220 11293 <2d5fa56c-d925-4b6b-90c8-b448e409058f@isocpp.org> article Path: news.gmane.org!not-for-mail From: mitchnull@gmail.com Newsgroups: gmane.comp.lang.c++.isocpp.proposals Subject: Re: return type sugar (orthogonal to auto foo() {} ) Date: Fri, 13 Jun 2014 01:04:35 -0700 (PDT) Lines: 141 Approved: news@gmane.org Message-ID: <2d5fa56c-d925-4b6b-90c8-b448e409058f@isocpp.org> 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="----=_Part_214_29830601.1402646675584" X-Trace: ger.gmane.org 1402646685 12819 80.91.229.3 (13 Jun 2014 08:04:45 GMT) X-Complaints-To: usenet@ger.gmane.org NNTP-Posting-Date: Fri, 13 Jun 2014 08:04:45 +0000 (UTC) To: std-proposals@isocpp.org Original-X-From: std-proposals+bncBC36XNFZ4YKBBFHB5KOAKGQEEFCUFIA@isocpp.org Fri Jun 13 10:04:38 2014 Return-path: Envelope-to: gclcip-std-proposals@m.gmane.org Original-Received: from mail-vc0-f199.google.com ([209.85.220.199]) by plane.gmane.org with esmtp (Exim 4.69) (envelope-from ) id 1WvMTV-0001Vs-SJ for gclcip-std-proposals@m.gmane.org; Fri, 13 Jun 2014 10:04:38 +0200 Original-Received: by mail-vc0-f199.google.com with SMTP id ij19sf6440100vcb.6 for ; Fri, 13 Jun 2014 01:04:37 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gmail.com; s=20120113; h=date:from:to: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 :content-type; bh=kDizpSMeR+oTChQ2ShKoEXXmXoCDtHRLbVydPq6yBSs=; b=F1biZbHzsWb9SgNoImBNk7SzH3IRoXUml/Cr5ZApxORxCkFMdZ3jvSSmOl3cUN9+V+ dMr5LfwKQVNq3lXXC1fJ/80iMwJkfIwf5qLFYSpdrypGV9ZzSEmbIiBX0vxHW4mmyUOh 74QAvnV29lx42PIx3weZAVHQJucfpXBVUmWYGP3ivT1v0KA3lNIErVi0OXPQyXu2yCFa UdBJC5KEQu5t6nue/FSPlpoN2oNFRmxrsE4UwAwhn5auxJTzvz9Khgh8DtJMflUsJX40 veB7GzBgeEh8uxL/Kw4Bjq5nf62VqxVJJy2PzMNLH6vdPSTmtt12XohafLlhTDG2DIXM /uCQ== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20130820; h=x-gm-message-state:date:from:to: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:content-type; bh=kDizpSMeR+oTChQ2ShKoEXXmXoCDtHRLbVydPq6yBSs=; b=lBqsiIXF97dz4XVFLzJzj0cdQ6dC+FtKUq6dQsJxSdar2O/1y+2LaoruklCOfT962z t0C5j6HLI/qhefFOTGN2vs/mXxPo3rLvrv61mhAfRlGi1IycXzQtPGKFbkVGQivEL3mv VKSkDWObASL29/gceK01/lsCdLjTCk3YbcYBZBkSsNJZqecDKkHfvQUTm0gycXeTBhHl KkNezYucAg7NpFNXGjyU+7IRM0lM8oBbyL9t52zuBCkBeo6ZxXhArSD6BbLdk8sGRw40 MwcytQ+kbpJiJv0mArNapknalGXzVVq/get7+Dm2xL/Cm8z2NR6wJhhAXfJok0mcgJek 1MoQ== X-Gm-Message-State: ALoCoQmfPCSc/IwHoqs5/bSV58Y0AVlbl7v3t6PN0Ry8QUhRSmqeOtLShUKOB2Jj9V+xXhpnRNqk X-Received: by 10.236.1.198 with SMTP id 46mr181047yhd.16.1402646676988; Fri, 13 Jun 2014 01:04:36 -0700 (PDT) X-BeenThere: std-proposals@isocpp.org Original-Received: by 10.140.30.165 with SMTP id d34ls3400875qgd.25.gmail; Fri, 13 Jun 2014 01:04:36 -0700 (PDT) X-Received: by 10.140.93.23 with SMTP id c23mr16715qge.14.1402646676244; Fri, 13 Jun 2014 01:04:36 -0700 (PDT) In-Reply-To: <30a83c0d-00e6-462a-822e-a1789787ec05@isocpp.org> X-Original-Sender: mitchnull@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:11293 Archived-At: ------=_Part_214_29830601.1402646675584 Content-Type: text/plain; charset=UTF-8 How about: auto foo(int bar, float baz) -> decltype(bar + baz) { decltype(foo(bar, baz)) res = bar + baz; return res; } this way you don't have to repeat the expression, you only need to change the type of "res" if the function name / parameters change. Having decltype(return) be just syntax sugar for the above would be nice and easy to do, so I think it would be nice to have a proposal for this. On Thursday, June 12, 2014 12:16:04 PM UTC+2, 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) > -- --- 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/. ------=_Part_214_29830601.1402646675584 Content-Type: text/html; charset=UTF-8 Content-Transfer-Encoding: quoted-printable
How about:

a= uto foo(int bar, float baz) ->= decltype(bar + baz) {<= br>    decltype(foo<= /span>(bar, baz)) res =3D bar + = baz;
   = ; return res<= span style=3D"color: #660;" class=3D"styled-by-prettify">;
}

this way you don't have to repeat the expression, you only need to change = the type of "res" if the function name / parameters change.  Having de= cltype(return) be just syntax sugar for the above would be nice and easy to= do, so I think it would be nice to have a proposal for this.

On Thursday, June 12, 2014 12:16:04 PM UTC+2, walter1234 wrote:<= blockquote class=3D"gmail_quote" style=3D"margin: 0;margin-left: 0.8ex;bord= er-left: 1px #ccc solid;padding-left: 1ex;">
Coming back to= C++ from Rust, one thing begin to miss is the 2way type inference: its a n= ice choice on their part, you write the types in the signature, then the ty= pes 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.

ima= gine

auto foo(  args...  )->decltype(= .....some expression based on args...) {

  &nb= sp;   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, alth= ough making it generic often works because of how the return types are infe= rred by callers)

--

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