From: William Djaja Tjokroaminata <billtj@...>
Date: 2002-10-28T23:49:39+09:00
Subject: Re: Inheritance Problem in Dynamic/Typeless Language

Hi Jim,

Jim Weirich <jweirich@one.net> wrote:
> The problem is retraining class writers (myself included) to
> do it the right way.

I don't think retraining will solve the vast existence of codes that have
been written in the "old" way, including the basic Ruby built-in classes
themselves.  That's why I am very interested whether from OO design point
of view, the current design is "flawed".  (I think OO has been around for
a long time, so it is hard to believe that this kind of problem is not
encountered/solved before.)

> This
> problem has little to do with static vs dynamic typing and can easily
> occur in C++ programs.

Well, it may occur in C++ programs, but it is not the intention.  Suppose

    derived a;
    parent  b;
    parent  c;
    ....
    a = b + c;

Assuming that this code compiles and executes, here we are guaranteed that
the class of a is "derived" (i.e., a will respond to methods that
are defined for class derived).  There may be some semantic/logic error
depending on the overloadings of the '+' and '=' operators, but that is a
separate issue.

> On a side node (a mild rant) ...

>> In a "typeless" language such as Ruby,

> Ruby is hardly "typeless".  It has all kinds of types.  Types are a very
> important part of programming in Ruby. (end of mild rant)

Oh, I agree completely.  I just use a terminology that apprently has been
used very often here.  I think the term "typed/typeless" is usually
used to refer to the variables themselves, and not the objects.

Regards,

Bill