220 33785 article Path: news.gmane.org!.POSTED!not-for-mail From: Nicol Bolas Newsgroups: gmane.comp.lang.c++.isocpp.proposals Subject: Re: properties? Date: Thu, 10 Aug 2017 07:18:13 -0700 (PDT) Lines: 123 Approved: news@gmane.org Message-ID: References: <6ed2bd55-5538-418f-8f1a-263a9958babd@isocpp.org> <9979b017-fc21-445f-a1d1-0f55f8e7bf3d@isocpp.org> <3784a92f-9045-e0e8-df9f-51a68f66ac99@gmail.com> Reply-To: std-proposals@isocpp.org NNTP-Posting-Host: blaine.gmane.org Mime-Version: 1.0 Content-Type: multipart/mixed; boundary="----=_Part_940_901225916.1502374693617" X-Trace: blaine.gmane.org 1502374705 16947 195.159.176.226 (10 Aug 2017 14:18:25 GMT) X-Complaints-To: usenet@blaine.gmane.org NNTP-Posting-Date: Thu, 10 Aug 2017 14:18:25 +0000 (UTC) Cc: ville.voutilainen@gmail.com, bop@gmb.dk To: ISO C++ Standard - Future Proposals Original-X-From: std-proposals+bncBCEKFTV6ZUMBBJWWWHGAKGQE3K7X6BQ@isocpp.org Thu Aug 10 16:18:20 2017 Return-path: Envelope-to: gclcip-std-proposals@m.gmane.org Original-Received: from mail-ua0-f199.google.com ([209.85.217.199]) by blaine.gmane.org with esmtp (Exim 4.84_2) (envelope-from ) id 1dfoHp-0003ci-IF for gclcip-std-proposals@m.gmane.org; Thu, 10 Aug 2017 16:18:09 +0200 Original-Received: by mail-ua0-f199.google.com with SMTP id f9sf3067982uaf.1 for ; Thu, 10 Aug 2017 07:18:15 -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=YQJEY6Z+1muxQwRvr/jaT64LYHhR4tJ72Xc6khTcKwg=; b=Xe7z+Z9N0OVNXaMhC7Z+pBUC0JPTmIc1C+I7i349EiOj4PNfPQmQGBWO9sAH2YAGt+ JSOzY3oUmh1jiZ3QqdZrvS27TbApvRrWQvUZIYkdVAjW0RP46vhkkvWl1Kb2Ux6UiYdd rTxpeOczdLtj1aII+af4Z9s4aNNQUj5YXbz6j59ignNBiElHJwBrd9YuVitYDiAULUAd UGR0qQakmRASyp34XBK6t0zORaXQkVBm88Z262/xNKXGneTN5L+TZo2zmoUmdFWmHT0U FrTpC48ZvZ3uTzALmOQBu/hpDwn6lf2MHG5miCYzmod4gz3aQKKNgEQodJfIy4zSGNSV PxfA== 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=YQJEY6Z+1muxQwRvr/jaT64LYHhR4tJ72Xc6khTcKwg=; b=HRyZk/HiVf8a+Oq9AQk1V8kO0r0NmI9zE+saxJOilTR6a1nS6FUYjqp5FwSCY5Uf11 NJvUQqt1lPowFO4iw4qUMbj94xhAA9WEHyxnWMNQEA5412POsV97ENhBNCs0nPxl4Yf/ uDFlw0mbdzXEKiFtKOzSAISyCxvpy3AqRe3ioJdN8ezLjS+CWtkcjGMeH38KyzOs06MP tgabb6neTNwJMLPNVNz5XHhaePEYuVuo4oklMAdXtDY7Exa45WG+sUOFQ+hcYBan2AD5 CqMz6SBxxV9LWjSq71xKIQ9szaxusiY50dS1ETjw1apBcVUGQHcVeOZI2JWfw0R3BgnU Mypw== 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=YQJEY6Z+1muxQwRvr/jaT64LYHhR4tJ72Xc6khTcKwg=; b=hIelFFf1Vkyas7jaGnWH2WhLwozTVDf1q7P+hbdIvFXRHNqqPFKQacisADyFs3cGh0 4Vrun1QPyOKGLonGVBu+OHUdTstUCYBIQoxreY9WREXgjrC9JYGb23NMYLD6zGCffjOC z6zVeOTZM5+fn4JNwoSkkrhpIhpMCxYmTmosr3KMWi4ViBmyP/AjhKWzdxI0tdPbOwPd Q5koy07bhucZi3win3m+909l8BuAmW/iGdmZXUkyalsXMY3Jzv2Q+KYvQokjh4qDRYYw vbAI1RT+chTjg6KedKOy9qFaUXvL82Uet7ZjpzDZs+vhBguzQ7tndn6bSgWbQzD3mKW2 jyiw== X-Gm-Message-State: AHYfb5izZOTf2qM08rQP4T2JeKyzLuUySF7lfRO940A66pp8nkNun/LQ ujba21Qg66ipQCZD X-Received: by 10.31.168.14 with SMTP id r14mr6836084vke.21.1502374695402; Thu, 10 Aug 2017 07:18:15 -0700 (PDT) X-BeenThere: std-proposals@isocpp.org Original-Received: by 10.36.197.194 with SMTP id f185ls10899760itg.4.canary-gmail; Thu, 10 Aug 2017 07:18:14 -0700 (PDT) X-Received: by 10.31.169.17 with SMTP id s17mr62047vke.11.1502374694083; Thu, 10 Aug 2017 07:18:14 -0700 (PDT) In-Reply-To: <3784a92f-9045-e0e8-df9f-51a68f66ac99@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:33785 Archived-At: ------=_Part_940_901225916.1502374693617 Content-Type: multipart/alternative; boundary="----=_Part_941_1951000555.1502374693617" ------=_Part_941_1951000555.1502374693617 Content-Type: text/plain; charset="UTF-8" On Thursday, August 10, 2017 at 10:05:17 AM UTC-4, Matthew Woehlke wrote: > > On 2017-08-10 02:35, Ville Voutilainen wrote: > > On 10 August 2017 at 09:19, Nicol Bolas > > wrote: > >> On Wednesday, August 9, 2017 at 10:12:36 PM UTC-4, Bo Persson wrote: > >>> On 2017-08-09 19:32, Evan Teran wrote: > >>>> std::cout < >>> > >>> This could already work if you just add () to each use of data. :-) > >> > >> Would it? Would this: > >> > >> some_function(value.data()); > >> > >> Would that allow `some_function` to set `data`'s value? To do that, you > >> would need to make `data()` return a proxy object, which can be > converted > >> into the appropriate type, but can also be assigned to the appropriate > type > >> and otherwise treated exactly like a reference to the other type. > >> > >> That's hardly "just" adding something. > > > > Gee, data() could just return a reference. > > ...which is only possible if it is okay for the user to directly assign > to the underlying data member. If something non-trivial needs to happen > when the property is assigned, then no, you'd need to return a proxy > object. (And, alas, some_function would need to be a template.) Not to mention that it assumes that there is actually an object behind `data()` that could be returned as a reference. Many properties are phantasmal; the actual data is not stored in the type it appears as. Indeed, one could say that the whole point of properties as a feature are that they *can be* phantasmal in such a way, without the user being aware of their nature. -- 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/ab000071-6881-487f-b507-bcd6d656bb52%40isocpp.org. ------=_Part_941_1951000555.1502374693617 Content-Type: text/html; charset="UTF-8" Content-Transfer-Encoding: quoted-printable
On Thursday, August 10, 2017 at 10:05:17 AM UTC-4, Matthew= Woehlke wrote:
On 2017-08-10 0= 2:35, Ville Voutilainen wrote:
> On 10 August 2017 at 09:19, Nicol Bolas <jmck...@gmail.com> w= rote:
>> On Wednesday, August 9, 2017 at 10:12:36 PM UTC-4, Bo Persson = wrote:
>>> On 2017-08-09 19:32, Evan Teran wrote:
>>>> =C2=A0 =C2=A0 =C2=A0std::cout <<value.data <&= lt;"\n"
>>>
>>> This could already work if you just add () to each use of = data. =C2=A0:-)
>>
>> Would it? Would this:
>>
>> some_function(value.data());
>>
>> Would that allow `some_function` to set `data`'s value? To= do that, you
>> would need to make `data()` return a proxy object, which can b= e converted
>> into the appropriate type, but can also be assigned to the app= ropriate type
>> and otherwise treated exactly like a reference to the other ty= pe.
>>
>> That's hardly "just" adding something.
>=20
> Gee, data() could just return a reference.

...which is only possible if it is okay for the user to directly assign
to the underlying data member. If something non-trivial needs to happen
when the property is assigned, then no, you'd need to return a prox= y
object. (And, alas, some_function would need to be a template.)

Not to mention that it assumes that there is actually an obj= ect behind `data()` that could be returned as a reference. Many properties = are phantasmal; the actual data is not stored in the type it appears as. In= deed, one could say that the whole point of properties as a feature are tha= t they can be phantasmal in such a way, without the user being aware= of their nature.

--
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