220 38038 article Path: news.gmane.org!.POSTED!not-for-mail From: Richard Smith Newsgroups: gmane.comp.lang.c++.isocpp.proposals Subject: Re: Fornux C++ Superset - Forward Declarations of Nested Structures Date: Tue, 1 May 2018 21:26:49 -0700 Lines: 164 Approved: news@gmane.org Message-ID: References: Reply-To: std-proposals@isocpp.org NNTP-Posting-Host: blaine.gmane.org Mime-Version: 1.0 Content-Type: multipart/alternative; boundary="00000000000010e017056b3180f8" X-Trace: blaine.gmane.org 1525235109 10648 195.159.176.226 (2 May 2018 04:25:09 GMT) X-Complaints-To: usenet@blaine.gmane.org NNTP-Posting-Date: Wed, 2 May 2018 04:25:09 +0000 (UTC) To: std-proposals@isocpp.org Original-X-From: std-proposals+bncBDVNBJG4YAIBBIX4UTLQKGQEV2N7AFQ@isocpp.org Wed May 02 06:25:05 2018 Return-path: Envelope-to: gclcip-std-proposals@m.gmane.org Original-Received: from mail-wr0-f197.google.com ([209.85.128.197]) by blaine.gmane.org with esmtp (Exim 4.84_2) (envelope-from ) id 1fDjKC-0002fS-Ga for gclcip-std-proposals@m.gmane.org; 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[81.27.85.19]) by mx.google.com with ESMTPS id o187si6308528wmd.139.2018.05.01.21.27.13 for (version=TLS1_2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128/128); Tue, 01 May 2018 21:27:13 -0700 (PDT) Received-SPF: neutral (google.com: 81.27.85.19 is neither permitted nor denied by best guess record for domain of richard@metafoo.co.uk) client-ip=81.27.85.19; Original-Received: from mail-ot0-f176.google.com ([74.125.82.176]:33508) by uk12.easy-internet.co.uk with esmtpsa (TLSv1.2:ECDHE-RSA-AES128-GCM-SHA256:128) (Exim 4.89_1) (envelope-from ) id 1fDjMD-0003cs-HK for std-proposals@isocpp.org; Wed, 02 May 2018 05:27:11 +0100 Original-Received: by mail-ot0-f176.google.com with SMTP id l22-v6so15135233otj.0 for ; Tue, 01 May 2018 21:27:10 -0700 (PDT) X-Received: by 2002:a9d:282d:: with SMTP id m42-v6mr13370002otb.64.1525235229710; Tue, 01 May 2018 21:27:09 -0700 (PDT) Original-Received: by 10.74.67.193 with HTTP; Tue, 1 May 2018 21:26:49 -0700 (PDT) In-Reply-To: X-Gmail-Original-Message-ID: X-OutGoing-Spam-Status: No, score=0.1 X-AntiAbuse: This header was added to track abuse, please include it with any abuse report X-AntiAbuse: Primary Hostname - uk12.easy-internet.co.uk X-AntiAbuse: Original Domain - isocpp.org X-AntiAbuse: Originator/Caller UID/GID - [47 12] / [47 12] X-AntiAbuse: Sender Address Domain - metafoo.co.uk X-Get-Message-Sender-Via: uk12.easy-internet.co.uk: authenticated_id: metafooc/from_h X-Authenticated-Sender: uk12.easy-internet.co.uk: richard@metafoo.co.uk X-Source: X-Source-Args: X-Source-Dir: X-Original-Sender: richard@metafoo.co.uk X-Original-Authentication-Results: mx.google.com; dkim=pass header.i=@metafoo.co.uk header.s=default header.b=NuS2XgtM; spf=neutral (google.com: 81.27.85.19 is neither permitted nor denied by best guess record for domain of richard@metafoo.co.uk) smtp.mailfrom=richard@metafoo.co.uk Precedence: list Mailing-list: list std-proposals@isocpp.org; contact std-proposals+owners@isocpp.org List-ID: X-Spam-Checked-In-Group: std-proposals@isocpp.org X-Google-Group-Id: 399137483710 List-Post: , List-Help: , List-Archive: List-Subscribe: , List-Unsubscribe: , Xref: news.gmane.org gmane.comp.lang.c++.isocpp.proposals:38038 Archived-At: --00000000000010e017056b3180f8 Content-Type: text/plain; charset="UTF-8" See http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2016/p0289r0.pdf The paper received some support from evolution. Some felt that the right answer was to wait for Modules. As noted in the above paper there are some open questions as to how this would actually work if we went forward with it. On 1 May 2018 at 19:26, Phil Bouchard wrote: > Greetings, > > In the development of the "Fornux C++ Superset" source-to-source compiler > and its Open Source memory manager counterpart "root_ptr": > https://github.com/philippeb8/root_ptr > > Like previously mentioned I noticed the following problems with the C++ > language: > - There is no distinction between a pointer and an iterator. > - There is no distinction between pointers to arrays of derived classes > and pointers to arrays of base classes. > > But I just realized the following also: > - The C++ language disallows top-level forward declarations of nested > classes. > > The latter becomes a problem if you want to, for example, specialize > metadata template classes. Ex: > > struct A > { > struct B > {}; > }; > > The transpiler will generate: > > struct A::B; > > namespace metadata > { > template <> > struct construct > { > template > A::B operator () (Args const &... args); > }; > } > > But the problem is the following statement is not legal: > struct A::B; > > So nested structures aren't commutative with template specializations > which makes it impossible to generate metadata on-the-fly. The problem was > always omnipresent but now it causes important problems in this case but > also prevents further extensions of the language. > > It's just a matter of making C++ less strict in this case... > > > Regards, > -Phil > > -- > You received this message because you are subscribed to the Google Groups > "ISO C++ Standard - Future Proposals" group. > To unsubscribe from this group and stop receiving emails from it, send an > email to std-proposals+unsubscribe@isocpp.org. > To post to this group, send email to std-proposals@isocpp.org. > To view this discussion on the web visit https://groups.google.com/a/ > isocpp.org/d/msgid/std-proposals/cab4cada-1abe-48b2- > 9a4b-d6c9f994b805%40isocpp.org > > . > -- You received this message because you are subscribed to the Google Groups "ISO C++ Standard - Future Proposals" group. To unsubscribe from this group and stop receiving emails from it, send an email to std-proposals+unsubscribe@isocpp.org. To post to this group, send email to std-proposals@isocpp.org. To view this discussion on the web visit https://groups.google.com/a/isocpp.org/d/msgid/std-proposals/CAOfiQqnoN-_KQ-AOTsAMCMnJK_nge1c59K0xOFy%2Bu0jQEtFnOw%40mail.gmail.com. --00000000000010e017056b3180f8 Content-Type: text/html; charset="UTF-8" Content-Transfer-Encoding: quoted-printable
See http://www.open-std.org/jtc1/sc22/wg21/docs/paper= s/2016/p0289r0.pdf

The paper received some suppo= rt from evolution. Some felt that the right answer was to wait for Modules.= As noted in the above paper there are some open questions as to how this w= ould actually work if we went forward with it.

On 1 May 2018 at 19:26, Phil Bouch= ard <philippeb8@gmail.com> wrote:
Greetings,

In the developmen= t of the "Fornux C++ Superset" source-to-source compiler and its = Open Source memory manager counterpart "root_ptr":

Like pre= viously mentioned I noticed the following problems with the C++ language:
- There is no distinction between a pointer and an iterator.
=
- There is no distinction between pointers to arrays of derived classe= s and pointers to arrays of base classes.

But I ju= st realized the following also:
- The C++ language disallows top-= level forward declarations of nested classes.

The = latter becomes a problem if you want to, for example, specialize metadata t= emplate classes. Ex:

struct A
{
=C2=A0 =C2=A0 struct B
=C2=A0 =C2=A0 {};
};

The transpiler will generate:

struct A::B;

namespace metadata
{
=
=C2=A0 =C2=A0 template <>
=C2=A0 =C2=A0 =C2=A0 =C2= =A0 struct construct<A::B>
=C2=A0 =C2=A0 =C2=A0 =C2=A0 {
=C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 template <typename... = Args>
=C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 = A::B operator () (Args const &... args);
=C2=A0 =C2=A0 =C2=A0= =C2=A0 };
}

But the problem i= s the following statement is not legal:
struct A::B;

So nested structures aren't commutative with template = specializations which makes it impossible to generate metadata on-the-fly. = The problem was always omnipresent but now it causes important problems in = this case but also prevents further extensions of the language.=C2=A0
=

It's just a matter of making C++ less strict in thi= s case...


Regards,
-Phil<= /div>

--
You received this message because you are subscribed to the Google Groups &= quot;ISO C++ Standard - Future Proposals" group.
To unsubscribe from this group and stop receiving emails from it, send an e= mail to std-proposals+unsubscribe@isocpp.org.
To post to this group, send email to std-proposals@isocpp.org.
To view this discussion on the web visit = https://groups.google.com/a/isocpp.org/d/msgid/std-proposals/cab4= cada-1abe-48b2-9a4b-d6c9f994b805%40isocpp.org.

--
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To unsubscribe from this group and stop receiving emails from it, send an e= mail to std-proposa= ls+unsubscribe@isocpp.org.
To post to this group, send email to std-proposals@isocpp.org.
To view this discussion on the web visit h= ttps://groups.google.com/a/isocpp.org/d/msgid/std-proposals/CAOfiQqnoN-_KQ-= AOTsAMCMnJK_nge1c59K0xOFy%2Bu0jQEtFnOw%40mail.gmail.com.
--00000000000010e017056b3180f8-- .