(Note to mod: I posted this previously thru google and it did not
appear)

A few weeks ago David Abrahams asked in a post if there was a way to
make the following
code work:

namespace { class M; }

class RD { friend class M; typedef int Q; };

namespace { class M { RD::Q i; }; }

-----

>From my reading of the standard (3.4.4, 3.4.1) the only thing needed
to make the above code work, is a standard compliant compiler (since M
is lookedup by unqualified name lookup which searches thru using
directives in a sense).

I tried the above code with comeau online and it claimed that M did
not have access to RD's privates.

The following did not work either (trying to use Qualified Name lookup
to prevent the auto-declaration 'feature' of friend declarations)

...
class RD { friend class ::M; ... };..
...

I believe the above is standard compliant too - and comeau does not
allow it.

Can someone please clarify these issues - either by quoting the
relevant passages in the std that mandate comeau's behavior or by
agreeing that this is indeed well-formed code and comeau should
compile it.


thanks,
Faisal Vali


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Faisal Vali wrote:
> (Note to mod: I posted this previously thru google and it did not
> appear)
>
> A few weeks ago David Abrahams asked in a post if there was a way to
> make the following
> code work:
>
> namespace { class M; }
>
> class RD { friend class M; typedef int Q; };
>
> namespace { class M { RD::Q i; }; }
>
> -----
>
>>From my reading of the standard (3.4.4, 3.4.1) the only thing needed
> to make the above code work, is a standard compliant compiler (since M
> is lookedup by unqualified name lookup which searches thru using
> directives in a sense).
>
> I tried the above code with comeau online and it claimed that M did
> not have access to RD's privates.
>
> The following did not work either (trying to use Qualified Name lookup
> to prevent the auto-declaration 'feature' of friend declarations)
>
> ...
> class RD { friend class ::M; ... };..
> ...
>
> I believe the above is standard compliant too - and comeau does not
> allow it.
>
> Can someone please clarify these issues - either by quoting the
> relevant passages in the std that mandate comeau's behavior or by
> agreeing that this is indeed well-formed code and comeau should
> compile it.

There is a core language issue (#138) that deals with this issue (and some
others).  In the current language, the situation is unclear.  The issue is still
open, but I've written a paper that suggests that this case should be well-formed.

John Spicer
Edison Design Group

>
>
> thanks,
> Faisal Vali
>
>
> ---
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> [              --- Please see the FAQ before posting. ---               ]
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>

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fvali@kumc.edu ("Faisal Vali") writes:
> A few weeks ago David Abrahams asked in a post if there was a way to
> make the following
> code work:
>
> namespace { class M; }
>
> class RD { friend class M; typedef int Q; };
>
> namespace { class M { RD::Q i; }; }
>
> -----
>
>>From my reading of the standard (3.4.4, 3.4.1) the only thing needed
> to make the above code work, is a standard compliant compiler (since M
> is lookedup by unqualified name lookup which searches thru using
> directives in a sense).

My reading of 11.4p7 is that M should be a friend of RD, since it the name M
is accessible in the scope of RD.

> I tried the above code with comeau online and it claimed that M did
> not have access to RD's privates.
>
> The following did not work either (trying to use Qualified Name lookup
> to prevent the auto-declaration 'feature' of friend declarations)
>
> ...
> class RD { friend class ::M; ... };..
> ...
>
> I believe the above is standard compliant too - and comeau does not
> allow it.

This won't work, since the qualified name of M is not knowable; this declares
that a class M in the global namespace, rather than the unnamed namespace, is
a friend.

Anthony
--
Anthony Williams
Senior Software Engineer, Beran Instruments Ltd.
Remove NOSPAM when replying, for timely response.

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