Re: abstract sub programs overriding

[Dmitry A. Kazakov <mailbox@dmitry-kazakov.de>]

On Thu, 11 Mar 2004 10:40:02 -0500, Hyman Rosen <hyrosen@mail.com>
wrote:

>Dmitry A. Kazakov wrote:
>> No, this is just a contract model.
>
>Between what parties?

Interface developer and its user

>> These are different things - to have a bad design or to have a good
>> one, but poorly coded one.
>
>You want your language to help you catch the poor coding. That's why
>Ada catches bounds errors, for example.

Exactly

>> You cannot do it right if the language does not support object
>> construction properly.
>
>The concept of two-phase initialization is a backward step in OO.

If that would be true, no C++ library would have Init() in each and
other class.

>The paradigm of C++'s *tor mechanism is that other methods don't
>ever need object validity checks, because constructors make the
>object kosher.

But they cannot do it, when dispaching methods need to be called as a
part of base specific object construction.

>> I tried to show that the source of the problem is that to construct T
>> /= to construct T'Class.
>
>This makes no sense.

Any primitive operation (method) can be either dispatching or
class-wide. So a constructor / destructor. This a programmer's choice,
not one of the language, if one wishes to make some parts of
constructor overridable (=dispatching), some not (=specific), and some
common for all descendants (=class-wide). 

> A general object, in the OO world, may have each
>derived class require services from its base class, even during object
>construction. Bases may need to invoke services from derived classes,
>such as in the template method design pattern. When the latter is
>invoked from the former, problems arise. I have no idea what this has
>to do with being classwide or not.

It quite obvious: "To invoke a service from a derived type" is a more
complicated way to say "to dispatch". But dispatching is possible on
class-wide objects only.

--
Regards,
Dmitry Kazakov
www.dmitry-kazakov.de