220 4686 article Path: news.gmane.org!not-for-mail From: Richard Smith Newsgroups: gmane.comp.lang.c++.isocpp.proposals Subject: Re: Re: Changing lambda scope Date: Tue, 28 May 2013 14:56:41 -0700 Lines: 170 Approved: news@gmane.org Message-ID: References: <01190eaa-6223-4d3c-a9d3-b0d850aab98e@isocpp.org> <35af8d3d-8ed6-441c-94d0-b898711190b1@isocpp.org> Reply-To: std-proposals@isocpp.org NNTP-Posting-Host: plane.gmane.org Mime-Version: 1.0 Content-Type: multipart/alternative; boundary=089e013cc32823061604ddce57b2 X-Trace: ger.gmane.org 1369778203 8649 80.91.229.3 (28 May 2013 21:56:43 GMT) X-Complaints-To: usenet@ger.gmane.org NNTP-Posting-Date: Tue, 28 May 2013 21:56:43 +0000 (UTC) To: std-proposals@isocpp.org Original-X-From: std-proposals+bncBDVNBJG4YAIBBGWQSSGQKGQEPXOU7YA@isocpp.org Tue May 28 23:56:44 2013 Return-path: Envelope-to: gclcip-std-proposals@m.gmane.org Original-Received: from mail-vc0-f199.google.com ([209.85.220.199]) by plane.gmane.org with esmtp (Exim 4.69) (envelope-from ) id 1UhRsp-0007vt-So for gclcip-std-proposals@m.gmane.org; Tue, 28 May 2013 23:56:44 +0200 Original-Received: by mail-vc0-f199.google.com with SMTP id hf12sf10472630vcb.10 for ; Tue, 28 May 2013 14:56:43 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gmail.com; s=20120113; h=x-beenthere:mime-version:sender:in-reply-to:references:date :message-id:subject:from:to:x-original-sender :x-original-authentication-results:reply-to:precedence:mailing-list :list-id:x-google-group-id:list-post:list-help:list-archive :list-subscribe:list-unsubscribe:content-type; bh=4pWvqUtBCwtHy3W6PUtJb5Jex1YyaQysNwS4XPJXUyw=; b=TSuk5r2p8/ZAkKkhd3SGL24UwysnN9RlyGqzwaSQK7uhlQaNF6JL2zCUwYa/w28HA1 x7QSTUcu3946iNstqPQIXxihh7PRnxciqm2y2Ow2Ki6t3gqd1dn5+fKA4UrbP9tBcYnK nDyGNmjLIsVRx6U7HYNdgp1L5+UHb4aiZTHNw+50JIjeqq32Ix0VB4+echTG2CHS5Vii 2hyw/w6BbiHupxtJ5rC+G8TaHZQm72fQfH3czCJkGiHYI9qMh+Z3ajKIO8UgGtVBOzmA rv+ncw6LujFqmQpsEdRy6VCFiK4+MA6LuMize4lwykLs4Tgie/kLRMU44K/b063PFLLd iDGg== X-Received: by 10.224.200.202 with SMTP id ex10mr212395qab.8.1369778203016; Tue, 28 May 2013 14:56:43 -0700 (PDT) X-BeenThere: std-proposals@isocpp.org Original-Received: by 10.49.60.231 with SMTP id k7ls3647811qer.22.gmail; Tue, 28 May 2013 14:56:42 -0700 (PDT) X-Received: by 10.52.163.207 with SMTP id yk15mr16145667vdb.42.1369778201969; Tue, 28 May 2013 14:56:41 -0700 (PDT) Original-Received: from mail-ve0-x233.google.com (mail-ve0-x233.google.com [2607:f8b0:400c:c01::233]) by mx.google.com with ESMTPS id sa4si19768209vdc.49.2013.05.28.14.56.41 for (version=TLSv1 cipher=ECDHE-RSA-RC4-SHA bits=128/128); Tue, 28 May 2013 14:56:41 -0700 (PDT) Received-SPF: pass (google.com: domain of metafoo@gmail.com designates 2607:f8b0:400c:c01::233 as permitted sender) client-ip=2607:f8b0:400c:c01::233; Original-Received: by mail-ve0-f179.google.com with SMTP id d10so4001702vea.38 for ; Tue, 28 May 2013 14:56:41 -0700 (PDT) X-Received: by 10.58.45.71 with SMTP id k7mr19346972vem.0.1369778201755; Tue, 28 May 2013 14:56:41 -0700 (PDT) Original-Sender: metafoo@gmail.com Original-Received: by 10.58.246.226 with HTTP; Tue, 28 May 2013 14:56:41 -0700 (PDT) In-Reply-To: <35af8d3d-8ed6-441c-94d0-b898711190b1@isocpp.org> X-Original-Sender: richard@metafoo.co.uk X-Original-Authentication-Results: mx.google.com; spf=pass (google.com: domain of metafoo@gmail.com designates 2607:f8b0:400c:c01::233 as permitted sender) smtp.mail=metafoo@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:4686 Archived-At: --089e013cc32823061604ddce57b2 Content-Type: text/plain; charset=ISO-8859-1 On Mon, May 27, 2013 at 5:18 AM, wrote: > > You can return a lambda or a local class from a lambda in C++11, so that >> doesn't count as an excuse for noticing this now because >> we can return local types from a non-lambda in C++14. >> > > Sort of. You can return it from a lambda but you can't return it out of > the enclosing non-lambda function scope. The only way to pass it out of the > *namespace*, which is what matters, is to pass it into a template, which > is what I did with my example. > > By the way, the language as-is seems deeply flawed. Only a singly-nested > class has an associated namespace; nest a class inside a nested class and > it becomes disconnected from its namespace. > > > - > > If T is a class type (including unions), its associated classes are: > the class itself; the class of which it is a member, if any; and its direct > and indirect base classes. Its associated namespaces are the namespaces of > which its associated classes are members. > > > GCC and Clang both incorrectly accept this example: > > namespace n { > struct s { struct n1 { struct n2 {}; }; }; > int f( s::n1::n2 ) { return 3; } > } > int i = f( n::s::n1::n2() ); > Core issue 557 appears to be responsible for this. Prior to that issue, the wording said "Its associated namespaces are the namespaces in which its associated classes are defined." which in this case includes 'n'. Presumably the intent here was to clarify that a::b would be the associated namespace for a::b::x here, not a: namespace a { namespace b { struct x; } struct b::x {}; } I don't know whether the change to deeply-nested member classes was intentional. Neither gcc nor clang treats n::s as an associated class, although both treat n as an associated namespace. EDG also treats n as an associated namespace, but this is not definitive because it also treats n::s as an associated class (contrary to the specification). -- --- 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. Visit this group at http://groups.google.com/a/isocpp.org/group/std-proposals/?hl=en. --089e013cc32823061604ddce57b2 Content-Type: text/html; charset=ISO-8859-1 Content-Transfer-Encoding: quoted-printable On Mon, May 27, 2013 at 5:18 AM, <potswa@gmail.com> wrote:

You can return a lambda or a local= class from a lambda in C++11, so that doesn't count as an excuse for n= oticing this now because
we can return local types from a non-lambda in C++14.
=

Sort of. You can return it from a lambda = but you can't return it out of the enclosing non-lambda function scope.= The only way to pass it out of the namespace, which is what matters= , is to pass it into a template, which is what I did with my example.

By the way, the language as-is seems deeply flawed. Only a singly-neste= d class has an associated namespace; nest a class inside a nested class and= it becomes disconnected from its namespace.

=09 =09 =09 =09 =09

  • If T is a class type (including unions), its associated classes are= : the class itself; the class of which it is a member, if any; and its direct and indirect base classes. Its associated na= mespaces are the namespaces of which its associated classes are members.

=09
GCC and Clang both incorrectly accept this example:

namespace n {
struct s { struct n1 { struct n2 {}; }; };<= /span>
int f( s::= n1::n2 ) { re= turn 3; }<= /span>
}
int i =3D f( n::s::n1::n2() );

Core issue 557 appears = to be responsible for this. Prior to that issue, the wording=A0said "I= ts associated namespaces are the namespaces in which its associated classes= are defined." which in this case includes 'n'. Presumably the= intent here was to clarify that a::b would be the associated namespace for= a::b::x here, not a:

namespace a {
=A0 namespace b { struct x; }
=A0 struct b::x {};
}

I don'= ;t know whether the change to deeply-nested member classes was intentional.= Neither gcc nor clang treats n::s as an associated class, although both tr= eat n as an associated namespace. EDG also treats n as an associated namesp= ace, but this is not definitive because it also treats n::s as an associate= d class (contrary to the specification).

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