220 32121 <23d75c32-3724-49fa-961a-cb4a2c7259b7@isocpp.org> article Path: news.gmane.org!.POSTED!not-for-mail From: Jakob Riedle Newsgroups: gmane.comp.lang.c++.isocpp.proposals Subject: Re: Allow to access member typedefs of a type from a reference type that's referring to that type Date: Thu, 20 Apr 2017 00:57:25 -0700 (PDT) Lines: 94 Approved: news@gmane.org Message-ID: <23d75c32-3724-49fa-961a-cb4a2c7259b7@isocpp.org> References: Reply-To: std-proposals@isocpp.org NNTP-Posting-Host: blaine.gmane.org Mime-Version: 1.0 Content-Type: multipart/mixed; boundary="----=_Part_1993_1787644953.1492675045360" X-Trace: blaine.gmane.org 1492675048 1701 195.159.176.226 (20 Apr 2017 07:57:28 GMT) X-Complaints-To: usenet@blaine.gmane.org NNTP-Posting-Date: Thu, 20 Apr 2017 07:57:28 +0000 (UTC) Cc: walter.heisenbug@outlook.com To: ISO C++ Standard - Future Proposals Original-X-From: std-proposals+bncBCX2XNFO6MPRBZWT4HDQKGQEXUYJJ7A@isocpp.org Thu Apr 20 09:57:22 2017 Return-path: Envelope-to: gclcip-std-proposals@m.gmane.org Original-Received: from mail-qt0-f198.google.com ([209.85.216.198]) by blaine.gmane.org with esmtp (Exim 4.84_2) (envelope-from ) id 1d16xt-0000HQ-Fh for gclcip-std-proposals@m.gmane.org; Thu, 20 Apr 2017 09:57:21 +0200 Original-Received: by mail-qt0-f198.google.com with SMTP id m91sf12093016qte.10 for ; Thu, 20 Apr 2017 00:57:27 -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=awwfSgBwT+Q/bGVFm8RKBpZtXdP5FP/ktJISpcng8yk=; b=Jf0ZVbqeiPJJZkPVdY3ffz2yYcocHgisapKD/IhNirXY1WJBRxQz5UB1Px87qVLIz0 2yNWrgfFExX/haJlxppafChsHoAOtL5ihFCNAc81f+GuL39ggcLG2KZNavCoXcGajfhQ X3TGXnbOd6DJYQPOyw9GEEgTaSHx5+ni+cmERZL/elmATEFghCQ509XgGTUYrXEFcLPd FdPFbe4oH6J17VBr6Bzgsk1HnAillIW5DmQku8OWuJ8qB4ZB7rdtePJKPeT6p0wZEK2i koLsi9KHOr6bjG3Rjybh8VIV2HL6fol9ADiYRcJP0Z/MctTxalYBT0+Sxg/HZPCdUPm9 IUyw== 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:x-spam-checked-in-group:list-post:list-help:list-archive :list-subscribe:list-unsubscribe; bh=awwfSgBwT+Q/bGVFm8RKBpZtXdP5FP/ktJISpcng8yk=; b=M3Znfm6CSjB8FIYGBcAV+vfEvtTSJbcjjd0xGMJXx5miLPKqHsTcYjR/Pf6GGcRcHd KHojGDZSFztzREWhkTXapyIoj5TNYQmRRcf3XIERzjxyrt2F6SaSCz1JIg61vEWgHJ/j yj7wH3WVRE2/Nr4cWiMqNoCOJ6qzIXyDbYa5QvZ+grWhjmvms6mLWNh1sh+pFjf8v0Sp brYsVOVgq5pS+qPs5yqTzeaoHQ6cg+841sPAS39J0Klf0VYjtGFTN6Dy9Dpzg0GJ719a sd7h1JujXUbWDfKoB9Ksw7nR5x0XjKsmNG1/QWBcqcz6rFdanxXcjVqDJbOJKt633RKs TNmA== 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=awwfSgBwT+Q/bGVFm8RKBpZtXdP5FP/ktJISpcng8yk=; b=tyTAMS14zblT0JuDwvlWath+MnVQhMzj9nSXVJPQnLk4li/PpcwydlzCL2YNg5d79X YYr68k1Y/E2quDZOsbh9o4c5HwjU9Zz2JQ0YD4/luClqvzqD71nzTICeroTNC2gpNIDa ZaFhQqWlwSHTCOLRPaa6PTb+GfCuYRd6ofgcu9pFgfEoExzsfZVdegnAm0Hf7xjgXJsx bIBS39h7wbEaiyLLTihQgGkDaFum/e/AavN+FKMT+C9KjMrj6wTbaodLoHSZ6XOpx44u UvWagqDy8JjgSjsMh73TMiomrme1Fee/Cv9KbyiUyHzGszO7TSdD4kdXQiL78pIehWHS AsYw== X-Gm-Message-State: AN3rC/4n7OIJoPzeh69gFvhRzQ2Yyss3pdsl68QtsinlxV9TIOj+qzsc f/0nV/AJzj42xg== X-Received: by 10.237.35.8 with SMTP id h8mr2945360qtc.67.1492675047007; Thu, 20 Apr 2017 00:57:27 -0700 (PDT) X-BeenThere: std-proposals@isocpp.org Original-Received: by 10.157.4.119 with SMTP id 110ls1414928otc.41.gmail; Thu, 20 Apr 2017 00:57:25 -0700 (PDT) X-Received: by 10.157.80.163 with SMTP id b35mr69656oth.16.1492675045859; Thu, 20 Apr 2017 00:57:25 -0700 (PDT) In-Reply-To: X-Original-Sender: jakob.riedle@gmail.com Precedence: list Mailing-list: list std-proposals@isocpp.org; contact std-proposals+owners@isocpp.org List-ID: 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:32121 Archived-At: ------=_Part_1993_1787644953.1492675045360 Content-Type: multipart/alternative; boundary="----=_Part_1994_1935460801.1492675045360" ------=_Part_1994_1935460801.1492675045360 Content-Type: text/plain; charset=UTF-8 I quite like this idea and I had this problem myself. The reason why compilers reject this code is because 'T is not a class, struct, or union type'. I don't know whether it is a good idea to consider *reference to class *a *class type.* It would be very misleading to do this if we allow references to class types to be usable as if they were the referenced class: struct A{}; struct B : A& {}; *References to objects* can be and are treated exactly like the referenced object itself. Note that this only concerns the *run-time*. On the other hand a *reference type* is not a class, it is ... a reference. IMHO it is very consequent, that e.g. T::r is not resolvable for T being a reference type, because its not a class, struct or union type. Cheers Jakob -- 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/23d75c32-3724-49fa-961a-cb4a2c7259b7%40isocpp.org. ------=_Part_1994_1935460801.1492675045360 Content-Type: text/html; charset=UTF-8 Content-Transfer-Encoding: quoted-printable
I quite like this idea and I had this problem myself. The = reason why compilers reject this code is because
'T is not a class, struct, or union type'. I don't know whether it is a good idea to consider reference to c= lass a class type.
It would be very misleading to do t= his if we allow references to class types to be usable as if they were the = referenced class:
struct A{= };
struct<= span style=3D"color: #000;" class=3D"styled-by-prettify"> B : A& {};

References= to objects can be and are treated exactly like the referenced object i= tself.
Note that this only concerns the run-time.
On the other hand a reference type is not a class, it is ... a ref= erence.

IMHO it is very consequent, that e.g. T::r=C2=A0is not resolvable fo= r=C2=A0T=C2=A0being a refe= rence type,
because its not a class, struct or union type.
<= div>
Cheers
Jakob

--
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-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 https://groups.google.= com/a/isocpp.org/d/msgid/std-proposals/23d75c32-3724-49fa-961a-cb4a2c7259b7= %40isocpp.org.
------=_Part_1994_1935460801.1492675045360-- ------=_Part_1993_1787644953.1492675045360-- .