1 files changed, 6 insertions, 9 deletions
diff --git a/activesupport/lib/active_support/json/encoding.rb b/activesupport/lib/active_support/json/encoding.rb
index d22fe14b33..469ae69258 100644
--- a/activesupport/lib/active_support/json/encoding.rb
+++ b/activesupport/lib/active_support/json/encoding.rb
@@ -1,6 +1,5 @@
 require 'active_support/core_ext/object/to_json'
 require 'active_support/core_ext/module/delegation'
-require 'active_support/deprecation'
 require 'active_support/json/variable'
 require 'active_support/ordered_hash'
 
@@ -14,6 +13,7 @@ require 'time'
 require 'active_support/core_ext/time/conversions'
 require 'active_support/core_ext/date_time/conversions'
 require 'active_support/core_ext/date/conversions'
+require 'set'
 
 module ActiveSupport
   class << self
@@ -38,8 +38,8 @@ module ActiveSupport
         attr_reader :options
 
         def initialize(options = nil)
-          @options = options
-          @seen = []
+          @options = options || {}
+          @seen = Set.new
         end
 
         def encode(value, use_options = true)
@@ -59,7 +59,7 @@ module ActiveSupport
         def options_for(value)
           if value.is_a?(Array) || value.is_a?(Hash)
             # hashes and arrays need to get encoder in the options, so that they can detect circular references
-            (options || {}).merge(:encoder => self)
+            options.merge(:encoder => self)
           else
             options
           end
@@ -71,13 +71,12 @@ module ActiveSupport
 
         private
           def check_for_circular_references(value)
-            if @seen.any? { |object| object.equal?(value) }
+            unless @seen.add?(value.__id__)
               raise CircularReferenceError, 'object references itself'
             end
-            @seen.unshift value
             yield
           ensure
-            @seen.shift
+            @seen.delete(value.__id__)
           end
       end
 
@@ -139,8 +138,6 @@ module ActiveSupport
       self.use_standard_json_time_format = true
       self.escape_html_entities_in_json  = false
     end
-
-    CircularReferenceError = Deprecation::DeprecatedConstantProxy.new('ActiveSupport::JSON::CircularReferenceError', Encoding::CircularReferenceError)
   end
 end