220 21056 article Path: news.gmane.org!not-for-mail From: Matthew Woehlke Newsgroups: gmane.comp.lang.c++.isocpp.proposals Subject: Re: Introducing the returntype keyword Date: Wed, 30 Sep 2015 14:38:44 -0400 Lines: 65 Approved: news@gmane.org Message-ID: References: <24e315aa-2daf-4e47-933b-1f45157a0f79@isocpp.org> <3a1c9a29-3c55-403c-9d94-1504eabc8e44@isocpp.org> <0c43e09d-a5a9-4c35-8db7-0ff0a77f81d1@isocpp.org> Reply-To: std-proposals@isocpp.org NNTP-Posting-Host: plane.gmane.org Mime-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: quoted-printable X-Trace: ger.gmane.org 1443638350 18015 80.91.229.3 (30 Sep 2015 18:39:10 GMT) X-Complaints-To: usenet@ger.gmane.org NNTP-Posting-Date: Wed, 30 Sep 2015 18:39:10 +0000 (UTC) To: std-proposals@isocpp.org Original-X-From: std-proposals+bncBC37LBFWUIFBBQ6YWCYAKGQEPBIXRRQ@isocpp.org Wed Sep 30 20:39:02 2015 Return-path: Envelope-to: gclcip-std-proposals@m.gmane.org Original-Received: from mail-la0-f71.google.com ([209.85.215.71]) by plane.gmane.org with esmtp (Exim 4.69) (envelope-from ) id 1ZhMHN-000519-9S for gclcip-std-proposals@m.gmane.org; Wed, 30 Sep 2015 20:39:01 +0200 Original-Received: by laer8 with SMTP id r8sf26554017lae.2 for ; Wed, 30 Sep 2015 11:39:00 -0700 (PDT) X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20130820; h=x-gm-message-state:to:from:subject:date:lines:message-id:references :mime-version:content-type:content-transfer-encoding:user-agent :in-reply-to: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=64459mDDwWxKlWfKddEcHizwWsm0WUUAp/pMebOULI4=; b=Zm13F6f3ZzfZGG8H6ypxRtvBfA1SQvp3CP2cwaEzyjUbyeYksHiczG2YlmzJ0VLswb +uCB29c+AfTRXD7Ea0OpB2CXQfHT4kGLjoo0wSXw286b3UXEclyfOF1JA8eX219yTUNi 4GYi0nvvfby5gdpnO5YU9ONWIFiRja+bd85gb5Et1EWsWvdYrMBFfGRy+wTNm9/nEB5n 1m1KAzYP8Fiv0sFF6wO73xB9plUe92ak47DDuUIAloR+FciVdOTegafHZY8dB1ROVjvT wSIBxp5wwPaGrPvBdOEe+6E2gDhqGWlQerfU6h/AzKyOvV3HCI9 X-Gm-Message-State: ALoCoQn8Q1+NIwpNhZXyvhZdF3quiDHEB5/qpYLadgVEHbH8rpgTP6qu3onFUEGkkDVN4wR6gt8N X-Received: by 10.180.12.170 with SMTP id z10mr904607wib.1.1443638340353; Wed, 30 Sep 2015 11:39:00 -0700 (PDT) X-BeenThere: std-proposals@isocpp.org Original-Received: by 10.152.9.69 with SMTP id x5ls72978laa.30.gmail; Wed, 30 Sep 2015 11:38:59 -0700 (PDT) X-Received: by 10.112.171.69 with SMTP id as5mr1548512lbc.111.1443638339114; Wed, 30 Sep 2015 11:38:59 -0700 (PDT) Original-Received: from plane.gmane.org (plane.gmane.org. [80.91.229.3]) by mx.google.com with ESMTPS id p72si837448lfp.112.2015.09.30.11.38.59 for (version=TLSv1 cipher=RC4-SHA bits=128/128); Wed, 30 Sep 2015 11:38:59 -0700 (PDT) Received-SPF: pass (google.com: domain of gclcip-std-proposals@m.gmane.org designates 80.91.229.3 as permitted sender) client-ip=80.91.229.3; Original-Received: from list by plane.gmane.org with local (Exim 4.69) (envelope-from ) id 1ZhMHI-0004y7-Rv for std-proposals@isocpp.org; Wed, 30 Sep 2015 20:38:57 +0200 Original-Received: from tripoint.kitware.com ([66.194.253.20]) by main.gmane.org with esmtp (Gmexim 0.1 (Debian)) id 1AlnuQ-0007hv-00 for ; Wed, 30 Sep 2015 20:38:56 +0200 Original-Received: from mwoehlke.floss by tripoint.kitware.com with local (Gmexim 0.1 (Debian)) id 1AlnuQ-0007hv-00 for ; Wed, 30 Sep 2015 20:38:56 +0200 X-Injected-Via-Gmane: http://gmane.org/ Original-Lines: 47 Original-X-Complaints-To: usenet@ger.gmane.org X-Gmane-NNTP-Posting-Host: tripoint.kitware.com User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:31.0) Gecko/20100101 Thunderbird/31.7.0 In-Reply-To: <0c43e09d-a5a9-4c35-8db7-0ff0a77f81d1@isocpp.org> X-Original-Sender: mwoehlke.floss@gmail.com X-Original-Authentication-Results: mx.google.com; spf=pass (google.com: domain of gclcip-std-proposals@m.gmane.org designates 80.91.229.3 as permitted sender) smtp.mailfrom=gclcip-std-proposals@m.gmane.org; dmarc=fail (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-Spam-Checked-In-Group: std-proposals@isocpp.org 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:21056 Archived-At: On 2015-09-29 00:01, Nicol Bolas wrote: > On Monday, September 28, 2015 at 11:01:21 PM UTC-4, Arthur O'Dwyer wrote: >> In other words, the cost of this feature is high; >=20 > No, the cost of this feature is actually quite low. As others have pointe= d=20 > out, you could spell it `decltype(return)`, so you don't have the cost of= =20 > an actual keyword. >=20 > Even in implementation time, I can't imagine that this feature would=20 > require much effort on the part of compiler writers. ....*if* it's an error to use it before the return type is known. Not that I consider that as a problem; just being pedantic :-). >> Also =E2=80=94 this isn't a killer, but =E2=80=94 it seems awkward to ha= ve *both* "parse=20 >> the body of the function to deduce the auto return type" *and* "while=20 >> parsing the body of a function, replace decltype(return) with the return= =20 >> type of the function" in the same language. The example where the type is not known but is early deduced is interesting in that respect; it's conceivable that you would indeed want to use both features in the same function. > This also made me realize that, outside of TMP or constexpr shenanigans, = I=20 > don't remember the last time I used direct "call myself"-style recursion.= =20 ....quicksort? ;-) (I don't mean that you personally have written a quicksort recently, just that there *are* reasonable cases for functions that call themselves.) Actually, I just wrote one the other day that checks for a certain error initially and resorts to a default behavior in such case. Later, other operations that fail can self-call with intentionally bad arguments to get back to the default-behavior case. Sure, I could structured it differently to avoid that (or use goto)... just saying, it's one case I actually have - recently - written a function that directly calls itself. I could imagine in the case of functions with a trampoline header that being able to name itself would be useful. (Meaning, for example, a function that, at the start of execution and based on some condition, either modifies its arguments and reinvokes itself, or schedules itself to be called again at a later time or in a different context, and then (usually) immediately exits without doing anything further. This is a fairly common pattern in some multi-threaded designs.) --=20 Matthew --=20 ---=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. Visit this group at http://groups.google.com/a/isocpp.org/group/std-proposa= ls/. .