metaprogramming - Ruby String#to_class

Question

Taken from a previous post with some modifications to respond to sepp2k's comment about namespaces, I have implemented String#to_class method. I'm sharing the code here and I do believe that it could be refactored someway specially the "i" counter. Your comments are appreciated.

 class String
   def to_class
     chain = self.split "::"
     i=0
     res = chain.inject(Module) do |ans,obj|
       break if ans.nil?
       i+=1
       klass = ans.const_get(obj)
       # Make sure the current obj is a valid class 
       # Or it's a module but not the last element, 
       # as the last element should be a class
       klass.is_a?(Class) || (klass.is_a?(Module) and i != chain.length) ? klass : nil
     end
   rescue NameError
     nil
   end
 end

 #Tests that should be passed.
 assert_equal(Fixnum,"Fixnum".to_class)
 assert_equal(M::C,"M::C".to_class)
 assert_nil "Math".to_class
 assert_nil "Math::PI".to_class
 assert_nil "Something".to_class

Answer 1

I would take a look at ActiveSupport::CoreExtensions::String::Inflections specifically it's constantize method:

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