Re: AQ&S Guidance on pragma Elaborate_Body

[jsa@alexandria (Jon S Anthony)]

In article <mheaney-ya023680002904972043250001@news.ni.net> mheaney@ni.net (Matthew Heaney) writes:

> I'm certainly not advocating large packages.  It's just that very often,
> there are a small number of types (read: 2) that need to know about each
> other's representation, or that one needs the know the represenation of the
> other (the iterator above).
> 
> This is just the concept of a friend in C++: to implement that in Ada, you
> put the types together in the same package.  No big deal.

I disagree.  "Friendship" typically has more to do with types that
need *implementation* information about one another in order to be
efficient.  And it is not bi directional - no mutual dependence. This
is almost always something that happens after the creation of one of
the types - a new type is defined which utilizes another as a
component [note: not as a parent class - that is handled by
inheritance and protection].  In Ada this sort of thing is handled by
child packages which can a) be defined way after the fact and b) still
have direct information about the implementation of the used type.

The notion of mutually dependent types is a very different thing
altogether.  In C++ this is handled (basically) via forward
declarations.  And there is no direct analog (capability) for this in
Ada except incomplete types.  But these require everything to be in
the same _immediate_ scope.

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