220 33583 <7fc5cc7e-b32f-4199-abc4-8eea86793226@isocpp.org> article Path: news.gmane.org!.POSTED!not-for-mail From: Barry Revzin Newsgroups: gmane.comp.lang.c++.isocpp.proposals Subject: Re: Re: Catch block for multiple exceptions Date: Fri, 4 Aug 2017 07:13:42 -0700 (PDT) Lines: 342 Approved: news@gmane.org Message-ID: <7fc5cc7e-b32f-4199-abc4-8eea86793226@isocpp.org> References: <4126837.jZlGhgVnua@tjmaciei-mobl1> <54580edb-4a76-4241-b5c8-19ccbc1a562e@isocpp.org> <4c872807-7d50-4b58-bbb5-595a8bac1246@isocpp.org> Reply-To: std-proposals@isocpp.org NNTP-Posting-Host: blaine.gmane.org Mime-Version: 1.0 Content-Type: multipart/mixed; boundary="----=_Part_750_1341051342.1501856022898" X-Trace: blaine.gmane.org 1501856025 5816 195.159.176.226 (4 Aug 2017 14:13:45 GMT) X-Complaints-To: usenet@blaine.gmane.org NNTP-Posting-Date: Fri, 4 Aug 2017 14:13:45 +0000 (UTC) To: ISO C++ Standard - Future Proposals Original-X-From: std-proposals+bncBCJJTG7CS4ARBF4CSLGAKGQECJIYKPA@isocpp.org Fri Aug 04 16:13:39 2017 Return-path: Envelope-to: gclcip-std-proposals@m.gmane.org Original-Received: from mail-yw0-f200.google.com ([209.85.161.200]) by blaine.gmane.org with esmtp (Exim 4.84_2) (envelope-from ) id 1dddMA-00018E-Mv for gclcip-std-proposals@m.gmane.org; Fri, 04 Aug 2017 16:13:39 +0200 Original-Received: by mail-yw0-f200.google.com with SMTP id t139sf29760926ywg.6 for ; Fri, 04 Aug 2017 07:13:45 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=isocpp-org.20150623.gappssmtp.com; s=20150623; 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; bh=h8s/nbcM1QPLOCT2QIWoxmPvIZpuxkPmBRnZKZ7/gMo=; b=eV1JwbpkH2bUZH7yd5+cAZxFKzy+Z5uR7Ta1XNeruSxIHCN4BepAZW3NdhyQQrpeD6 Q9oOLSp+YgJ7wRa8RSURmMF7sDAHv4HJPvgKnkkZXB60IRkQupwuk+VtPHmTv+4lPdCY AWRYi5uOhhogTUw4Lsgy3Ksh1kj0s/8oiK5Ghwr0g7rwuJbKEXB2Fj6bCAOeRjXCMB6w ZWMyPo8gKqB1xripmcb6NG8dHDpEOeHhLEkak2/Ga3rbu+C7k9b9QUuHieQg2VFdDTbM 1/rBetcV8ed0+zWb/GINfkrjpTtDB7kSBelLUGk+Z7+CT6cLjru2U1INQ8J3essA1kXb EaRA== DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gmail.com; s=20161025; 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; bh=h8s/nbcM1QPLOCT2QIWoxmPvIZpuxkPmBRnZKZ7/gMo=; b=lWTrmT9X0yQYV1kV+sER3Vr3QNNXq9Hi6tv83BP9NS4t/T1NLpAgkbODE0lEoCqSbl ts/DCtwbBr04eJxf2uOAe8q+CMi/NChMey5S3bHDpo7Ts1H2qSuONppB4Rws4zgAhPiA KVtKB64dwy0iaP6ax/mgi4aIA8AJeEF/houm3hV0NWDeVMLGf59U6DQ2xOSYTo/LH7qa ETgWTrwlho2x3N4lMD0keYljqt7xNYhcxEwZzjNZofeYNqn7sjT7ZgdHeJxgzM8o/0dk J05ps2HBO40+0zDFPucE8KfCz5L1yWSGh71SJZR7LdM3rRLK/QsZxBKbf+SO6b2N71h9 E/QQ== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20161025; h=x-gm-message-state:date:from:to:message-id:in-reply-to:references :subject:mime-version: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=h8s/nbcM1QPLOCT2QIWoxmPvIZpuxkPmBRnZKZ7/gMo=; b=T+SST/45LBWJ7dW58GklqWwQOvldv7EBTMhNyNcFzV/qLzaVPJdTOb3jZVld4Uf8fa /7chQaAVQYOv+/W9ZcA/r1Rny7dvoLTyrEzFq5fta13R2D/EbUM2ZTcxXbq4W7V67tWN vX6TjizbrNlJsxltqtu9sFiH4zcbiVo5WdOCX39QI6GdEB96PPII6onue4QrplN2Lu/W u770oZFN16QY7CT87OsUrkHcpR+APrvcYPq0PzRsbJ99RJHKXdoCJ/bFZ7VIHE3Ab9Wh +xHJ2SOEO0yr9uqXYlMFCxcHLDqf+eoJieL0kuDg4qwmmgfpA62kHZ9J648tGnkUaef6 /VIw== X-Gm-Message-State: AHYfb5jWCJwmFvPV/UWHEkxitJSWdWGDPAca5H1bl1dSkqhKiiL0xYAy /nWrH7KNSMJUQYNW X-Received: by 10.129.178.202 with SMTP id q193mr1186202ywh.123.1501856024737; Fri, 04 Aug 2017 07:13:44 -0700 (PDT) X-BeenThere: std-proposals@isocpp.org Original-Received: by 10.107.146.87 with SMTP id u84ls3418010iod.11.gmail; Fri, 04 Aug 2017 07:13:43 -0700 (PDT) X-Received: by 10.31.142.14 with SMTP id q14mr9360vkd.19.1501856023410; Fri, 04 Aug 2017 07:13:43 -0700 (PDT) In-Reply-To: <4c872807-7d50-4b58-bbb5-595a8bac1246@isocpp.org> X-Original-Sender: Barry.Revzin@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:33583 Archived-At: ------=_Part_750_1341051342.1501856022898 Content-Type: multipart/alternative; boundary="----=_Part_751_997747254.1501856022899" ------=_Part_751_997747254.1501856022899 Content-Type: text/plain; charset="UTF-8" > > Do you think LEWG would be amenable to a proposal to make std::any_cast an >> all-purpose "type-un-erasing" mechanism in C++2a? >> > Right now we have a different type-un-erasure mechanism for each > type-erased type, and more proliferating with each revision of the Standard: > > std::any a = xx;assert( std::any_cast(a) == 42 ); > std::function f = xx;assert( *f.target() == xx ); > std::shared_ptr p(new int, xx);assert( *std::get_deleter(p) == xx ); > > (from > https://stackoverflow.com/questions/44788017/retrieve-typeid-of-shared-ptr-deleter > ) > (and from this thread, we can add std::exception_ptr to the list of > type-erased types) > > Depending on how broadly you want to define type erasure and the existence of conditional casts to specific types, you could also throw in: std::variant var = a; assert(std::get_if(&var) == &a); assert(std::get_if<0>(&var) == &a); Base* p = some_derived; assert(dynamic_cast(p) == some_derived); Not really. The key difference being that `any_cast` typically returns a > copy of the object, while the exception pointer cast would return a pointer. I don't understand the use of "typically", the overloads that take an any* return a pointer. -- 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. To view this discussion on the web visit https://groups.google.com/a/isocpp.org/d/msgid/std-proposals/7fc5cc7e-b32f-4199-abc4-8eea86793226%40isocpp.org. ------=_Part_751_997747254.1501856022899 Content-Type: text/html; charset="UTF-8" Content-Transfer-Encoding: quoted-printable
Do you think LEWG would be amenable to a proposa= l to make std::any_cast an all-purpose "type-un-erasing" mechanis= m in C++2a?
Right now we have a different type-un-eras= ure mechanism for each type-erased type, and more proliferating with each r= evision of the Standard:

std::any a =3D xx;
asser=
t( std::any_cast<=
span style=3D"font-family:inherit;font-size:inherit;font-style:inherit;line=
-height:inherit;vertical-align:baseline;color:rgb(48,51,54)"><Type>(a) =3D=3D 42 );

std::=
function<long=
()>=
 f =3D xx;
asser=
t( *f.target<Type>() =3D=3D xx );

std::=
shared_ptr<int&=
gt; p<=
/span>(new<=
span style=3D"font-family:inherit;font-size:inherit;font-style:inherit;line=
-height:inherit;vertical-align:baseline;color:rgb(48,51,54)"> int, xx);
asser=
t( *std::get_deleter<Type>(p) =3D=3D xx );
(and from = this thread, we can add std::exception_ptr to the list of type-erased types= )


Depending on h= ow broadly you want to define type erasure and the existence of conditional= casts to specific types, you could also throw in:

std<= span style=3D"color: #660;" class=3D"styled-by-prettify">::variant<A, B, C> var =3D a;
assert(std::get_if<= A>(&= ;var) =3D=3D &a);
assert(std::get_if<0>(&= amp;var) =3D=3D &a);

Base* p =3D some_derived;
= assert(dynamic_cast<Derived*>(p) =3D=3D some_derived);


Not really. The key differen= ce being that `any_cast` typically returns a copy of the object, while the = exception pointer cast would return a pointer.

<= div>I don't understand the use of =C2=A0"typically", the over= loads that take an any* return= a pointer.=C2=A0

--
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.
To view this discussion on the web visit https://groups.google.= com/a/isocpp.org/d/msgid/std-proposals/7fc5cc7e-b32f-4199-abc4-8eea86793226= %40isocpp.org.
------=_Part_751_997747254.1501856022899-- ------=_Part_750_1341051342.1501856022898-- .