JRuby: improve constantize performance. [#410 state:resolved]

activesupport/lib/active_support/inflector.rb

@@ -291,11 +291,14 @@ def foreign_key(class_name, separate_class_name_and_id_with_underscore = true)
     # NameError is raised when the name is not in CamelCase or the constant is
     # unknown.
     def constantize(camel_cased_word)
-      unless /\A(?:::)?([A-Z]\w*(?:::[A-Z]\w*)*)\z/ =~ camel_cased_word
-        raise NameError, "#{camel_cased_word.inspect} is not a valid constant name!"
-      end
+      names = camel_cased_word.split('::')
+      names.shift if names.empty? || names.first.empty?
 
-      Object.module_eval("::#{$1}", __FILE__, __LINE__)
+      constant = Object
+      names.each do |name|
+        constant = constant.const_defined?(name) ? constant.const_get(name) : constant.const_missing(name)
+      end
+      constant
     end
 
     # Turns a number into an ordinal string used to denote the position in an
@@ -326,4 +329,4 @@ def ordinalize(number)
 require 'active_support/core_ext/string/inflections'
 unless String.included_modules.include?(ActiveSupport::CoreExtensions::String::Inflections)
   String.send :include, ActiveSupport::CoreExtensions::String::Inflections
-end
\ No newline at end of file
+end