Lazy allocate `@forced_changes`

It is almost no longer used in Active Record.
---
 .../lib/active_model/attribute_mutation_tracker.rb  | 13 ++++++++-----
 1 file changed, 8 insertions(+), 5 deletions(-)

diff --git a/activemodel/lib/active_model/attribute_mutation_tracker.rb b/activemodel/lib/active_model/attribute_mutation_tracker.rb
index d8cd48a53b..e46d2e76da 100644
--- a/activemodel/lib/active_model/attribute_mutation_tracker.rb
+++ b/activemodel/lib/active_model/attribute_mutation_tracker.rb
@@ -7,9 +7,8 @@ module ActiveModel
   class AttributeMutationTracker # :nodoc:
     OPTION_NOT_GIVEN = Object.new
 
-    def initialize(attributes, forced_changes = Set.new)
+    def initialize(attributes)
       @attributes = attributes
-      @forced_changes = forced_changes
     end
 
     def changed_attribute_names
@@ -62,11 +61,15 @@ module ActiveModel
     end
 
     def force_change(attr_name)
-      forced_changes << attr_name
+      forced_changes[attr_name] = fetch_value(attr_name)
     end
 
     private
-      attr_reader :attributes, :forced_changes
+      attr_reader :attributes
+
+      def forced_changes
+        @forced_changes ||= {}
+      end
 
       def attr_names
         attributes.keys
@@ -82,7 +85,7 @@ module ActiveModel
   end
 
   class ForcedMutationTracker < AttributeMutationTracker # :nodoc:
-    def initialize(attributes, forced_changes = {})
+    def initialize(attributes)
       super
       @finalized_changes = nil
     end