1 files changed, 41 insertions, 24 deletions
diff --git a/activesupport/lib/active_support/inflector.rb b/activesupport/lib/active_support/inflector.rb
index 9fb7540ea2..4921b99677 100644
--- a/activesupport/lib/active_support/inflector.rb
+++ b/activesupport/lib/active_support/inflector.rb
@@ -330,30 +330,47 @@ module ActiveSupport
       underscore(demodulize(class_name)) + (separate_class_name_and_id_with_underscore ? "_id" : "id")
     end
 
-    # Tries to find a constant with the name specified in the argument string:
-    #
-    #   "Module".constantize     # => Module
-    #   "Test::Unit".constantize # => Test::Unit
-    #
-    # The name is assumed to be the one of a top-level constant, no matter whether
-    # it starts with "::" or not. No lexical context is taken into account:
-    #
-    #   C = 'outside'
-    #   module M
-    #     C = 'inside'
-    #     C               # => 'inside'
-    #     "C".constantize # => 'outside', same as ::C
-    #   end
-    #
-    # NameError is raised when the name is not in CamelCase or the constant is
-    # unknown.
-    def constantize(camel_cased_word)
-      names = camel_cased_word.split('::')
-      names.shift if names.empty? || names.first.empty?
-
-      constant = Object
-      names.each { |name| constant = constant.const_get(name) }
-      constant
+    # Ruby 1.9 introduces an inherit argument for Module#const_get and
+    # #const_defined? and changes their default behavior.
+    if Module.method(:const_get).arity == 1
+      # Tries to find a constant with the name specified in the argument string:
+      #
+      #   "Module".constantize     # => Module
+      #   "Test::Unit".constantize # => Test::Unit
+      #
+      # The name is assumed to be the one of a top-level constant, no matter whether
+      # it starts with "::" or not. No lexical context is taken into account:
+      #
+      #   C = 'outside'
+      #   module M
+      #     C = 'inside'
+      #     C               # => 'inside'
+      #     "C".constantize # => 'outside', same as ::C
+      #   end
+      #
+      # NameError is raised when the name is not in CamelCase or the constant is
+      # unknown.
+      def constantize(camel_cased_word)
+        names = camel_cased_word.split('::')
+        names.shift if names.empty? || names.first.empty?
+
+        constant = Object
+        names.each do |name|
+          constant = constant.const_defined?(name) ? constant.const_get(name) : constant.const_missing(name)
+        end
+        constant
+      end
+    else
+      def constantize(camel_cased_word) #:nodoc:
+        names = camel_cased_word.split('::')
+        names.shift if names.empty? || names.first.empty?
+
+        constant = Object
+        names.each do |name|
+          constant = constant.const_get(name, false) || constant.const_missing(name)
+        end
+        constant
+      end
     end
 
     # Turns a number into an ordinal string used to denote the position in an