class ActiveSupport::Cache::Entry

def dup_value!

serialize entries to protect against accidental cache modifications.
Duplicates the value in a class. This is used by cache implementations that don't natively 
def dup_value!
  if @value && !compressed? && !(@value.is_a?(Numeric) || @value == true || @value == false)
    if @value.is_a?(String)
      @value = @value.dup
    else
      @value = Marshal.load(Marshal.dump(@value))
    end
  end
end