220 39436 <2a326be3-4a3d-466e-819f-56dbac65b620@isocpp.org> article Path: news.gmane.org!.POSTED!not-for-mail From: Nicol Bolas Newsgroups: gmane.comp.lang.c++.isocpp.proposals Subject: Re: Allow use of "->" when operator* presents Date: Sat, 28 Jul 2018 22:12:54 -0700 (PDT) Lines: 87 Approved: news@gmane.org Message-ID: <2a326be3-4a3d-466e-819f-56dbac65b620@isocpp.org> References: <53f13047-62e7-4b31-ab7d-f3134e15eb08@isocpp.org> Reply-To: std-proposals@isocpp.org NNTP-Posting-Host: blaine.gmane.org Mime-Version: 1.0 Content-Type: multipart/mixed; boundary="----=_Part_1560_851785953.1532841174290" X-Trace: blaine.gmane.org 1532841050 27472 195.159.176.226 (29 Jul 2018 05:10:50 GMT) X-Complaints-To: usenet@blaine.gmane.org NNTP-Posting-Date: Sun, 29 Jul 2018 05:10:50 +0000 (UTC) Cc: junekey91@gmail.com To: ISO C++ Standard - Future Proposals Original-X-From: std-proposals+bncBCEKFTV6ZUMBBV4Z6XNAKGQEPAIPOKY@isocpp.org Sun Jul 29 07:10:46 2018 Return-path: Envelope-to: gclcip-std-proposals@m.gmane.org Original-Received: from mail-yb0-f198.google.com ([209.85.213.198]) by blaine.gmane.org with esmtp (Exim 4.84_2) (envelope-from ) id 1fjdyf-00071X-U0 for gclcip-std-proposals@m.gmane.org; Sun, 29 Jul 2018 07:10:46 +0200 Original-Received: by mail-yb0-f198.google.com with SMTP id a12-v6sf5026909ybe.21 for ; Sat, 28 Jul 2018 22:12:57 -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:list-post:list-help:list-archive:list-subscribe :list-unsubscribe; bh=q1VELVmiucW6w3KIVOOfIWljSzy4NHqfeHglkiJTIoc=; b=afjs4IIoXDSNZdgQQvoa97gWfxQSfuB4rp80f/67n5CBRJA+aSTZ/WL77vUboQansx VbF4g9iO6x/nB2RpR7nRlkeNJPIqxvhOf+riRP4cVoB56NxVT1JaZH2pkXKNZ2jjI2bu Bvo3J3K4Q7tPDnENFJhia1YNORMt0enMlTnz666LG5zZgqVAmavSAGDY/Zx4ZWgOQFSn aWDtvWghTvtJZ+errlJT2gypCjR9PEp2KKFWv5dOVA8zKQB+1rkyo2W3VF730RJKpRSO 1mPwz/Y551pN6I5/YdhyMTuDM0Z8ummcSseD5E9Q5GOZScgv5OJ7gpWYSHd+hFRs9ZYP t7xg== DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gmail.com; s=20161025; h=date:from:to:cc:message-id:in-reply-to:references:subject :mime-version:x-original-sender:reply-to:precedence:mailing-list :list-id:list-post:list-help:list-archive:list-subscribe :list-unsubscribe; bh=q1VELVmiucW6w3KIVOOfIWljSzy4NHqfeHglkiJTIoc=; b=YwpOdOV5MNhAzlbx799Nn9vV1BE2MxCOvwwpLfwdwTVuCqt1ip6Klg4VHDSDyWNHVk iEm5zJ32id/6z93Oj/Y4rPP4UPjkJeMdzvtVOeyI0rZW8h35WnOiPndYBENhLidUmKt7 tBPmPIEyzh5ytomgG5pN0pihm/dLpeo3XhFVqhbl6DZw0TLGoSpP9CbZoJQboHEjb2gT 6pvZmpRzZbVa9W3lFDJ1kzfN+HVe2Qn3zV/zW8/NGoVIqjm+uuDTAs/Ft4UPBQ1BIf2R 0qIf5jtd2GnFXpd2NFRtZIDc4JSww4fiRSyhUCEQdNJJDUMW+SS8uf6ck4bO8a+slZSs RgrA== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20161025; 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=q1VELVmiucW6w3KIVOOfIWljSzy4NHqfeHglkiJTIoc=; b=p/Aqsvw6IoEIenJH0TRQF0E+zvc6sMcWeWD/wflOtd0cQBCbIVz5f6pqn1TPl3iWw/ pmG/8vCoYNVKGTO5xXn/0GlXKbkx3jMUCqtPJO6mOE4bNduW/khTNilR7Y/2z2Yg7jOD Dp0ElclO7uJ7302VGeE+yvvcHCaP5wZkwj7jLpdCBnDkzVJxDA6eFs2kp1e9/eq2++/U U59dcXCruhBATzEj8B3WV8+ORNM4ZHOp6uOcUQvosumofG/j3sBKZ8Dd7Bpx0HF64kic b2bribQClPJYTC+6x/BY5Wf69GBYEBStsajYPvEYNpUh/sNc2kHaZCdcLT9v3UEFsz5I yhJA== X-Gm-Message-State: AOUpUlEcS+fCDUYacr8c62gOn1n4/1zRdJ6J4nvk4/CDU8TbD4/BuHW/ GrZ6vjtGM1o8bkqK2rFcfHUwWw== X-Google-Smtp-Source: AAOMgpeDmvjIp0qqUiS2+2TIfQDWFUFJuBnlgrDTXaLU5C7NwQdGJOSCEkIu1RYBwy/BSzLUU6zjXA== X-Received: by 2002:a5b:b4a:: with SMTP id b10-v6mr3719630ybr.33.1532841176541; Sat, 28 Jul 2018 22:12:56 -0700 (PDT) X-BeenThere: std-proposals@isocpp.org Original-Received: by 2002:a25:5502:: with SMTP id j2-v6ls1692457ybb.7.gmail; Sat, 28 Jul 2018 22:12:55 -0700 (PDT) X-Received: by 2002:a25:8448:: with SMTP id r8-v6mr124554ybm.2.1532841174910; Sat, 28 Jul 2018 22:12:54 -0700 (PDT) In-Reply-To: <53f13047-62e7-4b31-ab7d-f3134e15eb08@isocpp.org> X-Original-Sender: jmckesson@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:39436 Archived-At: ------=_Part_1560_851785953.1532841174290 Content-Type: multipart/alternative; boundary="----=_Part_1561_923636987.1532841174290" ------=_Part_1561_923636987.1532841174290 Content-Type: text/plain; charset="UTF-8" On Saturday, July 28, 2018 at 5:56:18 PM UTC-4, june...@gmail.com wrote: > > The main motivation is that the language rule requires us to (eventually) > return raw pointers in operator->. There's another motivation: Concepts and `operator->` don't mix. The current iterators in the Range TS/C++20 don't require `operator->`. One of the reasons for this is that it's actually very hard to specify that behavior via an expression. After all, `->` has to be followed by a member name, and what if a template type doesn't have members? Overall, there's not a simple way to check that `operator->` exists. By contrast, it's easy to have `{*it} -> some_type;` in a requires clause. Of course, we can still have our iterators provide an `operator->`. And since there is no concept checking of implementations, the implementation of a function that takes a Range TS iterator can still invoke `operator->`, which will work with the existing iterators. If we just say that we can synthesize an `operator->` if `operator*` exists, then we don't have a problem. Concepts can just require `operator*` using appropriate requirements, and the behavior of any usage of `->` is expected to conform to the return value from `operator*`. The implementation of a concept can use `->` when it is appropriate, and everyone is happy. -- 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/2a326be3-4a3d-466e-819f-56dbac65b620%40isocpp.org. ------=_Part_1561_923636987.1532841174290 Content-Type: text/html; charset="UTF-8" Content-Transfer-Encoding: quoted-printable
On Saturday, July 28, 2018 at 5:56:18 PM UTC-4, june...@gm= ail.com wrote:
The main motivat= ion is that the language rule requires us to (eventually) return raw pointe= rs in operator->.

There's another mo= tivation: Concepts and `operator->` don't mix.

<= div>The current iterators in the Range TS/C++20 don't require `operator= ->`. One of the reasons for this is that it's actually very hard to = specify that behavior via an expression. After all, `->` has to be follo= wed by a member name, and what if a template type doesn't have members?= Overall, there's not a simple way to check that `operator->` exists= .. By contrast, it's easy to have `{*it} -> some_type;` in a requires= clause.

Of course, we can still have our iter= ators provide an `operator->`. And since there is no concept checking of= implementations, the implementation of a function that takes a Range TS it= erator can still invoke `operator->`, which will work with the existing = iterators.

If we just say that we can synthesize a= n `operator->` if `operator*` exists, then we don't have a problem. = Concepts can just require `operator*` using appropriate requirements, and t= he behavior of any usage of `->` is expected to conform to the return va= lue from `operator*`. The implementation of a concept can use `->` when = it is appropriate, and everyone is happy.

--
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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.
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To view this discussion on the web visit https://groups.google.= com/a/isocpp.org/d/msgid/std-proposals/2a326be3-4a3d-466e-819f-56dbac65b620= %40isocpp.org.
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