How do I get class-object from string "A::B::C" in Ruby?

The following example fails

class A
  class B
  end
end
p Object.const_get 'A' # => A
p Object.const_get 'A::B' # => NameError: wrong constant name A::B

UPDATE

Questions about the topic asked earlier:

1. Cast between String and Classname
2. Ruby String#to_class
3. Get a class by name in Ruby?

The last one gives a nice solution which can be evolved into

class String
  def to_class
    self.split('::').inject(Object) do |mod, class_name|
      mod.const_get(class_name)
    end
  end
end

class A
  class B
  end
end
p "A::B".to_class # => A::B