make a singleton for AssociationScope

AssociationScope no longer maintains state, so we're safe to keep a
singleton and save on GC time

3 files changed, 8 insertions, 3 deletions

diff --git a/activerecord/lib/active_record/associations/association.rb b/activerecord/lib/active_record/associations/association.rb
index 2dba33898c..4e46256862 100644
--- a/activerecord/lib/active_record/associations/association.rb
+++ b/activerecord/lib/active_record/associations/association.rb
@@ -94,7 +94,7 @@ module ActiveRecord
       # actually gets built.
       def association_scope
         if klass
-          @association_scope ||= AssociationScope.new.scope(self, klass.connection)
+          @association_scope ||= AssociationScope.scope(self, klass.connection)
         end
       end
 
diff --git a/activerecord/lib/active_record/associations/association_scope.rb b/activerecord/lib/active_record/associations/association_scope.rb
index cd2911e0a4..1bc998d20c 100644
--- a/activerecord/lib/active_record/associations/association_scope.rb
+++ b/activerecord/lib/active_record/associations/association_scope.rb
@@ -1,6 +1,12 @@
 module ActiveRecord
   module Associations
     class AssociationScope #:nodoc:
+      INSTANCE = new
+
+      def self.scope(association, connection)
+        INSTANCE.scope association, connection
+      end
+
       def scope(association, connection)
         klass         = association.klass
         reflection    = association.reflection
diff --git a/activerecord/test/cases/associations/association_scope_test.rb b/activerecord/test/cases/associations/association_scope_test.rb
index f9793277e5..c78b036f53 100644
--- a/activerecord/test/cases/associations/association_scope_test.rb
+++ b/activerecord/test/cases/associations/association_scope_test.rb
@@ -6,8 +6,7 @@ module ActiveRecord
   module Associations
     class AssociationScopeTest < ActiveRecord::TestCase
       test 'does not duplicate conditions' do
-        association_scope = AssociationScope.new
-        scope = association_scope.scope(Author.new.association(:welcome_posts),
+        scope = AssociationScope.scope(Author.new.association(:welcome_posts),
                                         Author.connection)
         wheres = scope.where_values.map(&:right)
         assert_equal wheres.uniq, wheres