220 32293 <9edfd06a-7421-4ce0-80fd-83c436ad7b20@isocpp.org> article Path: news.gmane.org!.POSTED!not-for-mail From: Nicol Bolas Newsgroups: gmane.comp.lang.c++.isocpp.proposals Subject: Re: Re: Controlled Argument Evaluation Date: Wed, 3 May 2017 12:59:32 -0700 (PDT) Lines: 135 Approved: news@gmane.org Message-ID: <9edfd06a-7421-4ce0-80fd-83c436ad7b20@isocpp.org> References: <04e0ce66-76df-43e2-a10a-77b4db64ca25@isocpp.org> <362f82cb-2516-93a8-09bc-b0208c21e8aa@weka.io> Reply-To: std-proposals@isocpp.org NNTP-Posting-Host: blaine.gmane.org Mime-Version: 1.0 Content-Type: multipart/mixed; boundary="----=_Part_100_88992680.1493841572198" X-Trace: blaine.gmane.org 1493841580 15935 195.159.176.226 (3 May 2017 19:59:40 GMT) X-Complaints-To: usenet@blaine.gmane.org NNTP-Posting-Date: Wed, 3 May 2017 19:59:40 +0000 (UTC) To: ISO C++ Standard - Future Proposals Original-X-From: std-proposals+bncBCEKFTV6ZUMBBJHNVDEAKGQEUKFSHII@isocpp.org Wed May 03 21:59:34 2017 Return-path: Envelope-to: gclcip-std-proposals@m.gmane.org Original-Received: from mail-pf0-f198.google.com ([209.85.192.198]) by blaine.gmane.org with esmtp (Exim 4.84_2) (envelope-from ) id 1d60Qq-0003rS-De for gclcip-std-proposals@m.gmane.org; Wed, 03 May 2017 21:59:28 +0200 Original-Received: by mail-pf0-f198.google.com with SMTP id j16sf54018pfk.4 for ; Wed, 03 May 2017 12:59:34 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=isocpp-org.20150623.gappssmtp.com; s=20150623; h=date:from:to: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=qHNMXI9rOOuzGDniultt6LUZv9bWEgSoVBSDS0lXroU=; b=alECxJAbj/DjvMgug3WawowiHVnQ0mu0xdbWgIs74w5RzX8ombN+/wyHA2ZJQowGa/ NwmeUL+BVVbIhV4BMKcrOfhlawcwyiufete6Et9aq6MZsoIWQuFIDAe0r5Fkh5lAV+PE aZTIt/hjlsHMwMYoB6/jZ6ESpIYJzYILQvVozKDTvyYIisd6LVY+Urn8zU38mn4Yk0Oa 5ypKjpXgQo6/uIlTLu+vRLwxadKnBvocUVLQ2oClwAOZhdc14YNo4/v/EiztoFSes4He XnIQVwo26kyVpqvH6TsGYICJBOhQoJdGb0+DlYeEDzkim10vjaG2jHTe4SyBIehW0tUf UbZw== DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gmail.com; s=20161025; h=date:from:to: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=qHNMXI9rOOuzGDniultt6LUZv9bWEgSoVBSDS0lXroU=; b=WZG76Wb9tzgSIkN5eJr7mUdxvU+0Nh1q7gP7hYr9ZQrzcbY5qxdFRFy3rftRpkqkBI 25m6BrZ19MCX6r7lH46mAX+u/Q77QWYVYn29B/nt9cIAGhk7uW3E1kuLsTis65l0LZ4m ZS/oPAS9SYeX5HyriLQIyofWhX3txtEUQggwJpi752+UmM/crGnl+tLhZOhWXJc7YSpO Nf++di7xbA2saK8HgXnqWpxtbglJIL2wJJLzRUdZs7iZ95cCRNAXoDkx50eliNbQdbeS TBLkPbsUlfepVq6WBZONkbDnHtbHqZBUeEp6oCykYE/sT40TAzzsNcMaqCZM46UfYVzZ M9yw== 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: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=qHNMXI9rOOuzGDniultt6LUZv9bWEgSoVBSDS0lXroU=; b=TjZ3racouFSd+3pCaVoTg9tEukKq9frJKkwS8SNcRSP+CAxxMwii7/IlrW2JJ3uNBs brQJbFsaPCcbiyabTRfxO7TLZbr/KuZKcXmTKVUTaRcli2jHi3wvFE3Of6zeTOlMiMus 17U/LwQmNcNgiJNQpDSAbQSvR/p3Z+6BQ+dSMCMxgQIEPK0dW5Kgv0DP/lr9vmsZrLWo Tny33gj+UucP1h4CNJOKg+9KalwX+r5K7daIdE8W2Ec7z2jX9eU+xdwQfvUp7MW2suwL CdopwVlQiuV8QN+cfM3EhdSeMo6LNZASrIjGPZ6eAhtSLEhQiLYEYNM+EAffYA3pyaYW WISg== X-Gm-Message-State: AN3rC/7XpKRR4M0kh5hgXoLlP77qdhSPjyqJ7/xKoIZXlS6/Ym5f24bJ gjawIrVgKalc+Q== X-Received: by 10.99.135.198 with SMTP id i189mr7863893pge.83.1493841573591; Wed, 03 May 2017 12:59:33 -0700 (PDT) X-BeenThere: std-proposals@isocpp.org Original-Received: by 10.157.6.201 with SMTP id 67ls4797473otx.29.gmail; Wed, 03 May 2017 12:59:32 -0700 (PDT) X-Received: by 10.157.55.133 with SMTP id x5mr320579otb.10.1493841572654; Wed, 03 May 2017 12:59:32 -0700 (PDT) In-Reply-To: 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:32293 Archived-At: ------=_Part_100_88992680.1493841572198 Content-Type: multipart/alternative; boundary="----=_Part_101_498146799.1493841572199" ------=_Part_101_498146799.1493841572199 Content-Type: text/plain; charset=UTF-8 On Wednesday, May 3, 2017 at 3:05:32 PM UTC-4, Hyman Rosen wrote: > > On Wed, May 3, 2017 at 2:34 PM, Shachar Shemesh > wrote: > >> On 27/04/17 22:29, Hyman Rosen wrote: >> >> On Thu, Apr 27, 2017 at 3:26 PM, Dan Raviv > > wrote: >> >>> Why not just use some sort of lazy evaluation class and wrap the >>> parameters you pass in with it? >>> >> >> Because a proposal like this should make it possible for user-written >> *operator&&*, *operator||*, and *operator,* to behave like their >> built-in counterparts. >> >> Can someone please explain to me why that is desirable? Preferrably with >> an example. >> > > The C++ language allows user-defined *operator&&*, *operator||*, and > *operator,* for classes. The built-in language versions are > short-circuiting for && and || and guarantee left-to-right evaluation for > comma. > The latter part of that is no longer true in C++17. The order of evaluation for comma is guaranteed regardless of whether it's calling `operator,` or using the built-in one: > Overloaded operators obey the rules for syntax and evaluation order specified in Clause 8, but the requirements of operand type and value category are replaced by the rules for function call. -- 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/9edfd06a-7421-4ce0-80fd-83c436ad7b20%40isocpp.org. ------=_Part_101_498146799.1493841572199 Content-Type: text/html; charset=UTF-8 Content-Transfer-Encoding: quoted-printable


On Wednesday, May 3, 2017 at 3:05:32 PM UTC-4, Hym= an Rosen wrote:
On Wed, May 3, 2017 at 2:34 PM, Shachar S= hemesh <sha...@weka.io> wrote:
=20 =20 =20 =20
On 27/04/17 22:29, Hyman Rosen wrote:
On Thu, Apr 27, 2017 at 3:26 PM, Dan Raviv <dan....@gmail.com> wrote:
Why not just use some sort of lazy evaluation class and wrap the parameters you pass in with it?

Because a proposal like this should make it possible for user-written opera= tor&&, operator||, and operator, to behave like their built-in counterparts.
Can someone please explain to me why that is desirable? Preferrably with an example.

The C++ language allows use= r-defined operator&&,=C2=A0operator||, and= =C2=A0operator, for classes.=C2=A0 The built-in language= versions are short-circuiting for && and || and guarantee left-to-= right evaluation for comma.

The latter part of that is no longer true in C++17. The order of evalu= ation for comma is guaranteed regardless of whether it's calling `opera= tor,` or using the built-in one:

> Overloaded operators obey the = rules for syntax and evaluation order specified in Clause 8, but the requir= ements of operand type and value category are replaced by the rules for fun= ction call.

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