220 7042 <04a0eaa5-ab73-4f0d-99ca-bf0802da73a9@isocpp.org> article Path: news.gmane.org!not-for-mail From: =?UTF-8?Q?Andrzej_Krzemie=C5=84ski?= Newsgroups: gmane.comp.lang.c++.isocpp.proposals Subject: Re: More converting constructors for Optional Date: Sat, 5 Oct 2013 12:38:50 -0700 (PDT) Lines: 120 Approved: news@gmane.org Message-ID: <04a0eaa5-ab73-4f0d-99ca-bf0802da73a9@isocpp.org> References: <417ebcd9-ff0b-49d8-b055-bd098e97dddc@isocpp.org> Reply-To: std-proposals@isocpp.org NNTP-Posting-Host: plane.gmane.org Mime-Version: 1.0 Content-Type: multipart/alternative; boundary="----=_Part_1164_632210.1381001930658" X-Trace: ger.gmane.org 1381001929 314 80.91.229.3 (5 Oct 2013 19:38:49 GMT) X-Complaints-To: usenet@ger.gmane.org NNTP-Posting-Date: Sat, 5 Oct 2013 19:38:49 +0000 (UTC) To: std-proposals@isocpp.org Original-X-From: std-proposals+bncBDT2DGOJ34DBBS6VYGJAKGQEHTKZ7SY@isocpp.org Sat Oct 05 21:38:53 2013 Return-path: Envelope-to: gclcip-std-proposals@m.gmane.org Original-Received: from mail-qc0-f200.google.com ([209.85.216.200]) by plane.gmane.org with esmtp (Exim 4.69) (envelope-from ) id 1VSXgi-00072b-OD for gclcip-std-proposals@m.gmane.org; Sat, 05 Oct 2013 21:38:53 +0200 Original-Received: by mail-qc0-f200.google.com with SMTP id x20sf10390565qcv.11 for ; Sat, 05 Oct 2013 12:38:51 -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 :x-original-sender:reply-to:precedence:mailing-list:list-id :list-post:list-help:list-archive:list-subscribe:list-unsubscribe :content-type; bh=DmbD/qSkOZQdU+lZz1cj+TSxUFh/GHyPyB+pQJk3iTs=; b=ZoLlQ+vySl802zjjd6+q1DIv3lQVl8pA9021EqiAsF/snhnrGJ1KV4ZiP8T9HCv/ZK sLc6aqJMT4oiShcZcfKvdYr9IoAQO7G6OtGhqzgL+SraTq2GOY+mjCBxft/lnLSxKtsU w8NW3IxIQ9BY6w5dktYDds1FMxsK4pqQCcqxLNd88/xCChmLTVRfmC3LhGSxQByc/BUU tl61cQoyF3zZFnf0AoTr/ne3whVFl2yTj6O2/42ytyYq9UgTB4t/fGrcroAvlGM6PGPA 0IoCpami3sGbduLw/hqYufUUTMzNzxugZWUuR1kOuZhC+W/GV2FRntZyAdbInPn2rxNj 2lWQ== X-Received: by 10.236.142.38 with SMTP id h26mr29133yhj.57.1381001931801; Sat, 05 Oct 2013 12:38:51 -0700 (PDT) X-BeenThere: std-proposals@isocpp.org Original-Received: by 10.49.99.10 with SMTP id em10ls1864498qeb.82.gmail; Sat, 05 Oct 2013 12:38:51 -0700 (PDT) X-Received: by 10.49.48.38 with SMTP id i6mr804342qen.4.1381001931112; Sat, 05 Oct 2013 12:38:51 -0700 (PDT) In-Reply-To: X-Original-Sender: akrzemi1@gmail.com Precedence: list Mailing-list: list std-proposals@isocpp.org; contact std-proposals+owners@isocpp.org List-ID: 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:7042 Archived-At: ------=_Part_1164_632210.1381001930658 Content-Type: text/plain; charset=ISO-8859-2 Content-Transfer-Encoding: quoted-printable W dniu sobota, 5 pa=BCdziernika 2013 21:30:10 UTC+2 u=BFytkownik Ville=20 Voutilainen napisa=B3: > > > > > On 5 October 2013 22:05, Andrzej Krzemie=F1ski > > wrote: > >> >> Oh, you spotted a different problem than I did. Mine was that (even if I= =20 >> fixed yours) it is not clear how to handle a case where *T* has a=20 >> constructor taking another optional. Consider a more tricky type: >> >> * struct Port >> { >> * >> * Port (optional oi); >> Port (int); >> };=20 >> * >> >> And now the code that uses it: >> >> >> * optional oi; >> ** optional op =3D oi;* >> >> Now, forget how optional is or might be implemented. As a user, which=20 >> constructor of *Port *would you expect to be called? >> >> > The one taking optional, since optional doesn't automatically conver= t=20 > to an int. If you > have > int i; > optional op =3D i; > then I expect Port(int) to be used. > Another (valid) expectation would be that constructor:=20 * template optional::optional( optional const& o );* does: * if (o) { *(*this) =3D *o; }* in which case *Port(int)* would be used. =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_1164_632210.1381001930658 Content-Type: text/html; charset=ISO-8859-2 Content-Transfer-Encoding: quoted-printable


W dniu sobota, 5 pa=BCdziernika 2013 21:30:10 UTC+= 2 u=BFytkownik Ville Voutilainen napisa=B3:



O= n 5 October 2013 22:05, Andrzej Krzemie=F1ski <a= krz...@gmail.com> wrote:

Oh, you spotted a = different problem than I did. Mine was that (even if I fixed yours) it is n= ot clear how to handle a case where T has a constructor taking anoth= er optional. Consider a more tricky type:

  struct Port
  {
    Por= t (optional<int> oi);
    Port (int);
  };

And now the code that uses it:


&= nbsp; optional<int> oi;
  optional<Port> op =3D = oi;

Now, forget how optional is or might be implemented. A= s a user, which constructor of Port would you expect to be called?

The one taking optional<= ;int>, since optional doesn't automatically convert to an int. If you
have
int i;
optional<Port> op =3D i;
then I expect Port(int) to be used.
<= /blockquote>

Another (valid) expectation would be that constructor:=

  template <class U> optional<T>::optional( op= tional<U> const& o );

does:

  if (o) { = *(*this) =3D *o; }

in which case Port(int) would be used.=
 

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