220 11295 article Path: news.gmane.org!not-for-mail From: =?UTF-8?Q?David_Rodr=C3=ADguez_Ibeas?= Newsgroups: gmane.comp.lang.c++.isocpp.proposals Subject: Re: return type sugar (orthogonal to auto foo() {} ) Date: Fri, 13 Jun 2014 09:12:37 -0400 Lines: 102 Approved: news@gmane.org Message-ID: References: <30a83c0d-00e6-462a-822e-a1789787ec05@isocpp.org> Reply-To: std-proposals@isocpp.org NNTP-Posting-Host: plane.gmane.org Mime-Version: 1.0 Content-Type: multipart/alternative; boundary=001a113a2a2e7408f304fbb76e4e X-Trace: ger.gmane.org 1402665166 3538 80.91.229.3 (13 Jun 2014 13:12:46 GMT) X-Complaints-To: usenet@ger.gmane.org NNTP-Posting-Date: Fri, 13 Jun 2014 13:12:46 +0000 (UTC) To: std-proposals@isocpp.org Original-X-From: std-proposals+bncBDIIVO6GQULBBRXR5OOAKGQE7D3QTJA@isocpp.org Fri Jun 13 15:12:40 2014 Return-path: Envelope-to: gclcip-std-proposals@m.gmane.org Original-Received: from mail-qa0-f72.google.com ([209.85.216.72]) by plane.gmane.org with esmtp (Exim 4.69) (envelope-from ) id 1WvRHb-0002eD-RW for gclcip-std-proposals@m.gmane.org; Fri, 13 Jun 2014 15:12:40 +0200 Original-Received: by mail-qa0-f72.google.com with SMTP id i13sf7575467qae.3 for ; Fri, 13 Jun 2014 06:12:39 -0700 (PDT) X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20130820; h=x-gm-message-state:mime-version:sender:in-reply-to:references:date :message-id:subject:from:to:x-original-sender :x-original-authentication-results:reply-to:precedence:mailing-list :list-id:list-post:list-help:list-archive:list-subscribe :list-unsubscribe:content-type; bh=LgO22+mdjc+jJZ5Nt34fDSsLkGl35wNjRrfZmcHdQyU=; b=iqh4GKjcvMSrKREflBqAGuqhvh6gbwah3Hcj0cUu7roB8l7ErbYipUJtPXA9rCMQj0 CE8KUJnoZLtx3OFLEXlvFIxsxGGuOhOuFnc8EKmZgcWSlBbvP7mIw16PVDpZxvIaaURM NAyQMg68eQwFx5gUbIH186b2sFlAgnwyEYzNeYACvFnc6n2GD/xOcSRAvEB2CvGLKhfB VexhJ7h4xFI1k4VIoGZ+ABfh+cJTNobgUGc7rAgdXg1PGPFN1nxQ8WAYvrKNdj7MTDwN eZIqULMrrAJQ+q5V0o/mocW05aO+rqADQTZr/gLGHzV3e/1FZqogDm4kFuZ95xoxzyoC U3Fg== X-Gm-Message-State: ALoCoQn82BGzIb3qtonkFI95tuwNnjWDy+5blBY+AcXjlklNIfzsI9oy/fELy4J/dPHGu3/spXrj X-Received: by 10.58.48.233 with SMTP id p9mr540058ven.31.1402665159028; Fri, 13 Jun 2014 06:12:39 -0700 (PDT) X-BeenThere: std-proposals@isocpp.org Original-Received: by 10.140.107.97 with SMTP id g88ls3298974qgf.40.gmail; Fri, 13 Jun 2014 06:12:38 -0700 (PDT) X-Received: by 10.224.38.4 with SMTP id z4mr3520860qad.94.1402665158078; Fri, 13 Jun 2014 06:12:38 -0700 (PDT) Original-Received: from mail-qc0-x235.google.com (mail-qc0-x235.google.com [2607:f8b0:400d:c01::235]) by mx.google.com with ESMTPS id c18si4546823qaq.0.2014.06.13.06.12.38 for (version=TLSv1 cipher=ECDHE-RSA-RC4-SHA bits=128/128); Fri, 13 Jun 2014 06:12:38 -0700 (PDT) Received-SPF: pass (google.com: domain of dribeas@gmail.com designates 2607:f8b0:400d:c01::235 as permitted sender) client-ip=2607:f8b0:400d:c01::235; Original-Received: by mail-qc0-f181.google.com with SMTP id x13so4072150qcv.26 for ; Fri, 13 Jun 2014 06:12:37 -0700 (PDT) X-Received: by 10.140.97.227 with SMTP id m90mr3322108qge.15.1402665157526; Fri, 13 Jun 2014 06:12:37 -0700 (PDT) Original-Sender: dribeas@gmail.com Original-Received: by 10.140.42.182 with HTTP; Fri, 13 Jun 2014 06:12:37 -0700 (PDT) In-Reply-To: X-Original-Sender: dibeas@ieee.org X-Original-Authentication-Results: mx.google.com; spf=pass (google.com: domain of dribeas@gmail.com designates 2607:f8b0:400d:c01::235 as permitted sender) smtp.mail=dribeas@gmail.com; dkim=pass header.i=@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:11295 Archived-At: --001a113a2a2e7408f304fbb76e4e Content-Type: text/plain; charset=UTF-8 On Thu, Jun 12, 2014 at 3:14 PM, walter1234 wrote: > auto foo(...) {return...} is certainly a great thing to have. > > the benefit of the type being in the signature however, is discoverability > and documentation - > .... and being able to use the return type in an SFINAE context. [Personally I believe that library code *should* always spell out the return type in the signature, trailing return type is fine, return type being deduced not so much]. This is a contrived example, but is concise enough to be sent over email: std::string f(int); void f(double); template auto g(T value) { return f(value); } template auto h(T value) -> decltype(g(value).size()) { return g(type).size(); } template size_t h(T value, ...) { return size_t(); } int main() { h(1.0); // hard error!! } If the return type of 'g' had not been deduced the above would have SFINAE-d out the first template and called the second overload of 'h'. David -- --- 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. Visit this group at http://groups.google.com/a/isocpp.org/group/std-proposals/. --001a113a2a2e7408f304fbb76e4e Content-Type: text/html; charset=UTF-8 Content-Transfer-Encoding: quoted-printable

= On Thu, Jun 12, 2014 at 3:14 PM, walter1234 <walter2bz@gmail.com&g= t; wrote:
auto foo(...) {return...} = =C2=A0 is certainly a great thing to have.

the benefit of the = type being in the signature however, is discoverability and documentation -= =C2=A0

... and being able to use the return type= in an SFINAE context. [Personally I believe that library code *should* alw= ays spell out the return type in the signature, trailing return type is fin= e, return type being deduced not so much].

This is a contrived example, but is concise enough to be sent over emai= l:

std::string f(int);
void =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0f(d= ouble);

template <typename T>
auto g(T value) {
= =C2=A0 =C2=A0 return f(value);
}

template <typename T>
auto h(T value) -> declty= pe(g(value).size())
{
=C2=A0 =C2=A0 return g(type).size();
}
te= mplate <typename T>
size_t h(T value, ...) {
=C2=A0 =C2=A0 retu= rn size_t();
}

int main() {
=C2=A0 =C2=A0 h(1.0); =C2=A0 =C2=A0 =C2=A0 // hard= error!!
}

If the return type of 'g' had not been deduced= the above would have SFINAE-d out the first template and called the second= overload of 'h'.

=C2=A0 =C2=A0 David

--

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