220 5025 <51bf2631-aed7-4433-b16d-15ee15e87f29@isocpp.org> article Path: news.gmane.org!not-for-mail From: tomaszkam@gmail.com Newsgroups: gmane.comp.lang.c++.isocpp.proposals Subject: Require that this should be always caputred by copy. Date: Thu, 13 Jun 2013 13:16:49 -0700 (PDT) Lines: 177 Approved: news@gmane.org Message-ID: <51bf2631-aed7-4433-b16d-15ee15e87f29@isocpp.org> Reply-To: std-proposals@isocpp.org NNTP-Posting-Host: plane.gmane.org Mime-Version: 1.0 Content-Type: multipart/alternative; boundary="----=_Part_1_13674258.1371154609502" X-Trace: ger.gmane.org 1371155964 27381 80.91.229.3 (13 Jun 2013 20:39:24 GMT) X-Complaints-To: usenet@ger.gmane.org NNTP-Posting-Date: Thu, 13 Jun 2013 20:39:24 +0000 (UTC) To: std-proposals@isocpp.org Original-X-From: std-proposals+bncBDNPVXXG6IGBB6W35CGQKGQEIKR6DUQ@isocpp.org Thu Jun 13 22:39:25 2013 Return-path: Envelope-to: gclcip-std-proposals@m.gmane.org Original-Received: from mail-gh0-f197.google.com ([209.85.160.197]) by plane.gmane.org with esmtp (Exim 4.69) (envelope-from ) id 1UnEIm-0005mJ-3j for gclcip-std-proposals@m.gmane.org; Thu, 13 Jun 2013 22:39:24 +0200 Original-Received: by mail-gh0-f197.google.com with SMTP id r20sf6300696ghr.8 for ; Thu, 13 Jun 2013 13:39:23 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gmail.com; s=20120113; h=x-beenthere:date:from:to:message-id:subject:mime-version :x-original-sender:reply-to:precedence:mailing-list:list-id :x-google-group-id:list-post:list-help:list-archive:list-subscribe :list-unsubscribe:content-type; bh=xHs4Qx3lz3SppivJyKl1PAyKddEqkL3+bMhMDG8cwds=; b=c+fvQisBKxD8BqZ16mkmtt3ivWJHJunrq2fZZoYtbiq/BNTC7TWEgIyMBGpTj/YTRs scMV+bgA9ovfNInlvdaKn9F0dSjeirDv7c2jonL/0QO71TsB+0hVOw7/gFoz6UQbtn0a r213FYQHI3vftuHF3BJ15xPy+2/NHKW8kc7Siljl8RrpMj5poR9zpPC++VL26mbtYQWR MPbYwPm5mrtfPfEl4mrhr42IPy/xA0HMYi10XCP8hZfr8CdJh7jdtL4zfgn9shNgXjqN Cw4uHGR3HhvVpbvkZJaKZaOP1Qs2WQmr+2gOUwgWSH2WR4hX/xp6UNSYIv5AdqaLm9GJ n7MA== X-Received: by 10.236.55.129 with SMTP id k1mr1226982yhc.1.1371155962596; Thu, 13 Jun 2013 13:39:22 -0700 (PDT) X-BeenThere: std-proposals@isocpp.org Original-Received: by 10.49.60.200 with SMTP id j8ls1172352qer.42.gmail; Thu, 13 Jun 2013 13:39:21 -0700 (PDT) X-Received: by 10.224.42.141 with SMTP id s13mr2269164qae.3.1371155961586; Thu, 13 Jun 2013 13:39:21 -0700 (PDT) Original-Received: by 10.224.181.75 with SMTP id bx11msqab; Thu, 13 Jun 2013 13:16:50 -0700 (PDT) X-Received: by 10.49.3.37 with SMTP id 5mr127780qez.30.1371154609925; Thu, 13 Jun 2013 13:16:49 -0700 (PDT) X-Original-Sender: tomaszkam@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:5025 Archived-At: ------=_Part_1_13674258.1371154609502 Content-Type: text/plain; charset=windows-1252 Content-Transfer-Encoding: quoted-printable Currently the standard (C++14 CD - NS3690) disallows explicit capture of=20 this by reference the this seems to be allowed to be captured implicit by= =20 reference by the [&]. $5.1.2: 15. An entity is captured by copy if it is implicitly captured and the=20 capture-default is =3D or if it is explicitly captured with a capture that does not include an &. For each entity=20 captured by copy, an unnamed non- static data member is declared in the closure type. The declaration order= =20 of these members is unspecified. The type of such a data member is the type of the corresponding captured=20 entity if the entity is not a reference to an object, or the referenced type otherwise. [ Note: If the=20 captured entity is a reference to a function, the corresponding data member is also a reference to a function.= =20 =97 end note ] An array of runtime bound (8.3.4) shall not be captured by copy. 16. An entity is captured by reference if it is implicitly or explicitly=20 captured but not captured by copy. It is unspecified whether additional unnamed non-static data members are declared= =20 in the closure type for entities captured by reference. [ Note: Capturing by reference an array of runtime= =20 bound also .. See also. this questions. Contrary the statement $5.1.2/18: Every id-expression that is an odr-use (3.2) of an entity captured by copy= =20 is transformed into an access to the corresponding unnamed data member of the closure type. [ Note: An=20 id-expression that is not an odr-use refers to the original entity, never to a member of the closure type.=20 Furthermore, such an id-expression does not cause the implicit capture of the entity. =97 end note ] *If this = is=20 captured, each odr-use of this is transformed into an access to the corresponding unnamed data member of= =20 the closure type, cast (5.4) to the type of this.* [ Note: The cast ensures that the transformed=20 expression is a prvalue. =97 end note ] Sugest that this is always stored in separate unnamed member of closuer=20 type, which with combination with $5.1.2/16: An entity is captured by reference if it is implicitly or explicitly=20 captured but not captured by copy.* It is unspecified whether additional unnamed non-static data members are declared= =20 in the closure type for entities captured by reference. *[ Note: Capturing by reference an array of runtime= =20 bound also implicitly captures the value of the bound to support the range-based for statement (6.5.4). = =97=20 end note ] So in combination this to statement suggests that this is always captured= =20 by copy. Is this the issue in the standard wording and the this was designed to be= =20 always captured by value? If so the point be changed to explicitly mention= =20 this. 15. An entity is captured by copy if it is *this or* implicitly captured=20 and the capture-default is =3D or if it is explicitly captured with a capture that does not include an &. For each entity=20 captured by copy, an unnamed non- static data member is declared in the closure type. The declaration order= =20 of these members is unspecified. The type of such a data member is the type of the corresponding captured=20 entity if the entity is not a reference to an object, or the referenced type otherwise. [ Note: If the=20 captured entity is a reference to a function, the corresponding data member is also a reference to a function.= =20 =97 end note ] An array of runtime bound (8.3.4) shall not be captured by copy. --=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_1_13674258.1371154609502 Content-Type: text/html; charset=windows-1252 Content-Transfer-Encoding: quoted-printable Currently the standard (C++14 CD - NS3690) disallows explicit capture of th= is by reference the this seems to be allowed to be captured implicit by ref= erence by the [&]. $5.1.2:
15. An entity is captured by copy if it is implicitly captured a= nd the capture-default is =3D or if it is explicitly
captured with a cap= ture that does not include an &. For each entity captured by copy, an u= nnamed non-
static data member is declared in the closure type. The decl= aration order of these members is unspecified.
The type of such a data m= ember is the type of the corresponding captured entity if the entity is not= a
reference to an object, or the referenced type otherwise. [ Note: If = the captured entity is a reference to a
function, the corresponding data= member is also a reference to a function. =97 end note ] An array of runti= me
bound (8.3.4) shall not be captured by copy.
16. An entity is capt= ured by reference if it is implicitly or explicitly captured but not captur= ed by copy. It is
unspecified whether additional unnamed non-static data= members are declared in the closure type for entities
captured by refer= ence. [ Note: Capturing by reference an array of runtime bound also<= br>. See also. this questions.

Cont= rary the statement $5.1.2/18:
Every id-expression that is an odr-use (3.2) of an entity capture= d by copy is transformed into an access to the
corresponding unnamed dat= a member of the closure type. [ Note: An id-expression that is not an odr-u= se
refers to the original entity, never to a member of the closure type.= Furthermore, such an id-expression
does not cause the implicit capture = of the entity. =97 end note ] If this is captured, each odr-use of this<= br>is transformed into an access to the corresponding unnamed data member o= f the closure type, cast (5.4)
to the type of this. [ Note: The cast= ensures that the transformed expression is a prvalue. =97 end note ]
Sugest that this is always stored in separate= unnamed member of closuer type, which with combination with $5.1.2/16:
= An entity is captured b= y reference if it is implicitly or explicitly captured but not captured by = copy. It is
unspecified whether additional unnamed non-static data me= mbers are declared in the closure type for entities
captured by referenc= e. [ Note: Capturing by reference an array of runtime bound also implic= itly captures
the value of the bound to support the range-based for stat= ement (6.5.4). =97 end note ]
So in combination thi= s to statement suggests that this is always captured by copy.

Is thi= s the issue in the standard wording and the this was designed to be always = captured by value? If so the point be changed to explicitly mention this.15. An entity is capt= ured by copy if it is this or <= /span>implicitly captured and the capture-default is =3D or if it is explic= itly
captured with a capture that does not include an &. For each en= tity captured by copy, an unnamed non-
static data member is declared in= the closure type. The declaration order of these members is unspecified.The type of such a data member is the type of the corresponding captured = entity if the entity is not a
reference to an object, or the referenced = type otherwise. [ Note: If the captured entity is a reference to a
funct= ion, the corresponding data member is also a reference to a function. =97 e= nd note ] An array of runtime
bound (8.3.4) shall not be captured by cop= y.

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