Revert "Simplify code in AS json encoder"

This reverts commit 046e27a733.
Check https://github.com/rails/rails/pull/8815#issuecomment-14026122 for
details.

activesupport/lib/active_support/json/encoding.rb

@@ -38,6 +38,7 @@ module ActiveSupport
       class CircularReferenceError < StandardError; end
 
       class Encoder
+        attr_reader :options
 
         def initialize(options = nil)
           @options = options || {}
@@ -62,9 +63,9 @@ module ActiveSupport
           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.dup
+            options.dup
           end
         end
 
@@ -251,6 +252,18 @@ class Regexp
 end
 
 module Enumerable
+  def as_json(options = nil) #:nodoc:
+    to_a.as_json(options)
+  end
+end
+
+class Range
+  def as_json(options = nil) #:nodoc:
+    to_s
+  end
+end
+
+class Array
   def as_json(options = nil) #:nodoc:
     # use encoder as a proxy to call as_json on all elements, to protect from circular references
     encoder = options && options[:encoder] || ActiveSupport::JSON::Encoding::Encoder.new(options)
@@ -263,12 +276,6 @@ module Enumerable
   end
 end
 
-class Range
-  def as_json(options = nil) #:nodoc:
-    to_s
-  end
-end
-
 class Hash
   def as_json(options = nil) #:nodoc:
     # create a subset of the hash by applying :only or :except