220 29942 article Path: news.gmane.org!.POSTED!not-for-mail From: "T. C." Newsgroups: gmane.comp.lang.c++.isocpp.proposals Subject: Re: Extending the scope of generalized lambda captures to include the lambda's trailing return type Date: Mon, 19 Dec 2016 14:32:17 -0800 (PST) Lines: 131 Approved: news@gmane.org Message-ID: References: <78e69be6-4dfd-4949-85d9-145097ea2580@isocpp.org> Reply-To: std-proposals@isocpp.org NNTP-Posting-Host: blaine.gmane.org Mime-Version: 1.0 Content-Type: multipart/mixed; boundary="----=_Part_1273_1934345736.1482186737480" X-Trace: blaine.gmane.org 1482186741 7404 195.159.176.226 (19 Dec 2016 22:32:21 GMT) X-Complaints-To: usenet@blaine.gmane.org NNTP-Posting-Date: Mon, 19 Dec 2016 22:32:21 +0000 (UTC) To: ISO C++ Standard - Future Proposals Original-X-From: std-proposals+bncBCQ43G7NQIIRB4V74HBAKGQECBKCFTQ@isocpp.org Mon Dec 19 23:32:17 2016 Return-path: Envelope-to: gclcip-std-proposals@m.gmane.org Original-Received: from mail-pg0-f70.google.com ([74.125.83.70]) by blaine.gmane.org with esmtp (Exim 4.84_2) (envelope-from ) id 1cJ6Te-0000h9-JG for gclcip-std-proposals@m.gmane.org; Mon, 19 Dec 2016 23:32:14 +0100 Original-Received: by mail-pg0-f70.google.com with SMTP id b1sf247279995pgc.5 for ; Mon, 19 Dec 2016 14:32:19 -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 :list-subscribe:list-unsubscribe; bh=Bvr0X7orrDnjEYTI2i050H6TUE46yw7KNBtSAX2Ngzo=; b=gszFI1BBqsD0Iw2EUwAQ1R9b4FPKyjEvT16hAccEBJrmIhXolX1cW1PyhXoKdqUzWz xohKLYFXMMCcrsJwbNz3yi7z7miAyhWGc3dzqFUYDIXeWAwb091T0rXi57X84p9ct5Ip 9j5eMkcb0s6r4h28yROUK510Le3qB3rohEzGhRAGVc4UYMQOZ5xK9bmXnNTjvCvEn4E/ UPVB4roGEp+QNWBY7kcx14c/KQjD7hg/5s9X09gpqfHgDuYDvyzZowUR2xDPT0JCJ1mH +2uvmPXXsaYrpanG/JiM00rfDfko3eTeZT+kEhgkMQUXiGzinabimAwpgHnn1VLlZ7q4 9G0A== DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gmail.com; s=20161025; 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 :list-subscribe:list-unsubscribe; bh=Bvr0X7orrDnjEYTI2i050H6TUE46yw7KNBtSAX2Ngzo=; b=FEtEGymk2QiPtPGIRkRzy9OZSvjtfJOLsfxJHxORFjr6E4zAWscx7jK/fklDIx5F3U 5CWypRgNMsmsjb27T874JrhvShPZUxfX1M+CDcdBOr0el2YOrEz68fysSqXi4fl9L17T 0w0QOqut1gf86FeXWzT182PQX/76wak1Aam7p1BGaRPmL7NmZFLCDdLUcXOq/KKccFSB /duZsyY+ggOIKT2PcOKDwjAv3nU30xvtZCIERHFbKhKwCicHNF1AxcD2RJHvaBbF769U HjwgmtHsjuauNjQRWc1XvwJ+teH8cEmrwAEPbXHVRIKTs3TSBHE1FxRJXRhQUabtesEp Lq0g== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20161025; 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:list-subscribe:list-unsubscribe; bh=Bvr0X7orrDnjEYTI2i050H6TUE46yw7KNBtSAX2Ngzo=; b=LQ6TIGakwnjQSUlGmSOaRZrohiDYMnJjzgYxZtWvvNS6s+z2Qe9s9emNyv1HNdKUgJ jLbk/9+c8vzuF2XWXi3LY7zSdZpg6A5s7pl+drKBJS19KQBFhU7qDf28uG102lMyV2qV ZA11elW0fSsKc7XeoFi/jqvlEv6TH+Oy55QtsBnIPrwPXkWml0HLxghV1gOYq/5HHTIe rHo0pYrexO4MyuWn3V7HGDs7LvTGsDC5X0ME9OBcurU+OrBrE2SRGWT8nUStrePCqWiO VQpV3NYWN4YtLdDp3+8SQYOwXLV8hYdEJboAcMVesYyxIQ8nbo0QxlIrQa83Uk32oxb9 fjZw== X-Gm-Message-State: AKaTC01EwKqsycIHgS7/AzuaSB2F1TdHUfXdZ/ftwjn83w5pjQK9ANvE4/XkeZn2ydxUDg== X-Received: by 10.99.43.70 with SMTP id r67mr10132920pgr.15.1482186738662; Mon, 19 Dec 2016 14:32:18 -0800 (PST) X-BeenThere: std-proposals@isocpp.org Original-Received: by 10.157.40.91 with SMTP id h27ls13953787otd.44.gmail; Mon, 19 Dec 2016 14:32:17 -0800 (PST) X-Received: by 10.157.27.9 with SMTP id l9mr848666otl.6.1482186737931; Mon, 19 Dec 2016 14:32:17 -0800 (PST) In-Reply-To: X-Original-Sender: rs2740@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:29942 Archived-At: ------=_Part_1273_1934345736.1482186737480 Content-Type: multipart/alternative; boundary="----=_Part_1274_1964153039.1482186737480" ------=_Part_1274_1964153039.1482186737480 Content-Type: text/plain; charset=UTF-8 On Monday, December 19, 2016 at 4:33:34 PM UTC-5, Vittorio Romeo wrote: > > ...but according to the note the decltype((x)) inside l2_const's > compound-statement should refer to the outer `x`, not to the captured `x`. > What's actually going on here? > > p20 and its special treatment for decltype((x)). > I said that I was getting disheartened because achieving consistency > between lambda and classes results in a lot of breaking changes. I would be > surprised if there isn't any code out there in the real world that uses > `decltype` of a simple-capture in either the lambda-declarator or the > lambda's compound-expression: making the behavior consistent with classes > would change the meaning of all that code. > > Do you think it makes sense to keep going in this direction (i.e. total > consistency between lambdas with captures and classes)? > On the other hand, the alternative option is focusing on making > init-captures accessible in the lambda-declarator, which would practically > introduce a "special case" for init-captures. It would lead to even more > inconsistency because: > * Non-odr uses of simple-captures in the lambda-declarator would refer to > the "outer" object, not the capture itself. > * Non-odr uses of init-captures in the lambda-declarator would refer to > the capture itself. > > Maybe what I really want is an alternative to the `this` keyword that > actually refers to the lambda itself... > [x](decltype(x)) {} // refers to outer x > [x](decltype(lambda->x)) {} // refers to captured x > `this` is only available after the cv-qualifier-seq (or its lambda equivalent), but perhaps that's enough for this. -- 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/ec154f31-d0a7-4e4d-910b-87986be2d720%40isocpp.org. ------=_Part_1274_1964153039.1482186737480 Content-Type: text/html; charset=UTF-8 Content-Transfer-Encoding: quoted-printable
On Monday, December 19, 2016 at 4:33:34 PM UTC-5, Vittorio= Romeo wrote:
=
...but according to the note the=C2=A0decltype((x))=C2=A0inside l2_= const's compound-statement should refer to the outer `x`, not to the ca= ptured `x`.
What's actually going on here?=C2=A0

=

p20 and its special treatment for decltype= ((x)).


I said that I was getting disheartened because achie= ving consistency between lambda and classes results in a lot of breaking ch= anges. I would be surprised if there isn't any code out there in the re= al world that uses `decltype` of a simple-capture in either the lambda-decl= arator or the lambda's compound-expression: making the behavior consist= ent with classes would change the meaning of all that code.

<= /div>
Do you think it makes sense to keep going in this direction (i.e.= total consistency between lambdas with captures and classes)?
On the ot= her hand, the alternative option is focusing on making init-captures access= ible in the lambda-declarator, which would practically introduce a "sp= ecial case" for init-captures. It would lead to even more inconsistenc= y because:
* Non-odr uses of simple-captures in the lambda-declarator wo= uld refer to the "outer" object, not the capture itself.
* Non= -odr uses of init-captures in the lambda-declarator would refer to the capt= ure itself.

Maybe what I really want is an alternative to= the `this` keyword that actually refers to the lambda itself...
[x](decltype(x))=C2=A0{} // = refers to outer x
[x<= /span>](decltype(lambda->x))= =C2=A0{} // refers to captured x

`this` =C2=A0is only = available after the cv-qualifier-seq=C2=A0(or its lambda equivalent), but p= erhaps that's enough for this.

--
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