From: Yohanes Santoso <ysantoso@...>
Date: 2002-11-09T01:54:11+09:00
Subject: Re: Making Instace Variables Private/Local

William Djaja Tjokroaminata <billtj@z.glue.umd.edu> writes:

> If I am the project manager, I will enforce this to my subordinates: when
> the class local variables are available, then everyone will use only class
> local (private) variables, and child classes will access the parent's data
> using methods, never the variables directly.  In this way there is no risk

Well, you could try the untested code below to privatise parent's
instance variables. You'll need Wayne Conrad's stack frame patch:
http://yagni.com/stack_frames/index.php

class Module
  def attr_local(*args)
    args.each {|arg|
      if not arg.is_a? Symbol
	raise "attr_local is supplied with non-symbol arguments"
      end
      get_block = %q{def #{arg.to_s}
                   if stack_frames[0].class.is_a? self 
                     raise "unauthorised access to local variable"
                   else
                     @#{arg.to_s}
                 end}
      set_block = %q{def #{arg.to_s}=(value)
                   if stack_frames[0].class.is_a? self 
                     raise "unauthorised access to local variable"
                   else
                     @#{arg.to_s} = value
                 end}
      module_eval get_block
      module_eval set_block
    }
  end
end


But, really, humans (programmers) must bear some responsibility. The
situation is like the interface. You can define interfaces, but those
who implement them are not guaranteed to give the functionality you
expect.

Like (java):

interface Consume {
public void eat();
}

class Human implements Consume { .... };
class IOStream implements Consume { ... };

Both classes implement two methods with the same name, but totally
different behaviours. So, in the end it's still the programmers'
responsibility to make things sensible.

YS.