Re: Design Question: How Best To Structure Cross-Referencing Types In Ada 95

[dewar@gnat.com]

In article <36A68FCA.E1EEAFFE@hiwaay.net>,
  aeg@hiwaay.net, glover@thaad.tecmasters.com wrote:
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> Since both types and some of the subprograms reference
> each other, I have to put them both in the same package.
> It turns out that I have about 5 types that
> behave like this and I end up with one large package.  I
> would rather have the types split into different
> packages, but I would get circular dependencies when
> compiling the specs.
>
> Is there a neat Ada95 way of getting around this
> cross-referencing problem?

This is an old and well discussed problem. Often you can
introduce a third package with the types alone to at least
factor this out, but the fundamental circularity problem
remains and there is no solution in pure Ada 95.

For JGNAT, the version of GNAT that generates code for the
JVM, we have found it important to deal with this problem
for the purpose of translating existing Java specs. We have
therefore implemented an extension, based on Tucker's "with
type" suggestion the last time around this was discussed,
and this extension will be available (controlled by a
switch of course) in version 3.12 of GNAT.

There are not many places where one can justify out and out
extensions of the language (and indeed I suppose one could
do this with a pragma, but it seems silly). This however,
seems an exception, where an extension is really needed.

Robert Dewar
Ada Core Technologies


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