Re: OO, C++, and something much better!

[dewar@merv.cs.nyu.edu (Robert Dewar)]

Ole-Hjalmar Kristensen FOU.TD/DELAB wrote:

> However, if I remember correctly, Alex Stepanov had earlier tried to
> implement a library like the C++ STL in Ada, but was incapable of
> doing it. This would indicate that the C++ template mechanism is more
> flexible than the Ada generics.
> Any comments?

Actually, when I talked to Alex, he indicated that there were critical
features in Ada 95 that were missing in C and C++ for this kind of
work. In particular, he noted that C lacks a general address comparison
operation, useful for hashing data structures, whereas Ada does have such
an operation (in System.Storage_Elements on type Integer_Address). It is
a bit ironic to identify this particular feature as crucial (since most
people mistakenly think that C has such a feature and Ada doesn't!)

He did also discuss problems in Ada 95, most notably the fact that generics
are less flexible than templates (that is to be expected, the flexibility
of templates comes of course at the expense of compile time checkability),
and also the lack of automatic instantiation in Ada.

Automatic instantiation is of course a dangerous tool, but in the hands
of those writing libraries of this type (Alex said to me that he thought
there were only about six people who should be writing such libraries and
he did not know who the other five were :-) :-) dangerous tools can be
put to good use, with the danger being insulated from the eventual client
at least in some cases.

There is a team at Rensaleer which has been working on duplicating STL
in Ada 95. The preliminary results looked very encouraging, I do not
know the status of this work.