220 19890 article Path: news.gmane.org!not-for-mail From: Matthew Woehlke Newsgroups: gmane.comp.lang.c++.isocpp.proposals Subject: Re: default arguments Date: Tue, 18 Aug 2015 10:03:18 -0400 Lines: 77 Approved: news@gmane.org Message-ID: References: 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 1439906625 7662 80.91.229.3 (18 Aug 2015 14:03:45 GMT) X-Complaints-To: usenet@ger.gmane.org NNTP-Posting-Date: Tue, 18 Aug 2015 14:03:45 +0000 (UTC) To: std-proposals@isocpp.org Original-X-From: std-proposals+bncBC37LBFWUIFBBN7WZSXAKGQETBSKJUY@isocpp.org Tue Aug 18 16:03:37 2015 Return-path: Envelope-to: gclcip-std-proposals@m.gmane.org Original-Received: from mail-lb0-f199.google.com ([209.85.217.199]) by plane.gmane.org with esmtp (Exim 4.69) (envelope-from ) id 1ZRhUH-0008Uo-A8 for gclcip-std-proposals@m.gmane.org; Tue, 18 Aug 2015 16:03:37 +0200 Original-Received: by lbcue2 with SMTP id ue2sf7084793lbc.1 for ; Tue, 18 Aug 2015 07:03:37 -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=D2KBTKHIIuWGMlD56fh0qJ6ANujgV8KMuAePhTybC6M=; b=Mhjf9xoddUaexI6AJCwb+xb/WAbEZ+LP9Ho+I9FpnwqXrwwWxX17/JZbIBvGCqzxD1 ozf7TUntZgX20kXmG02NpcrfIrJj3SmqFewvU9OwnPfgj3kH2eenzFTKZ9tTsrBWczS/ fhdRZYyoDZVKqzotColnGZGibVFJFh9CLWfXbj3lI+TPonKq73JOWVjqL44UHjWbKQar yqUN6JQahnqgRw+VJiZqbuOCOdX8wHGeso2Sq8sbsa1d741Fe95tWWHXB8ctxCAlul28 7ofrtp9gDY4flNUbyaThfXI5ZuweGdt+e1HSjdlL9oJNpZBo3AV X-Gm-Message-State: ALoCoQlWnEiA12nRTCrDwjdGdmQshP4QgI8I26bzZp6NKfWYWC0ob6NtRQIQHeOYY2RWJLFftEak X-Received: by 10.180.90.106 with SMTP id bv10mr6374523wib.6.1439906616942; Tue, 18 Aug 2015 07:03:36 -0700 (PDT) X-BeenThere: std-proposals@isocpp.org Original-Received: by 10.152.88.7 with SMTP id bc7ls804697lab.74.gmail; Tue, 18 Aug 2015 07:03:35 -0700 (PDT) X-Received: by 10.112.210.137 with SMTP id mu9mr6265672lbc.95.1439906615010; Tue, 18 Aug 2015 07:03:35 -0700 (PDT) Original-Received: from plane.gmane.org (plane.gmane.org. [80.91.229.3]) by mx.google.com with ESMTPS id to6si14170247lbb.131.2015.08.18.07.03.34 for (version=TLSv1 cipher=RC4-SHA bits=128/128); Tue, 18 Aug 2015 07:03:35 -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 1ZRhUD-0008ST-R9 for std-proposals@isocpp.org; Tue, 18 Aug 2015 16:03:34 +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 ; Tue, 18 Aug 2015 16:03:33 +0200 Original-Received: from mwoehlke.floss by tripoint.kitware.com with local (Gmexim 0.1 (Debian)) id 1AlnuQ-0007hv-00 for ; Tue, 18 Aug 2015 16:03:33 +0200 X-Injected-Via-Gmane: http://gmane.org/ Original-Lines: 57 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: 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:19890 Archived-At: On 2015-08-18 06:22, David Rodr=C3=ADguez Ibeas wrote: > On Tue, Aug 18, 2015 at 10:42 AM, Arthur Tchaikovsky wrote: >> On Tuesday, 18 August 2015 10:34:39 UTC+1, Johannes Schaub wrote: >>> I would also wanna solve this with named arguments >>> >>> f(.b =3D 2, .d =3D 4) >> >> That genuinely seems pointless/silly to me, unless you can provide some >> convincing use cases. > > Any use case in which you may end up using 'default' in your proposal is = a > use case for these two approaches. In the first case, it lets you focus = on > what parameters are being configured (rather than defaulted) without havi= ng > to look at the function declaration, 'f(.b =3D 2, .d =3D 4)' is equivalen= t to > 'f(default, 2, default, 4)' and I find the former easier to read. It's also self-documenting. Consider Arthur O'Dwyer's examples; which is easier to understand? auto cptr =3D new C(); // usually the defaults are okay auto c2ptr =3D new C(2048); // use a bigger buffer auto c3ptr =3D new C(default, 1); // use a shorter timeout - vs. - auto cptr =3D new C{}; auto c2ptr =3D new C{.buffer =3D 2048}; auto c3ptr =3D new C{.timeout =3D 1}; There's a reason named arguments are so popular in Python :-). > int a[10] =3D { [3] =3D 1, [2] =3D 5, 6 }; // what values are in the arra= y? This never happens because your example is ill-formed. Parameters that are neither named nor indexed must precede parameters that are. (In Python also, and for similar reasons.) > Still, that might be easier than implementing named arguments. The "name= d" > arguments work nicely with a 'struct' since the type can be defined only > once, but it leads to different sorts of confusion for functions that may > have multiple declarations: >=20 > void f(int a =3D 1, int b =3D 2); > void f(int b =3D 1, int a =3D 2); // redeclaration >=20 > Which AFAIK is one of the issues that this form of proposals have faced i= n > the past. I recall also some discussions in this forum (or maybe even > papers?) aiming for a syntax that would allow this by enabling > warning/errors when a redeclaration used different names than the origina= l > declaration but I did not see any of those prosper. Probably there should be a way of naming parameters that "codifies" the name, making it part of the ABI. And, yes, such redeclarations would be disallowed. --=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/. .