220 19937 <5F6E90B3-44BE-4A37-BE8F-91E1255E6407@gmail.com> article Path: news.gmane.org!not-for-mail From: David Krauss Newsgroups: gmane.comp.lang.c++.isocpp.proposals Subject: Re: default arguments Date: Thu, 20 Aug 2015 09:59:00 +0800 Lines: 157 Approved: news@gmane.org Message-ID: <5F6E90B3-44BE-4A37-BE8F-91E1255E6407@gmail.com> References: <89bf9d09-00ed-45db-bf88-39c844707bd1@isocpp.org> Reply-To: std-proposals@isocpp.org NNTP-Posting-Host: plane.gmane.org Mime-Version: 1.0 (Mac OS X Mail 8.2 \(2098\)) Content-Type: multipart/alternative; boundary="Apple-Mail=_DB5477E2-B84A-45DE-AD7C-95E5C8FE6C41" X-Trace: ger.gmane.org 1440035966 13974 80.91.229.3 (20 Aug 2015 01:59:26 GMT) X-Complaints-To: usenet@ger.gmane.org NNTP-Posting-Date: Thu, 20 Aug 2015 01:59:26 +0000 (UTC) To: std-proposals@isocpp.org Original-X-From: std-proposals+bncBCW25A7E3QCRB27I2SXAKGQECFFKB7Q@isocpp.org Thu Aug 20 03:59:13 2015 Return-path: Envelope-to: gclcip-std-proposals@m.gmane.org Original-Received: from mail-io0-f200.google.com ([209.85.223.200]) by plane.gmane.org with esmtp (Exim 4.69) (envelope-from ) id 1ZSF8H-0002xd-FA for gclcip-std-proposals@m.gmane.org; Thu, 20 Aug 2015 03:59:09 +0200 Original-Received: by iofe124 with SMTP id e124sf42072388iof.2 for ; Wed, 19 Aug 2015 18:59:08 -0700 (PDT) X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20130820; h=x-gm-message-state:from:content-type:message-id:mime-version :subject:date:references:to: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=0cft4+EdoQUmt8c3rDfxGXQoIc0F6Rhp3f7Qj2jWGUI=; b=HM055ZsSntMJE8IHmzydVivUTWFartBPoR7hjPe9+maqGM1D15Tcr3c8fpp7DZs8EO JeMeRe/VFEqIg8s2zqsEFq+LS6BHzCZ7e/BKDTNrthxduu2qvbkc8skTzeoq1vi2Uyyk 3Y+GJUtz7yC6S8Xzo4Lp7de4bgv3WuHMJz5FfalCyyTwzRDCf0iwF8+DdbZ+qYyxct9W g6Y2Aqd4J3GdXPr1TTp0Yi+A7Tjlx+0V1w0LwvQ9womL4EU46311YYWsM5zqQ0PHVB9r v8w2j258MYp+x4hN/8ershy3W0jU1NN84QHKZHxjyTiuTaUHa0hsX8K80Uezv9OiSfCx UkOQ== X-Gm-Message-State: ALoCoQmplDEjY1qnN1KkSCQTaDim0zwJcXcp5v5664SWJynMHoEykneJUhLvccgm3x+KUTp/omzh X-Received: by 10.107.28.2 with SMTP id c2mr474270ioc.16.1440035948331; Wed, 19 Aug 2015 18:59:08 -0700 (PDT) X-BeenThere: std-proposals@isocpp.org Original-Received: by 10.107.16.163 with SMTP id 35ls291418ioq.71.gmail; Wed, 19 Aug 2015 18:59:07 -0700 (PDT) X-Received: by 10.68.125.200 with SMTP id ms8mr1298074pbb.135.1440035947454; Wed, 19 Aug 2015 18:59:07 -0700 (PDT) Original-Received: from mail-pd0-x22e.google.com (mail-pd0-x22e.google.com. [2607:f8b0:400e:c02::22e]) by mx.google.com with ESMTPS id bc7si4684677pdb.228.2015.08.19.18.59.07 for (version=TLS1_2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128/128); Wed, 19 Aug 2015 18:59:07 -0700 (PDT) Received-SPF: pass (google.com: domain of potswa@gmail.com designates 2607:f8b0:400e:c02::22e as permitted sender) client-ip=2607:f8b0:400e:c02::22e; Original-Received: by pdrh1 with SMTP id h1so8136707pdr.0 for ; Wed, 19 Aug 2015 18:59:07 -0700 (PDT) X-Received: by 10.70.96.40 with SMTP id dp8mr1274797pdb.109.1440035946694; Wed, 19 Aug 2015 18:59:06 -0700 (PDT) Original-Received: from [172.20.10.2] ([121.54.54.184]) by smtp.gmail.com with ESMTPSA id c6sm2301694pat.13.2015.08.19.18.59.04 for (version=TLSv1 cipher=ECDHE-RSA-RC4-SHA bits=128/128); Wed, 19 Aug 2015 18:59:05 -0700 (PDT) In-Reply-To: X-Mailer: Apple Mail (2.2098) X-Original-Sender: potswa@gmail.com X-Original-Authentication-Results: mx.google.com; spf=pass (google.com: domain of potswa@gmail.com designates 2607:f8b0:400e:c02::22e as permitted sender) smtp.mailfrom=potswa@gmail.com; dkim=pass header.i=@gmail.com; dmarc=pass (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:19937 Archived-At: --Apple-Mail=_DB5477E2-B84A-45DE-AD7C-95E5C8FE6C41 Content-Transfer-Encoding: quoted-printable Content-Type: text/plain; charset=UTF-8 > On 2015=E2=80=9308=E2=80=9320, at 7:53 AM, Arthur O'Dwyer wrote: >=20 > On the subject of C and named parameters, I'll add that Ben Klemens' "21s= t Century C" shows a ver= y nice idiom for getting Python-style named parameters out of a C99 compile= r. I'm paraphrasing from memory a bit in the code sample below=E2=80=A6 Perhaps the syntax of an expression-list beginning with =E2=80=9C.=E2=80=9D= should indicate implicit braces, added as sugar. I think that passing a st= ruct is a superior design when lots of parameters are present, and one supp= orted by decades of experience. struct parameters { int buffer_size =3D 1024; int timeout =3D 10; int tries =3D 3; }; int foo( parameters ); int x =3D foo( .buffer_size =3D 100, .timeout =3D 2, .tries =3D 3 ); // imp= licit braces class non_aggregate { public: non_aggregate( int, int, int ); // A non_aggregate( parameters ); // B }; non_aggregate a( 1, 2, 3 ); // A non_aggregate b{ 1, 2, 3 }; // A non_aggregate c({ .buffer_size =3D 100, .timeout =3D 2, .tries =3D 3 }); //= B (no extension beyond designated initializers) non_aggregate d{{ .buffer_size =3D 100, .timeout =3D 2, .tries =3D 3 }}; //= B (no extension beyond designated initializers) non_aggregate e( .buffer_size =3D 100, .timeout =3D 2, .tries =3D 3 ); // B= (implicit braces) non_aggregate f{ .buffer_size =3D 100, .timeout =3D 2, .tries =3D 3 }; // e= rror: braces are implicit only inside parens It=E2=80=99s better to disallow the last case, because list-initialization = should represent aggregation; it shouldn=E2=80=99t be used to express gener= ating an object from a set of abstract parameters or constraints. --=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/. --Apple-Mail=_DB5477E2-B84A-45DE-AD7C-95E5C8FE6C41 Content-Transfer-Encoding: quoted-printable Content-Type: text/html; charset=UTF-8
On 2015=E2=80=9308= =E2=80=9320, at 7:53 AM, Arthur O'Dwyer <arthur.j.odwyer@gmail.com> wrote:

On the subject of C and named parameters, I'll add= that Ben Klemens' "21st Cen= tury C" shows a very = nice idiom for getting Python-style named parameters out of a C99 compiler.= I'm paraphrasing from memory a bit in the code sample below=E2=80=A6
=

Perhaps the s= yntax of an expression-list beginning with =E2= =80=9C.=E2=80=9D should indicate i= mplicit braces, added as sugar. I think that passing a struct is a superior design when lots o= f parameters are present, and one supported by decades of experience.

struct parameters {
&n= bsp; int buffer_size =3D 1024;
  int timeout =3D 10;
  int tries = =3D 3;
};

int foo( parameters );
int x =3D f= oo( .b= uffer_size =3D 100, .timeout =3D 2, .tries =3D 3 ); // implicit braces

class non_aggregate {
public:
  non_aggrega= te( int, int, int ); // A
  non_aggregate( parameters ); // B
};

non_aggregate a( 1, 2, 3 ); // A
non_aggregate = b{ 1, 2, 3 }; // A
non_aggregate c({ .buffer_size =3D= 100, .timeout =3D 2, .tries =3D 3 }); // B (no extension beyond designated initia= lizers= )
non_aggregate d{{ .buffer_size =3D 100, .timeout =3D 2, .tries =3D 3 }};<= /font> // B (no extensi= on&nbs= p;beyo= nd designated initializers)
non_aggregate e( .buffer_size =3D 100,= .timeout =3D 2, .tries =3D 3 ); // B (implicit braces)
non_= aggregate f{ .buffer_size =3D 100, .timeout =3D 2, .tries =3D 3 }; // error= : braces are implicit only inside parens

It=E2=80=99s better to dis= allow the last case, because list-initialization should represent aggregati= on; it shouldn=E2=80=99t be used to express generating an object from a set= of abstract parameters or constraints.

--

---
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