220 25035 article Path: news.gmane.org!not-for-mail From: Morwenn Newsgroups: gmane.comp.lang.c++.isocpp.proposals Subject: Re: Lambdas in unevaluated contexts: a proposal Date: Mon, 7 Mar 2016 13:03:40 -0800 (PST) Lines: 95 Approved: news@gmane.org Message-ID: References: <97f4407a-4965-41ab-bbbd-00cbf37f7588@isocpp.org> Reply-To: std-proposals@isocpp.org NNTP-Posting-Host: plane.gmane.org Mime-Version: 1.0 Content-Type: multipart/mixed; boundary="----=_Part_633_1310372131.1457384620888" X-Trace: ger.gmane.org 1457384644 4564 80.91.229.3 (7 Mar 2016 21:04:04 GMT) X-Complaints-To: usenet@ger.gmane.org NNTP-Posting-Date: Mon, 7 Mar 2016 21:04:04 +0000 (UTC) To: ISO C++ Standard - Future Proposals Original-X-From: std-proposals+bncBC2ZP4V74IFBBLWZ663AKGQEBWGCCMQ@isocpp.org Mon Mar 07 22:03:51 2016 Return-path: Envelope-to: gclcip-std-proposals@m.gmane.org Original-Received: from mail-oi0-f70.google.com ([209.85.218.70]) by plane.gmane.org with esmtp (Exim 4.69) (envelope-from ) id 1ad2Jc-0003sW-1X for gclcip-std-proposals@m.gmane.org; Mon, 07 Mar 2016 22:03:44 +0100 Original-Received: by mail-oi0-f70.google.com with SMTP id d205sf155067110oia.0 for ; Mon, 07 Mar 2016 13:03:43 -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 :x-original-sender:reply-to:precedence:mailing-list:list-id :x-spam-checked-in-group:list-post:list-help:list-archive:sender :list-subscribe:list-unsubscribe; bh=Rekz6zMxxIFFzSe8+K5DbGFxalpCjw0z+viPdvfuNgg=; b=gkt1vtfN5rYkugSYIYXLEJJhMJhbt4YjuP65fMTxGgNH4t0dKdxMdVkoBCeiZ7uS6i jfDFaRD75zAwkVWwwkBgcm2xBXvpq8OEh2t7omIb+Wgou+kC7/PJhTAmtSndNIrvWxNm /X7eOjn0ksaK4Zdl8pJWy5N4oelx/0kZ9fEbmcv17w3LiLZ3JHMZwJBKrLOlXibaVnos VWmlZBQdeCL4tXjGFWecpsR66SIjXF24NKJSuVtpafRH8cZskvLejZD8ptfxWcJ1VAEq S91seWKWDWek1u1psM3oMpZ1iTPJEM8EdEStZ4ZN5Dn2K2rb43dop/MTED2llzyECsUp P9Fg== 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 :x-spam-checked-in-group:list-post:list-help:list-archive:sender :list-subscribe:list-unsubscribe; bh=Rekz6zMxxIFFzSe8+K5DbGFxalpCjw0z+viPdvfuNgg=; b=djtd7spE8q8r46GpVZjUpCx4Omj5FtOicctv11W8wZdV3vG3wYzIdVdDW2K41u6ykv PrEN6UZsyiLhBbCEngZ51ejpqAyqE1ai85dx5ZEo7gI2Ju+AlMkJBaHC613ShOqSnOap ZyFyIj2UHVgzI9XAbLk0Y72zT3rKRaKhv+QhdiaW0HKobguQFDT2vvGpNxzVqgYMV6wd DTKqoxXNRFnj4cCS1vCwgUymxZsv9K+X/LMN8Z2Y4hwJjfIWn79xbcWT/JDDe17bkxQO z/m8HX6A0Dgc488cn5BrfBwQehpiQoR7w6Zyg2gkrgHuQoc//wlLuhIhSxCIAO1/0aNQ nNdQ== 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:x-spam-checked-in-group:list-post:list-help :list-archive:sender:list-subscribe:list-unsubscribe; bh=Rekz6zMxxIFFzSe8+K5DbGFxalpCjw0z+viPdvfuNgg=; b=BIPv+qTIC2fsurC/38DG2yfie/IQeqZuDpCbTdoCX73N93uqr0Hfxj9lCyjTFgtDVT fUrx/L8aKLxxZlsXvq9PgX42nSyyMc7uMHu9kZhXP4FBal+FdPSQ4sm+9zbudDjzx+Pq I2vh/7ewYMze7cXPacSt3d4U8i16OsUuINlBamZd+JsNIDXbqb0RzEgHM2oOPynP+3oD FN55vUdTmx9OZ0d+H8WMJuTKTo+UmDYd1qPoqAtBHi7BPqKXeWE2fiOCfBK78cZMvtCn +3DxpvCZI7A83mJpwYsLAM06O3J+99JvQoHQbsyNe+PYy/XCKcu+NpizDH18tXH8l41t SLFQ== X-Gm-Message-State: AD7BkJLFyyj9ciPOfQkyZQfoVThGYBKbUnmqFaYTh35XjcNvZMSJhaRT9LCohJ30RtPOHQ== X-Received: by 10.182.20.195 with SMTP id p3mr18824370obe.47.1457384623165; Mon, 07 Mar 2016 13:03:43 -0800 (PST) X-BeenThere: std-proposals@isocpp.org Original-Received: by 10.50.112.98 with SMTP id ip2ls1097444igb.27.canary; Mon, 07 Mar 2016 13:03:41 -0800 (PST) X-Received: by 10.50.18.42 with SMTP id t10mr103806igd.6.1457384621880; Mon, 07 Mar 2016 13:03:41 -0800 (PST) In-Reply-To: <97f4407a-4965-41ab-bbbd-00cbf37f7588@isocpp.org> X-Original-Sender: morwenn29@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: Original-Sender: std-proposals@isocpp.org List-Subscribe: , List-Unsubscribe: , Xref: news.gmane.org gmane.comp.lang.c++.isocpp.proposals:25035 Archived-At: ------=_Part_633_1310372131.1457384620888 Content-Type: multipart/alternative; boundary="----=_Part_634_593805798.1457384620888" ------=_Part_634_593805798.1457384620888 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: quoted-printable A few times I wished I could use lambdas in decltype to find the return=20 type of an ADL-found function: using whatever_t =3D decltype([]{ using std::abs; return abs(foo); }()); It's not a clean way to do that, but the current solution of using an=20 adl_detail namespace to perform the same kind of trick isn't clan either. Le lundi 7 mars 2016 17:13:07 UTC+1, Louis Dionne a =C3=A9crit : > > Hi, > > I have previously raised the issue of lambdas in unevaluated contexts on= =20 > this list, and the > conclusion seemed to be that the restriction was now obsolete. Hence, I= =20 > have written a > proposal to rectify the current situation. > > I attached the proposal to this message; it is only a draft and I welcome= =20 > all constructive > comments. My hope is that the paper can be discussed at Oulu, and perhaps= =20 > even make > it into C++17 in-extremis, given its small scope. > > Regards, > Louis Dionne > > --=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. To view this discussion on the web visit https://groups.google.com/a/isocpp= ..org/d/msgid/std-proposals/a1af4744-b2eb-42ee-8460-bc6866b02c34%40isocpp.or= g. ------=_Part_634_593805798.1457384620888 Content-Type: text/html; charset=UTF-8 Content-Transfer-Encoding: quoted-printable
A few times I wished I could use lambdas in decltype to find the return ty= pe of an ADL-found function:

using whatever_t =3D decltyp= e([]{ using std::abs; return abs(foo); }());

It's n= ot a clean way to do that, but the current solution of using an adl_detail namespace to per= form the same kind of trick isn't clan either.

Le lundi 7 mars 2= 016 17:13:07 UTC+1, Louis Dionne a =C3=A9crit=C2=A0:
Hi,

I have previo= usly raised the issue of lambdas in unevaluated contexts on this list, and = the
conclusion seemed to be that the restriction was now obsolete= .. Hence, I have written a
proposal to rectify the current situati= on.

I attached the proposal to this message; it is= only a draft and I welcome all constructive
comments. My hope is= that the paper can be discussed at Oulu, and perhaps even make
i= t into C++17 in-extremis, given its small scope.

R= egards,
Louis Dionne

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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/a1af4744-b2eb-42ee-8460-bc6866b02c34= %40isocpp.org.
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