Re: Using "with function"

["Matthew Heaney" <mheaney@on2.com>]

"Richard Riehle" <richard@adaworks.com> wrote in message
news:3BDFA1A2.EAF8B6AA@adaworks.com...
> It is nice to hear from Matthew Heaney.  He has been absent for far too
> long from this forum, and we always enjoy his comments.

Good to be back.  Hope you're looking forward to some arguments!

> I am going to respectfully disagree with Matthew on this.   While using
the
> "box" makes it easier to instantiate the "with function" it also carries
with
> it some danger.   Both Booch and Ed Berard made the case many years
> ago for avoiding the use of operators directly in generic formal function
> parameters.

Do you mean operatORS specifically, or any generic formal subprogram?

Also, can you be more specific about what their objection is?  Do you have
any references?

> In the GRACE components it was common to see somethin
> like this:
>
>      generic
>         type Element_Type is private;
>         with function Is_Equal(L, R : Element_Type) return Boolean;
>      package GP ...
>
> This has the effect of demanding that the instantiating unit supply a
> generic actual parameter.

But isn't this required only because Ada83 wouldn't let you pass the
operator form for equality?  In Ada83 you *had* to do it this way, or resort
to loopholes like the Goodenough Trick.

> I recall a PhD thesis from Ohio State (apologize for forgetting the
> author's name) in which the case was made for making all generic
> formal parameters limited private and requiring the instantiation
> to provide all kinds of operations, including a copy procedure
> since assignment cannot be overloaded.

Do you have a more specific reference?  If you can narrow down the year then
maybe we can do a UMI search.

> Of course, now that we can create generic signature packages in
> Ada 95, that is packages that contain only generic formal parameters
> for further instantiation of generic formal package parameters, the
> Ohio State thesis gains a bit more credibility.

Generic formal package parameters are very helpful.