220 19952 article Path: news.gmane.org!not-for-mail From: Richard Smith Newsgroups: gmane.comp.lang.c++.isocpp.proposals Subject: Re: Address of a reference: determining the value category of what it refers? Date: Fri, 21 Aug 2015 18:14:47 -0700 Lines: 233 Approved: news@gmane.org Message-ID: References: <76fe342f-3342-4355-af20-1c41b21e54aa@isocpp.org> <1115b787-4cfd-4052-9f49-ece9c4bdf2ec@isocpp.org> Reply-To: std-proposals@isocpp.org NNTP-Posting-Host: plane.gmane.org Mime-Version: 1.0 Content-Type: multipart/alternative; boundary=bcaec51d225441a9de051ddc1cf0 X-Trace: ger.gmane.org 1440206092 3094 80.91.229.3 (22 Aug 2015 01:14:52 GMT) X-Complaints-To: usenet@ger.gmane.org NNTP-Posting-Date: Sat, 22 Aug 2015 01:14:52 +0000 (UTC) To: "std-proposals@isocpp.org" Original-X-From: std-proposals+bncBDVNBJG4YAIBBCE236XAKGQEHZKNK3Q@isocpp.org Sat Aug 22 03:14:52 2015 Return-path: Envelope-to: gclcip-std-proposals@m.gmane.org Original-Received: from mail-pa0-f69.google.com ([209.85.220.69]) by plane.gmane.org with esmtp (Exim 4.69) (envelope-from ) id 1ZSxOU-0008H6-Ey for gclcip-std-proposals@m.gmane.org; Sat, 22 Aug 2015 03:14:50 +0200 Original-Received: by pacgr6 with SMTP id gr6sf14626309pac.3 for ; Fri, 21 Aug 2015 18:14:49 -0700 (PDT) X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20130820; h=x-gm-message-state:mime-version:sender:in-reply-to:references:date :message-id:subject:from:to:content-type:x-original-sender :x-original-authentication-results:reply-to:precedence:mailing-list :list-id:x-spam-checked-in-group:list-post:list-help:list-archive :list-subscribe:list-unsubscribe; bh=do1hgZYI8SKLLLtYZqOaHfQweHPjrV56i+5qMPgigmc=; b=MAcRIFYm2i7Lv/KBSSaX3tGIeocpHF6ea70PGtCY8dULTXAZooZ2aAt9b9Ce5wwpxO MinOjV+pTi1Yboy3uZK2/gg2ArgGE6/rUZk+5WZ5pUzwoS7LttNsoJhWY4gPfbLfxgHk O22b9Wds0fwqpvZd388e/Ur+z2Kmz0fVG/uBJJPhQ0drpAriyPpL4x4bJMcywathCNm1 KB7dq5aAd6/MUbI4Yj10poYsDkIiTJjz2yCm81ytv6KgvPjchDG8KumEdQ8UDgZCEaak OQH/1IkiM7gJ1qDuaBByNxqwb+749Srh8uQ2/F61cdhfcwh/Lk6lHdUYrw3gQCGexLLr 2yxA== X-Gm-Message-State: ALoCoQk0V1Z0gZnurNn+U+SI6HSmvGsk32AIoWrhk/XQexWUi10R5aqVq7U7GY8z5n7SsUknEL7F X-Received: by 10.66.163.162 with SMTP id yj2mr8805557pab.27.1440206088962; Fri, 21 Aug 2015 18:14:48 -0700 (PDT) X-BeenThere: std-proposals@isocpp.org Original-Received: by 10.182.29.137 with SMTP id k9ls1774981obh.81.gmail; Fri, 21 Aug 2015 18:14:48 -0700 (PDT) X-Received: by 10.53.12.229 with SMTP id et5mr13871349vdd.73.1440206088128; Fri, 21 Aug 2015 18:14:48 -0700 (PDT) Original-Received: from mail-vk0-x235.google.com (mail-vk0-x235.google.com. [2607:f8b0:400c:c05::235]) by mx.google.com with ESMTPS id yr14si13082410vdb.81.2015.08.21.18.14.47 for (version=TLSv1.2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128/128); Fri, 21 Aug 2015 18:14:48 -0700 (PDT) Received-SPF: pass (google.com: domain of metafoo@gmail.com designates 2607:f8b0:400c:c05::235 as permitted sender) client-ip=2607:f8b0:400c:c05::235; Original-Received: by vkm66 with SMTP id 66so38008309vkm.1 for ; Fri, 21 Aug 2015 18:14:47 -0700 (PDT) X-Received: by 10.52.30.136 with SMTP id s8mr13926041vdh.38.1440206087627; Fri, 21 Aug 2015 18:14:47 -0700 (PDT) Original-Sender: metafoo@gmail.com Original-Received: by 10.31.237.70 with HTTP; Fri, 21 Aug 2015 18:14:47 -0700 (PDT) In-Reply-To: <1115b787-4cfd-4052-9f49-ece9c4bdf2ec@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:c05::235 as permitted sender) smtp.mailfrom=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-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:19952 Archived-At: --bcaec51d225441a9de051ddc1cf0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: quoted-printable On Fri, Aug 21, 2015 at 5:52 PM, NDos Dannyu wrote: > > > 2015=EB=85=84 8=EC=9B=94 22=EC=9D=BC =ED=86=A0=EC=9A=94=EC=9D=BC =EC=98= =A4=EC=A0=84 8=EC=8B=9C 49=EB=B6=84 45=EC=B4=88 UTC+9, Matt Calabrese =EB= =8B=98=EC=9D=98 =EB=A7=90: > >> Taking the address of an object in C++ doesn't yield a null pointer, and >> users should be able to dereference the address of an object to retrieve >> the original value. >> > A reference ISN'T an object; it is, literally, a reference to an object. > But *const int &rcr(0)* doesn't refer to an object. It refers to zero, > which isn't an object. Zero doesn't have an address, so rcr should also n= ot > have an address. > That's not correct. "const int &rcr(0)" implicitly creates a temporary object of type int and binds the reference to that object. (The reference binding then extends the lifetime of that temporary object to the lifetime of the reference.) > This also wouldn't really be implementable anyway > > I thought the compiler would know what a reference is and what the > reference refers to. Isn't it implementable built-in then...? > >> since soon as you introduce a level of indirection by passing the objec= t >> by reference to a function, you'd no longer know that it referred to a >> literal > > I don't get it. For example: > *int &foor(int &r) {* > * return r;* > * }* > * const int &foocr(const int &rc) {* > * return cr;* > * }* > *int &&foorr(int &&rr) {* > * return rr;* > * }* > * int main() {* > * int i(0);* > * foor(i); // OK* > * // foor(0); // error: r can't be initialized with 0* > * foocr(i); // OK* > * foocr(0); // OK* > * // foorr(i); // error: rr can't be initialized with i* > * foorr(0); // OK* > * }* > A function every argument is initialized when it is called; the function > well-knows what its arguments exactly are. No problem. > > My original intentions were: > > I have a value class indicating a finite discrete random variable. > But I had a problem. For example, assume that I have a variable named X. > But how can P(X it? > Things will get much more complicated if I have multiple variables, X, Y > and Z, > and I have to do like P(X|Z|) or something. > So I decided to make a bind of variables. > It would be a tree structure, consisting of other binds or variables. > If it consists of references of variables, it will know what variables ar= e > same(or dependant) and what variables are different(or indepentant). > But how can I deal with rvalues? For examples, 1 can be seen as a variabl= e > which is always 1. > But it has no name. It is just 1. It is always indepentant from > other variables. > So I made it to consist of const lvalue references, > which can initialized with lvalue or rvalue. > But how can I determine it refers to lvalue or rvalue?? I couldn't find > any solution from the standard library. > > > > > > > -- > > --- > 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/. > --=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/. --bcaec51d225441a9de051ddc1cf0 Content-Type: text/html; charset=UTF-8 Content-Transfer-Encoding: quoted-printable
On F= ri, Aug 21, 2015 at 5:52 PM, NDos Dannyu <ndospark320@naver.com>= ; wrote:


= 2015=EB=85=84 8=EC=9B=94 22=EC=9D=BC =ED=86=A0=EC=9A=94=EC=9D=BC =EC=98=A4= =EC=A0=84 8=EC=8B=9C 49=EB=B6=84 45=EC=B4=88 UTC+9, Matt Calabrese =EB=8B= =98=EC=9D=98 =EB=A7=90:
Taking the address of an object in = C++ doesn't yield a null pointer, and users should be able to dereferen= ce the address of an object to retrieve the original value.
A reference ISN'T an object; it is, l= iterally, a reference to an object.
But const int &rc= r(0) doesn't refer to an object. It refers to zero, which isn&= #39;t an object. Zero doesn't have an address, so rcr should also not h= ave an address.

That's not = correct. "const int &rcr(0)" implicitly creates a temporary o= bject of type int and binds the reference to that object. (The reference bi= nding then extends the lifetime of that temporary object to the lifetime of= the reference.)
=C2=A0
This also wouldn't really= be implementable anyway
I thought the compiler wou= ld know what=C2=A0a=C2=A0reference is and what the reference refers to. Isn= 't=C2=A0it implementable built-in then...?
=C2=A0since soon as you introduce a level of indirection by pass= ing the object by reference to a function, you'd no longer know that it= referred to a literal
I don't get it.=C2=A0For= example:
=C2=A0=C2=A0=C2=A0=C2=A0int=C2=A0&foor(int = &r) {
=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0= =C2=A0 return r;
=C2=A0=C2=A0=C2=A0 }
=C2=A0=C2=A0=C2=A0 const int &foocr(const int &rc)= {
=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0 re= turn cr;
=C2=A0=C2=A0=C2=A0 }
=C2=A0=C2=A0=C2=A0 int &&foorr(int &&rr) {
=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0 return rr;
=C2=A0=C2=A0=C2=A0 }
= =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 foor(i); // OK
=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0 // foor(0); // error: r can'= ;t be initialized with 0
=C2=A0=C2=A0=C2=A0=C2= =A0=C2=A0=C2=A0=C2=A0 foocr(i); // OK
=C2=A0=C2= =A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0 foocr(0); // OK
=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0 // foorr(i); // error: rr can&= #39;t be initialized with i
=C2=A0=C2=A0=C2=A0= =C2=A0=C2=A0=C2=A0=C2=A0 foorr(0); // OK
=C2=A0= =C2=A0=C2=A0 }
A function every argument is initialized = when it is called; the function well-knows what its arguments exactly are. = No problem.

My original intentions were:
I have a value class indicating a finite discrete random variable.<= /div>
But I had a problem. For example, assume that=C2=A0I have a varia= ble named X.
But=C2=A0how=C2=A0can=C2=A0P(X<X=C2=B2) interpret= ed? X is still X, even it is squared, isn't it?
Things will g= et much more complicated if=C2=A0I have multiple variables, X, Y and Z,
and I have to do like P(X<X=C2=B2=3DY>|Z|) or something.=C2=A0=
So I decided to=C2=A0make a bind of variables.
It woul= d be a tree structure, consisting of=C2=A0other=C2=A0binds=C2=A0or variable= s.
If=C2=A0it=C2=A0consists=C2=A0of references of variables, it w= ill know what variables are same(or dependant) and=C2=A0what variables are = different(or indepentant).
But=C2=A0how can I deal with rvalues?= =C2=A0For examples, 1 can be seen as a variable which is always 1.
But it has=C2=A0no name. It is just 1. It=C2=A0is always indepentant from= other=C2=A0variables.
So I=C2=A0made it=C2=A0to consist of const= lvalue references, which=C2=A0can=C2=A0initialized=C2=A0with lvalue or rva= lue.
But=C2=A0how can I determine it=C2=A0refers to lvalue or rva= lue?? I couldn't find any solution from the standard library.=C2=A0
=C2= =A0
=C2=A0
=C2=A0
=C2=A0

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You received this message because you are subscribed to the Google Groups &= quot;ISO C++ Standard - Future Proposals" group.
To unsubscribe from this group and stop receiving emails from it, send an e= mail to std-proposa= ls+unsubscribe@isocpp.org.
To post to this group, send email to std-proposals@isocpp.org.
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