220 29996 <25614213-fc89-43e3-a17d-228fe01a9d01@isocpp.org> article Path: news.gmane.org!.POSTED!not-for-mail From: curious Newsgroups: gmane.comp.lang.c++.isocpp.proposals Subject: Return type deduction into a template parameter Date: Fri, 23 Dec 2016 21:27:11 -0800 (PST) Lines: 106 Approved: news@gmane.org Message-ID: <25614213-fc89-43e3-a17d-228fe01a9d01@isocpp.org> Reply-To: std-proposals@isocpp.org NNTP-Posting-Host: blaine.gmane.org Mime-Version: 1.0 Content-Type: multipart/mixed; boundary="----=_Part_995_1486324719.1482557231300" X-Trace: blaine.gmane.org 1482557238 22487 195.159.176.226 (24 Dec 2016 05:27:18 GMT) X-Complaints-To: usenet@blaine.gmane.org NNTP-Posting-Date: Sat, 24 Dec 2016 05:27:18 +0000 (UTC) To: ISO C++ Standard - Future Proposals Original-X-From: std-proposals+bncBCB57BFXS4MRBMEO7DBAKGQEZAKKXKQ@isocpp.org Sat Dec 24 06:27:14 2016 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 1cKerM-0004Gg-1N for gclcip-std-proposals@m.gmane.org; Sat, 24 Dec 2016 06:27:08 +0100 Original-Received: by mail-ua0-f197.google.com with SMTP id 96sf39265826uaq.7 for ; Fri, 23 Dec 2016 21:27:13 -0800 (PST) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=isocpp-org.20150623.gappssmtp.com; s=20150623; h=date:from:to:message-id: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=xp4c0WwxMmqwx3VD52fnMyKio3Vz37+VIZWLicjghdI=; b=klUVpgqhBH97y32LzIgijokHEpZ27I5m7cXyCfzHkryB3SuN8mV1uIvU442lYGYa47 jwvbQBkI2Ni1/Q5jOPpzMs+Y2mgyoSNmVnVY4U66ywBNOPSRaxMHp731B+ipTLR4hEtD L9BlCUd//oVyV8P672jOy5KLkOlTHnELlsZPq+Rs+Oz6tYLKsDi8hyGJ++USeGV3me3O cJsdUs7a3aeIIs4fw85sG3nZHe1qC7j8LsAPDmLqFPU/OM7Ux2CkHn5JOvGRAiwErzF0 2DW+PMBs7BN+UsPesK15bAXYczGXm3hk4HbAw21LSnwEGWWaOPa3Q/iXqaePew/pcbl4 awog== DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=umich.edu; s=google-2016-06-03; h=date:from:to:message-id: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=xp4c0WwxMmqwx3VD52fnMyKio3Vz37+VIZWLicjghdI=; b=Y9H2diPVSds3WNf6GovVbgMG01LWeyuFnbGV9Or8gQY/ylOq7MygsUdfSEJ28jlx6/ yjtksRRpMdDkYlNVGg6fGk41bEWFpfzgSOYS1lX++7kWJOCTAu/46Q6Mm9N117uzw2ez sa9JbR0Tc+1AUB1j5Jx4v/Sx/QvX2+iy4amtCqySy/wHqPXe1PZsoTdCZhRecsTkw1uJ 0bJm2iEVh3aWxPr+0Izvfmiv2pxt/81iF4QnMSpbPBwFFQoDBdCjWOgyQX00t3c4ICdC gZCWRRs8ekkZ801D8fvsRiAmCJysjKt8Fz8lquTh3dzkZY700H56ort259p3sryrB+LS RZNw== 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:message-id: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=xp4c0WwxMmqwx3VD52fnMyKio3Vz37+VIZWLicjghdI=; b=TLGUrZ66AcKpIggYo47+MkoGmzxOUb5u6z1BqEazK+l/ZJelvMABaX1p9lL9dTe6il RwbYxmxgGmg24im2S/jaidv3U/G1VKXfWlGh9VcayTMrimAcChlCFgwHsbpvzSM1iyCo Wt3A3Zle/su7Hx8w7Xi/rCNR4yQyF2dPBvatQXeFBihSFcomN9qFLknsBlnEYrF+R/Ls vqFx/EdcQMP6Oy9zjGWmzvYi0Jv6suiT1ToBKv7AHu3deCNyAtwvlVac7YMHUgQCJpNL T9QNl9NVaIwsPHZ1FxMKtCNoxZ7ndVyL9PvcBk4T45g57cVq3SZOGC8XGlGSarcom3y2 YQgw== X-Gm-Message-State: AIkVDXINhPFgX0vdcVaMmwBGiastKpJvClkHSxIDmNoH9do76G7lOYnSpY2PM/y5SUjXzA== X-Received: by 10.159.48.30 with SMTP id h30mr8287453uab.6.1482557232579; Fri, 23 Dec 2016 21:27:12 -0800 (PST) X-BeenThere: std-proposals@isocpp.org Original-Received: by 10.157.63.53 with SMTP id m50ls27481772otc.10.gmail; Fri, 23 Dec 2016 21:27:11 -0800 (PST) X-Received: by 10.157.20.197 with SMTP id r5mr1322851otr.9.1482557231911; Fri, 23 Dec 2016 21:27:11 -0800 (PST) X-Original-Sender: aary@umich.edu 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:29996 Archived-At: ------=_Part_995_1486324719.1482557231300 Content-Type: multipart/alternative; boundary="----=_Part_996_1759476799.1482557231301" ------=_Part_996_1759476799.1482557231301 Content-Type: text/plain; charset=UTF-8 Hey guys, The proposal here is to allow the return type deduction syntax to be extendible to more versatile situations for example as a template parameter. Consider the following code template auto return_something(const Something& something); This interface gives the reader little to no information about what actually is being returned from the function, they have no way of knowing how they should go about interacting with the returned object. If instead something like the following could be done // in the .hpp file, this is the declaration of the function, exposing useful // information to the user about the return type of the function, they now // know that they can interact with the return type every way that the // SomeInterfaceOrConcept class can be used. template SomeInterfaceOrConcept return_something(const Something& something); Now the reader instantly knows that the return type is an instantiation of the SomeInterfaceOrConcept class, and this function has therefore been documented well without requiring the reader to look into the implementation of the function or look at a trailing return type, which can sometimes be just as complicated as looking at the actual function body itself. Further sometimes it is convenient to skip the trailing return type entirely. Another thing this enables is the ability to add concept checks to the return type. Giving the reader a better idea of the value being returned without knowing its actual concrete type. -- 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/25614213-fc89-43e3-a17d-228fe01a9d01%40isocpp.org. ------=_Part_996_1759476799.1482557231301 Content-Type: text/html; charset=UTF-8 Content-Transfer-Encoding: quoted-printable
Hey guys,

The proposal here is to allow= the return type deduction syntax to be extendible to more versatile situat= ions for example as a template parameter. =C2=A0Consider the following code=

template &l= t;typename Something>
auto return_something(const Something& something);

This interface gives the reader little to no informatio= n about what actually is being returned from the function, they have no way= of knowing how they should go about interacting with the returned object. = =C2=A0If instead something like the following could be done

// in the .hpp file, this is the declaration of th= e function, exposing useful
// information to the user about the return type of the functio= n, they now
// know = that they can interact with the return type every way that the
=
// SomeInterfaceOrConcept class = can be used. =C2=A0
= template <typename Something>
SomeInterfaceOrConcept<auto> return_something(const S= omething& something);

Now the reader instantly knows that the return type = is an instantiation of the Som= eInterfaceOrConcept class, and this= function has therefore been documented well without requiring the reader t= o look into the implementation of the function or look at a trailing return= type, which can sometimes be just as complicated as looking at the actual = function body itself. =C2=A0Further sometimes it is convenient to skip the = trailing return type entirely. =C2=A0

Another= thing this enables is the ability to add concept checks to the return type= .. =C2=A0Giving the reader a better idea of the value being returned without= knowing its actual concrete type. =C2=A0

--
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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/25614213-fc89-43e3-a17d-228fe01a9d01= %40isocpp.org.
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