220 36755 <11f9c7ff-aa76-46a5-94b2-0692171ab0ff@isocpp.org> article Path: news.gmane.org!.POSTED!not-for-mail From: bastienpenava@gmail.com Newsgroups: gmane.comp.lang.c++.isocpp.proposals Subject: meta members: a 0+ cost properties & dot operator Date: Sat, 27 Jan 2018 21:26:25 -0800 (PST) Lines: 556 Approved: news@gmane.org Message-ID: <11f9c7ff-aa76-46a5-94b2-0692171ab0ff@isocpp.org> Reply-To: std-proposals@isocpp.org NNTP-Posting-Host: blaine.gmane.org Mime-Version: 1.0 Content-Type: multipart/mixed; boundary="----=_Part_6987_1551178034.1517117185589" X-Trace: blaine.gmane.org 1517117074 5529 195.159.176.226 (28 Jan 2018 05:24:34 GMT) X-Complaints-To: usenet@blaine.gmane.org NNTP-Posting-Date: Sun, 28 Jan 2018 05:24:34 +0000 (UTC) To: ISO C++ Standard - Future Proposals Original-X-From: std-proposals+bncBCG3XHNI6IDRBAV6WXJQKGQEPLKQHUY@isocpp.org Sun Jan 28 06:24:29 2018 Return-path: Envelope-to: gclcip-std-proposals@m.gmane.org Original-Received: from mail-ua0-f197.google.com ([209.85.217.197]) by blaine.gmane.org with esmtp (Exim 4.84_2) (envelope-from ) id 1effS3-0000ko-Fa for gclcip-std-proposals@m.gmane.org; Sun, 28 Jan 2018 06:24:23 +0100 Original-Received: by mail-ua0-f197.google.com with SMTP id j3sf3442412ual.3 for ; Sat, 27 Jan 2018 21:26:28 -0800 (PST) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=isocpp-org.20150623.gappssmtp.com; s=20150623; h=date:from:to:message-id:subject:mime-version:x-original-sender :reply-to:precedence:mailing-list:list-id:list-post:list-help :list-archive:list-subscribe:list-unsubscribe; bh=FoOV4A66FWgoh6f2XqfZ8lV95V1+08jlPwh6Atq3RI0=; b=mDDxC/lmuMHvSV1Gxmm0pfR7a66Woc0UOAnOlPUSIXQ8pSdLoQXsdQoZzbuhXNGE8K YXHTw4rC+mmsc0iMI8Wkf32nxH5Tt7Ptd8EGjdnV3mIaX84K5oCgbUKZEVdLPXKyU+yG M1whdvOZCH4xx/DAEaIqIJBpPbedMPQExZV3423oRJ5V9Xn45NauzJQRPF/FgHzGef4f sndeDduRR4MqjTw3dLfbH1ioAsnB1txn0NPTw7pQ5yWkSO9Wvqw0RWfu1AorvX9S55gL /f8QZZpwQorOH5ts9RWeiq9CXhAmP0BAu2DkyBb+aRpBIRn7U5PYQFlyvvpYEn4G3yKl crhg== DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gmail.com; s=20161025; h=date:from:to:message-id:subject:mime-version:x-original-sender :reply-to:precedence:mailing-list:list-id:list-post:list-help :list-archive:list-subscribe:list-unsubscribe; bh=FoOV4A66FWgoh6f2XqfZ8lV95V1+08jlPwh6Atq3RI0=; b=gix3JzVDbq/0l+EV/T/Sdr6h9A4OQy1zWA1iDKW7LHlPN67TPV6vJWfakJ3mA0fsQQ 0I/5tnxMVTfi450ijhgCT94sJkcnLVuW/XmI3O/s6kLqEvSKENBLH2y0+/gvkvPHBt/B i6uDrVgQMXsW3JrjUvmRq9zof3Ig6FTBZm7OxQB3aNiq056nxC7WgW3EsaFucrxIw2d8 w1oGYcT2yZUYLv/Yex4VxwJRZdy4BxEep0xxtRY5uqqw8Ml2zdTs+F2lJJ+AwnvUK4Qk tCGLIzTxaWhSOKfnGluDFjjp1ZGM5LXIWLkUfuvEPyMkuowh8ZPfD4EW2tHBFMBW1tHM WEjA== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20161025; h=x-gm-message-state:date:from:to:message-id:subject:mime-version :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=FoOV4A66FWgoh6f2XqfZ8lV95V1+08jlPwh6Atq3RI0=; b=IOurQIi2bblSFl2of0DYcjhOdTJemowcxu1oKLaiAVsMdw/ZidGq5cW85IT4RF5AXT zxtwEC1c0rSD0hVRMi34jhHKe0JEBD0ihdEYsbzu3uHqZQqEarNFdO8hTyD5N6dUmXog bTToW5PLm0AZsCrnLgImtcIP9hTTdz3sYFUjUyMht/z5vByR7CJbtxG3BD0Nw/3ZQhCQ thNbk9Qv+ZRHJ1pxjxM2t0OvnOdJKH3pxv95pPo25XQfqEOz/j2Q1fXDOR56lKa4FtbN 2LoowrmXxQolt/KQ5ReiI67P1bspw/01cFqELKdyrVeXJMVZ5a7oI2gUiNcCiyiiUpVV OS/Q== X-Gm-Message-State: AKwxyteFfHmnIS4dxYuUtziSayMczNmFUJZ9xnM8k0mQm3xHwHqrRDlk YLDoUPo4AKFcP5w0jGzQd1UpAw== X-Google-Smtp-Source: AH8x2243slawRRQDtHxtMeZ80D31vTHj6JF/94pk0lPtmflBx7YgAqQcb4koB+NdUgGXuosSFWWVVw== X-Received: by 10.176.10.9 with SMTP id q9mr9738043uah.103.1517117187900; Sat, 27 Jan 2018 21:26:27 -0800 (PST) X-BeenThere: std-proposals@isocpp.org Original-Received: by 10.31.67.196 with SMTP id q187ls6795585vka.21.gmail; Sat, 27 Jan 2018 21:26:26 -0800 (PST) X-Received: by 10.31.169.23 with SMTP id s23mr2048752vke.1.1517117186181; Sat, 27 Jan 2018 21:26:26 -0800 (PST) X-Original-Sender: BastienPenava@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:36755 Archived-At: ------=_Part_6987_1551178034.1517117185589 Content-Type: multipart/alternative; boundary="----=_Part_6988_1837822128.1517117185590" ------=_Part_6988_1837822128.1517117185590 Content-Type: text/plain; charset="UTF-8" Hi, So I was toying with the idea of named tuple when I remembered D's name resolution operator and check if it was possible to implement in C++. For those not familiar to the idea it's manly an operator that receives the unknown member access as a template non-type parameter instead of causing an error. To my surprise it is an is quite cheap to implement (50 lines for GCC) and could quite powerful (particularly if combined with reflection). To avoid creating a new operator i'm using the operator* with a template non-type reference parameter as the 'new' operator :* template auto operator*();* One of the motivations to use this operator is because it allows out-of-class definitions. You can try and check some exemple here if you wish : http://dispatch.gcc-future.tk/# The reason why I bring this up is that I believe that It could solve a bunch of demands that have been unsuccessful in the past (generally due to their coast being to great compared to the supposed benefit. ie: new operator, keyword, syntax, etc...). Mainly the dot operator, properties, out of class method definition and UCS. Here are a few examples. logging class with reflection: template struct logger { T _value; template requires reflexpr(T).has_member_of_method(Str) //not actual syntax for the reflection proposal. decltype(auto) operator*() { if constexpr (reflexpr(T).is_method(Str)) return [&_value](Args&&... args) -> decltype(auto) { scope_exit _out = []{ std::cout << "[out " << &_value << "]: " << Str << std::endl; }; std::cout << "[in " << &_value << "]: " << Str; return reflexpr(_value).get_methods_by_name().call(std:: forward(args)...); }; else { std::cout << "[using " << &_value << "]: " << Str << std::endl; return reflexpr(_value).get_member_by_name(); } } }; properties, simulate inheritance, multiple names: struct A { std::string x; template requires (is_one_of) size_t operator*() { return x.size(); } }; A tmp; //tmp.size, tmp.length,tmp.Size and tmpl.Length usable. standard layout, pod: struct complex { double alpha; double length; }; template requires (is_one_of) auto operator*(complex self) { if constexpr (is_same_ref_v) return std::cos(self.alpha) * self.length; else return std::sin(self.alpha) * self.length; } //complex remains standard layout/pod but has fake members 'real' and 'img' Out of class method definition / templated this / UCS: template requires (is_same_ref_v) void operator*(T&& x) { return [&x]{ std::cout << x << std::endl; }; } std::string x: x.println(); -- 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. To view this discussion on the web visit https://groups.google.com/a/isocpp.org/d/msgid/std-proposals/11f9c7ff-aa76-46a5-94b2-0692171ab0ff%40isocpp.org. ------=_Part_6988_1837822128.1517117185590 Content-Type: text/html; charset="UTF-8" Content-Transfer-Encoding: quoted-printable
Hi,

So I was toying with the idea of na= med tuple when I remembered D's name resolution operator=C2=A0and check i= f it was possible to implement in C++.
For those not familiar to = the idea it's manly an operator that receives the unknown member access= as a template non-type parameter instead of causing an error.
To= my surprise it is an is quite cheap to implement (50 lines for GCC) and co= uld quite powerful (particularly if combined with reflection).
To= avoid creating a new operator i'm using the operator* with a template = non-type reference parameter as the 'new' operator : template<= ;auto& memberName> auto operator*();
One of the motiva= tions to use this operator is because it allows out-of-class definitions.
You can try and check some exemple here if you wish :=C2=A0http://dispatch.gcc-future.tk/#

The reason why I bring this up is that I believe= that It could solve a bunch of demands that have been unsuccessful in the = past (generally due to their coast being to great compared to the supposed = benefit. ie: new operator, keyword, syntax, etc...).
Mainly the d= ot operator, properties, out of class method definition and UCS.
=
Here are a few examples.

logging cl= ass with reflection:
template<class T>
struct logger
{
=C2=A0 =C2=A0 T _value;

=C2=A0 =C2=A0 template<auto &Str>
=C2=A0 =C2=A0 requires reflexpr(T).has_member_of_method(Str) = //not actual syntax for the reflection proposal.
=C2=A0 =C2=A0 decltype(auto) operator*()
=C2=A0 =C2=A0 {
=C2=A0 =C2=A0 =C2=A0 if constexpr (reflexpr<= span style=3D"color: #660;" class=3D"styled-by-prettify">(T).is_method(Str))
=C2=A0 =C2=A0 =C2=A0 =C2=A0 return [&_value]<class...= Args>(Args&&... args) -> decltype(auto= )
=C2=A0 =C2=A0 = =C2=A0 =C2=A0 =C2=A0 {
=C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 scope_exit _out =3D []{ std::cout << "[out " &= lt;< &= _value << "]: " << Str << std::e= ndl; };
=C2=A0 =C2=A0 =C2=A0 =C2=A0 = =C2=A0 =C2=A0 std::c= out <&l= t; = "[in "<= /span> << &_value << "]: " << Str;
= =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 return reflexpr(_value).get_methods_by_name<= ;St= r>().call<= span style=3D"color: #660;" class=3D"styled-by-prettify">(std::forward<Args>(args)...);
=C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 };
=C2=A0 =C2=A0 =C2=A0 else
=C2=A0 =C2=A0 =C2=A0 {
=C2=A0 =C2=A0 =C2=A0 =C2=A0 std<= /span>::cout << "[using " << &_value << "]: " << Str << std::endl;
=C2=A0 =C2=A0 =C2=A0 =C2=A0 return reflexpr(_value).get_member_by_name<Str>= ();=
=C2=A0 =C2=A0 =C2=A0 }
=C2=A0 =C2=A0 }
}= ;

properties, simulate inherit= ance, multiple names:
struct A
{
=C2=A0 =C2=A0std::string= x;=

=C2=A0 = =C2=A0 tem= plate<<= /span>auto= &Str>
=C2=A0 =C2=A0 requires (is_one_of<Str, "size", "= ;length", "Size"= ;,<= span style=3D"color: #000;" class=3D"styled-by-prettify"> "Length">)
=C2=A0 =C2=A0 size_t= operator<= /span>*()<= span style=3D"color: #000;" class=3D"styled-by-prettify"> { return x.size(); }
};

A tmp;
//tmp.size, tmp.length,tmp.Size and tmpl.Length = usable.

standard layout, pod:<= /div>
struct<= /span> complex{<= span style=3D"color: #000;" class=3D"styled-by-prettify">
=C2=A0 =C2=A0<= /span>double alpha;
=C2=A0 =C2=A0double length;
};

template<auto &St= r>
requires (is_one_of<Str, "real", "img">)
auto= operator<= /span>*(complex self) {
=C2=A0 =C2=A0if constexpr (is_same_= ref_v<<= /span>Str<= span style=3D"color: #660;" class=3D"styled-by-prettify">, "real">) return std::cos(= self.alpha) * self.length;
=C2= =A0 =C2=A0= else return std::sin(self.alpha) * self.length;
}

//complex remains standard layout/pod but has fake members 'real'= and 'img'

Out of clas= s method definition / templated this / UCS:
template<auto &Str, class T>
requires (is_same_ref_v<Str, "println">)
void = operator*(T&& x)
{
=C2=A0 =C2=A0return [&x]{= std::cout << x << std::endl; = };
}

std::string x:
x.println();


--
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.
To view this discussion on the web visit https://groups.google.= com/a/isocpp.org/d/msgid/std-proposals/11f9c7ff-aa76-46a5-94b2-0692171ab0ff= %40isocpp.org.
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