220 22440 <2a117f5e-0cb9-4c2e-aec1-d49b423140a5@isocpp.org> article Path: news.gmane.org!not-for-mail From: leni536@gmail.com Newsgroups: gmane.comp.lang.c++.isocpp.proposals Subject: Re: std::vector (and other containers) to have a perfect forwarding constructor Date: Wed, 11 Nov 2015 03:52:37 -0800 (PST) Lines: 106 Approved: news@gmane.org Message-ID: <2a117f5e-0cb9-4c2e-aec1-d49b423140a5@isocpp.org> References: <14fb89ea-443b-4696-93ec-29889f642bca@isocpp.org> Reply-To: std-proposals@isocpp.org NNTP-Posting-Host: plane.gmane.org Mime-Version: 1.0 Content-Type: multipart/mixed; boundary="----=_Part_280_1923550331.1447242757223" X-Trace: ger.gmane.org 1447242772 31607 80.91.229.3 (11 Nov 2015 11:52:52 GMT) X-Complaints-To: usenet@ger.gmane.org NNTP-Posting-Date: Wed, 11 Nov 2015 11:52:52 +0000 (UTC) To: ISO C++ Standard - Future Proposals Original-X-From: std-proposals+bncBDXJR44QUQHBBBWYRSZAKGQE5YWIOSA@isocpp.org Wed Nov 11 12:52:45 2015 Return-path: Envelope-to: gclcip-std-proposals@m.gmane.org Original-Received: from mail-pa0-f72.google.com ([209.85.220.72]) by plane.gmane.org with esmtp (Exim 4.69) (envelope-from ) id 1ZwTxA-0007tb-3M for gclcip-std-proposals@m.gmane.org; Wed, 11 Nov 2015 12:52:40 +0100 Original-Received: by paak3 with SMTP id k3sf14355657paa.3 for ; Wed, 11 Nov 2015 03:52:38 -0800 (PST) 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 :content-type: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=JG0CKLtevZEhRO5JjrJyMWN9ungvfJiGWsd57xCCI2A=; b=wnpEd5RdlDxwr9+uPYf+z8YCyyOrtz6KhJuoDCraAGfuBtpUF5RUSng2m2KOahBORm HSdEXuBS2JRr70btmuIgcEvJf3N8gOIYt5GjyxjhxnVnWv8v2D/FxVtyBClCaDxG06g6 Kchz7aM993QsV+80sqYhnY8p7TwHQKlsrB5BEOP1em1tpm+bHq83LVmFeKY23XJNubKS GjpkvjhHrAIT9HF1wVO+4FL3gTUAT0N/gPHuqPCitpLXKbtT1WPhlGkrQIjeHT2Scso8 A6mkGMX115pgeZfuSQtrHEMjPZEolfFl9/CWXDC6McPBIejNjm5WZu4fO0by6x4cyV6O 0yJA== 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 :content-type: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=JG0CKLtevZEhRO5JjrJyMWN9ungvfJiGWsd57xCCI2A=; b=xelyna9pcmVOZhqw1cNnF7hs8OxEukp5LQfojmSWlKlMUjRQ6Nojt1arb6TS6NVbYQ HVBouVRpXqrlnCI3n0a/P/QEqgvbuSdIPov2pRWD/DiTCgz2G3/1BhCfkifHGiSvSZAA mjrIPwILLphSp0iwgf/AFU2cYS1GFqODiP5QUMdSH/duRk8zNpfLrirL1Mdmumf/86fI mmEO6A92/XdAUb/uf3wMh3izuRGtGm5ZSe05RhBEY/KwraxDQp5R59QXLeL9Dl4Rqymd K4jGlEeH2RqnkA0Xfn6N5a4Ig6yROBJE69MOKhBTL5KaYyaxRjViWvZxSAs8/fXhszaF jO/w== 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:content-type: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=JG0CKLtevZEhRO5JjrJyMWN9ungvfJiGWsd57xCCI2A=; b=ZrfXT8XinuDrvtQqysdSpaFoXGU+vzgsW+wDTwGdk5ngDb8CDmTkgyb2xI+AJqEwhl clj+MqMtRwBs4x0vJxm/Lc+5a9DLALgIfjexBKCxj2HvYN2vSqTn4kYLLYvB/X8CQHrv rjttpoprFurtqa9COMc8BQFipqJFPw3LFt7wYPibJtxC7NNDId+zpXz+JpW2b+kbytLf 5tpiQtGqx2UzGPXfmIYNBIaPtk8WK+pIVc1xtRQE+kuTjXReEsO13KOwbzV1QGE1EJQ4 OJuiZ+8PPE5/bFk05QIxyFd9coU5zTbSntZfMyJV3M/G3RjB8t3MYw3h/4dHZn43Pkbk 5GeQ== X-Gm-Message-State: ALoCoQlhmE6w31J3WIt/PJ8i+TtuwYe0T3zzj6ov86/XnmmqErjUoE5Z6RcR4yLWlWQnyUBRMprh X-Received: by 10.66.154.132 with SMTP id vo4mr7837499pab.14.1447242758790; Wed, 11 Nov 2015 03:52:38 -0800 (PST) X-BeenThere: std-proposals@isocpp.org Original-Received: by 10.107.132.78 with SMTP id g75ls190957iod.2.gmail; Wed, 11 Nov 2015 03:52:37 -0800 (PST) X-Received: by 10.50.112.201 with SMTP id is9mr521951igb.10.1447242757864; Wed, 11 Nov 2015 03:52:37 -0800 (PST) In-Reply-To: X-Original-Sender: leni536@gmail.com Precedence: list Mailing-list: list std-proposals@isocpp.org; contact std-proposals+owners@isocpp.org List-ID: X-Spam-Checked-In-Group: std-proposals@isocpp.org 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:22440 Archived-At: ------=_Part_280_1923550331.1447242757223 Content-Type: multipart/alternative; boundary="----=_Part_281_757264474.1447242757223" ------=_Part_281_757264474.1447242757223 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: quoted-printable Oh, also about mutable lvalues. I see no reason to not accept them=20 especially if value_type's constructor accepts them (like passing a random= =20 engine, which is mutable). On Wednesday, November 11, 2015 at 10:33:49 AM UTC+1, Daniel Kr=C3=BCgler w= rote: > > 2015-11-11 10:20 GMT+01:00 >:=20 > > Yeah, that was truly a mistake by me, perfect forwarding really doesn't= =20 > make=20 > > sense in this context. Shouldn't this work though?=20 > >=20 > > vector(size_type n,vector::forward_args_type,Args&... args);=20 > >=20 > > This way even if something in args is an rvalue reference its type woul= d=20 > be=20 > > deduced to be an lvalue reference.=20 > > I would say the arguments should also be declared as references to=20 > const, because you can also have the same effect for mutable lvalues.=20 > And surely you would like to construct from a pack from literals=20 > (which are rvalues in basically all cases), which would not be=20 > possible with your revised form:=20 > > std::vector v(100, 12.123); // Wouldn't work=20 > > - Daniel=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_281_757264474.1447242757223 Content-Type: text/html; charset=UTF-8 Content-Transfer-Encoding: quoted-printable
Oh, also about mutable lvalues. I see no reason to not acc= ept them especially if value_type's constructor accepts them (like pass= ing a random engine, which is mutable).

On Wednesday, November 11, 2= 015 at 10:33:49 AM UTC+1, Daniel Kr=C3=BCgler wrote:
2015-11-11 10:20 GMT+01:00 =C2=A0<len...@gmail.com&= gt;:
> Yeah, that was truly a mistake by me, perfect forwarding really do= esn't make
> sense in this context. Shouldn't this work though?
>
> vector(size_type n,vector::forward_args_type,Args&... arg= s);
>
> This way even if something in args is an rvalue reference its type= would be
> deduced to be an lvalue reference.

I would say the arguments should also be declared as references to
const, because you can also have the same effect for mutable lvalues.
And surely you would like to construct from a pack from literals
(which are rvalues in basically all cases), which would not be
possible with your revised form:

std::vector<Foo> v(100, 12.123); // Wouldn't work

- Daniel

--

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