220 32215 <14a2d202-4b34-4e5b-b4f7-bfcfe090408f@isocpp.org> article Path: news.gmane.org!.POSTED!not-for-mail From: Dan Raviv 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, 27 Apr 2017 13:23:22 -0700 (PDT) Lines: 104 Approved: news@gmane.org Message-ID: <14a2d202-4b34-4e5b-b4f7-bfcfe090408f@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_15_269917534.1493324602096" X-Trace: blaine.gmane.org 1493324604 27040 195.159.176.226 (27 Apr 2017 20:23:24 GMT) X-Complaints-To: usenet@blaine.gmane.org NNTP-Posting-Date: Thu, 27 Apr 2017 20:23:24 +0000 (UTC) Cc: walter.heisenbug@outlook.com To: ISO C++ Standard - Future Proposals Original-X-From: std-proposals+bncBC5YJREBWAGRBOVGRHEAKGQEVXLE5HY@isocpp.org Thu Apr 27 22:23:19 2017 Return-path: Envelope-to: gclcip-std-proposals@m.gmane.org Original-Received: from mail-ua0-f197.google.com ([209.85.217.197]) by blaine.gmane.org with esmtp (Exim 4.84_2) (envelope-from ) id 1d3pwc-0006uN-0K for gclcip-std-proposals@m.gmane.org; Thu, 27 Apr 2017 22:23:18 +0200 Original-Received: by mail-ua0-f197.google.com with SMTP id z29sf7754254uab.0 for ; Thu, 27 Apr 2017 13:23:24 -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=QqsnbHRaucLsCe7wE5WZ3zg2NTWZ0u6Sxmi/BDy+tmQ=; b=iKuG6Y5e/si+PQCV1188qQl/KYjRiIR1w94SYZs/rhENX0/zP4uB4X5XHHZno+tEr/ /xD2Oy/DmzO4HECEFiYHA3gGNud38J8L0LgY/BG8IPrxWQZ72X/l9yc/VV0Y1LP6CzjH 8BxYExTFoVFQ9SDOaJDgkXugU0TshEwh7vlgE4xd7p2z0/jaez+wTzWqKknmEDAbWAMC uWpvqbFs0thK0lrGcNHestP769Y9xHq5tdxc52nUDpaTaDwG4NnI5kesQQ69zFqHNqa2 iXQFk5/4fN9qrBCnm/jO8MzotuyQXOT0M6Qd5tHSPpXBAfVkyZ8U4DMsOWhqTOBj7Umt HiQQ== 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=QqsnbHRaucLsCe7wE5WZ3zg2NTWZ0u6Sxmi/BDy+tmQ=; b=YlR6hQymd2hsRVPQ0ieyqH3TDWAud9dYTQGzvAHkpUDfmFPt8Yc06hExv+RtnfkZgq oWiW+tKvI0Uqjz9iRB4Hj/mplEXGFGaY96yB881KBv0yNtqVMr1xyrHPw9PKkZ7CVrmC CE2f8xYHy5p5crFwcmmWPDqtVDnC57YIygJvV9pO8c6A0EwIZYYfFK28UiYMeaco0vkU YmvVzl55FS5Gr/3ak5gJG8TJ+ovMhfXy0w6uZDYX0j6DCba0CrT376b6T3j4AsWy33w/ GT7GKXtq8KwDw7GXp9Q1GNdfLE+KJtUqDg1Wi9sHKDCsuYGnZeTmhzPV7rmmNrI1ueUK ty3A== 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=QqsnbHRaucLsCe7wE5WZ3zg2NTWZ0u6Sxmi/BDy+tmQ=; b=fYy9c8Yadh3Qu5DWMexlTVBfDIN+MhuhCC4agl9Glf1aEZc9ulzBBk3SrMSrLHGr/1 8OGKEh5ngsCm6Kz9oyYypv+z5eBYQWAjUYJmvQnGX+n9EDTs5CHWvbSUlCp7M86u34eh SRxrpbNBwV8H0DzcIc2lriNhcRsGD3O2Dh5tsYyo5JJi8WE3qtPigAczvkASRJoUdOX0 8vVVu2PGQLBjI/QgYaw72eqf8Os7GAqjELa6tTUs/ehlzmLiLC4L90GME9cf5dQ+jPPr twFg46t8u7pmeM1d7DxARtDLBjzsxiuaaL6ZAop86Zd8T79H7lX5ug0cA67COJ+NQLW9 7E5g== X-Gm-Message-State: AN3rC/54o4VgnOgdxIY7SxD158BFx009m0RiOCUeqjtj8wzfoARv2DlQ VN+5JH3LR2qGtA== X-Received: by 10.31.164.14 with SMTP id n14mr2878833vke.36.1493324603458; Thu, 27 Apr 2017 13:23:23 -0700 (PDT) X-BeenThere: std-proposals@isocpp.org Original-Received: by 10.157.40.137 with SMTP id s9ls4258586ota.44.gmail; Thu, 27 Apr 2017 13:23:22 -0700 (PDT) X-Received: by 10.157.17.23 with SMTP id g23mr34828ote.4.1493324602568; Thu, 27 Apr 2017 13:23:22 -0700 (PDT) In-Reply-To: X-Original-Sender: dan.raviv@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:32215 Archived-At: ------=_Part_15_269917534.1493324602096 Content-Type: multipart/alternative; boundary="----=_Part_16_1675324590.1493324602096" ------=_Part_16_1675324590.1493324602096 Content-Type: text/plain; charset=UTF-8 +1 for this non-breaking feature which has a similar precedent (cv-qualifiers listed in Richard's answer), and which would simplify writing (and *reading*) generic code. Cheers, Dan On Tuesday, March 14, 2017 at 7:03:06 PM UTC+1, Walter Heisenbug wrote: > > Currently to access a member type from a reference type means you have to > do all the dancing with removing the reference. > > template > void f(T&& x) > { > typedef typename std::remove_reference_t::member_type mem; > mem y; > use(std::forward(x), y); > } > > This could be simplified, if we allow to access the member types of a type > from a reference types: > > template > void f(T&& x) > { > typedef typename T::member_type mem; > mem y; > use(std::forward(x), y); > } > > I'm not aware of any potential problems, since the reference types don't > have any member types, so there's no ambiguity with the existing code. -- 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/14a2d202-4b34-4e5b-b4f7-bfcfe090408f%40isocpp.org. ------=_Part_16_1675324590.1493324602096 Content-Type: text/html; charset=UTF-8 Content-Transfer-Encoding: quoted-printable
+1 for this non-breaking feature which has a similar prece= dent (cv-qualifiers listed in Richard's answer), and which would simpli= fy writing (and *reading*) generic code.

Cheers,
Dan
<= br>On Tuesday, March 14, 2017 at 7:03:06 PM UTC+1, Walter Heisenbug wrote:<= blockquote class=3D"gmail_quote" style=3D"margin: 0;margin-left: 0.8ex;bord= er-left: 1px #ccc solid;padding-left: 1ex;">Currently to access a member ty= pe from a reference type means you have to do all the dancing with removing= the reference.=20

template<typename T>
void f(T&& x)
{
=C2=A0=C2=A0=C2=A0 typedef typename std::remove_reference_t<T>::<= wbr>member_type mem;
=C2=A0=C2=A0=C2=A0 mem y;
=C2=A0=C2=A0=C2=A0 use(std::forward<T>(x), y);
}

This could be simplified, if we allow to access the member types of a t= ype from a reference types:

template<typename T>
void f(T&& x)
{
=C2=A0 =C2=A0 typedef typename T::member_type mem;
=C2=A0 =C2=A0 mem y;
=C2=A0 =C2=A0 use(std::forward<T>(x), y);
}

I'm not aware of any potential problems, since the reference types = don't have any member types, so there's no ambiguity with the exist= ing code.

--
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