220 11978 <8021febe-7c98-400e-8167-3d6dbb695a12@isocpp.org> article Path: news.gmane.org!not-for-mail From: Matthew Fioravante Newsgroups: gmane.comp.lang.c++.isocpp.proposals Subject: Re: Controversy and debate: Uninitialized variables by default is a bug Date: Sun, 20 Jul 2014 21:00:51 -0700 (PDT) Lines: 116 Approved: news@gmane.org Message-ID: <8021febe-7c98-400e-8167-3d6dbb695a12@isocpp.org> References: <60caa4ef-b32d-40fe-97b6-8918fbb2bd51@isocpp.org> <20140620202026.GA29898@bacon.lysator.liu.se> <0329E32D-0EC2-4BE0-85D0-492A4CF22B0B@gmail.com> Reply-To: std-proposals@isocpp.org NNTP-Posting-Host: plane.gmane.org Mime-Version: 1.0 Content-Type: multipart/alternative; boundary="----=_Part_1726_159171850.1405915251688" X-Trace: ger.gmane.org 1405915264 10404 80.91.229.3 (21 Jul 2014 04:01:04 GMT) X-Complaints-To: usenet@ger.gmane.org NNTP-Posting-Date: Mon, 21 Jul 2014 04:01:04 +0000 (UTC) To: std-proposals@isocpp.org Original-X-From: std-proposals+bncBDELF54RTIGRB5FAWKPAKGQEA2JQV2A@isocpp.org Mon Jul 21 06:00:57 2014 Return-path: Envelope-to: gclcip-std-proposals@m.gmane.org Original-Received: from mail-wg0-f70.google.com ([74.125.82.70]) by plane.gmane.org with esmtp (Exim 4.69) (envelope-from ) id 1X94mV-0007cZ-6B for gclcip-std-proposals@m.gmane.org; Mon, 21 Jul 2014 06:00:55 +0200 Original-Received: by mail-wg0-f70.google.com with SMTP id l18sf4153683wgh.1 for ; Sun, 20 Jul 2014 21:00:54 -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 :x-original-sender:reply-to:precedence:mailing-list:list-id :list-post:list-help:list-archive:list-subscribe:list-unsubscribe :content-type; bh=VjMGjXeDpsN4gfLEXLQl1xvguWPm0VjmqRILqd9zwjk=; b=yZwjOQVJR0fTpCZvqD5ERRPwgQ95CsSHO25HolK2oEPzw0Z3J3jxfrVNBwsW8oaNDt iP+c1dsA50xR6oZFCCXmoobzLIsKNrqLiFyoo+g0Uct4jEDB4zL8ZhRzp+op8rXg+Knc sOT/fgHXyy43bVSYJSDox8Xzn3tww52XbiveEmjhnOQIuBy69Y01nszpNdpdgr3WosbU qNZJunypJXiJUKIMqvRwsX2qbiH/HJUCsi3tPHcPrdYIgmtOyYL0zcZ7iZLi0hf3nxEH vka7arzQGP1ScNHcHMHahofWpkSxIR1QNBBddTbXNApBcYhaD62YjYdp63qdUpe7iNVA whRQ== 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:x-original-sender:reply-to:precedence :mailing-list:list-id:list-post:list-help:list-archive :list-subscribe:list-unsubscribe:content-type; bh=VjMGjXeDpsN4gfLEXLQl1xvguWPm0VjmqRILqd9zwjk=; b=XGYUcar3AkskkBTOlwZMTjfmt+enNRzYNoYBJl3Jhvtcu/S95u8MH3xfCeYsjR48bY FL2Nm5t7qZ0JFuKt4skaZ8ZE8NAkmuN50tu0H08gbl8VKg6QPJzKN+AtAusVeeNnFsBj LW/Y2CHs/3VH2KrkdBgPkhKfUNypfwuEs/P3tIPqsUPUph7Y8B2PeeQz+R72Ykhs4X/f mGcEI9BE5AQUDDvvvyiU9sRAMeK0r615PFSH3SCavl155ZdvSPuxvt5vzeOVr7X1OT4L 4MOeONlZkKpfToUJ1xAeUENyo38GrFOIOzSflC3nbRnJZu2bpoB6WaN1NUyMQzatitl2 /bJw== X-Gm-Message-State: ALoCoQkQB5vAs/KtYf1u1lweIBOhHLXuAO7efYM5bsDd7Qzj5W/xUSebsL5nt3fHJfgcIPKabCw4 X-Received: by 10.112.0.162 with SMTP id 2mr1650194lbf.3.1405915254716; Sun, 20 Jul 2014 21:00:54 -0700 (PDT) X-BeenThere: std-proposals@isocpp.org Original-Received: by 10.140.95.193 with SMTP id i59ls1755980qge.20.gmail; Sun, 20 Jul 2014 21:00:52 -0700 (PDT) X-Received: by 10.140.30.52 with SMTP id c49mr9933qgc.7.1405915252417; Sun, 20 Jul 2014 21:00:52 -0700 (PDT) In-Reply-To: <0329E32D-0EC2-4BE0-85D0-492A4CF22B0B@gmail.com> X-Original-Sender: fmatthew5876@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:11978 Archived-At: ------=_Part_1726_159171850.1405915251688 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: quoted-printable Why not just a std::noinit wrapper? std::vector>; //Does not initialize contents on=20 construction Then the non-initialization is documented and enforced by the type system.= =20 Another option is a simple std::allocator implementation. On Monday, June 30, 2014 11:52:45 AM UTC-4, David Krauss wrote: > > > On 2014=E2=80=9306=E2=80=9321, at 4:20 AM, Magnus Fromreide > wrote:=20 > > > That would probably require some way to detect=20 > explicit-non-initialization=20 > > in order to support=20 > >=20 > > std::vector v(MEGABYTE, __no_init__); // a megabyte vector with=20 > > // unspecified content=20 > >=20 > > which seems like a natural extension if explicit non-initialization is= =20 > > added to the language.=20 > > > __no_init__ (or uninitialized, or whatever) could be like nullptr, a sole= =20 > value of its type.=20 > > A library-only solution (with conversion functions) would even be=20 > workable, but for the fact that you cannot copy an uninitialized object.= =20 > > It sounds like a nice core language extension.=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_1726_159171850.1405915251688 Content-Type: text/html; charset=UTF-8 Content-Transfer-Encoding: quoted-printable
Why not just a std::noinit<T> wrapper?

std::vector<std::noinit<int>>; //Does not initialize cont= ents on construction

Then the non-initialization i= s documented and enforced by the type system. Another option is a simple st= d::allocator implementation.


On Monday, June 3= 0, 2014 11:52:45 AM UTC-4, David Krauss wrote:

On 2014=E2=80=9306=E2=80=9321, at 4:20 AM, Magnus Fromreide <ma...@lysator.liu.se> wrote:

> That would probably require some way to detect explicit-non-initia= lization
> in order to support
>=20
> std::vector<int> v(MEGABYTE, __no_init__); // a megabyte vec= tor with
>                   &nb= sp;                     &= nbsp; // unspecified content
>=20
> which seems like a natural extension if explicit non-initializatio= n is
> added to the language.


__no_init__ (or uninitialized, or whatever) could be like nullptr, a so= le value of its type.

A library-only solution (with conversion functions) would even be worka= ble, but for the fact that you cannot copy an uninitialized object.

It sounds like a nice core language extension.

--

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