Re: Q: access to subprogram

[Magnus.Kempe@di.epfl.ch (Magnus Kempe)]

ncohen@watson.ibm.com (Norman H. Cohen) writes:
: 
: Bill Taylor's contribution was part of an ongoing discussion in the form
: of comments sent to the Mapping/Revision Team during the design of Ada 9X.

If I remember correctly, the final decision was based on arguments about
displays (Dewar arguing against a more generalized 'Access), alternatives
using generics and abstract types (Barnes arguing de facto against a more
generalized 'Access), and the bad mistake made in Ada 83 (the lack
of access to subprograms, as compared to C, Pascal, etc.).

This is not the only decision that was made on the basis of some implementors'
fears rather than for the sake of Ada users.  For instance, at some point
in the revision process child units of generics were rejected; the "solution"
was a compromise so that some implementors would not need to make any changes
in their linking steps when updating their compiler from Ada 83 to Ada 95.
The consequence is that not all non-generic hierarchies of packages can be
turned into generic hierarchies (just adding "generic" doesn't work, e.g.
if some child unit needs to "with" another child unit in the same hierarchy).

As Norm mentioned, most of these issues are documented in the "mrtcomments"
available online.  I hope the designers of Ada 0Y (oh-why) will read these
discussions carefully for the next revision--if there is one--so that they
can make a list of the fallacious arguments that will no doubt pop up again.

In the meantime, I think it is a very bad idea to try to "fix" such
mistakes by the introduction of an ever-increasing number of "hacking"
attributes.  For one thing, this tends to make Ada programs less portable
(from one compiler to another).

-- 
Magnus Kempe                  "I know not what course others may take, but as
Magnus.Kempe@di.epfl.ch        for me, Give me Liberty... or give me Death!"
http://lglwww.epfl.ch/Team/MK/                               -- Patrick Henry