Re: Inherited Methods and such

[Maciej Sobczak <see.my.homepage@gmail.com>]

On 26 Wrz, 14:26, Robert A Duff <bobd...@shell01.TheWorld.com> wrote:

> > Let's also not forget that Initialize is useless as a constructor (and
> > thus incomparable to C++) anyway due to the lack of parameters. But so-
> > called "constructor functions" will not solve this problem.
>
> I've lost track of this discussion (sorry -- it's gotten rather
> philosophical at times!).

Yes, but I don't feel guilty. ;-)

> Could you please explain exactly what this
> constructor problem is?

The constructor, as known from many other languages, can have
parameters that can possibly influence its work. Ada does not provide
anything built-in for this.

> And why "constructor functions" do not solve
> it?

Constructor functions in Ada are functions that return new objects
(most useful for limited types since Ada 2005) can have parameters,
but they still don't acknowledge the "progressive" nature of the whole
process. This means that no matter whether we use Initialize or
constructor functions, the final type of the object is established at
the very beginning and is kept during the whole construction process.
If this process involves some activities on various levels of the type
inheritance chain, the ugly effects like the one from my example can
result, because primitive operations can be called bypassing the
intended order of component construction.

> Are there other languages (c++, perhaps?) that have a complete solution
> to this problem?

My claim in this lengthy and philosophical discussion is that C++
provides a complete solution which can be shortly described like this:
the final type is not established from the very beginning, but is
progressively moving along the inheritance chain as the subsequent
constructors of base types complete their work. Thank's to this,
primitive operations never dispatch further than what can be
statically reasoned about.

Implementation-wise, this can be done with "just" changing the tag of
the object as each base constructor completes.

--
Maciej Sobczak
http://www.msobczak.com/