220 3896 article Path: news.gmane.org!not-for-mail From: Faisal Vali Newsgroups: gmane.comp.lang.c++.isocpp.proposals Subject: Re: Possible to access invented template parameters in N3649 generic lambdas for perfect forwarding? Date: Wed, 24 Apr 2013 10:12:01 -0500 Lines: 136 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: multipart/alternative; boundary=14dae9340445553c7e04db1cb999 X-Trace: ger.gmane.org 1366816323 25108 80.91.229.3 (24 Apr 2013 15:12:03 GMT) X-Complaints-To: usenet@ger.gmane.org NNTP-Posting-Date: Wed, 24 Apr 2013 15:12:03 +0000 (UTC) Cc: std-proposals@isocpp.org To: rob.desbois@gmail.com Original-X-From: std-proposals+bncBDDKRIXX5YARBRHM36FQKGQEFVA4G6A@isocpp.org Wed Apr 24 17:12:07 2013 Return-path: Envelope-to: gclcip-std-proposals@m.gmane.org Original-Received: from mail-ia0-f198.google.com ([209.85.210.198]) by plane.gmane.org with esmtp (Exim 4.69) (envelope-from ) id 1UV1Mb-000700-O4 for gclcip-std-proposals@m.gmane.org; Wed, 24 Apr 2013 17:12:06 +0200 Original-Received: by mail-ia0-f198.google.com with SMTP id t4sf2757200iag.1 for ; Wed, 24 Apr 2013 08:12:04 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gmail.com; s=20120113; h=x-received:x-beenthere:x-received:received-spf:mime-version :x-received:reply-to:in-reply-to:references:date:message-id:subject :from:to:cc:x-original-sender:x-original-authentication-results :precedence:mailing-list:list-id:x-google-group-id:list-post :list-help:list-archive:list-subscribe:list-unsubscribe:content-type; bh=CtQShXXzaJ2ElymqWMlW+fYa3J8NhodJBFBWUXl3q/I=; b=D9jRiLmOAybKIq1lyg9lzxgaY0Gxd5Mw63g6kgtdXbrJGn/IxKbZgQ1hVhR2IMkToq iV1ajoQW8RtsHOohra4Tu8zdlueoJjuOGDxf3ApoGcumLL8y6dKvNyY3ISaAtTtgw9D4 hi9eX8brwq+ZB3fRcKKzgQoUc+YEKdxSP4AfaOWUzLJyMeRuxOEQjnw4XQjWKc5cXtvw Gd3Z5ghtDhH8+f8ARayAsZHZGGmH2UA4bT4PmulpYymuyyp6R7aeHMdsQwHMiwBPOsmS IU9z5rIiBPzqtqsY3R1gcJBazirkpDrgc67GHrfNWkvL3jplZ9lOu6pdTykuMOMD3G9 X-Received: by 10.43.62.4 with SMTP id wy4mr3871798icb.25.1366816324766; Wed, 24 Apr 2013 08:12:04 -0700 (PDT) X-BeenThere: std-proposals@isocpp.org Original-Received: by 10.50.209.67 with SMTP id mk3ls3723912igc.5.canary; Wed, 24 Apr 2013 08:12:03 -0700 (PDT) X-Received: by 10.50.72.3 with SMTP id z3mr28132522igu.47.1366816323380; Wed, 24 Apr 2013 08:12:03 -0700 (PDT) Original-Received: from mail-ie0-x229.google.com (mail-ie0-x229.google.com [2607:f8b0:4001:c03::229]) by mx.google.com with ESMTPS id bb7si4048498icc.91.2013.04.24.08.12.02 for (version=TLSv1 cipher=ECDHE-RSA-RC4-SHA bits=128/128); Wed, 24 Apr 2013 08:12:02 -0700 (PDT) Received-SPF: pass (google.com: domain of faisalv@gmail.com designates 2607:f8b0:4001:c03::229 as permitted sender) client-ip=2607:f8b0:4001:c03::229; Original-Received: by mail-ie0-f169.google.com with SMTP id ar20so2227360iec.14 for ; Wed, 24 Apr 2013 08:12:01 -0700 (PDT) X-Received: by 10.50.42.165 with SMTP id p5mr28524317igl.75.1366816321778; Wed, 24 Apr 2013 08:12:01 -0700 (PDT) Original-Received: by 10.50.128.82 with HTTP; Wed, 24 Apr 2013 08:12:01 -0700 (PDT) In-Reply-To: X-Original-Sender: faisalv@gmail.com X-Original-Authentication-Results: mx.google.com; spf=pass (google.com: domain of faisalv@gmail.com designates 2607:f8b0:4001:c03::229 as permitted sender) smtp.mail=faisalv@gmail.com; dkim=pass header.i=@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:3896 Archived-At: --14dae9340445553c7e04db1cb999 Content-Type: text/plain; charset=windows-1252 Content-Transfer-Encoding: quoted-printable Since there was initial confusion here on my part, I included the following example in the wording (N3649) to illustrate the use of std::forward with variadic auto: [ Example: auto glambda =3D [](auto a, auto&& b) { return a < b; }; bool b =3D glambda(3, 3.14); // OK auto vglambda =3D [](auto printer) { return [=3D](auto&& ... ts) { // OK: ts is a function parameter pac= k printer(std::forward(ts)...); //<-- NOTE this line return [=3D]() { printer(ts ...); }; }; }; auto p =3D vglambda( [](auto v1, auto v2, auto v3) { std::cout << v1 << v2 << v3; } ); auto q =3D p(1, 'a', 3.14); // OK: outputs 1a3.14 q(); // OK: outputs 1a3.14 =97 end example] Faisal Vali On Wed, Apr 24, 2013 at 9:41 AM, wrote: > On Wednesday, 24 April 2013 12:23:13 UTC+1, faisalv wrote: > > >> On Wed, Apr 24, 2013 at 6:13 AM, Daniel Kr=FCgler = wrote: >> >>> > When used with identifiers, decltype returns the type they were >>> declared >>> > with. >>> >>> Yes, you are right, I was on the wrong track here. >>> >> >> As was I, until Ville and Doug showed me the error of my ways (while >> discussing this in EWG). >> >> > > I think that is exactly what had me confused too > Ville's 2nd proposed syntax looks like it'll do the trick. > > Thanks all :-) > --rob > --=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/?hl=3Den. --14dae9340445553c7e04db1cb999 Content-Type: text/html; charset=windows-1252 Content-Transfer-Encoding: quoted-printable
Since there was initial confusion here on my part, I inclu= ded the following example in the wording (N3649) to illustrate the use of s= td::forward with variadic auto:

=A0[ Example:
=A0=A0=A0 auto glam= bda=A0 =3D [](auto a, auto&& b) { return=A0 a < b; };
=A0 bool b =3D glambda(3, 3.14);=A0=A0=A0=A0=A0=A0 // OK
=A0 auto vglamb= da =3D [](auto printer) {
=A0=A0=A0=A0 return [=3D](auto&& ... t= s) {=A0=A0 // OK: ts is a=A0 function parameter pack
=A0=A0=A0=A0=A0=A0= =A0=A0 printer(std::forward<decltype(ts)>(ts)...);=A0 //<-- NOTE t= his line
=A0=A0=A0=A0=A0=A0=A0=A0 return [=3D]() {
=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0= printer(ts ...);
=A0=A0=A0=A0=A0=A0=A0=A0 };
=A0=A0=A0=A0 };
=A0 = };

=A0 auto p =3D vglambda( [](auto v1, auto v2, auto v3)=A0=A0=A0 <= br>=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0= { std::cout << v1 << v2 << v3; } );
=A0 auto q =3D p(1, 'a', 3.14);=A0 // OK: outputs 1a3.14
=A0 q()= ;=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0 // OK: = outputs 1a3.14
=97 end example]

Faisal Vali



On Wed, Apr 24, 2013 at 9:41 AM, <= rob.desbois@gmail.com> wrote:
On Wednesday, 24 April 2013 12:23:13 UTC+1, faisalv wrote:


On Wed, Apr 24, 2013 at 6:13 AM, Daniel Kr=FCgler <= daniel....@gmail.com> wrote:
> When used with identifiers, declty= pe returns the type they were declared
> with.

Yes, you are right, I was on the wrong track here.

As was I, until Ville and Dou= g showed me the error of my ways=A0 (while discussing this in EWG).
=A0<= br>

I think t= hat is exactly what had me confused too
Ville's 2nd proposed syntax looks like it'll do the trick.

Thanks all :-)
--rob

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