Re: Once again, Ada absent from DoD SBIR solicitation

[brett@ada9x.enet.dec.com (Bevin R. Brett)]

In article <3262572D.4E79@watson.ibm.com>, "Norman H. Cohen" <ncohen@watson.ibm.com> writes...
>Mitch Gart wrote:
> 
>> Ada package notation makes it worse:
>> 
>>    pkg1.func(obj, param);
>> 
>> can really call the code in the body of pkg2, instead of pkg1, if there is
>> dispatching.  To me in this case the Ada syntax is lying to the person who
>> is reading the program.  It makes the code hard to read correctly in my opinion.
> 
>This is the wrong way to think about it.  pkg1.func, called with a
>classwide argument, is a polymorphic subprogram that is introduced in
>pkg1.
> 
>The dispatching is part of the implementation of the polymorphic
>subprogram, not part of its interface.  When manipulating an object
>through a classwide view, one should, in most circumstances, not be
>concerned with the specific type of the object.  From the caller's level
>of abstraction, a dispatching call on pkg1.func is invoking the
>polymorphic interface declared in pkg1.  The fact that the polymorphic
>behavior may implemented by dispatching to a body in pkg2 should be
>irrelevant to the caller.
> 
>A comment in pkg1 should specify the behavior of func in general terms
>that will apply to all future overridings of func.  That is, when func
>is overridden, the overriding subprogram should satisfy the
>specifications of pkg1.func (and possibly additional specifications as
>well).  When calling pkg1.func, the caller should rely only on the more
>general specifications that apply to pkg1.func and ALL its overridings.
> 
>-- 
>Norman H. Cohen
>mailto:ncohen@watson.ibm.com
>http://www.research.ibm.com/people/n/ncohen