Re: Eiffel and Java + Ada dispatching

[jsa@alexandria (Jon S Anthony)]

In article <5563vp$1of@buggy.news.easynet.net> Sacha@easynet.fr (Vincent WEBER) writes:

> In article <E00t53.CG2@syd.csa.com.au>, donh@syd.csa.com.au says...
> 
> >
> >Don't mistake Ada's symmetrical syntax for multiple dispatching (binding
> >driven by more than one parameter). Ada is still single dispatched so for
> >dispatching operations, the symmetry is syntactic rather than semantic.  
> >
>
> Hum... I'm lost, two ada specialists saying two different things :)

Well, the problem is that Don is not an "ada specialist" and is in
error about there not being any semantics to this (or maybe just
simplifying to avoid the details).  There are indeed semantic aspects
as I point out in another note, but these do not imply multiple
dispatch.  So, that part is certainly correct.


> Let me cote an article from the french magazine "L'Objet" (Vol 1, no
> 1, Spring 95), by Antoine Bertier (Tomson Software Products) and
> Pascal Plisson (Alsys). I tried to translate from french to english,
> please apologize the mistakes if any :) "It is important to note
> than tags of all the parameters have to be identical at run-time to
> have the dispatching done to only one effective operation.
> Therefore there is no priviliged parameter for dispatching as it is
> the case in other languages. This is an important advantage of Ada
> 95 's model compared to other languages such as C++, that break the
> natural symetry of some operations in privileging the parameter used
> for the dispatching ( et need a way to reference this parameter :
> "this" in C++). For instance :

Yes, this is true and captures some (I suppose most) of the semantic
aspects.  But note that there is no conflict here with the assertion
that these are _not_ multi-dispatch.


> Well I think that one of the two parts is wrong :) any comment ?

Don's statement at face value is in error, but not on the salient part
of multiple-dispatch.


/Jon
-- 
Jon Anthony
Organon Motives, Inc.
Belmont, MA 02178
617.484.3383
jsa@organon.com