220 33743 article Path: news.gmane.org!.POSTED!not-for-mail From: Nicol Bolas Newsgroups: gmane.comp.lang.c++.isocpp.proposals Subject: Re: properties? Date: Wed, 9 Aug 2017 13:20:11 -0700 (PDT) Lines: 109 Approved: news@gmane.org Message-ID: References: <6ed2bd55-5538-418f-8f1a-263a9958babd@isocpp.org> <10557c71-2b0f-6675-305e-1267eeda1ed6@gmail.com> Reply-To: std-proposals@isocpp.org NNTP-Posting-Host: blaine.gmane.org Mime-Version: 1.0 Content-Type: multipart/mixed; boundary="----=_Part_155_2040492007.1502310011167" X-Trace: blaine.gmane.org 1502310012 368 195.159.176.226 (9 Aug 2017 20:20:12 GMT) X-Complaints-To: usenet@blaine.gmane.org NNTP-Posting-Date: Wed, 9 Aug 2017 20:20:12 +0000 (UTC) Cc: evan.teran@gmail.com To: ISO C++ Standard - Future Proposals Original-X-From: std-proposals+bncBCEKFTV6ZUMBB664VXGAKGQEW4RKUJY@isocpp.org Wed Aug 09 22:20:07 2017 Return-path: Envelope-to: gclcip-std-proposals@m.gmane.org Original-Received: from mail-vk0-f71.google.com ([209.85.213.71]) by blaine.gmane.org with esmtp (Exim 4.84_2) (envelope-from ) id 1dfXSZ-0008Ei-7C for gclcip-std-proposals@m.gmane.org; Wed, 09 Aug 2017 22:20:07 +0200 Original-Received: by mail-vk0-f71.google.com with SMTP id s197sf28025787vkb.15 for ; Wed, 09 Aug 2017 13:20:13 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=isocpp-org.20150623.gappssmtp.com; s=20150623; h=date:from:to:cc:message-id:in-reply-to:references:subject :mime-version:x-original-sender:reply-to:precedence:mailing-list :list-id:list-post:list-help:list-archive:list-subscribe :list-unsubscribe; bh=E1s5+K0zgtv128qElPW2K4evTPZHnlze7WFQLn3kCCA=; b=giwaxt296bpfjZxbN+dfZrTq9Nsm836uHqrhibOi1E7iUnTnaHVBUWWQA48Oy/k2Sv rZUl/CrFOaKJ9p0+OV8zXjFDoIlGhUT3zx0A3xFkodW0v4BPYdH/E0tRThL49daD0i5X JvLb0NbW2RJ881+uhLELB7l7W4podF3d6SRPYyNHsCCrBI3M+DRNxA0QnxRXEJ20SShF 5eFP/q8x+ZdXlqIezFk2NAZbYCegyqX+hEH0i9Ylr8ONej6s/ECz/IvH4rrRWNAegaSu bhkoFAwDGN+SJR+U5KWEtZ+e6wcH3Ml/n9y2L4hXMxaRiHkGZ1mnFaUjjlldlLBGOE2Q oHMQ== DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gmail.com; s=20161025; h=date:from:to:cc:message-id:in-reply-to:references:subject :mime-version:x-original-sender:reply-to:precedence:mailing-list :list-id:list-post:list-help:list-archive:list-subscribe :list-unsubscribe; bh=E1s5+K0zgtv128qElPW2K4evTPZHnlze7WFQLn3kCCA=; b=NvPoqeMciHYNQICv384vHAXnugz1x/4HmFxDt7pZn9XZ93QeUir0cCo+v5fS2CftO3 nl/M4vzSm8yr+inlYG92XEN7TxTYTkobxvo1hNY7Kfl1ZbTR43pMEuEZXWd6QMzF9SEo sLOgEhZkQ3rRcWTCQa+wItlbxL2HEU28tgRvE6eZDRppPa18ox8XSddVNnD/QUL33+zg L2P+ZmHz4TQRlAKYAsoOIpZVrUF4R5l/rfImT7EePcr6bR9UZO5fvvggMhmLNk1SX2WZ L/niBwJySGwOrsVk7SahjOqwvHQOkrRcCSLOUo2UraglVdm1YB4xEqCtQYihq/iWuws+ ljIw== 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:cc:message-id:in-reply-to :references: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=E1s5+K0zgtv128qElPW2K4evTPZHnlze7WFQLn3kCCA=; b=Eqi3NhNq3Lx6a2ETRTqyYeIGGymLYRcVcDq5E1vLnWSt8yZBwox6VybdAqMANzotZd kX5IvoJUlCtWSqePzkJVbpeZARwIrhnlXSbEyJLbZYzQ5+CiEDDcfIpHza3mOZ9ApnHJ ZNgmZ0kXz0KJ7+3h32LJsmEkKJFnNmHJAl/JNHNga51haAmCJH5Qe8yafDZXt2E6r15d hLHBFgtFiCOApDGhs3vfUKkjg5w+il2vsXRlShG9JQRVz8sQ0OfFpRnnrDBHA9BSuMaE vhhw9OsaKpxXlWPSqw7oVEyaiotIk6UzTpOqsj8+NIenlr0gGlmL3nccJ2BTOaqw2pfO RTcw== X-Gm-Message-State: AHYfb5hz5ZLdbIQueoNPCnBDBIFWsBOxJS8vfiIgUO1cIZv13zbFRBWu fosnXUl/aS13AFl1 X-Received: by 10.176.76.4 with SMTP id l4mr5471269uaf.8.1502310012984; Wed, 09 Aug 2017 13:20:12 -0700 (PDT) X-BeenThere: std-proposals@isocpp.org Original-Received: by 10.36.81.65 with SMTP id s62ls6307084ita.9.canary-gmail; Wed, 09 Aug 2017 13:20:11 -0700 (PDT) X-Received: by 10.31.99.198 with SMTP id x189mr50805vkb.24.1502310011657; Wed, 09 Aug 2017 13:20:11 -0700 (PDT) In-Reply-To: <10557c71-2b0f-6675-305e-1267eeda1ed6@gmail.com> X-Original-Sender: jmckesson@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:33743 Archived-At: ------=_Part_155_2040492007.1502310011167 Content-Type: multipart/alternative; boundary="----=_Part_156_1543909948.1502310011167" ------=_Part_156_1543909948.1502310011167 Content-Type: text/plain; charset="UTF-8" On Wednesday, August 9, 2017 at 1:59:24 PM UTC-4, Matthew Woehlke wrote: > > On 2017-08-09 13:32, Evan Teran wrote: > > I never brought it up before because I assumed that it MUST have been > > discussed in the past... > > It has. To death. Properties are contentious. > > (Nicol and I came up with something maybe a year ago that seemed > plausible and had additional benefits, but I don't know if it ever got > written up...) > I poked around with the ideas for a while. The basic idea was to provide 3 independently-useful features that, when combined, would allow you to develop a zero-overhead, low-boilerplate library implementation of properties. Those features being stateless member subobjects (so that the property would just be a member), inner classes (so that the property could just be an inner class, which would have access to its owning subobject, no matter where it was), and language-support for CRTP-base class (so that you could write the implementation of the inner class outside of the inner class itself, and thus reuse boilerplate). My biggest stumbling block was the latter. I realized that I was basically creating "mixins," but though inheritance. The problem there is that the derived class is incomplete until the template instantiation of the base class, so the CRTP-base class can only access features of the derived class within functions. That made doing simple things like iterator traits impossible without some external class (like `iterator_traits`). So if I wanted to do mixins without a bunch of arbitrary limitations, they'd need to not just be some base class using template trickery, but a true, first-class feature that was separate from template instantiation. -- 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/cd0988be-8dc0-43be-96b1-94ec6f8e5e91%40isocpp.org. ------=_Part_156_1543909948.1502310011167 Content-Type: text/html; charset="UTF-8" Content-Transfer-Encoding: quoted-printable


On Wednesday, August 9, 2017 at 1:59:24 PM UTC-4, = Matthew Woehlke wrote:
On 2017-= 08-09 13:32, Evan Teran wrote:
> I never brought it up before because I assumed that it MUST have b= een=20
> discussed in the past...

It has. To death. Properties are contentious.

(Nicol and I came up with something maybe a year ago that seemed
plausible and had additional benefits, but I don't know if it ever = got
written up...)

I poked around with the ideas for a while. The ba= sic idea was to provide 3 independently-useful features that, when combined= , would allow you to develop a zero-overhead, low-boilerplate library imple= mentation of properties. Those features being stateless= member subobjects (so that the property would just be a member), inner= classes (so that the property could just be an inner class, which would ha= ve access to its owning subobject, no matter where it was), and language-su= pport for CRTP-base class (so that you could write the implementation of th= e inner class outside of the inner class itself, and thus reuse boilerplate= ).

My biggest stumbling block was the latter. I realized that I was = basically creating "mixins," but though inheritance. The problem = there is that the derived class is incomplete until the template instantiat= ion of the base class, so the CRTP-base class can only access features of t= he derived class within functions. That made doing simple things like itera= tor traits impossible without some external class (like `iterator_traits`).=

So if I wanted to do mixins without a bunch of arbitrary limitation= s, they'd need to not just be some base class using template trickery, = but a true, first-class feature that was separate from template instantiati= on.

--
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/cd0988be-8dc0-43be-96b1-94ec6f8e5e91= %40isocpp.org.
------=_Part_156_1543909948.1502310011167-- ------=_Part_155_2040492007.1502310011167-- .