220 11278 article Path: news.gmane.org!not-for-mail From: Mikhail Semenov Newsgroups: gmane.comp.lang.c++.isocpp.proposals Subject: Re: return type sugar (orthogonal to auto foo() {} ) Date: Thu, 12 Jun 2014 16:03:03 +0100 Lines: 162 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=047d7bfd01668f2e8404fba4db9f X-Trace: ger.gmane.org 1402585396 11936 80.91.229.3 (12 Jun 2014 15:03:16 GMT) X-Complaints-To: usenet@ger.gmane.org NNTP-Posting-Date: Thu, 12 Jun 2014 15:03:16 +0000 (UTC) To: std-proposals@isocpp.org Original-X-From: std-proposals+bncBDC55PNFRYGRBKEC46OAKGQE7APSDSI@isocpp.org Thu Jun 12 17:03:08 2014 Return-path: Envelope-to: gclcip-std-proposals@m.gmane.org Original-Received: from mail-lb0-f200.google.com ([209.85.217.200]) by plane.gmane.org with esmtp (Exim 4.69) (envelope-from ) id 1Wv6Wv-0007mw-VW for gclcip-std-proposals@m.gmane.org; Thu, 12 Jun 2014 17:03:06 +0200 Original-Received: by mail-lb0-f200.google.com with SMTP id z11sf937921lbi.7 for ; Thu, 12 Jun 2014 08:03:05 -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: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=oUNJ+w7HNSPG4WJp2TtCZf3m2LdG93g99lJNtrGKOKY=; b=BLYHKe6b1kQlSnoTALF+uKsn6lyja4AppeaiPgXWUt4yoOWiGfvKBaM44c2x0kD6KI 7VXTE6xHMq/RuMO/eqoWM6DQ8gYaCZ/Ql9c8GF+891dc2xTDktRyK/nr2yDW3Lu3SaES sV+I/Q3DIVcXNpSRfq9FCcLYE/33KLV/vHrcNa/rO9Q5cukT8GsOcX0PWLVjxtxSxIUf bK9u5vnmVldXhXfdS7O87SxMIUp5NfVKjPtCoTk6oNYJ/Dp0vmtOZzMdDkGgRiq6Q1bw MVZ4oCuaW4KMMXDYu7thVFYs97NTUXRf9Ft1TD4+UNT7lhlRmmrpqQ0Uuh2RDRPYEKYD +YBA== X-Gm-Message-State: ALoCoQkjjbnX+m1A9OFFx3w5iZWddC0crMInY2/Rr5cSbXQJigmIcqAYkxPakv4UqrMd2PQ3+6BS X-Received: by 10.112.14.5 with SMTP id l5mr5611583lbc.6.1402585385760; Thu, 12 Jun 2014 08:03:05 -0700 (PDT) X-BeenThere: std-proposals@isocpp.org Original-Received: by 10.180.81.164 with SMTP id b4ls435653wiy.8.canary; Thu, 12 Jun 2014 08:03:04 -0700 (PDT) X-Received: by 10.180.211.36 with SMTP id mz4mr7540656wic.20.1402585384303; Thu, 12 Jun 2014 08:03:04 -0700 (PDT) Original-Received: from mail-wi0-x22e.google.com (mail-wi0-x22e.google.com [2a00:1450:400c:c05::22e]) by mx.google.com with ESMTPS id r4si3607951wiv.24.2014.06.12.08.03.04 for (version=TLSv1 cipher=ECDHE-RSA-RC4-SHA bits=128/128); Thu, 12 Jun 2014 08:03:04 -0700 (PDT) Received-SPF: pass (google.com: domain of mikhailsemenov1957@gmail.com designates 2a00:1450:400c:c05::22e as permitted sender) client-ip=2a00:1450:400c:c05::22e; Original-Received: by mail-wi0-f174.google.com with SMTP id bs8so3621851wib.1 for ; Thu, 12 Jun 2014 08:03:03 -0700 (PDT) X-Received: by 10.194.92.148 with SMTP id cm20mr6147110wjb.57.1402585383642; Thu, 12 Jun 2014 08:03:03 -0700 (PDT) Original-Received: by 10.216.51.143 with HTTP; Thu, 12 Jun 2014 08:03:03 -0700 (PDT) In-Reply-To: X-Original-Sender: mikhailsemenov1957@gmail.com X-Original-Authentication-Results: mx.google.com; spf=pass (google.com: domain of mikhailsemenov1957@gmail.com designates 2a00:1450:400c:c05::22e as permitted sender) smtp.mail=mikhailsemenov1957@gmail.com; dkim=pass header.i=@gmail.com; dmarc=pass (p=NONE dis=NONE) header.from=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:11278 Archived-At: --047d7bfd01668f2e8404fba4db9f Content-Type: text/plain; charset=UTF-8 You can already write: auto foo(int x, double y)->decltype(x+y) { ... } On 12 June 2014 15:10, Sebastian Gesemann wrote: > On Thu, Jun 12, 2014 at 12:16 PM, walter1234 wrote: > > Coming back to C++ from Rust, one thing begin to miss is the 2way type > > inference: its a nice choice on their part, you write the types in the > > signature, then the types in the body are inferred. > > > > But perhaps a significant amount of this use could be covered by having > > sugar to access the declared return type of a function within its own > body. > > > > imagine > > > > auto foo( args... )->decltype(....some expression based on args...) { > > > > return_type accumulator; // 'return_type' is a shortcut for > > whatever this functions declared return type is.. > > ... do stuff with accumulator... > > > > return accumulator. > > } > > > > ways of doing that without a new keyword, perhaps 'decltype(return)' , > any > > other ideas.. > > In some ways this would go beyond what rust currently does. (rust can't > yet > > use an expression for the return type, although making it generic often > > works because of how the return types are inferred by callers) > > I'm not sure about the utility for such a short cut -- given the fact > that in C++14 you can do something like this: > > // note: no trailing return type > auto foo(int x, double y) { > return x+y; > } > > Compared to what you suggest, this is the other way around: The return > type can be deduced from whatever the function returns. > > -- > > --- > 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/. > -- --- 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/. --047d7bfd01668f2e8404fba4db9f Content-Type: text/html; charset=UTF-8 Content-Transfer-Encoding: quoted-printable
You can already write:
auto foo(int x, doub= le y)->decltype(x+y)
{
=C2=A0=C2=A0=C2=A0=C2=A0...
}


= On 12 June 2014 15:10, Sebastian Gesemann <s.gesemann@gmail.com>= wrote:
On Thu, Jun 12, 2014 at 12:16 PM, walte= r1234 wrote:
> Coming back to C++ from Rust, one thing begin to miss is the 2way type=
> inference: its a nice choice on their part, you write the types in the=
> signature, then the types in the body are inferred.
>
> But perhaps a significant amount of this use could be covered by havin= g
> sugar to access the declared return type of a function within its own = body.
>
> imagine
>
> auto foo( =C2=A0args... =C2=A0)->decltype(....some expression based= on args...) {
>
> =C2=A0 =C2=A0 =C2=A0 return_type =C2=A0accumulator; =C2=A0 =C2=A0 // &= #39;return_type' is a shortcut for
> whatever this functions declared return type is..
> =C2=A0 =C2=A0 =C2=A0 ... do stuff with accumulator...
>
> =C2=A0 =C2=A0 =C2=A0return accumulator.
> }
>
> ways of doing that without a new keyword, perhaps 'decltype(return= )' , any
> other ideas..
> In some ways this would go beyond what rust currently does. (rust can&= #39;t yet
> use an expression for the return type, although making it generic ofte= n
> works because of how the return types are inferred by callers)

I'm not sure about the utility for such a short cut -- given the = fact
that in C++14 you can do something like this:

=C2=A0 // note: no trailing return type
=C2=A0 auto foo(int x, double y) {
=C2=A0 =C2=A0 return x+y;
=C2=A0 }

Compared to what you suggest, this is the other way around: The return
type can be deduced from whatever the function returns.

--

---
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-propo= sals+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/gro= up/std-proposals/.

--

---
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.
Visit this group at http://groups.google.com/a/isocpp.org/group/std-proposals/<= /a>.
--047d7bfd01668f2e8404fba4db9f-- .