220 26355 <74885fa3-1a38-4394-b017-9a102001f199@isocpp.org> article Path: news.gmane.org!not-for-mail From: "T. C." Newsgroups: gmane.comp.lang.c++.isocpp.proposals Subject: Re: Float the idea: Forward declaring inner classes Date: Mon, 20 Jun 2016 17:42:18 -0700 (PDT) Lines: 205 Approved: news@gmane.org Message-ID: <74885fa3-1a38-4394-b017-9a102001f199@isocpp.org> References: <299109ab-04d2-462f-8f50-ce31206e96b3@isocpp.org> Reply-To: std-proposals@isocpp.org NNTP-Posting-Host: plane.gmane.org Mime-Version: 1.0 Content-Type: multipart/mixed; boundary="----=_Part_1457_1346568539.1466469738269" X-Trace: ger.gmane.org 1466469776 27079 80.91.229.3 (21 Jun 2016 00:42:56 GMT) X-Complaints-To: usenet@ger.gmane.org NNTP-Posting-Date: Tue, 21 Jun 2016 00:42:56 +0000 (UTC) Cc: xaxxon@gmail.com To: ISO C++ Standard - Future Proposals Original-X-From: std-proposals+bncBCQ43G7NQIIRB242UK5QKGQENMCJOWA@isocpp.org Tue Jun 21 02:42:43 2016 Return-path: Envelope-to: gclcip-std-proposals@m.gmane.org Original-Received: from mail-qk0-f199.google.com ([209.85.220.199]) by plane.gmane.org with esmtp (Exim 4.69) (envelope-from ) id 1bF9ll-0002zN-As for gclcip-std-proposals@m.gmane.org; Tue, 21 Jun 2016 02:42:21 +0200 Original-Received: by mail-qk0-f199.google.com with SMTP id z142sf2694111qkb.0 for ; Mon, 20 Jun 2016 17:42:21 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=isocpp-org.20150623.gappssmtp.com; s=20150623; h=date:from:to:cc:message-id:in-reply-to:references:subject :mime-version:x-original-sender:reply-to:precedence:mailing-list :list-id:x-spam-checked-in-group:list-post:list-help:list-archive :list-subscribe:list-unsubscribe; bh=b6YPAXo5NDDQ2POJuIXZ1xD1wZkj6l7js4setUCobG0=; b=LUl5NH0DmI2IS9pavuqiUZBsfsGy7UQ9vUqXbNtJo7R6OZj4fVwHxit+xDdswomLuH 0vpgxj+HHJYsDaMlZ0XzgofurJuvg9L38MVqmhbXTLQ0zN23ewfQtfjwH+dBR2K9RMIL xcWKvR34wj/VPeRMkosUuLHEz5T6jqyVgQoSjxBRAQJpX+iGCV7j2IWl0a5fNrSyeZ98 A+uf2tn3BLOjTYjN4io5sFn/RJeg3aW4075y8nCtARJhlJwFbUc5fBEj6ERr/6r1GH7B PooPRw5/OwaxzcH+QmoIrbCMvAogxWROZS9s7QNCm2pW5VSy8cszQUQWW2PQgJNXwVOb D+/Q== DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gmail.com; s=20120113; h=date:from:to:cc:message-id:in-reply-to:references:subject :mime-version:x-original-sender:reply-to:precedence:mailing-list :list-id:x-spam-checked-in-group:list-post:list-help:list-archive :list-subscribe:list-unsubscribe; bh=b6YPAXo5NDDQ2POJuIXZ1xD1wZkj6l7js4setUCobG0=; b=ZRwmdiFDmWZhiM32NPGdu/pY6HkjAYtoZp76kBiEyXcHOmHMKrwUsWbQQNZtulEuG3 CMN7Mh/lXGBkZRRh5LVujZXAldh3uWbegVvEl/uk1XBwO74aooM+aC5kk92CvxZnOGqG R6lX9tNrHtMGOkWKk58hAJokk6XneoXNvRutaTy2IzLOXnzw9RBSEJVntGfnMMgK2Pg4 i1VkRj3Dl9E+AYGxiqdDjCuLvN7dlCs2sNo24TMzkNV16IXDaCqWHPm642eeAniK8ZvP giFI8B8FTDAGutqbB+bWwt6C3zd0yiORHWKjCJJXBM4oqcvxgcYXv2KmJcDzaKUIycb6 PGzw== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20130820; h=x-gm-message-state:date:from:to:cc:message-id:in-reply-to :references:subject:mime-version:x-original-sender:reply-to :precedence:mailing-list:list-id:x-spam-checked-in-group:list-post :list-help:list-archive:list-subscribe:list-unsubscribe; bh=b6YPAXo5NDDQ2POJuIXZ1xD1wZkj6l7js4setUCobG0=; b=dw5OKZZ+IsBYBrwRyGbs5nIjrATOODj/+gYk2Kc4nEMve9A1aUy/aMn8baRwHCkfWp 5HE9sOZLfjF2fedY3RLKbglGO8F9JsCTE7DBVL0WcN5qZNDYW7hGieuJ2ys/kETfBvSi Y3NKjQp1/jQo2MtP/tp7nr4HVowFJfZ4HLLIz9btjIK330nftigiAjiAbAOobj9fTN4B nto8KQIG+9uLjLglhVu4wPX4at3W9AWNRhMr9/cU1Uxig0EdEciApNBtUYmn5XO8knsA KwWeOjDil+XnEzIGfKMvzm7vUmd2hLo6qD508KUSUqklaPvjw+4udzhky7h8NPXofWui QgqQ== X-Gm-Message-State: ALyK8tK4/RFrlBzVoy8X9Ff1Cq6H366h+iqsPaka3F0h2/s/4eWLZA0g3BayOyA4wAkx7g== X-Received: by 10.129.159.208 with SMTP id w199mr23850546ywg.41.1466469740458; Mon, 20 Jun 2016 17:42:20 -0700 (PDT) X-BeenThere: std-proposals@isocpp.org Original-Received: by 10.107.176.66 with SMTP id z63ls1737743ioe.64.gmail; Mon, 20 Jun 2016 17:42:19 -0700 (PDT) X-Received: by 10.36.1.15 with SMTP id 15mr15827itk.6.1466469739350; Mon, 20 Jun 2016 17:42:19 -0700 (PDT) In-Reply-To: <299109ab-04d2-462f-8f50-ce31206e96b3@isocpp.org> X-Original-Sender: rs2740@gmail.com 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:26355 Archived-At: ------=_Part_1457_1346568539.1466469738269 Content-Type: multipart/alternative; boundary="----=_Part_1458_241192018.1466469738270" ------=_Part_1458_241192018.1466469738270 Content-Type: text/plain; charset=UTF-8 http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2016/p0289r0.pdf On Monday, June 20, 2016 at 7:35:29 PM UTC-4, xax...@gmail.com wrote: > > I've never written anything to this list before and am trying to follow > the instructions here: https://isocpp.org/std/submit-a-proposal > > I'd like to allow forward declarations of inner classes. Here is a > situation I've run into where it seems that forward declaring the inner > classes would allow this to work: > > > class Outer1; // <== potentially optional > class Outer::Inner; //<== NEW > > > class Outer2; // <== potentially optional > class Outer2::Inner; //<== NEW > > > template > class SomeClass { > > // !!error: no type named 'Inner' in 'Outer1' <== clang error in current > c++ > typename T::Inner * some_func(); > }; > > > class Outer1 : public SomeClass { > public: > class Inner { > }; > }; > > > class Outer2 : public SomeClass { > public: > class Inner { > }; > }; > > > While there are certainly workarounds, I find this organizational > structure to be useful in other languages and would have used it in c++ had > it been available. > > Live code: https://godbolt.org/g/A5jd87 > > The workaround I've found is this, but the code doesn't match my intent > nearly as well. > class Outer1Inner {}; > class Outer1 : public SomeClass {}; > > > > Thank you for your feedback - either on the actual proposal or on proposal > procedure. > > --Zac > -- 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/74885fa3-1a38-4394-b017-9a102001f199%40isocpp.org. ------=_Part_1458_241192018.1466469738270 Content-Type: text/html; charset=UTF-8 Content-Transfer-Encoding: quoted-printable
http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2016/p0= 289r0.pdf

On Monday, June 20, 2016 at 7:35:29 PM UTC-4, xax...@gmail= ..com wrote:
I've never written anything to this list before and am trying to fol= low the instructions here:=C2=A0htt= ps://isocpp.org/std/submit-a-proposal

I'd like to allow forward declarations of inner classes. =C2=A0Here is= a situation I've run into where it seems that forward declaring the in= ner classes would allow this to work:


class Outer1; // <=3D=3D potentially optional
class Outer::Inner; //<=3D=3D NEW=


class Outer2; // <=3D=3D potentially optionalclass= Outer2= ::Inner= ; //<= ;=3D=3D NEW


template<class T>
class SomeClass {

// !!error: no = type named 'Inner' in 'Outer1' <=3D=3D clang error in cu= rrent c++
=C2=A0 typename T::Inner * some_func();
};


class<= span style=3D"color:#000"> Outer1<= span style=3D"color:#000"> : public SomeClass<Outer1= > {
=C2=A0 public:
=C2=A0 class = Inner {=
=C2=A0 };
};


class Outer2 : public SomeClass<Outer2> {
=C2=A0 public:
=C2=A0 class Inner {
=C2=A0 <= span style=3D"color:#660">};
};


While there are certainly workarounds, I find this = organizational structure to be useful in other languages and would have use= d it in c++ had it been available. =C2=A0=C2=A0


The workaround I've found is this, but the code doesn't match= my intent nearly as well. =C2=A0
<= div>class Outer1Inner= {};class = Outer1 = : public SomeClass<= ;Outer1Inner> {};

<= div>

Thank you for your feedback - either on the actual p= roposal or on proposal procedure.

--Zac

--
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