220 19951 <1115b787-4cfd-4052-9f49-ece9c4bdf2ec@isocpp.org> article Path: news.gmane.org!not-for-mail From: NDos Dannyu 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 17:52:59 -0700 (PDT) Lines: 191 Approved: news@gmane.org Message-ID: <1115b787-4cfd-4052-9f49-ece9c4bdf2ec@isocpp.org> References: <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_324_626021455.1440204779259" X-Trace: ger.gmane.org 1440204784 18427 80.91.229.3 (22 Aug 2015 00:53:04 GMT) X-Complaints-To: usenet@ger.gmane.org NNTP-Posting-Date: Sat, 22 Aug 2015 00:53:04 +0000 (UTC) To: ISO C++ Standard - Future Proposals Original-X-From: std-proposals+bncBCX7FRO67EHRB3EP36XAKGQEPC33B2Q@isocpp.org Sat Aug 22 02:53:03 2015 Return-path: Envelope-to: gclcip-std-proposals@m.gmane.org Original-Received: from mail-pd0-f197.google.com ([209.85.192.197]) by plane.gmane.org with esmtp (Exim 4.69) (envelope-from ) id 1ZSx3O-0003sS-Tl for gclcip-std-proposals@m.gmane.org; Sat, 22 Aug 2015 02:53:03 +0200 Original-Received: by pdph1 with SMTP id h1sf155684034pdp.0 for ; Fri, 21 Aug 2015 17:53:01 -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:in-reply-to:references :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=T5RGi+mqaHrmcm2gGxSyrNe9BKtgMWv4Hj6UG7vku4o=; b=iJhTRd2gNh46jU66DXgZr3+NVXiskF0kLv52wDLJ8AdBq7TdjtZ1K+11sjtGtDRXe4 eisPVEGLwsWfoC9lBOqvAR51x2rf/kQOR6OnNLmAbTZlOEXAgEcKZJYAvds5AWO479ZY HacvfwG0AssQORBWNH0g2DlDjZxae/oQOEOzmiy0FQGv4854C32YeVaBKwuME+holXsE Cnpf/lqlHbYPMXTgAYgGFJjv3WaLgZcwTkNNhM9FJu8PT1RNxudepe0szFKFeSgZTn/O 2niyM7SlelqoQM+59Xcu3s+Mp6k1bG1iyDSRbWVbxRTfjvEhhWSd8yStV/m7gn/Jfu+e +maw== X-Gm-Message-State: ALoCoQn3O3fmu2jcsTQzWWd8WzllaabgV0Ak+8fQsep02YM3ETxR2ryvy2yCoZ5R+E63PxuAQEW1 X-Received: by 10.66.119.201 with SMTP id kw9mr9146982pab.4.1440204781757; Fri, 21 Aug 2015 17:53:01 -0700 (PDT) X-BeenThere: std-proposals@isocpp.org Original-Received: by 10.107.16.163 with SMTP id 35ls937680ioq.71.gmail; Fri, 21 Aug 2015 17:53:00 -0700 (PDT) X-Received: by 10.50.28.19 with SMTP id x19mr115327igg.16.1440204780812; Fri, 21 Aug 2015 17:53:00 -0700 (PDT) In-Reply-To: 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:19951 Archived-At: ------=_Part_324_626021455.1440204779259 Content-Type: multipart/alternative; boundary="----=_Part_325_475612207.1440204779259" ------=_Part_325_475612207.1440204779259 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: quoted-printable 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= =20 > users should be able to dereference the address of an object to retrieve= =20 > the original value.=20 > 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,=20 which isn't an object. Zero doesn't have an address, so rcr should also not= =20 have an address. > This also wouldn't really be implementable anyway I thought the compiler would know what a reference is and what the=20 reference refers to. Isn't it implementable built-in then...? > since soon as you introduce a level of indirection by passing the object= =20 > by reference to a function, you'd no longer know that it referred to a=20 > 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=20 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

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 addres= s 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 valu= e.
A reference ISN'T an objec= t; 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 not have an address.
This also woul= dn't really be implementable anyway
I thought the comp= iler would 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 p= assing 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 exa= mple:
=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 return c= r;
=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= 9;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 whe= n 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=C2=A0I have a variab= le named X.
But=C2=A0how=C2=A0can=C2=A0P(X<X=C2=B2) interprete= d? X is still X, even it is squared, isn't it?
Things will ge= t 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<= /div>
So I decided to=C2=A0make a bind of variables.
It would= be a tree structure, consisting of=C2=A0other=C2=A0binds=C2=A0or variables= ..
If=C2=A0it=C2=A0consists=C2=A0of references of variables, it wi= ll know what variables are same(or dependant) and=C2=A0what variables are d= ifferent(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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