Re: "private with" proposal

[Stephen Leake <Stephen.A.Leake@nasa.gov>]

Vincent Marciante <INALID_EXCEPT_FOR_marciant@earthlink.net> writes:

> "with private" is a proposed addition to Ada; see 
> http://www.ada-auth.org/cgi-bin/cvsweb.cgi/AIs/AI-00262.TXT?rev=1.13
> 
> I do not understand why the extra syntax (adding "private" to
> the context clause) is necessary.  Can't the rules be simply
> be changed as outlined in the proposal?  If compilers at this 
> time already do enough to recognize withing a private unit 
> in a public spec couldn't they be made to allow usage of withed 
> private units only in the private part (and body)?

You are correct, the "extra syntax" of "private" in the context clause
is not strictly necessary; the compiler and reader could figure out
what's going on.

But what is the downside of having the extra syntax? The syntax alone
is a trivial addition to the compiler; the semantics is more complex.

The upside of the extra syntax is significant; the compiler can tell
if some later maintenance code breaks a design decision; the reader
can tell that package "foo" is implementation only, and not part of
the visible spec.

So i'd prefer to keep the "with private".

In addition, there are some cases with generics where it really is
necessary, to keep the generic contract. I posted a note about that
here a while back (and to the ARG, as well).

-- 
-- Stephe