220 27460 article Path: news.gmane.org!.POSTED!not-for-mail From: Tony V E Newsgroups: gmane.comp.lang.c++.isocpp.proposals Subject: Re: Proposal - non allocating std::function Date: Mon, 1 Aug 2016 12:55:35 -0400 Lines: 171 Approved: news@gmane.org Message-ID: References: <892618b7-19a9-4950-b552-ea5d5185362f@isocpp.org> Reply-To: std-proposals@isocpp.org NNTP-Posting-Host: blaine Mime-Version: 1.0 Content-Type: multipart/alternative; boundary=001a114b703a20706005390578c0 X-Trace: blaine.gmane.org 1470070543 8875 195.159.176.226 (1 Aug 2016 16:55:43 GMT) X-Complaints-To: usenet@blaine.gmane.org NNTP-Posting-Date: Mon, 1 Aug 2016 16:55:43 +0000 (UTC) To: Standard Proposals Original-X-From: std-proposals+bncBCUZ5QWKNQIIT7X5XQCRUBF4EHIT4@isocpp.org Mon Aug 01 18:55:39 2016 Return-path: Envelope-to: gclcip-std-proposals@m.gmane.org Original-Received: from mail-wm0-f69.google.com ([74.125.82.69]) by blaine.gmane.org with esmtp (Exim 4.84_2) (envelope-from ) id 1bUGV8-00023z-Mp for gclcip-std-proposals@m.gmane.org; Mon, 01 Aug 2016 18:55:38 +0200 Original-Received: by mail-wm0-f69.google.com with SMTP id l4sf86095725wml.0 for ; Mon, 01 Aug 2016 09:55:39 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=isocpp-org.20150623.gappssmtp.com; s=20150623; h=mime-version:in-reply-to:references:from:date:message-id:subject:to :x-original-sender:x-original-authentication-results:reply-to :precedence:mailing-list:list-id:x-spam-checked-in-group:list-post :list-help:list-archive:list-subscribe:list-unsubscribe; bh=He6kQjHJL7cUnhZ7zi7OvBMEhZzLa5T3eqiiJrC+EBU=; b=ygGcSIqN1jN1UaWnW2+XFa4T3S14XS1atCRnK/PFmHlr+Rkrtt77tyEeKu+Mxw+Xfg lW1STQeUpVHIwX1bYULfnQcE+3vxTtMZwpMyt6NDU6KvF/BniU7ce49c5dhNVs0v98zd ma93LOAQYFojUWg0pRLa+QnofGZXqdBMMNGYSU4NV6UhEZTHNxCIHHgmzfNDwF0dHAuZ HaFk5xJakZq47jjktbF9nWYEMdcrYeEM6X0OrodcOKaCC6WXfRScnRoD9HBqIJOOsA7Y 8HZTaImun5t5Lf7Xcb3P7aYzNkr5OzVD6lguonQGGwmfcPJYCvcrmjPcgaTII3bvKZM0 vm/Q== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20130820; h=x-gm-message-state:mime-version:in-reply-to:references:from:date :message-id:subject:to:x-original-sender :x-original-authentication-results:reply-to:precedence:mailing-list :list-id:x-spam-checked-in-group:list-post:list-help:list-archive :list-subscribe:list-unsubscribe; bh=He6kQjHJL7cUnhZ7zi7OvBMEhZzLa5T3eqiiJrC+EBU=; b=ZfBzGoK3ZKCZNWOX7wk8L/y24F8D0GVuGO4Nx6Kq9lRmYDS0GHbAKrWUupDK6fZ72t l4+U+iM8y7zJQsYLhKW4GS1NK2h5ISIwsvar2ZreHpTEms8xjgnU61qMV17NwM4MeSQd b5tUpGE9zr4BOH6V7yo0KG1Syo+y7tWOoZLVwbv5alt0Z8nYBO6GhvPZCC7kzcHdLElK i3QnT0UW/i9aKiKWB1C3eN6afzHm+AXn6RmI1AYz3kwMq4SdgG8aaL4xySMr204hrt7U ekD4mWez8lqF5MGqMXwDnU3PrNJhDY7YmyuLkBSGkRizc1NPZmHRVHsjAVYVrfY3VpZG ge1w== X-Gm-Message-State: AEkoouu7UbQ0XztIY7qe2AIc73+Wc2eDLMM1iAj4dQ4pB7SXiMk/PzvIM6iueIypvlxCPw== X-Received: by 10.28.27.8 with SMTP id b8mr2143893wmb.0.1470070538051; Mon, 01 Aug 2016 09:55:38 -0700 (PDT) X-BeenThere: std-proposals@isocpp.org Original-Received: by 10.28.137.4 with SMTP id l4ls1934361wmd.26.gmail; Mon, 01 Aug 2016 09:55:37 -0700 (PDT) X-Received: by 10.28.127.209 with SMTP id a200mr54860956wmd.99.1470070537058; Mon, 01 Aug 2016 09:55:37 -0700 (PDT) Original-Received: from mail-wm0-x232.google.com (mail-wm0-x232.google.com. [2a00:1450:400c:c09::232]) by mx.google.com with ESMTPS id bf8si32315163wjb.121.2016.08.01.09.55.37 for (version=TLS1_2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128/128); Mon, 01 Aug 2016 09:55:37 -0700 (PDT) Received-SPF: pass (google.com: domain of tvaneerd@gmail.com designates 2a00:1450:400c:c09::232 as permitted sender) client-ip=2a00:1450:400c:c09::232; Original-Received: by mail-wm0-x232.google.com with SMTP id i5so253472814wmg.0 for ; Mon, 01 Aug 2016 09:55:37 -0700 (PDT) X-Received: by 10.28.61.11 with SMTP id k11mr58762500wma.34.1470070536563; Mon, 01 Aug 2016 09:55:36 -0700 (PDT) Original-Received: by 10.28.131.143 with HTTP; Mon, 1 Aug 2016 09:55:35 -0700 (PDT) In-Reply-To: <892618b7-19a9-4950-b552-ea5d5185362f@isocpp.org> X-Original-Sender: tvaneerd@gmail.com X-Original-Authentication-Results: mx.google.com; dkim=pass header.i=@gmail.com; spf=pass (google.com: domain of tvaneerd@gmail.com designates 2a00:1450:400c:c09::232 as permitted sender) smtp.mailfrom=tvaneerd@gmail.com; dmarc=pass (p=NONE dis=NONE) header.from=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:27460 Archived-At: --001a114b703a20706005390578c0 Content-Type: text/plain; charset=UTF-8 On Sun, Jul 31, 2016 at 9:53 AM, Nicol Bolas wrote: > > > On Friday, July 15, 2016 at 3:13:58 AM UTC-4, Nevin ":-)" Liber wrote: >> >> On 14 July 2016 at 23:30, Nicol Bolas wrote: >> >>> The use case of "someone used `std::function` in an interface, but I use >>> `std::inplace_function` internally, and I need to talk to their code." >>> Right now, `std::function` is how lots of C++ code takes callbacks, and for >>> good reason. But if I've wrapped some function in an `inplace_function`, I >>> still need to be able to talk to them. >>> >> >> Maybe std::function is the wrong vocabulary type for interfaces, just >> like std::string is the wrong vocabulary type for interfaces, hence we will >> have std::string_view. Having something like llvm::function_ref that >> Richard Smith described earlier might be a better fit (and LEWG might ask >> Carl to add such a beast to his proposal). >> > > That's a really good analogy. I think the principle concern for the user > is this. `string_view` is a great interface type because you can use it to > construct pretty much any kind of string you like. It isn't limited to just > `std::string` construction. > I don't think that's why string_view is great. Rather, string_view is great because you probably don't need to create anything at all. You probably just need to *use* the characters, not keep them. ie a file_open(string_view) could (in theory at least) just use the characters in the string_view to open the file, it doesn't need to create a string of any kind to keep around. (unfortunately, in real life the OS probably needs a null-terminated string). > Would a hypothetical `function_view` have an interface that could be used > to construct any kind of function wrapper? That is, how could it expose the > actual type of the callable in such a way that someone could copy it out? > > Same with function vs function_ref. In most uses, you want to *call* the function, not keep it or a copy of it. Like sort(container, my_less). You want to call my_less, not keep it for later. Tony > Though we could probably get away with just allowing it to be converted to > a `function`. Or rather more specifically, allowing `function` to be > constructed from a `function_view`. > > -- > 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/892618b7-19a9-4950-b552-ea5d5185362f%40isocpp.org > > . > -- Be seeing you, Tony -- 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/CAOHCbivQ9cj%3DiMu9g1_AZha6Z27U%3DmDv%2BkdKxj%3DQqSw2Sp3zFw%40mail.gmail.com. --001a114b703a20706005390578c0 Content-Type: text/html; charset=UTF-8 Content-Transfer-Encoding: quoted-printable


On Sun, Jul 31, 2016 at 9:53 AM, Nicol Bolas <jmckesson@gmail.com> wrote:

=
On Friday, July 15, 2016 at 3:13:58 AM UTC-4, Nevin ":-)" Lib= er wrote:
On 14 July 2016 at 23:30, Nicol Bolas <<= a rel=3D"nofollow">jmck...@gmail.com> wrote:
The use case of "som= eone used `std::function` in an interface, but I use `std::inplace_function= ` internally, and I need to talk to their code." Right now, `std::func= tion` is how lots of C++ code takes callbacks, and for good reason. But if = I've wrapped some function in an `inplace_function`, I still need to be= able to talk to them.

Maybe std::function = is the wrong vocabulary type for interfaces, just like std::string is the w= rong vocabulary type for interfaces, hence we will have std::string_view.= =C2=A0 Having something like llvm::function_ref that Richard Smith describe= d earlier might be a better fit (and LEWG might ask Carl to add such a beas= t to his proposal).

That's = a really good analogy. I think the principle concern for the user is this. = `string_view` is a great interface type because you can use it to construct= pretty much any kind of string you like. It isn't limited to just `std= ::string` construction.

I don&= #39;t think that's why string_view is great.=C2=A0 Rather, string_view = is great because you probably don't need to create anything at all.=C2= =A0 You probably just need to *use* the characters, not keep them.=C2=A0 ie= a file_open(string_view) could (in theory at least) just use the character= s in the string_view to open the file, it doesn't need to create a stri= ng of any kind to keep around. (unfortunately, in real life the OS probably= needs a null-terminated string).
=C2=A0
Would a hypothetical `function_view` have an= interface that could be used to construct any kind of function wrapper? Th= at is, how could it expose the actual type of the callable in such a way th= at someone could copy it out?


Same with function vs function_ref.=C2=A0 In most uses, you want to = *call* the function, not keep it or a copy of it.=C2=A0 Like sort(container= , my_less).=C2=A0 You want to call my_less, not keep it for later.

<= /div>
Tony
=C2=A0
Though we could probably get away with just allowing= it to be converted to a `function`. Or rather more specifically, allowing = `function` to be constructed from a `function_view`.

--
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-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/892618b7-19a9-= 4950-b552-ea5d5185362f%40isocpp.org.



--
Be seeing = you,
Tony

--
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To view this discussion on the web visit https://groups.google.com/a/isocpp.org/d/msgid/std-proposals/CAOHCbivQ= 9cj%3DiMu9g1_AZha6Z27U%3DmDv%2BkdKxj%3DQqSw2Sp3zFw%40mail.gmail.com. --001a114b703a20706005390578c0-- .