220 17577 article Path: news.gmane.org!not-for-mail From: "dgutson ." Newsgroups: gmane.comp.lang.c++.isocpp.proposals Subject: Re: explicit[ly] require initialization of attributes Date: Wed, 29 Apr 2015 17:13:07 -0300 Lines: 176 Approved: news@gmane.org Message-ID: References: Reply-To: std-proposals@isocpp.org NNTP-Posting-Host: plane.gmane.org Mime-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: quoted-printable X-Trace: ger.gmane.org 1430338391 15192 80.91.229.3 (29 Apr 2015 20:13:11 GMT) X-Complaints-To: usenet@ger.gmane.org NNTP-Posting-Date: Wed, 29 Apr 2015 20:13:11 +0000 (UTC) To: std-proposals Original-X-From: std-proposals+bncBDE3NBMV6UFBBU7WQSVAKGQEK5VMD6A@isocpp.org Wed Apr 29 22:13:11 2015 Return-path: Envelope-to: gclcip-std-proposals@m.gmane.org Original-Received: from mail-ig0-f199.google.com ([209.85.213.199]) by plane.gmane.org with esmtp (Exim 4.69) (envelope-from ) id 1YnYM1-0005Zu-0Z for gclcip-std-proposals@m.gmane.org; Wed, 29 Apr 2015 22:13:09 +0200 Original-Received: by igchq3 with SMTP id hq3sf98130182igc.1 for ; Wed, 29 Apr 2015 13:13:08 -0700 (PDT) X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20130820; h=x-gm-message-state:mime-version:in-reply-to:references:date :message-id:subject:from:to:content-type:content-transfer-encoding :x-original-sender:x-original-authentication-results:reply-to :precedence:mailing-list:list-id:list-post:list-help:list-archive :list-subscribe:list-unsubscribe; bh=CP+fAVaD9iA5zHSTac24+Pfc+oPVrU69u1dZw+jMaC8=; b=RR/VoSW3x7SSViVorq2fIZcANGlshCWsDAsBdNFR8D+DQAdd9Za0MQyLss5MIdwEHz YzHRy0mp7ZLKutPmgdyRDSfl2j0XUCKxI0ZGneVkcW9AupxGOVLzvLUn3Uv3ar096l4t MmRcGPVaczy0MQ70t7x/JC3AsLyxuj8noeEABugl18mOss/Nd8fcoNFlct8VM8/Fkp8/ snu7YWAf5HXqnB5awrPtSxSxNq07jVKf/iab3rmyCWo+5j6AxNyZWCY4c/X+lpNOF4Ce uvsMsWPNPUIlAiY3/UGZ6sSOtyy1IwvJWMLGiFVVAYZNISrRWL40WoXWjnTzN5PnYed9 EjZQ== X-Gm-Message-State: ALoCoQm+nWi2AjfkA/99J+I16WGoretoO/wGX1KhSlkAlKY2lQqO/6wpM2JfL68JI+Sf57hBWYjR X-Received: by 10.50.134.202 with SMTP id pm10mr16640067igb.2.1430338388037; Wed, 29 Apr 2015 13:13:08 -0700 (PDT) X-BeenThere: std-proposals@isocpp.org Original-Received: by 10.50.138.138 with SMTP id qq10ls2217127igb.35.canary; Wed, 29 Apr 2015 13:13:07 -0700 (PDT) X-Received: by 10.107.134.206 with SMTP id q75mr1092596ioi.27.1430338387573; Wed, 29 Apr 2015 13:13:07 -0700 (PDT) Original-Received: from mail-ig0-x231.google.com (mail-ig0-x231.google.com. [2607:f8b0:4001:c05::231]) by mx.google.com with ESMTPS id gy8si391903icb.23.2015.04.29.13.13.07 for (version=TLSv1.2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128/128); Wed, 29 Apr 2015 13:13:07 -0700 (PDT) Received-SPF: pass (google.com: domain of danielgutson@gmail.com designates 2607:f8b0:4001:c05::231 as permitted sender) client-ip=2607:f8b0:4001:c05::231; Original-Received: by igblo3 with SMTP id lo3so127792391igb.1 for ; Wed, 29 Apr 2015 13:13:07 -0700 (PDT) X-Received: by 10.50.93.69 with SMTP id cs5mr2692646igb.4.1430338387364; Wed, 29 Apr 2015 13:13:07 -0700 (PDT) Original-Received: by 10.36.55.5 with HTTP; Wed, 29 Apr 2015 13:13:07 -0700 (PDT) In-Reply-To: X-Original-Sender: danielgutson@gmail.com X-Original-Authentication-Results: mx.google.com; spf=pass (google.com: domain of danielgutson@gmail.com designates 2607:f8b0:4001:c05::231 as permitted sender) smtp.mail=danielgutson@gmail.com; dkim=pass header.i=@gmail.com; dmarc=pass (p=NONE dis=NONE) header.from=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:17577 Archived-At: On Wed, Apr 29, 2015 at 5:09 PM, 'Matt Calabrese' via ISO C++ Standard - Future Proposals wrote: > Can't this be done with C++11 attributes? It could just be a datamember I don't back the attributes-solution because those are ignorable, and I'm looking for a tool for the programmer to make a program ill-formed if the data member wasn't initialized (or in Ville's, example, the function argument comes from a conversion). > attribute that requires that member to be explicitly constructed. It woul= d > be something like [[explicit_construction]] and would suggest that the > compiler emits a diagnostic if the member is not explicitly initialized. > > I'm not a fan of the template approach because it changes the type of the > datamember and requires indirect access through the new datamember type > (i.e. via a get() accessor), all simply because we want the member to be Well, a getter wouldn't be necessary in a good library design. > explicitly initialized. If this is really a desired feature, I think it > makes more sense as an in-language specifier/attribute. > > On Wed, Apr 29, 2015 at 11:57 AM, dgutson . wrot= e: >> >> I think I've seen this. >> >> Problem: >> - when adding a new ctor, a programmer may inadvertently leave >> uninitialized attributes (specially PODs). Similarly, when adding a >> new attribute, a programmer may forget to call its ctor (or initialize >> it) in all the ctors of the class (again, specially when the new >> attribute is a POD). >> >> Problem Example1: >> >> //before the change: >> struct S >> { >> int x; >> S(/*some signature*/) : x(1) {} >> }; >> >> //after the change: >> struct S >> { >> int x; >> S(/*some signature*/) : x(1) {} >> S(/*some OTHER signature*/) {} // x is uninitialized >> }; >> >> Problem Example 2: >> //before the change: >> struct S >> { >> int x; >> S(/*some signature*/) : x(1) {} >> }; >> >> //after the change: >> struct S >> { >> int x; >> int y; // new attribute >> S(/*some signature*/) : x(1) {} // y is uninitialized >> }; >> >> - Why this problem is important? >> The more attributes / ctors the class has, the problem gets worse >> (though that might be caused by a bad design of poor modularization). >> The problem is relevant when writing maintainable code, since >> future maintainers may incur in the errors mentioned above. >> >> - How people is working around this issue nowadays? >> There are both static checkers and dynamic checkers (such as >> valgrind) that may detect use of uninitialized data. >> People can =3Ddelete the default ctor of the contained objects. >> >> - Alternative proposed solutions >> Solution 1: library approach. Provide a type wrapper without a >> default ctor (such as initialization_required). Such wrapper could >> be implemented extending the template type (inheriting from it) and >> removing the default ctor, and should be template-specialized for PODs >> with all the operations of each POD. >> >> struct S >> { >> initialization_required x; >> initialization_required y; >> S(/*some signature*/) : x(1) {} // error: y initialization missing >> }; >> >> Solution 2: prefix the attribute declaration with some keyword >> (such as "explicit"). >> >> struct S >> { >> explicit int x; >> explicit int y; >> S(/*some signature*/) : x(1) {} // error: y is uninitialized >> }; >> >> - Discussion: what happens with inheritance? >> As mentioned above, this problem gets relevant with PODs so >> inheritance wouldn't apply in that case (unless we propose the ability >> to extend from PODs some day ;-) ). >> Nevertheless, both solutions could be applicable to inheritance: >> >> Sol1: struct S : initialization_required { ... }; >> Sol2: struct S : explicit T { ... }; >> >> Ideas? Is this worth to write a formal proposal? >> >> Thanks, >> >> Daniel. >> >> >> >> -- >> Who=E2=80=99s got the sweetest disposition? >> One guess, that=E2=80=99s who? >> Who=E2=80=99d never, ever start an argument? >> Who never shows a bit of temperament? >> Who's never wrong but always right? >> Who'd never dream of starting a fight? >> Who get stuck with all the bad luck? >> >> -- >> >> --- >> You received this message because you are subscribed to the Google Group= s >> "ISO C++ Standard - Future Proposals" group. >> To unsubscribe from this group and stop receiving emails from it, send a= n >> 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/. > > > -- > > --- > 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/. --=20 Who=E2=80=99s got the sweetest disposition? One guess, that=E2=80=99s who? Who=E2=80=99d never, ever start an argument? Who never shows a bit of temperament? Who's never wrong but always right? Who'd never dream of starting a fight? Who get stuck with all the bad luck? --=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/. .