Re: Is the Writing on the Wall for Ada?

[aek@vib.usr.pu.ru (Alexander Kopilovitch)]

olehjalmar kristensen wrote:

> In fact, one of the *nice* things about the C++ multiple
> inheritance is that it allows me to express roles (a la Reenskaug) and
> then combine different roles in the same object without jumping
> through hoops.

Combining different roles in the same object may be a good thing
as far as those roles do not interfere with each other.
But in reality they may interfere by subtle and unforeseen way,
in some singular points of the problem space. Therefore it is
generally important (for the kinds of projects, for which Ada was
primarily designed) to maintain organized responsibility among
the roles, and this naturally leads to strict prioritization of
individual role's authority and responsibility. Single inheritance
ideally provides that prioritization, while full-scale multiple
inheritance symmetrically spreads responsibilty among several
ancestors, and did not provide any guidance for resolving of
apparent conflicts between the roles.

> In Smalltalk you need an extra tool to do this, in C++
> all you need is a little care. I suppose it *could* be done in Ada
> with generics, but I have not tried it, and it would certainly be more
> obfuscated.

Well, sometimes it may be done with generics, but anyway you may
always use straightforward delegation instead of multiple inheritance.
In fact, a delegation adds not so much code, and do not harm readability
(assuming regular attentive reading, not a brief glance).



Alexander Kopilovitch                      aek@vib.usr.pu.ru
Saint-Petersburg
Russia