extract method 'normalize_id' from 'StripeObject#initialize' & 'ListObject#retrieve'

lib/stripe/list_object.rb

@@ -16,12 +16,7 @@ module Stripe
     end
 
     def retrieve(id, opts={})
-      if id.kind_of?(Hash) # overloaded id
-        retrieve_params = id
-        id = retrieve_params.delete(:id)
-      else
-        retrieve_params = {}
-      end
+      id, retrieve_params = Util.normalize_id(id)
       response, opts = request(:get,"#{url}/#{CGI.escape(id)}", retrieve_params, opts)
       Util.convert_to_stripe_object(response, opts)
     end

lib/stripe/stripe_object.rb

@@ -10,15 +10,7 @@ module Stripe
     end
 
     def initialize(id=nil, opts={})
-      # parameter overloading!
-      if id.kind_of?(Hash)
-        @retrieve_params = id.dup
-        @retrieve_params.delete(:id)
-        id = id[:id]
-      else
-        @retrieve_params = {}
-      end
-
+      id, @retrieve_params = Util.normalize_id(id)
       @opts = opts
       @values = {}
       # This really belongs in APIResource, but not putting it there allows us

lib/stripe/util.rb

@@ -133,5 +133,15 @@ module Stripe
         raise TypeError.new('normalize_opts expects a string or a hash')
       end
     end
+
+    def self.normalize_id(id)
+      if id.kind_of?(Hash) # overloaded id
+        params_hash = id.dup
+        id = params_hash.delete(:id)
+      else
+        params_hash = {}
+      end
+      [id, params_hash]
+    end
   end
 end