220 19873 article Path: news.gmane.org!not-for-mail From: Arthur Tchaikovsky Newsgroups: gmane.comp.lang.c++.isocpp.proposals Subject: Re: default arguments Date: Tue, 18 Aug 2015 02:20:20 -0700 (PDT) Lines: 322 Approved: news@gmane.org Message-ID: References: <736eb378-52a4-43ba-b3b5-a73719ba70af@isocpp.org> <86717349-1fce-4247-9372-08eedce4cd30@isocpp.org> Reply-To: std-proposals@isocpp.org NNTP-Posting-Host: plane.gmane.org Mime-Version: 1.0 Content-Type: multipart/mixed; boundary="----=_Part_4029_420810057.1439889620237" X-Trace: ger.gmane.org 1439889625 20312 80.91.229.3 (18 Aug 2015 09:20:25 GMT) X-Complaints-To: usenet@ger.gmane.org NNTP-Posting-Date: Tue, 18 Aug 2015 09:20:25 +0000 (UTC) Cc: bop@gmb.dk To: ISO C++ Standard - Future Proposals Original-X-From: std-proposals+bncBDL6FI4NYYERBVPRZOXAKGQEIDAYR2Q@isocpp.org Tue Aug 18 11:20:25 2015 Return-path: Envelope-to: gclcip-std-proposals@m.gmane.org Original-Received: from mail-ig0-f200.google.com ([209.85.213.200]) by plane.gmane.org with esmtp (Exim 4.69) (envelope-from ) id 1ZRd4B-0007kC-CN for gclcip-std-proposals@m.gmane.org; Tue, 18 Aug 2015 11:20:23 +0200 Original-Received: by igxp17 with SMTP id p17sf171474384igx.3 for ; Tue, 18 Aug 2015 02:20:22 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gmail.com; s=20120113; h=date:from:to:cc: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=OIr39DwHJxQECGeAvuNKj6CTw8dQ19ptTWtljz8vi+k=; b=XINhc8Xw3WD7ZqX71IhNEgY/0ZRhLSbWzdjR4/AVpCpWkUjV8dbzpxhzVIVtPpCUsK bUXuwIcLpvXKhuCUODEzi1Yl/O4SfLdjwHNqgy8Klp6rxmFnlaEf8eeJtSF5/5zHHbto xRhy3ACo2B0J1Gq97IqzvWSCGIauuhC8iGYAyJg1hYnXiEq7zwG/oJisjytmZd+pV70W FcxJyy44bXbTEC2eiOU6S8Uz7JOt3gZTHGXkNIBBSDQjeiALPgdHHT1qF68hjBC3SC6h QCGAoA4lsO4zX7a3uBHyUp4VGfeQ9TNcJYSe/H9lDUwSiCHmjUJ4DU79m739eq32wTfi av6A== 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:cc: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=OIr39DwHJxQECGeAvuNKj6CTw8dQ19ptTWtljz8vi+k=; b=Om0QzmhBhkgTNLXf0VFxO2Q6yPkmmQK+9fXD7N9FSABKlYkolikkrwaa43QSRlNgCZ 9JBQFH4EMTodx4tLUShhjoSwrHWCUuDXumcCI5cktUhVkKVouE8wm2IztfRmc2ACgleu ZjreSacdY1R3wSoOpG+MiWOm+vtImxqt0sVqnr9kgNQzmEFrBPmhlcMbrP0bXC4aBjss 5Y0vjbIQx7r48XIJEBuPaAS2yOr245S3Ks2GCMmGnhs+GE3A4jGaCzcvQ3KCDcJDFjAt 1W79LWZ0kD2ieHMEOCwoQyY0EiWaNd1dFC44vJul+IHpXR+hm9t4wJKY/8/9/29FYivI +doQ== X-Gm-Message-State: ALoCoQnMZvZFcp1EeK63kyAKgL5N0qtOqzjKtsGpLXGM1vdH75tQo98ozgQbnz/HtmC/ZBl+l+ys X-Received: by 10.182.247.2 with SMTP id ya2mr4820287obc.37.1439889622406; Tue, 18 Aug 2015 02:20:22 -0700 (PDT) X-BeenThere: std-proposals@isocpp.org Original-Received: by 10.140.103.149 with SMTP id y21ls2610245qge.42.gmail; Tue, 18 Aug 2015 02:20:21 -0700 (PDT) X-Received: by 10.140.91.86 with SMTP id y80mr66429qgd.39.1439889621113; Tue, 18 Aug 2015 02:20:21 -0700 (PDT) In-Reply-To: <86717349-1fce-4247-9372-08eedce4cd30@isocpp.org> 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:19873 Archived-At: ------=_Part_4029_420810057.1439889620237 Content-Type: multipart/alternative; boundary="----=_Part_4030_460870604.1439889620237" ------=_Part_4030_460870604.1439889620237 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: quoted-printable "I would MUCH rather just rewrite all these constructors" But did you do it or simply wish that at some point you will find the time= =20 (and will) to do it, but in the mean time you are still using those "old"= =20 constructors? Because I also would MUCH rather have C++ cleaned up, yet=20 this will never happen, and I need to use C++ in its current state. What I= =20 wish is very different to what I have. And as for you saying that defaulted constructors are antipattern, is that= =20 a fact or it is simply your opinion? On Monday, 17 August 2015 23:52:24 UTC+1, Arthur O'Dwyer wrote: > > I work on a codebase where this feature would have lots of use-cases,=20 > because we have lots of classes whose constructors have defaulted=20 > parameters: > > C(int buffer_size =3D 1024, int timeout =3D 10, int tries =3D 3) :=20 > buffer_size_(buffer_size), timeout_(timeout), tries_(tries) {} > > 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(1024, 1); // use the default buffer size but wi= th=20 > a shorter timeout > auto c4ptr =3D new C(2048, 10, 5); // testing: bump up the number of= =20 > tries > > It would be marginally more convenient (and refactor-proof) to be able to= =20 > write > > 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 the default buffer size but= =20 > with a shorter timeout > auto c4ptr =3D new C(2048, default, 5); // testing: bump up the numb= er=20 > of tries > > However, I consider defaulted parameters in general to be a huge=20 > antipattern, and this constructor pattern in particular to be even worse. > I would MUCH rather just rewrite all these constructors so that they coul= d=20 > be used as > > auto cptr =3D new C(); // usually the defaults are okay > auto c2ptr =3D new C().withBufferSize(2048); // use a bigger buffer > auto c3ptr =3D new C().withTimeout(1); // use the default buffer siz= e=20 > but with a shorter timeout > auto c4ptr =3D new C().withBufferSize(2048).withTries(5); // testing= :=20 > bump up the number of tries > > or > > auto cptr =3D new C(); // usually the defaults are okay > auto c2ptr =3D new C(C::BufferSize(2048)); // use a bigger buffer > auto c3ptr =3D new C(C::Timeout(1)); // use the default buffer size = but=20 > with a shorter timeout > auto c4ptr =3D new C(C::BufferSize(2048), C::Tries(5)); // testing:= =20 > bump up the number of tries > > or (the most conservative way to rewrite our existing code) > > static constexpr int default_buffer_size =3D 1024; > static constexpr int default_timeout =3D 10; > static constexpr int default_tries =3D 3; > C() : buffer_size_(default_buffer_size), timeout_(default_timeout),= =20 > tries_(default_tries) {} > C(int buffer_size, int timeout, int tries) :=20 > buffer_size_(buffer_size), timeout_(timeout), tries_(tries) {} > > auto cptr =3D new C(); // usually the defaults are okay > auto c2ptr =3D new C(2048, C::default_timeout, C::default_tries); //= =20 > use a bigger buffer > auto c3ptr =3D new C(C::default_buffer_size, 1, C::default_tries); /= /=20 > use the default buffer size but with a shorter timeout > auto c4ptr =3D new C(2048, C::default_timeout, 5); // testing: bump = up=20 > the number of tries > > I don't really want to make it *easier* for people to write the "function= =20 > taking tons of defaulted parameters" antipattern. > Let's teach people how to avoid the use of defaulted parameters, instead. > > =E2=80=93Arthur > > > On Monday, August 17, 2015 at 11:58:41 AM UTC-7, Bo Persson wrote: >> >> On 2015-08-17 20:37, Arthur Tchaikovsky wrote:=20 >> > I would really appreciate some feedback from people, or is this=20 >> proposal=20 >> > so uninteresting that there is no point in wasting keyboard on it?=20 >> >> You might wonder how widely used it will be?=20 >> >> If not all parameters are of the same type, you can already get some of= =20 >> the effect with a few overloads:=20 >> >> void f(int a =3D 0, string b =3D "1",=20 >> complex c =3D 2.0, type4 d =3D 3);=20 >> >> inline void f(int a, complex c)=20 >> { f(a, "1", c, 3); }=20 >> >> inline void f(string b, complex c)=20 >> { f(0, b, c, 3); }=20 >> >> assuming that d is put last because you hardly ever want to change the= =20 >> default.=20 >> >> Just saying that you can already do this without a language change.=20 >> >> >> Bo Persson=20 >> >> >> >> >=20 >> > On Saturday, 15 August 2015 17:49:50 UTC+1, Arthur Tchaikovsky wrote:= =20 >> >=20 >> > Hi,=20 >> > Does anyone see helpfulness of such solution:=20 >> > Having fnc:=20 >> >=20 >> > void f(int a =3D 0, int b =3D 1, int c =3D 2, int d =3D 3);=20 >> >=20 >> > I think that it would be nice to be able to say whilst calling it= =20 >> > and requiring only some of those args to be non-default:=20 >> >=20 >> > f(default,2,default,4);=20 >> >=20 >> > Thoughts?=20 >> >=20 >> >=20 >> >> >> --=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_4030_460870604.1439889620237 Content-Type: text/html; charset=UTF-8 Content-Transfer-Encoding: quoted-printable
"I would MUCH rather just rewrite all these construct= ors"

But did you do it or simply wish that at some point you wi= ll find the time (and will) to do it, but in the mean time you are still us= ing those "old" constructors? Because I also would MUCH rather ha= ve C++ cleaned up, yet this will never happen, and I need to use C++ in its= current state. What I wish is very different to what I have.

And as= for you saying that defaulted constructors are antipattern, is that a fact= or it is simply your opinion?

On Monday, 17 August 2015 23:52:24 UT= C+1, Arthur O'Dwyer wrote:
I work on a codebase where this feature would have lots o= f use-cases, because we have lots of classes whose constructors have defaul= ted parameters:

=C2=A0 =C2=A0 C(int buffer_size =3D 1024= , int timeout =3D 10, int tries =3D 3) : buffer_size_(buffer_size), timeout= _(timeout), tries_(tries) {}

=C2=A0 =C2=A0 auto cp= tr =3D new C(); =C2=A0// usually the defaults are okay
=C2=A0 =C2= =A0 auto c2ptr =3D new C(2048); =C2=A0// use a bigger buffer
=C2=A0 =C2= =A0 auto c3ptr =3D new C(1024, 1); =C2=A0// use the default buffer size but= with a shorter timeout
=C2=A0 =C2=A0 auto c4ptr =3D new C(2048, = 10, 5); =C2=A0// testing: bump up the number of tries

<= div>It would be marginally more convenient (and refactor-proof) to be able = to write

=C2=A0 =C2=A0 auto cptr =3D new C();= =C2=A0// usually the defaults are okay
=C2=A0 =C2=A0 auto c2ptr = =3D new C(2048); =C2=A0// use a bigger buffer
=C2=A0 =C2=A0 auto c3ptr = =3D new C(default, 1); =C2=A0// use the default buffer size but with a shor= ter timeout
=C2=A0 =C2=A0 auto c4ptr =3D new C(2048,=C2=A0default= , 5); =C2=A0// testing: bump up the number of tries

However, I consider defaulted parameters in general to be a huge antipatt= ern, and this constructor pattern in particular to be even worse.
I would MUCH rather just rewrite all these constructors so that they could= be used as

=C2=A0 =C2=A0 auto cptr =3D new C(); = =C2=A0// usually the defaults are okay
=C2=A0 =C2=A0 auto c2ptr = =3D new C().withBufferSize(2048); =C2=A0// use a bigger buffer
=C2=A0 = =C2=A0 auto c3ptr =3D new C().withTimeout(1); =C2=A0// use the default buff= er size but with a shorter timeout
=C2=A0 =C2=A0 auto c4ptr =3D n= ew C().withBufferSize(2048).withTries(5); =C2=A0// testing: bump up th= e number of tries

or

=C2=A0 =C2=A0 auto cptr =3D new C(); =C2=A0// usually the defaults are oka= y
=C2=A0 =C2=A0 auto c2ptr =3D new C(C::BufferSize(2048)); =C2=A0= // use a bigger buffer
=C2=A0 =C2=A0 auto c3ptr =3D new C(C::Timeout(1))= ; =C2=A0// use the default buffer size but with a shorter timeout
=C2=A0 =C2=A0 auto c4ptr =3D new C(C::BufferSize(2048), C::Tries(5)); =C2= =A0// testing: bump up the number of tries

o= r (the most conservative way to rewrite our existing code)

=C2=A0 =C2=A0 static constexpr int default_buffer_size =3D 1024;
=C2=A0 =C2=A0 static constexpr int default_timeout =3D 10;
=C2=A0 =C2=A0 static constexpr int default_tries =3D 3;
=
=C2=A0 =C2=A0 C() : buffer_size_(default_buffer_size),= timeout_(default_timeout), tries_(default_tries) {}
=C2=A0 =C2=A0 C(int buffer_size, int timeout, int tries) : buffer_size_(b= uffer_size), timeout_(timeout), tries_(tries) {}

=C2=A0 =C2=A0 auto cptr =3D new C(); =C2=A0// usually= the defaults are okay
=C2=A0 =C2=A0 auto c2ptr =3D new = C(2048, C::default_timeout, C::default_tries); =C2=A0// use a bigger buffer=
=C2=A0 =C2=A0 auto c3ptr =3D new C(C::default_buffer_size, 1, C::defaul= t_tries); =C2=A0// use the default buffer size but with a shorter timeout
=C2=A0 =C2=A0 auto c4ptr =3D new C(2048, C::default_timeout, 5); = =C2=A0// testing: bump up the number of tries

I don't really want to make it easier for people to write the = "function taking tons of defaulted parameters" antipattern.
=
Let's teach people how to avoid the use of defaulted parameters, i= nstead.

=E2=80=93Arthur

<= br>
On Monday, August 17, 2015 at 11:58:41 AM UTC-7, Bo Persson wrote:=
On 2015-08-17 20:37, Arthur Tchaiko= vsky wrote:
> I would really appreciate some feedback from people, or is this pr= oposal
> so uninteresting that there is no point in wasting keyboard on it?

You might wonder how widely used it will be?

If not all parameters are of the same type, you can already get some of= =20
the effect with a few overloads:

=C2=A0 =C2=A0 =C2=A0void f(int a =3D 0, string b =3D "1",
=C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 complex<double> c =3D 2= ..0, type4 d =3D 3);

=C2=A0 =C2=A0 =C2=A0inline void f(int a, complex<double> c)
=C2=A0 =C2=A0 =C2=A0{ f(a, "1", c, 3); }

=C2=A0 =C2=A0 =C2=A0inline void f(string b, complex<double> c)
=C2=A0 =C2=A0 =C2=A0{ f(0, b, c, 3); }

assuming that d is put last because you hardly ever want to change the= =20
default.

Just saying that you can already do this without a language change.


=C2=A0 =C2=A0 Bo Persson



>
> On Saturday, 15 August 2015 17:49:50 UTC+1, Arthur Tchaikovsky wro= te:
>
> =C2=A0 =C2=A0 Hi,
> =C2=A0 =C2=A0 Does anyone see helpfulness of such solution:
> =C2=A0 =C2=A0 Having fnc:
>
> =C2=A0 =C2=A0 void f(int a =3D 0, int b =3D 1, int c =3D 2, int d = =3D 3);
>
> =C2=A0 =C2=A0 I think that it would be nice to be able to say whil= st calling it
> =C2=A0 =C2=A0 and requiring only some of those args to be non-defa= ult:
>
> =C2=A0 =C2=A0 f(default,2,default,4);
>
> =C2=A0 =C2=A0 Thoughts?
>
>


--

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