220 30002 <1634996.i8lsGMFXel@tjmaciei-mobl1> article Path: news.gmane.org!.POSTED!not-for-mail From: Thiago Macieira Newsgroups: gmane.comp.lang.c++.isocpp.proposals Subject: Re: Re: Return type deduction into a template parameter Date: Sat, 24 Dec 2016 14:15:32 -0200 Lines: 79 Approved: news@gmane.org Message-ID: <1634996.i8lsGMFXel@tjmaciei-mobl1> References: <25614213-fc89-43e3-a17d-228fe01a9d01@isocpp.org> <2def9f74-1a39-405c-8ae3-87336d646ee2@isocpp.org> <3490b351-9080-4fa1-af35-f43cb315d278@isocpp.org> Reply-To: std-proposals@isocpp.org NNTP-Posting-Host: blaine.gmane.org Mime-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: quoted-printable X-Trace: blaine.gmane.org 1482596155 30331 195.159.176.226 (24 Dec 2016 16:15:55 GMT) X-Complaints-To: usenet@blaine.gmane.org NNTP-Posting-Date: Sat, 24 Dec 2016 16:15:55 +0000 (UTC) User-Agent: KMail/5.3.3 (Linux/4.8.13-1-default; KDE/5.28.0; x86_64; ; ) To: std-proposals@isocpp.org Original-X-From: std-proposals+bncBCB4TK757YBRBON67LBAKGQERE3362Q@isocpp.org Sat Dec 24 17:15:49 2016 Return-path: Envelope-to: gclcip-std-proposals@m.gmane.org Original-Received: from mail-lf0-f69.google.com ([209.85.215.69]) by blaine.gmane.org with esmtp (Exim 4.84_2) (envelope-from ) id 1cKoz7-00078S-6s for gclcip-std-proposals@m.gmane.org; Sat, 24 Dec 2016 17:15:49 +0100 Original-Received: by mail-lf0-f69.google.com with SMTP id d16sf40638533lfb.7 for ; Sat, 24 Dec 2016 08:15:54 -0800 (PST) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=isocpp-org.20150623.gappssmtp.com; s=20150623; h=from:to:subject:date:message-id:user-agent:in-reply-to:references :mime-version:content-transfer-encoding:x-original-sender :x-original-authentication-results:reply-to:precedence:mailing-list :list-id:x-spam-checked-in-group:list-post:list-help:list-archive :list-subscribe:list-unsubscribe; bh=wBxODR/Dsf0xBVT2LrBLnMdntwGHW5KowzJaGubTik4=; b=Gu2OCcDeTFTV3LqXDNrn/YX0fv7+WVlnCCrPryaL/8jGFFIwbiT29R73tP7fgtdP4y R0J0G9ic/scxOnBq8d+aZvJ4LLJMF5RkuueGNTZM72tRIGFqMdW1qTlxoBnLsq06fxX9 Pd0OKChePCHE9iLWUMlPqCQFZAaUM3osKw1wMVpKOTLvP42Zv/NTCnIjeXm0dL70sgg0 vUmiCvSjNwnLRFB40LrTCSEkyYRe3QgWsvQKl1UuLKw0dz8F+YvKCPW5+QQppCKcFXEA i9GO3plwESxqq9HltqFcxUoGTq7fs/hrMFPECb4I+59GJgAO38LDw8V0/WwdyJYE2K51 X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20161025; h=x-gm-message-state:from:to:subject:date:message-id:user-agent :in-reply-to:references:mime-version:content-transfer-encoding :x-original-sender:x-original-authentication-results:reply-to :precedence:mailing-list:list-id:x-spam-checked-in-group:list-post :list-help:list-archive:list-subscribe:list-unsubscribe; bh=wBxODR/Dsf0xBVT2LrBLnMdntwGHW5KowzJaGubTik4=; b=AF9HH5gdQaHOj/u5r3CjAbta5+pEtFkpu4FIdpUzRr+7+17cY9MlSp+8yzEX6LyyIH DjfWipbQm2bD45IUAA6d9tP+dItV2wq8/ckFYxI6hpq5uvSR5qyuZjV9obKz9/x8B7Lt km/qHRl11Z2O/OIWpU6pA90eiBUKqqOkvcyihraWgaNZeSqJH+S9ejMo6v3su8hyDD/3 ZhpZKiN4rK9F2ECcjbSECsPVspJmL4eaf3hUuWrCgxx0/FjByOkk9Ze0YTxnFZCsIW90 DIxy3Ui2PMVRTd4EGf1byjJnIWbEbBhRk7U29Nte4Bb3+xfqJJeu9BMuWozswJJ2aWnR X-Gm-Message-State: AIkVDXKPBPYFBgJYRu51oIYvFfE5qg3cbpet1/WUkq4tWqABMCr6VCF911ykBfGhCBzTdg== X-Received: by 10.46.33.214 with SMTP id h83mr2101955lji.24.1482596154034; Sat, 24 Dec 2016 08:15:54 -0800 (PST) X-BeenThere: std-proposals@isocpp.org Original-Received: by 10.28.47.204 with SMTP id v195ls3155061wmv.3.gmail; Sat, 24 Dec 2016 08:15:52 -0800 (PST) X-Received: by 10.194.246.170 with SMTP id xx10mr17815150wjc.174.1482596152655; Sat, 24 Dec 2016 08:15:52 -0800 (PST) Original-Received: from gondolin.macieira.info (gondolin.macieira.info. [2a01:4f8:d13:f81:21c:14ff:fe01:12a3]) by mx.google.com with ESMTP id qj8si39734011wjb.165.2016.12.24.08.15.52 for ; Sat, 24 Dec 2016 08:15:52 -0800 (PST) Received-SPF: pass (google.com: domain of thiago@macieira.org designates 2a01:4f8:d13:f81:21c:14ff:fe01:12a3 as permitted sender) client-ip=2a01:4f8:d13:f81:21c:14ff:fe01:12a3; Original-Received: from tjmaciei-mobl1.localnet (unknown [189.110.133.253]) by gondolin.macieira.info (Postfix) with ESMTPSA id 08A2911B5D9 for ; Sat, 24 Dec 2016 08:15:35 -0800 (PST) In-Reply-To: <3490b351-9080-4fa1-af35-f43cb315d278@isocpp.org> X-Original-Sender: thiago@macieira.org X-Original-Authentication-Results: mx.google.com; spf=pass (google.com: domain of thiago@macieira.org designates 2a01:4f8:d13:f81:21c:14ff:fe01:12a3 as permitted sender) smtp.mailfrom=thiago@macieira.org 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:30002 Archived-At: Em s=C3=A1bado, 24 de dezembro de 2016, =C3=A0s 07:50:23 BRST, aary@umich.e= du escreveu: > That still requires the user to read the code and find the return > statement, further the situation is complicated when the function is the > last one in a chain of functions that return a value, in which case the > user has to trace the return statements all the way to the first function > that returned the actual type. Or alternatively use an IDE. But having > this there still means that the language syntax is more clear to the > reader. If the user has to trace something, then the API is badly designed. Don't= =20 change the language to correct an API design flaw. Just design the API in a= =20 better way. Or, alternatively, make it so the user doesn't have to read the function an= d=20 doesn't need to know what the actual type is. It's perfectly fine to have= =20 complex or automatically-deduced return types that aren't evident. The user= =20 will use auto too and that's that. The user will never store that in a member or global variable. That's all. > What I meant to say was that the object returned would be an an object of > an instantiation of the class template with the type of the return > parameter. I could not figure out how to edit my post :(. For instance = if > you consider the following code >=20 > template > class Interface { > Interface(Type&& object_in) : object{std::forward(object_in) {} > Type object; > }; >=20 > class Something { > public: > using value_type =3D int; > }; >=20 > Interface return_something(const Something& something) { > return something::value_type{1}; > } is already in use by Concepts. Is your proposal aligned with that? If not, please find a different syntax. > This would return an Interface object with the integer 1 as a member It would return an Interfact object. > variable. I do not know whether this idea already exists built I thought > this feature could be more flexible than just a concept, as it allows the > usage of templates with the automatic return type deduction (which is an > awesome idea), and does not require the use of trailing return types (whi= ch > are verbose and sometimes not required). Please take a look at Concepts Lite. It may solve what you're looking for. = Or=20 it may be a conflicting use of the syntax. --=20 Thiago Macieira - thiago (AT) macieira.info - thiago (AT) kde.org Software Architect - Intel Open Source Technology Center --=20 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 e= mail 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/1634996.i8lsGMFXel%40tjmaciei-mobl1. .