220 19943 article Path: news.gmane.org!not-for-mail From: Arthur Tchaikovsky Newsgroups: gmane.comp.lang.c++.isocpp.proposals Subject: Re: default arguments Date: Thu, 20 Aug 2015 02:57:10 -0700 (PDT) Lines: 186 Approved: news@gmane.org Message-ID: References: <55D56B72.7010907@wanadoo.fr> Reply-To: std-proposals@isocpp.org NNTP-Posting-Host: plane.gmane.org Mime-Version: 1.0 Content-Type: multipart/mixed; boundary="----=_Part_2777_1614810103.1440064631073" X-Trace: ger.gmane.org 1440064635 14020 80.91.229.3 (20 Aug 2015 09:57:15 GMT) X-Complaints-To: usenet@ger.gmane.org NNTP-Posting-Date: Thu, 20 Aug 2015 09:57:15 +0000 (UTC) To: ISO C++ Standard - Future Proposals Original-X-From: std-proposals+bncBDL6FI4NYYERB6GI22XAKGQES4FU23Y@isocpp.org Thu Aug 20 11:57:15 2015 Return-path: Envelope-to: gclcip-std-proposals@m.gmane.org Original-Received: from mail-pa0-f72.google.com ([209.85.220.72]) by plane.gmane.org with esmtp (Exim 4.69) (envelope-from ) id 1ZSMaw-0006aB-BR for gclcip-std-proposals@m.gmane.org; Thu, 20 Aug 2015 11:57:14 +0200 Original-Received: by pano2 with SMTP id o2sf8371180pan.3 for ; Thu, 20 Aug 2015 02:57:13 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gmail.com; s=20120113; h=date:from:to:message-id:in-reply-to:references:subject:mime-version :content-type: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=VeoHfBgaylTkz5q6ing1WGTgej/2c49+ekh+tS3VVRQ=; b=dITIOGBkcciG6+BtY51/wpvO5SoQnrXnHFLodYSaz/NM/e84UrjOx3wQPa3JDqhBNl 4RCjU5JN/V3Zc3jNm8zL+YRvrkE4qO4Lkq1EEJkYjvMNzPRbn4vBV63sUF3VBIeUwnop G+0+5kOyGyViTyPsrbKoXM5yk0ffqCbakSQiO2YA/K4i0+pMO3KN82VpHMyq4b5yzXpI eyGq91cKS+zNXjBf/RgqNiJrbSaoxP4QtOuJ+wc1/F+Ovo0Nit2qJaJZh6xMHpJQ23uT 1Gz3l+wkkTCvLxzI6r6yXXOtWE4cma9oVuVD4PgK5lgv7H32D9QOtT7Tyw/pg4A6ovOT W08A== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20130820; h=x-gm-message-state:date:from:to:message-id:in-reply-to:references :subject:mime-version:content-type: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=VeoHfBgaylTkz5q6ing1WGTgej/2c49+ekh+tS3VVRQ=; b=iz8XycoZWXF9rXX8AsR+dQXJmx/t9KVSxcQ6GxVqF74ne1AkKr0KyHc7hBsPZifQ81 HOjZj7ZMBqXVLwjPq6DtUQ4S8rtuFLXC0bR9SJm2jdf3bF6NnsXAoy/L2k5IROosdZ4V z9MmPw3U96qoAE/64jZuKE2bxytUXK2v2qGaetRbrxFFbrHWgY8eE/tqIYl1p54LCMub UDiYdGA7BSlqO13+5Z1Pkr/XIb/hq4OsY5DdjXv++wsC7Cs6QVc2VIYFsC04ePAmxVDq GnqNbrZtpLzNDpPt6ZTnnD7vDKQCwSeuGrP8oCUnZgHlON+L2nUFMhv9cgnKclc2W+f1 n0Hw== X-Gm-Message-State: ALoCoQlinnE0WnpO7zPb78Om4bPhNFCTKjSFb+M4HikNdcrtmNXVc55UuffLc7ERMX8AK+oq24N0 X-Received: by 10.68.104.161 with SMTP id gf1mr1607243pbb.11.1440064632969; Thu, 20 Aug 2015 02:57:12 -0700 (PDT) X-BeenThere: std-proposals@isocpp.org Original-Received: by 10.182.78.106 with SMTP id a10ls247812obx.43.gmail; Thu, 20 Aug 2015 02:57:11 -0700 (PDT) X-Received: by 10.182.105.34 with SMTP id gj2mr9789obb.34.1440064631954; Thu, 20 Aug 2015 02:57:11 -0700 (PDT) In-Reply-To: <55D56B72.7010907@wanadoo.fr> X-Original-Sender: atch.cpp@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:19943 Archived-At: ------=_Part_2777_1614810103.1440064631073 Content-Type: multipart/alternative; boundary="----=_Part_2778_268999758.1440064631073" ------=_Part_2778_268999758.1440064631073 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: quoted-printable Hi Vincente, Thank you for your words. As you yourself noted, the alternative is cumbersome and error prone. On=20 top of that, there is a huge amount of work left to the=20 designer/implementer of said function to provide all valid overloads which= =20 I'm not sure that if real world devs would really go to such extend and do= =20 it. With my proposal, all this burden, that is cumbersomeness, error=20 proneness and a work of developer/designer of such function are simply=20 removed. All is left is nice, natural syntax for users to use if they wish= =20 to. I know that is my proposal and I shouldn't really say it, but I=20 genuinely fail to see bad/weak points of my proposal. It fits so nicely=20 with C++ both philosophy (give a choice) and syntax that I really hope this= =20 will get voted into C++. Thank you. On Thursday, 20 August 2015 06:53:59 UTC+1, Vicente J. Botet Escriba wrote: > > Le 15/08/15 18:49, Arthur Tchaikovsky a =C3=A9crit : > > 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 a= n=20 > 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, ti= meout, 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= useof the constants is however error prone. > > IMO, this kind of approach should appear in a possible proposal as your p= roposal solves all the issues of this approach. =20 > > 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/. ------=_Part_2778_268999758.1440064631073 Content-Type: text/html; charset=UTF-8 Content-Transfer-Encoding: quoted-printable
Hi Vincente,
Thank you for your words.
As you yourse= lf noted, the alternative is cumbersome and error prone. On top of that, th= ere is a huge amount of work left to the designer/implementer of said funct= ion to provide all valid overloads which I'm not sure that if real worl= d devs would really go to such extend and do it. With my proposal, all this= burden, that is cumbersomeness, error proneness and a work of developer/de= signer of such function are simply removed. All is left is nice, natural sy= ntax for users to use if they wish to. I know that is my proposal and I sho= uldn't really say it, but I genuinely fail to see bad/weak points of my= proposal. It fits so nicely with C++ both philosophy (give a choice) and s= yntax that I really hope this will get voted into C++.

Thank you.
On Thursday, 20 August 2015 06:53:59 UTC+1, Vicente J. Botet Escriba = wrote:
=20 =20 =20
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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