220 19926 <89bf9d09-00ed-45db-bf88-39c844707bd1@isocpp.org> article Path: news.gmane.org!not-for-mail From: "S.B." Newsgroups: gmane.comp.lang.c++.isocpp.proposals Subject: Re: default arguments Date: Wed, 19 Aug 2015 08:08:52 -0700 (PDT) Lines: 200 Approved: news@gmane.org Message-ID: <89bf9d09-00ed-45db-bf88-39c844707bd1@isocpp.org> References: Reply-To: std-proposals@isocpp.org NNTP-Posting-Host: plane.gmane.org Mime-Version: 1.0 Content-Type: multipart/mixed; boundary="----=_Part_5858_1598653176.1439996932421" X-Trace: ger.gmane.org 1439996951 21738 80.91.229.3 (19 Aug 2015 15:09:11 GMT) X-Complaints-To: usenet@ger.gmane.org NNTP-Posting-Date: Wed, 19 Aug 2015 15:09:11 +0000 (UTC) To: ISO C++ Standard - Future Proposals Original-X-From: std-proposals+bncBDLPV3M6UAHBBBNY2KXAKGQELCDDAQA@isocpp.org Wed Aug 19 17:09:09 2015 Return-path: Envelope-to: gclcip-std-proposals@m.gmane.org Original-Received: from mail-io0-f197.google.com ([209.85.223.197]) by plane.gmane.org with esmtp (Exim 4.69) (envelope-from ) id 1ZS4z2-0006Xe-7u for gclcip-std-proposals@m.gmane.org; Wed, 19 Aug 2015 17:08:56 +0200 Original-Received: by iodt126 with SMTP id t126sf17028419iod.0 for ; Wed, 19 Aug 2015 08:08:54 -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=oII9HcnRKX2WKXRzAVZdHfTZchqwpI8S06bvD2psI5Q=; b=Pdo9m3i/tuEkdaDWwOk2AIOTsZZGSYqmmqHy96TGsEJQhCgmav4FRB9FAJLLH+4f6Y b+ABhqkoi1fA2KEOBy1q3xIXXiRgr7b3tXX5sFeK39eo7YfzepjRF1Vy8O3UmM14hFle avsOu91UVH+VQTBmquLsDGNYwFcKv6eHSQakXbfIyzQS5p8z0Uc6gYPfhhcJdfA0KhIh 2128GldyYoO5+SefWfhD9LWIbgQIu1OsLZJAYYnvcjD2DPuvrg2BhTbOX7T5O5kSDkpt DTj3AjhvtnJ5J/7d6SlEq3UI8pYFNvpe1LbM20USNyYnVvIYaxDSAX757e7QRGF7XZcG QE7Q== 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=oII9HcnRKX2WKXRzAVZdHfTZchqwpI8S06bvD2psI5Q=; b=HBCx+uEEyUOyrewyepmOHgvLwWIPJrSXohxYqu8InMKFEi4NvcqNYRDd11B2n8LxIV uGjpn3Z0LWzW1VCBi1wpdiZnrEMcypx/oGNyYRjqVfx+/c8/SE4q/pD5lRUetH2U34D2 U/77sUuRWiVHxE6o1g5lSnR7AuxX6JMf0PyCBVFBOarvR5QJM/qxKUKWv7NNmbI3EsKE EtEmoVl6QOh0x5fDCZM9nu4/FC0GDqrbkhJAwhujz+xVaa4JjlzJhuKhjo8SYz4/5XMO 6jODi4guOhmpkAmlPXtcftklaJKuyRMAa4IZdGCd3XJEFjulr7HYNjIELK5XAPpnOWKy z87w== X-Gm-Message-State: ALoCoQnYqtRLtO5o5B/ktxliRUILmyvTuj3Dy3uyuROwZSVLjNn0u+BZ3l4wUH1yHy94aGwgBacV X-Received: by 10.107.170.212 with SMTP id g81mr10579558ioj.19.1439996934604; Wed, 19 Aug 2015 08:08:54 -0700 (PDT) X-BeenThere: std-proposals@isocpp.org Original-Received: by 10.140.44.66 with SMTP id f60ls156963qga.6.gmail; Wed, 19 Aug 2015 08:08:53 -0700 (PDT) X-Received: by 10.140.19.208 with SMTP id 74mr176108qgh.0.1439996933204; Wed, 19 Aug 2015 08:08:53 -0700 (PDT) In-Reply-To: X-Original-Sender: I.and.my.little.friends@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:19926 Archived-At: ------=_Part_5858_1598653176.1439996932421 Content-Type: multipart/alternative; boundary="----=_Part_5859_389752403.1439996932421" ------=_Part_5859_389752403.1439996932421 Content-Type: text/plain; charset=UTF-8 It's even simpler if we could write struct s { int a = 1337; int b = 4096; }; int main() { s x; s y { 42 }; // or s y { .a = 42 }; s z { .b = 42 }; return 0; } :) On Wednesday, August 19, 2015 at 2:02:01 PM UTC+8, Max Truxa wrote: > > I have to agree with Matt Calabrese completely. As it was already asserted > named arguments are not going to happen anytime soon (if at all). > > Earlier in this thread there were workarounds listed which are more or > less comparable to the proposal in their effect. > I would like to elaborate some more on one of these workarounds, as it can > be mapped pretty much 1-to-1 to the proposal and it happens to be the > solution I employ when encountering this kind of problem. > > > # Current workaround. > > struct s { > static int const default_a = 1337; > static int const default_b = 4096; > s(int a = default_a, int b = default_b) > : a(a), b(b) { } > int a; > int b; > }; > > int main() { > s x; > s y(42); > s z(s::default_a, 42); > return 0; > } > > See working code here: http://ideone.com/OKtbuc > > > # Using the proposed syntax. > > struct s { > s(int a = 1337, int b = 4096) > : a(a), b(b) { } > int a; > int b; > }; > > int main() { > s x; > s y(42); > s z(default, 42); > return 0; > } > > The current solution has a number of drawbacks. > 1) It's unnecessarily verbose. > 2) It's easy to mess up for parameters that have the same type. (`s > z(s::default_b, 42)` - Oops, passed `default_b` as `a`.) > 3) When looking up the actual default values there is one more hop to > make. It's not sufficient to look at the function declaration but > additionally we have to look for e.g. default_a. > > -- --- 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 email 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-proposals/. ------=_Part_5859_389752403.1439996932421 Content-Type: text/html; charset=UTF-8 Content-Transfer-Encoding: quoted-printable
It's even simpler if we could write

struct s {
=C2=A0 =C2=A0 int a =3D 1337;
= =C2=A0 =C2=A0 int b = =3D= 4096;
};
=C2=A0
int main() {
=C2=A0 =C2= =A0 s x;
=C2=A0 = =C2=A0 s y { = 42 }; // or s y { .a =3D 42 };
=C2=A0 =C2=A0 s z { .b =3D = 42 = };
=C2=A0 =C2=A0 = return 0;
}

:)

On Wednesd= ay, August 19, 2015 at 2:02:01 PM UTC+8, Max Truxa wrote:
I have to agree with Matt Calabrese completely.= As it was already asserted named arguments are not going to happen anytime= soon (if at all).

Earlier in this thread there were workarounds listed w= hich are more or less comparable to the proposal in their effect.
I woul= d like to elaborate some more on one of these workarounds, as it can be map= ped pretty much 1-to-1 to the proposal and it happens to be the solution I = employ when encountering this kind of problem.


# Current workarou= nd.

struct s {
=C2=A0 =C2=A0 static int const default_a =3D 1337;<= br>=C2=A0 =C2=A0 static int const default_b =3D 4096;
=C2=A0 =C2=A0 s(in= t a =3D default_a, int b =3D default_b)
=C2=A0 =C2=A0 =C2=A0 =C2=A0 : a= (a), b(b) { }
=C2=A0 =C2=A0 int a;
=C2=A0 =C2=A0 int b;
};
=C2= =A0
int main() {
=C2=A0 =C2=A0 s x;
=C2=A0 =C2=A0 s y(42);
=C2= =A0 =C2=A0 s z(s::default_a, 42);
=C2=A0 =C2=A0 return 0;
}

See= working code here: http:/= /ideone.com/OKtbuc


# Using the proposed syntax.

struct = s {
=C2=A0 =C2=A0 s(int a =3D 1337, int b =3D 4096)
=C2=A0 =C2=A0 = =C2=A0 =C2=A0 : a(a), b(b) { }
=C2=A0 =C2=A0 int a;
=C2=A0 =C2=A0 int= b;
};
=C2=A0
int main() {
=C2=A0 =C2=A0 s x;
=C2=A0 =C2=A0 = s y(42);
=C2=A0 =C2=A0 s z(default, 42);
=C2=A0 =C2=A0 return 0;
}=

The current solution has a number of drawbacks.
1) It's unnec= essarily verbose.
2) It's easy to mess up for parameters that have t= he same type. (`s z(s::default_b, 42)` - Oops, passed `default_b` as `a`.)<= br>3) When looking up the actual default values there is one more hop to ma= ke. It's not sufficient to look at the function declaration but additio= nally we have to look for e.g. default_a.

--

---
You received this message because you are subscribed to the Google Groups &= quot;ISO C++ Standard - Future Proposals" group.
To unsubscribe from this group and stop receiving emails from it, send an e= mail to std-proposa= ls+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-proposals/<= /a>.
------=_Part_5859_389752403.1439996932421-- ------=_Part_5858_1598653176.1439996932421-- .