Ruby: Trying to add some decorations to core classes, but only have them apply within a specific module.

gistfile1.rb

# The result I'm looking for

module Herp
  "".respond_to?( :whizbangify )  # true
  File.respond_to?( :take_ownership )   # true
end

"".respond_to?( :whizbangify )  # false
File.respond_to?( :take_ownership )   # false



# What I tried

module CustomString
  def whizbangify
    puts "whizbangify"
  end
end

module CustomFile
  def self.take_ownership
    puts "take ownership"
  end
end

module Herp
  class HerpString < String
    include CustomString
  end

  class HerpFile < File
    include CustomFile
  end
end

Herp::String = Herp::HerpString
Herp::File   = Herp::HerpFile

"".respond_to?( :whizbangify )                   # false (correct)
Herp::HerpString.new.respond_to?(:whizbangify)   # true (correct)
Herp::String.new.respond_to?(:whizbangify)       # true (correct)

module Herp
  def self.test
    "".respond_to?( :whizbangify )
  end
end
Herp.test         # false (not the behavior I hoped for)

# So, is there a way to get this behavior?  I was hoping that, within the module,
# any references to String would go to HerpString first, but it doesn't seem to
# work that way.  I've been getting "superclass mismatch" errors.