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From: Adam Beneschan <adam@irvine.com>
Newsgroups: comp.lang.ada
Subject: Re: parent package referring to child
Date: Thu, 11 Oct 2007 08:21:34 -0700
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On Oct 10, 9:12 pm, "Randy Brukardt" <ra...@rrsoftware.com> wrote:
> "Adam Beneschan" <a...@irvine.com> wrote in message
>
> news:1192047607.865747.220890@50g2000hsm.googlegroups.com...
>
> > On Oct 10, 12:32 pm, Matthew Heaney <mhea...@on2.com> wrote:
> ...
> > > No, that's wrong.  In this case you can use mode inout because type T
> > > is tagged (meaning that it's passed by reference).
>
> > I don't see what the parameter mode has to do with it.
>
> The mode has nothing do to with it; but the rule is that a tagged incomplete
> type (which is what you get in a limited view) can be used as a parameter.
> See 3.101(8.2/2).
>
> >  I can't find a rule that would make "procedure Op (O : in P.C.T);"
>
> illegal.
>
> It's the absence of a rule: see the only allowed uses for incomplete types:
> see 3.10.1(5-9.4/2). Note that 3.10.1(9.4/2) says that no other uses are
> allowed. Use as a parameter is not allowed for untagged types.

Right... I was under the impression that we were assuming T was
tagged.


> > Also, the "by reference" comment isn't relevant either.
>
> It is relevant as it is the reason that tagged incomplete types can be used
> as parameters (because the compiler doesn't need to know the real type in
> order to know how it is passed as a parameter - this same property is needed
> to be able to deal with classwide types which is why it is fundamental to
> tagged types); you don't know that for untagged types so they aren't
> allowed.

Yep, that makes sense.  My point was that using a parameter is illegal
for untagged by-reference types, just as for untagged by-copy types.
But if you're looking at a limited view, you aren't allowed to know
enough about the type to know whether an untagged type is by-reference
or by-copy.  I missed that---thanks for the explanation.

                  -- Adam