220 29561 article Path: news.gmane.org!.POSTED!not-for-mail From: Domen Vrankar Newsgroups: gmane.comp.lang.c++.isocpp.proposals Subject: Re: Instantiation of default destructor Date: Mon, 28 Nov 2016 20:17:12 +0100 Lines: 139 Approved: news@gmane.org Message-ID: References: Reply-To: std-proposals@isocpp.org NNTP-Posting-Host: blaine.gmane.org Mime-Version: 1.0 Content-Type: multipart/alternative; boundary=001a114fce3a10dc91054261542d X-Trace: blaine.gmane.org 1480360679 13928 195.159.176.226 (28 Nov 2016 19:17:59 GMT) X-Complaints-To: usenet@blaine.gmane.org NNTP-Posting-Date: Mon, 28 Nov 2016 19:17:59 +0000 (UTC) To: std-proposals@isocpp.org Original-X-From: std-proposals+bncBCHJ3Z4NUUFBBYUF6LAQKGQES4KKTBA@isocpp.org Mon Nov 28 20:17:54 2016 Return-path: Envelope-to: gclcip-std-proposals@m.gmane.org Original-Received: from mail-pg0-f69.google.com ([74.125.83.69]) by blaine.gmane.org with esmtp (Exim 4.84_2) (envelope-from ) id 1cBRR1-0002df-CH for gclcip-std-proposals@m.gmane.org; Mon, 28 Nov 2016 20:17:51 +0100 Original-Received: by mail-pg0-f69.google.com with SMTP id q10sf378000192pgq.7 for ; Mon, 28 Nov 2016 11:17:55 -0800 (PST) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=isocpp-org.20150623.gappssmtp.com; s=20150623; h=mime-version:in-reply-to:references:from:date:message-id:subject:to :x-original-sender:x-original-authentication-results:reply-to :precedence:mailing-list:list-id:x-spam-checked-in-group:list-post :list-help:list-archive:list-subscribe:list-unsubscribe; bh=fqi70YNoAcnhgahsjFYBFcxKIve/HM7mnpGrPTQjZz4=; b=MsccngRUtYtZ5ugsB84gTX2SDwCFtd6xDEhT3N4JzhXv4QpEqWRRJDddTi8S2LPd6U PEmHjNWPHSXFynf3r+G7P/8jQWXGmk5kad96DHkjpt8nOkr6PPAXhnjZaGySis22iymM TRUYtV8MXQsvWfaBpadR7z7qUSPzltNOLN5vRmf6V514JLLObRRF9XSwFkJ3uhnb8ER7 k/FnUX4ho72JKeOVdlJ4A9EIK7QCfR5zOoiLxgyl3NikmfyBexyVVPuL5mQtJohh9xb4 3Dfd6LJJXdUHHN5xR0Kry1ngSA+w9dCV5z5aL3i8eWgFEoN0EA3yPxozG2d+lU+a/z7f pliQ== 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:from:date :message-id:subject:to:x-original-sender :x-original-authentication-results:reply-to:precedence:mailing-list :list-id:x-spam-checked-in-group:list-post:list-help:list-archive :list-subscribe:list-unsubscribe; bh=fqi70YNoAcnhgahsjFYBFcxKIve/HM7mnpGrPTQjZz4=; b=E+rPp7OhgFQ69C4vou2KzMuWotTwnLqik5UfuIuI13lUz6AYaO1Dmv30ar53oyNHid +j60SzXA4KXA7afUcaU3PjBXA4Em8xNXQIyj8jKgKnG8Ae1VfCEwnOkZaxlBN68MkQO8 9JsH9h/PQunrnog5BIO7LDScG7qULhBnbFo9B7P8W74oLaaIV1n3kHAUuplxNrRvZsp7 L2G/UhLLHLWhfM6rJKWE17pnr83af3V5CTok0/qUArv2OR7c22XCopfrGsS8v1ZWyYGL Cfwu9LiAMiCm5lNqee+78rcOnqClV+UfdkSVw1b9OcwTvswYpaUjgXX2Ri+v60QB4MH2 k8PQ== X-Gm-Message-State: AKaTC02HpBM4hbl8EMSGzKjT2zogDWIcrtL1ig8odZoeOEpr5k7qFKFLX6JBJ8aUQoQ9Eg== X-Received: by 10.99.164.25 with SMTP id c25mr11131048pgf.114.1480360674849; Mon, 28 Nov 2016 11:17:54 -0800 (PST) X-BeenThere: std-proposals@isocpp.org Original-Received: by 10.36.79.145 with SMTP id c139ls3342829itb.8.gmail; Mon, 28 Nov 2016 11:17:53 -0800 (PST) X-Received: by 10.36.66.143 with SMTP id i137mr20274447itb.43.1480360673805; Mon, 28 Nov 2016 11:17:53 -0800 (PST) Original-Received: from mail-io0-x231.google.com (mail-io0-x231.google.com. [2607:f8b0:4001:c06::231]) by mx.google.com with ESMTPS id j9si19856061itj.82.2016.11.28.11.17.53 for (version=TLS1_2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128/128); Mon, 28 Nov 2016 11:17:53 -0800 (PST) Received-SPF: pass (google.com: domain of domen.vrankar@gmail.com designates 2607:f8b0:4001:c06::231 as permitted sender) client-ip=2607:f8b0:4001:c06::231; Original-Received: by mail-io0-x231.google.com with SMTP id m5so109900444ioe.3 for ; Mon, 28 Nov 2016 11:17:53 -0800 (PST) X-Received: by 10.107.20.77 with SMTP id 74mr20110641iou.66.1480360673203; Mon, 28 Nov 2016 11:17:53 -0800 (PST) Original-Received: by 10.50.235.15 with HTTP; Mon, 28 Nov 2016 11:17:12 -0800 (PST) In-Reply-To: X-Original-Sender: Domen.Vrankar@gmail.com X-Original-Authentication-Results: mx.google.com; dkim=pass header.i=@gmail.com; spf=pass (google.com: domain of domen.vrankar@gmail.com designates 2607:f8b0:4001:c06::231 as permitted sender) smtp.mailfrom=domen.vrankar@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:29561 Archived-At: --001a114fce3a10dc91054261542d Content-Type: text/plain; charset=UTF-8 2016-11-28 20:03 GMT+01:00 Nevin Liber : > On Mon, Nov 28, 2016 at 6:14 AM, Domen Vrankar > wrote: > >> For me it's not a big deal to write A::~A() = default; in cpp file but >> still since we've had that debate I was wondering if it would be feasible >> to change the wording (don't know how much the standard would have to be >> changed for that) so that implicit default destructor would be added to the >> code at the point of first constructor implementation (in the above example >> at the point of A::A(T* ptr_); implementation in .cpp file) and not at the >> end of the file where the class was declared? >> > > Define "first constructor implementation". > //a.h // guard & include memory struct B; struct A { A(int i); // first constructor as it is declared first A(); std::shared_ptr ptr; }; //a_1.cpp #include "a.h" // compiler sees the declaration and remembers that it needs to generate a destructor implementation #include "b.h" A::A() {} // end of file - compiler did not find the implementation of first constructor so it just wasted space and time checking for the location during compilation //a_2.cpp #include "a.h" // compiler sees the declaration... #include "b.h" A::A(int i) {} // implementation of the first constructor so destructor is generated here as if writing A::~A() = default; after this line > Different constructors for the same class may be declared in different > compilation units (different .cpp files). Right now the implicit ones work > as if declared "inline", which is what allows class declaration headers to > be included by multiple .cpp files, as well as making it easier to inline. > IMHO, changing this is a non-starter. > Hm forgot about no longer implicitly inlining drawback/change that my proposal would cause... This started out as a possibly bad idea but now it starts to look as a really bad idea :) Thanks, Domen -- 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/CAKgx6BK4yf6YexmGyFKPg2cyStMxdNp7-gJQy%3DcTehbw_xk%3DaQ%40mail.gmail.com. --001a114fce3a10dc91054261542d Content-Type: text/html; charset=UTF-8 Content-Transfer-Encoding: quoted-printable


2016-11-28 20:03 GMT+01:00 Nevin Liber <nevin@eviloverlord.com>:
On Mon, Nov 28, = 2016 at 6:14 AM, Domen Vrankar <domen.vrankar@gmail.com> wrote:
For me it's not a big deal to write A::~A() =3D def= ault; in cpp file but still since we've had that debate I was wondering= if it would be feasible to change the wording (don't know how much the= standard would have to be changed for that) so that implicit default destr= uctor would be added to the code at the point of first constructor implemen= tation (in the above example at the point of A::A(T* ptr_); implementation = in .cpp file) and not at the end of the file where the class was declared?<= br>

Define "first constructor imple= mentation".

//a.h
= // guard & include memory
struct B;
struct A
{
=C2=A0 A(int i); // first constru= ctor as it is declared first
=C2=A0 A();
=C2=A0 std::shared_ptr<B> ptr;
= };

//a_1.cpp
#include "a.h" // co= mpiler sees the declaration and remembers that it needs to generate a destr= uctor implementation
#include "b.h"

A::A() {}

// end of file - compiler did not find the i= mplementation of first constructor so it just wasted space and time checkin= g for the location during compilation

//a_2.cp= p
#include "a.h" // compiler sees the declaration..= ..
#include "b.h"

A::A(int i) {} /= / implementation of the first constructor so destructor is generated here a= s if writing A::~A() =3D default; after this line
=C2=A0
Different constructors for the same class may be declar= ed in different compilation units (different .cpp files).=C2=A0 Right now t= he implicit ones work as if declared "inline", which is what allo= ws class declaration headers to be included by multiple .cpp files, as well= as making it easier to inline.=C2=A0 IMHO, changing this is a non-starter.=

Hm forgot about no longer = implicitly inlining drawback/change that my proposal would cause... This st= arted out as a possibly bad idea but now it starts to look as a really bad = idea :)

Thanks,
Domen
=

--
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