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Botet Escriba" Newsgroups: gmane.comp.lang.c++.isocpp.proposals Subject: Re: default arguments Date: Thu, 20 Aug 2015 07:53:54 +0200 Lines: 143 Approved: news@gmane.org Message-ID: <55D56B72.7010907@wanadoo.fr> References: Reply-To: std-proposals@isocpp.org NNTP-Posting-Host: plane.gmane.org Mime-Version: 1.0 Content-Type: multipart/alternative; boundary="------------030205020903080201030404" X-Trace: ger.gmane.org 1440050050 15440 80.91.229.3 (20 Aug 2015 05:54:10 GMT) X-Complaints-To: usenet@ger.gmane.org NNTP-Posting-Date: Thu, 20 Aug 2015 05:54:10 +0000 (UTC) To: std-proposals@isocpp.org Original-X-From: std-proposals+bncBDH67CONY4PBB5GW2WXAKGQEZ5RQB5A@isocpp.org Thu Aug 20 07:54:01 2015 Return-path: Envelope-to: gclcip-std-proposals@m.gmane.org Original-Received: from mail-la0-f69.google.com ([209.85.215.69]) by plane.gmane.org with esmtp (Exim 4.69) (envelope-from ) id 1ZSInW-0005FO-LP for gclcip-std-proposals@m.gmane.org; Thu, 20 Aug 2015 07:53:58 +0200 Original-Received: by labpx14 with SMTP id px14sf7865465lab.1 for ; Wed, 19 Aug 2015 22:53:58 -0700 (PDT) X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20130820; h=x-gm-message-state:subject:to:references:from:message-id:date :user-agent:mime-version:in-reply-to:content-type: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=gbHEPm1z3DU6/GUsQyAKNOVbcUAg489NEMHhGuA80Nc=; b=G7bJbwv6j9FzQZr9jDU7jsDKt1QMLjoYJ3P6E3id0TBVB7MgN5J+uExvQwNCBcESx7 rHYQddgd9p8wLXkDGZpIt869fTKoAX1K/04bvUMbCJg9YaG9k5hYMH19aoE3S8+dp1QI Fgk+e7fwGkgql4j4miD1MN3/ZTArdKLGXDaSxthh6u+y8PQXByklOtryuppPkYrSzowD tIiUt5MnN0olyEWzqTaHADvWAA0x3Mu8OPAZK7vvRcUKcNUy+LJGpY+81zBtw6m1CbeI C5dYYQx7s6M5FALDIjs5FnxMJPAjoCvbDL1fVyRq795oRwYEdXrdywLf6e4KkMgROCkJ fFCw= X-Gm-Message-State: ALoCoQlkecZo2rfNxPTO5MFmrzKBcXsP1M+gEpBN9d+JuDnSdJJGFG08Mt6uHzRB53yF9HRIsJdE X-Received: by 10.194.115.135 with SMTP id jo7mr340702wjb.7.1440050038010; Wed, 19 Aug 2015 22:53:58 -0700 (PDT) X-BeenThere: std-proposals@isocpp.org Original-Received: by 10.180.106.5 with SMTP id gq5ls53495wib.31.gmail; Wed, 19 Aug 2015 22:53:55 -0700 (PDT) X-Received: by 10.194.85.130 with SMTP id h2mr2790789wjz.2.1440050035532; Wed, 19 Aug 2015 22:53:55 -0700 (PDT) Original-Received: from smtp.smtpout.orange.fr (smtp04.smtpout.orange.fr. [80.12.242.126]) by mx.google.com with ESMTPS id e16si7148674wiv.48.2015.08.19.22.53.55 for (version=TLSv1 cipher=RC4-SHA bits=128/128); Wed, 19 Aug 2015 22:53:55 -0700 (PDT) Received-SPF: neutral (google.com: 80.12.242.126 is neither permitted nor denied by best guess record for domain of vicente.botet@wanadoo.fr) client-ip=80.12.242.126; Original-Received: from new-host.home ([81.53.62.61]) by mwinf5d51 with ME id 6ttu1r0091KGt4H03ttume; Thu, 20 Aug 2015 07:53:55 +0200 X-ME-Helo: new-host.home X-ME-Auth: dmljZW50ZS5ib3RldEB3YW5hZG9vLmZy X-ME-Date: Thu, 20 Aug 2015 07:53:55 +0200 X-ME-IP: 81.53.62.61 User-Agent: Mozilla/5.0 (Macintosh; Intel Mac OS X 10.7; rv:38.0) Gecko/20100101 Thunderbird/38.2.0 In-Reply-To: X-Original-Sender: vicente.botet@wanadoo.fr X-Original-Authentication-Results: mx.google.com; spf=neutral (google.com: 80.12.242.126 is neither permitted nor denied by best guess record for domain of vicente.botet@wanadoo.fr) smtp.mailfrom=vicente.botet@wanadoo.fr 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:19939 Archived-At: This is a multi-part message in MIME format. --------------030205020903080201030404 Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: quoted-printable Le 15/08/15 18:49, Arthur Tchaikovsky a =C3=A9crit : > Hi, > Does anyone see helpfulness of such solution: > Having fnc: > > void f(int a =3D 0, int b =3D 1, int c =3D 2, int d =3D 3); > > I think that it would be nice to be able to say whilst calling it and > requiring only some of those args to be non-default: > > f(default,2,default,4); > > Thoughts? > > Hi, note that I'm not against the proposal. Just wanted to share a way to do what you are proposing in C++14. It is=20 an alternative that is cumbersome and error prone. It consist in using=20 overloading and a default_t type and a default_ instance of default_t. f(int buffer_size =3D 1024, int timeout =3D 10, int tries =3D 3); f(default_t, int timeout =3D 10, int tries =3D 3) { return f(1024, tim= eout, tries); } f(int buffer_size, default_t, int tries =3D 3) { return f(buffer_size,= 10, tries); } f(); f(default_, 0); f(default_, default_, 20); The function provider can use constant for the defaults of course but the u= seof the constants is however error prone. IMO, this kind of approach should appear in a possible proposal as your pro= posal solves all the issues of this approach. Vicente --=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/. --------------030205020903080201030404 Content-Type: text/html; charset=UTF-8 Content-Transfer-Encoding: quoted-printable
Le 15/08/15 18:49, Arthur Tchaikovsky a =C3=A9crit=C2=A0:
Hi,=20
Does anyone see helpfulness of such solution:
Having fnc:

void f(int a =3D 0, int b =3D 1, int c =3D 2, int d =3D 3);

I think that it would be nice to be able to say whilst calling it and=20
requiring only some of those args to be non-default:

f(default,2,default,4);

Thoughts?
Hi, note that I'm not against the proposal.

Just wanted to share a way to do what you are proposing in C++14. It is an alternative that is cumbersome and error prone. It consist in using overloading and a default_t type and a default_ instance of default_t.

    f(int buffer_size =3D 1024, int timeout =3D 10, int =
tries =3D 3);
    f(default_t, int timeout =3D 10, int tries =3D 3) { return f(1024, time=
out, tries); }
    f(int buffer_size, default_t, int tries =3D 3) { return f(buffer_size, =
10, tries); }

f();
f(default_, 0);
f(default_, default_, 20);

The function provider can use constant for the defaults of course but the u=
seof the constants is however error prone.

IMO, this kind of approach should appear in a possible proposal as your pro=
posal solves all the issues of this approach. =20

Vicente

--

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