220 5306 <6ed86280-bff9-4dc5-bef3-28be8981770b@isocpp.org> article Path: news.gmane.org!not-for-mail From: andrewtomazos@gmail.com Newsgroups: gmane.comp.lang.c++.isocpp.proposals Subject: Re: Overloaded Declarators Date: Fri, 5 Jul 2013 16:05:18 -0700 (PDT) Lines: 235 Approved: news@gmane.org Message-ID: <6ed86280-bff9-4dc5-bef3-28be8981770b@isocpp.org> References: <82b89c5e-ce4e-49c0-82b2-d6032631e3e3@isocpp.org> Reply-To: std-proposals@isocpp.org NNTP-Posting-Host: plane.gmane.org Mime-Version: 1.0 Content-Type: multipart/alternative; boundary="----=_Part_5125_32488359.1373065518132" X-Trace: ger.gmane.org 1373065519 1377 80.91.229.3 (5 Jul 2013 23:05:19 GMT) X-Complaints-To: usenet@ger.gmane.org NNTP-Posting-Date: Fri, 5 Jul 2013 23:05:19 +0000 (UTC) To: std-proposals@isocpp.org Original-X-From: std-proposals+bncBD5KHQXXWYPRBLVC3WHAKGQEMHMOGVQ@isocpp.org Sat Jul 06 01:05:20 2013 Return-path: Envelope-to: gclcip-std-proposals@m.gmane.org Original-Received: from mail-qc0-f197.google.com ([209.85.216.197]) by plane.gmane.org with esmtp (Exim 4.69) (envelope-from ) id 1UvF44-0003V5-Gd for gclcip-std-proposals@m.gmane.org; Sat, 06 Jul 2013 01:05:20 +0200 Original-Received: by mail-qc0-f197.google.com with SMTP id u12sf3252781qcx.8 for ; Fri, 05 Jul 2013 16:05:19 -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:in-reply-to:references: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=vwq8uxvmNck/zpYNSCbuSHtsy/Ii1bJmTM07hCGq62E=; b=ealmEn7NBJqvLWD4jC9ooZRMkXh2FH4KJT00T6/lcH6m60KIwqcNZmH4Y+EvYpK9uR IgmCnsqy5Wa5XCqHS9HBKNQ7Sr6iUHuhXYt9slYeLuqH8fz6a0bj6Mv2xburAeZA41N8 RGmqTAs52LLoFQ2H0zsZobdtp6nwIv6ApRVLiA5SB4/qnQG9oBThK8l/itot03a4Vbrr Q8QzkPNCNFJXKFkJc4rhKFrNfCNEXljAQou194zHY1esKm8dw1Xj7/VPndKBOw3Ivf+J 8wvto/kYdjwr6foKpn+JrIfTfv0Ds/Cf1ysaOPuGHkK/07W3QmL/Xe4rPH/tBR9AjiMq R7Gw== X-Received: by 10.224.55.200 with SMTP id v8mr14599698qag.7.1373065519618; Fri, 05 Jul 2013 16:05:19 -0700 (PDT) X-BeenThere: std-proposals@isocpp.org Original-Received: by 10.49.108.74 with SMTP id hi10ls1205596qeb.50.gmail; Fri, 05 Jul 2013 16:05:18 -0700 (PDT) X-Received: by 10.49.63.195 with SMTP id i3mr273700qes.29.1373065518550; Fri, 05 Jul 2013 16:05:18 -0700 (PDT) In-Reply-To: X-Original-Sender: andrewtomazos@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:5306 Archived-At: ------=_Part_5125_32488359.1373065518132 Content-Type: text/plain; charset=ISO-8859-1 Content-Transfer-Encoding: quoted-printable > What if I want an actual pointer now? Suppose you overload unary operator& on a class: struct X { Y operator&(); } What if I want the actual address of an object of type X now? You use=20 std::addressof. In a similar fashion alias templates could be provided in the standard=20 library, for example std::pointerto, such that even if the * declarator= =20 was overloaded for that class, pointerto would always give you the type= =20 "pointer to T": -Andrew. On Friday, July 5, 2013 3:57:23 PM UTC+2, R. Martinho Fernandes wrote: > > What if I want an actual pointer now?=20 > Mit freundlichen Gr=FC=DFen,=20 > > Martinho=20 > > > On Fri, Jul 5, 2013 at 8:32 AM, >=20 > wrote:=20 > > If we view for a moment the various parts of a declarator as operations= =20 > on=20 > > types:=20 > >=20 > > T*: T -> pointer-to-T=20 > > T&: T -> lvalue-reference-to-T=20 > > T&&: T -> rvalue-reference-to-T=20 > > T[]: T -> array-of-T=20 > > T(): T -> function-returning-T=20 > > and so forth=20 > >=20 > > These operations take one or more types as input and produce a type as= =20 > > output.=20 > >=20 > > This is not dissimilar to an alias template:=20 > >=20 > > template=20 > > using MakePointer =3D T*;=20 > >=20 > > template=20 > > using MakeReference =3D T&;=20 > >=20 > > In fact we could almost say that functions are to the built-in=20 > expression=20 > > operators, as alias templates are to the built-in declarators.=20 > >=20 > > So the proposed feature "Overloaded Declarators" is to enable a=20 > user-defined=20 > > alias template to redefine the built-in meaning of a declarator.=20 > >=20 > > Overloaded Declarators are to the built-in declarators, as Overloaded= =20 > > Operators are to the built-in expression operators:=20 > >=20 > > struct Foo{}=20 > >=20 > > template=20 > > using operator* =3D shared_ptr;=20 > >=20 > > Foo* p; // p has type shared_ptr=20 > >=20 > > The above shows a key use case, specializing the declarator `T*` to=20 > > designate a user-defined smart pointer class instead of pointer-to-T fo= r=20 > > some set of types.=20 > >=20 > > Just a random idea.=20 > >=20 > > Enjoy,=20 > > Andrew.=20 > >=20 > > --=20 > >=20 > > ---=20 > > You received this message because you are subscribed to the Google=20 > Groups=20 > > "ISO C++ Standard - Future Proposals" group.=20 > > To unsubscribe from this group and stop receiving emails from it, send= =20 > an=20 > > email to std-proposal...@isocpp.org .=20 > > To post to this group, send email to std-pr...@isocpp.org = ..=20 > > > Visit this group at=20 > > http://groups.google.com/a/isocpp.org/group/std-proposals/.=20 > >=20 > >=20 > --=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_5125_32488359.1373065518132 Content-Type: text/html; charset=ISO-8859-1 Content-Transfer-Encoding: quoted-printable > What if I want an actual pointer now?

Suppose you overload unar= y operator& on a class:

    struct X
 &nb= sp;  {
        Y operator&()= ;
    }

What if I want the actual address of an ob= ject of type X now?  You use std::addressof.

In a similar fashi= on alias templates could be provided in the standard library, for example s= td::pointerto<T>, such that even if the * declarator was overloaded f= or that class, pointerto<T> would always give you the type "pointer t= o T":
    -Andrew.

On Friday, July 5, 2013 3:57:23= PM UTC+2, R. Martinho Fernandes wrote:
What if I want an actual pointer now?
Mit freundlichen Gr=FC=DFen,

Martinho


On Fri, Jul 5, 2013 at 8:32 AM,  <andrew...@gmail.com= > wrote:
> If we view for a moment the various parts of a declarator as opera= tions on
> types:
>
>     T*: T -> pointer-to-T
>     T&: T -> lvalue-reference-to-T
>     T&&: T -> rvalue-reference-to-T
>     T[]: T -> array-of-T
>     T(): T -> function-returning-T
>     and so forth
>
> These operations take one or more types as input and produce a typ= e as
> output.
>
> This is not dissimilar to an alias template:
>
>    template<class T>
>    using MakePointer =3D T*;
>
>    template<class T>
>    using MakeReference =3D T&;
>
> In fact we could almost say that functions are to the built-in exp= ression
> operators, as alias templates are to the built-in declarators.
>
> So the proposed feature "Overloaded Declarators" is to enable a us= er-defined
> alias template to redefine the built-in meaning of a declarator.
>
> Overloaded Declarators are to the built-in declarators, as Overloa= ded
> Operators are to the built-in expression operators:
>
>    struct Foo{}
>
>    template<class T>
>    using operator*<Foo> =3D shared_ptr<T>;
>
>    Foo* p;  // p has type shared_ptr<T>
>
> The above shows a key use case, specializing the declarator `T*` t= o
> designate a user-defined smart pointer class instead of pointer-to= -T for
> some set of types.
>
> Just a random idea.
>
> Enjoy,
> Andrew.
>
> --
>
> ---
> 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-proposal...@isocpp.org.
> To post to this group, send email to std-pr...@isocpp.org.
> Visit this group at
> http://groups.google.com/a/isocpp.org/group/std= -proposals/.
>
>

--
 
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