From: Dmitry Bilunov <kmeaw@...>
Date: 2007-08-08T06:41:12+09:00
Subject: non-constant strings

Hello. Why does Ruby have non-constant strings? It seems there is a way
to bypass object encapsulation paradigm and break object integrity. Here
is any example:

class SecureRunner
# This class implements a sudo-like
# runner

  def initialize(command)
  # Creates an instance. Guaranties, that a command is safe.
    if command.safe?
      @comamnd = command
    else
      raise RuntimeError, "Security check failed!"
    end
  end

  def run
  # Only safe commands should be run
    system(@command)
  end
end

# This class seems to be safe
# Here is a way to bypass security check:

command = "some_safe_command"
runner = SecureRunner.new(command)
# a command is safe, so check will be passed

command.replace("evil_command")  # BYPASS THE CHECK

runner.run # runs evil_command, that is not safe

The same can be done to fields of instances, which are exported as
read-only (attr_reader). I know there is a way to fix it (using .clone
or .dup), but what is the reason Ruby has non-constant strings, as most
languages (Java, Python) do? Is there a way to disable such behaviour
($SAFE will not help, because internal class methods will not be able to
change instance-variable strings too).
-- 
Posted via http://www.ruby-forum.com/.