Ada 0y wish list: "with private"

["Thierry Lelegard" <thierry.lelegard@canal-plus.fr>]

Recently, several wishlist items for Ada 0y were posted in c.l.a.
Like many old Ada users, I have a couple of them. I would like to
propose one for discussion: a "with private" extension.

The idea is to specify in a context clause of a unit spec that an
external unit can be used only in the private part.

Example:

with A;
with private B;
package C is
   X : A.TA;
private
   Y : B.TB; -- legal only in private part
end C;

There are two advantages:

1) Readability. The user of package C is only interested in the public
   interface of C. Reading "with private B", the user knows that he may
   safely ignore what the strange unit B is all about.

2) Use of private packages in private parts. Example:

package Lib is ...

private package Lib.Internals is ....

with private Lib.Internals;
package Lib.Public is
    ....
private
    type TP is new Lib.Internals.TI ...
end Lib.Public;

The second point is, of course, more important than the first one. Some
of my recent code could have been much simpler with such a possibility.
In Ada 95, a private package cannot be referenced at all in the spec
of a public package, even in the private part, since the context clause
"with Lib.Internals" is simply refused.

Two points:
- The "with private" syntax is, of course, only a suggestion.
- Maybe there is some implementation flaw that I missed.

Any ideas or objections?
-Thierry
____________________________________________________________________________

Thierry Lelegard, "The Jazzing Troll", Email: thierry.lelegard@canal-plus.fr
CANAL+ Technologies, 34 place Raoul Dautry, 75516 Paris Cedex 15, France
Tel: +33 1 71 71 54 30   Fax: +33 1 71 71 52 08   Mobile: +33 6 03 00 65 75
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