220 19949 <76fe342f-3342-4355-af20-1c41b21e54aa@isocpp.org> article Path: news.gmane.org!not-for-mail From: NDos Dannyu Newsgroups: gmane.comp.lang.c++.isocpp.proposals Subject: Address of a reference: determining the value category of what it refers? Date: Fri, 21 Aug 2015 16:24:30 -0700 (PDT) Lines: 155 Approved: news@gmane.org Message-ID: <76fe342f-3342-4355-af20-1c41b21e54aa@isocpp.org> Reply-To: std-proposals@isocpp.org NNTP-Posting-Host: plane.gmane.org Mime-Version: 1.0 Content-Type: multipart/mixed; boundary="----=_Part_110_1071755105.1440199470671" X-Trace: ger.gmane.org 1440199475 10284 80.91.229.3 (21 Aug 2015 23:24:35 GMT) X-Complaints-To: usenet@ger.gmane.org NNTP-Posting-Date: Fri, 21 Aug 2015 23:24:35 +0000 (UTC) To: ISO C++ Standard - Future Proposals Original-X-From: std-proposals+bncBCX7FRO67EHRBMHG32XAKGQEJE5J64A@isocpp.org Sat Aug 22 01:24:34 2015 Return-path: Envelope-to: gclcip-std-proposals@m.gmane.org Original-Received: from mail-oi0-f71.google.com ([209.85.218.71]) by plane.gmane.org with esmtp (Exim 4.69) (envelope-from ) id 1ZSvfl-00033u-P8 for gclcip-std-proposals@m.gmane.org; Sat, 22 Aug 2015 01:24:33 +0200 Original-Received: by oifo84 with SMTP id o84sf118958261oif.3 for ; Fri, 21 Aug 2015 16:24:33 -0700 (PDT) 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:subject:mime-version :content-type: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=FHeslqp8Hvw6y7LQ/XfUgQcseAsdALlphhDKzPDrB7o=; b=l1R+1wvBuaO4xlj8CxafWQuUZBijO90r8BRcta3Hdhs/O8R5Pi2aSZa6FHlh1tT+aJ pNv0ILE5quVv+GhIsQ+DVUr89N509WDLfSdjvvf3LjLvMx6CN1iWIXI6oQdRoB0xKk1b lAp7OY+6pYYI6qx9pbzXQP2lIqKoYCBdNaidTjo49buISQwJ0I/vQe2ZimmA1oEC7fBB 7tRWDwCabG7MHqx1lmoKWFC9hts9wZCW/yPq85FxMAyRmYPlA24cj4mhAFtDbF4CpuQK zE+meLY2GxDS4IepIYG7RqrsAoDJjABVA2V00G82aM5i1eTSq6YKzQbs9qy0srUyV1Bc T3Pg== X-Gm-Message-State: ALoCoQmSjwoVDSkYlE0TkAz4j9JjAG2A4yUmRE5CM837QFXRTlF1KtAw+U/tlLc1CJG/9klSJu8Z X-Received: by 10.50.3.97 with SMTP id b1mr5049636igb.10.1440199472986; Fri, 21 Aug 2015 16:24:32 -0700 (PDT) X-BeenThere: std-proposals@isocpp.org Original-Received: by 10.107.131.17 with SMTP id f17ls925242iod.24.gmail; Fri, 21 Aug 2015 16:24:32 -0700 (PDT) X-Received: by 10.50.50.167 with SMTP id d7mr112712igo.10.1440199472244; Fri, 21 Aug 2015 16:24:32 -0700 (PDT) X-Original-Sender: ndospark320@naver.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: List-Subscribe: , List-Unsubscribe: , Xref: news.gmane.org gmane.comp.lang.c++.isocpp.proposals:19949 Archived-At: ------=_Part_110_1071755105.1440199470671 Content-Type: multipart/alternative; boundary="----=_Part_111_1680266912.1440199470672" ------=_Part_111_1680266912.1440199470672 Content-Type: text/plain; charset=UTF-8 Hi. I'm a bit confused about the exact nature of references, and I have to determine the value category of what it refers. For example, * const int i(0);* * const int &lcr(i);* * const int &rcr(0);* both references are valid, but lcr refers to i, but rcr refers to 0; they are different, and they have to be distinguished. Another example, * #include * * int main() {* * int i(0);* * int &r1(i);* * int &r2(i);* * std::printf("%p %p\n", (void *)&r1, (void *)&r2);* * }* this prints out two same address, which are the address of i. It makes sense, but * #include * * int main() {* * int i(0);* * int &r(i);* * const int &lcr(i);* * const int &rcr(0);* * int &&rr(0);* * std::printf("%p %p %p %p\n", (void *)&r, (void *)&lcr**", (void *)&rcr, (void *)&rr**);* * }* &r and &lcr prints out &i, but &rcr and &rr have their own unique value. It doesn't make sense, as what rcr and rr refer to are what don't have an address, they are just zeros. So, I suggest them to be nullptrs. More precisely, in terms of built-in operators: *template * * T *operator & (/* a value v */) {* * return /* The address of v */;* * }* * template * * const T *operator & (/* a const value cv */) {* * return /* The add ress of cv */;* * }* * template * * T *operator & (/* a lvalue reference r */) {* * return /* The address of what r refers to */;* * }* * template * * const T *operator & (/* a const lvalue reference cr */) {* * if (/* cr refers to a lvalue */) /* The address of what cr refers to */;* * else return (const T *)nullptr;* * }* * template * * T *operator & (/* a rvalue reference rr */) {* * return (T *)nullptr;* * }* so the value category of what a const reference refers to can be determined, by comparing the address of it with nullptr. -- --- 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/. ------=_Part_111_1680266912.1440199470672 Content-Type: text/html; charset=UTF-8 Content-Transfer-Encoding: quoted-printable
Hi.
I'm a bit confused about the exact = nature of references, and I have to determine the value category of what it= refers.
For example,
=C2=A0=C2=A0=C2=A0 const = int i(0);
=C2=A0=C2=A0=C2=A0 const int &lcr(= i);
=C2=A0=C2=A0=C2=A0 const int &rcr(0);
both references are valid, but lcr refers to i, but rcr re= fers to 0; they are different, and they have to be distinguished.
Another example,
=C2=A0=C2=A0=C2=A0 #include <cstdio&= gt;
=C2=A0=C2=A0=C2=A0 int main() {
=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0 int i(0);
=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0 int &r1(= i);
=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0 i= nt &r2(i);
=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2= =A0=C2=A0 std::printf("%p %p\n", (void *)&r1, (void *)&r2= );
=C2=A0=C2=A0=C2=A0 }
this = prints out two same address, which are the address of i.=C2=A0It makes sens= e, but
=C2=A0=C2=A0=C2=A0 #include <cstdio>
=C2=A0=C2=A0=C2=A0 int main() {
=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0 int i(0);
=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0 int &r(i);
=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0 const in= t &lcr(i);
=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2= =A0=C2=A0 const int &rcr(0);
=C2=A0=C2=A0=C2= =A0=C2=A0=C2=A0=C2=A0=C2=A0 int &&rr(0);
=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0 std::printf("%p %p %p %p\n= ", (void *)&r, (void *)&lcr", (void *)&a= mp;rcr, (void *)&rr);
=C2= =A0=C2=A0=C2=A0 }
&r and &lcr prints out &i,= but &rcr and &rr have their own unique value. It doesn't make = sense, as what rcr and rr refer to are what don't have an address, they= are just zeros.
So, I suggest them to be nullptrs. More precisel= y, in terms of built-in operators:
=C2=A0=C2=A0=C2=A0 tem= plate <class T>
=C2=A0=C2=A0=C2=A0 T *oper= ator & (/* a value v */) {
=C2=A0=C2=A0=C2= =A0=C2=A0=C2=A0=C2=A0=C2=A0 return /* The address of v */;
=C2=A0=C2=A0=C2=A0 }
=C2=A0=C2=A0=C2= =A0 template <class T>
=C2=A0=C2=A0=C2=A0 = const T *operator & (/* a const value cv */) {
=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0 return /* The add ress of cv = */;
=C2=A0=C2=A0=C2=A0 }
=C2=A0=C2=A0=C2=A0 template <class T>
= =C2=A0=C2=A0=C2=A0 T *operator & (/* a lvalue reference r */) {
=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0 return /* Th= e address of what r refers to */;
=C2=A0=C2=A0= =C2=A0 }
=C2=A0=C2=A0=C2=A0 template <class T= >
=C2=A0=C2=A0=C2=A0 const T *operator & = (/* a const lvalue=C2=A0reference cr */) {
=C2= =A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0 if (/* cr refers to a lvalue */) /*= The address of what cr refers to */;
=C2=A0=C2= =A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0 else return (const T *)nullptr;<= /div>
=C2=A0=C2=A0=C2=A0 }
=C2=A0=C2= =A0=C2=A0 template <class T>
=C2=A0=C2=A0= =C2=A0 T *operator & (/* a rvalue reference rr */) {
=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0 return (T *)nullptr;
=C2=A0=C2=A0=C2=A0 }
so the val= ue category=C2=A0of=C2=A0what a=C2=A0const reference refers to can be deter= mined, by comparing the address of it with nullptr.

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