Re: Generic procedures and their parameters

["Randy Brukardt" <randy@rrsoftware.com>]

"Dmitry A. Kazakov" <mailbox@dmitry-kazakov.de> wrote in message
news:g3c05xzf7uad$.wucggq0h6wuy$.dlg@40tude.net...
...
> Yes, that's when somebody wanted to have different orders. But that in my
> view is a different case, in which "<" should be better passed to Sort as
a
> plain parameter, rather than generic or primitive subprogram.

We considered that, too, and decided not to do it because it because it
doesn't work well in Ada. "<" is usually Intrinsic, and Intrinsic things
cannot be passed as access-to-subprogram parameters. So you'd have to
explicitly build a wrapper function, with all of the possibilities for error
that that exposes. Generic instantiations don't have that limitation (as
they are are considered more heavyweight than a simple 'Access).

> I think the difference between two scenarios is whether the order is
arbitrary, ad-hoc
> or else involved in some loose set of operations. In the first case "<"
> should be a parameter in the latter case a part of the interface (be it
> generic or primitive operation).

We really wanted to avoid having a lot of different sorting routines,
because that then forces users to decide which one that they need to use.
Most of the time, the choice is not particularly important (if it is not a
critical operation), and excess choices just take mental energy away from
solving the problem at hand. (That's why I'd be opposed to having multiple
kinds of lists [like doubly and singly linked] in the Ada Containers
library; the space and performance differences would be slight, but they'd
add an additional complexity to deciding what container to use.)

But you are correct that there usually is a "natural" comparison operation
and then secondary orderings -- one could consider these as different cases,
simply as one would be named "<" and the other would have some other name..

                       Randy.