220 14040 article Path: news.gmane.org!not-for-mail From: chris.kohlhoff@gmail.com Newsgroups: gmane.comp.lang.c++.isocpp.proposals Subject: Re: Re: Comment on N4244 Date: Sun, 19 Oct 2014 13:50:01 -0700 (PDT) Lines: 139 Approved: news@gmane.org Message-ID: References: <0632b234-2e7b-489f-a640-aa927648eaf7@isocpp.org> <02d9673d-3dd3-4fec-aa7a-b925b73f9893@isocpp.org> <6d5e0622-29bb-4196-ad7b-9c6b5f08f8cb@isocpp.org> <75c80e2f-e1a1-4e5f-8ae3-10ba25baad64@isocpp.org> <15c7ed1d-55c5-4329-9ada-605ee4c27080@isocpp.org> Reply-To: std-proposals@isocpp.org NNTP-Posting-Host: plane.gmane.org Mime-Version: 1.0 Content-Type: multipart/alternative; boundary="----=_Part_403_1565842355.1413751801166" X-Trace: ger.gmane.org 1413751813 28252 80.91.229.3 (19 Oct 2014 20:50:13 GMT) X-Complaints-To: usenet@ger.gmane.org NNTP-Posting-Date: Sun, 19 Oct 2014 20:50:13 +0000 (UTC) To: std-proposals@isocpp.org Original-X-From: std-proposals+bncBCS7VEH374ORB6WHSCRAKGQEF65VXKI@isocpp.org Sun Oct 19 22:50:04 2014 Return-path: Envelope-to: gclcip-std-proposals@m.gmane.org Original-Received: from mail-ob0-f199.google.com ([209.85.214.199]) by plane.gmane.org with esmtp (Exim 4.69) (envelope-from ) id 1XfxQS-00015B-Eq for gclcip-std-proposals@m.gmane.org; Sun, 19 Oct 2014 22:50:04 +0200 Original-Received: by mail-ob0-f199.google.com with SMTP id va2sf21868281obc.2 for ; Sun, 19 Oct 2014 13:50:03 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gmail.com; s=20120113; h=date:from:to: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 :content-type; bh=LcdwRfN40pQkPGvWw1JpiNxgaPrHMto9VXrYp9Gik28=; b=AyN1B5XhxedO74ERP2lUENqSIm9Os7HibunZGc5j9awJ6X7I3Qx9eQ6K2JP+RlDIUs KDtRJ8BpjLySem2PYgUCVXmNV7nxH5GxFup4FnOtdarWV4zWjqt7AmN/9UCib/X5xRqx XcOzhe9xIy8fsdGOU8fGgWdGSFfmFnIdCOaEIPVSZNHpT5CC7qnn7ZKoNCA+POX9kqAR CuRseDCu1pkndzX5RWGpRKJHBhewX0DctzAh5FPcCsXRNXwGfXGUyM+AwInQaH9D9HZz 6C4R6m6iEZuM8VPKAP8Ab5zGRffo1W9Gxe8yIvjWDCaRCaz/yUW0eK+f5EumIMjTbHsh S6sQ== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20130820; 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:list-post:list-help:list-archive :list-subscribe:list-unsubscribe:content-type; bh=LcdwRfN40pQkPGvWw1JpiNxgaPrHMto9VXrYp9Gik28=; b=gomksuD3KLqmPyjvMgYSH+ghGIm5cZzseWJqSjaxZO8ZA1Dv8HYxkZd5FP/UlyEXmb 3bJ2293sxztPznds5cnBMlkgnyhP4Xc9pJ9d4Gsl+Hczbt8mx0c/hHyPoGkTWj4jii7T gIFvrQ6voQcMuMbiVKWqPzIWeRiQHfUaX3dgomUl9pd8dTcd7eRpNPBbA0aM7eT7ioES iWT7IC3jMJzug8kLwADgliK7aOmUuG3F4ZHux7+1SvoXpxZM+F6UjWptfeAb+wMc2+y2 ESdg8+CeT26Xjkz4u44qe2GgghYYvFr/9PCQxw98/aAgalrRnI9NanphwvEuY7HlyEf0 F4Qg== X-Gm-Message-State: ALoCoQmB1UdTVMGdBs4nxRRzl8KYMHpt1ySnSysBjLHpmk2LQk1dOv1cLZ+qPz3XIBReDH+IpXvQ X-Received: by 10.50.134.131 with SMTP id pk3mr9181883igb.8.1413751803476; Sun, 19 Oct 2014 13:50:03 -0700 (PDT) X-BeenThere: std-proposals@isocpp.org Original-Received: by 10.51.16.66 with SMTP id fu2ls464817igd.0.canary; Sun, 19 Oct 2014 13:50:02 -0700 (PDT) X-Received: by 10.50.43.232 with SMTP id z8mr127508igl.13.1413751802851; Sun, 19 Oct 2014 13:50:02 -0700 (PDT) In-Reply-To: X-Original-Sender: chris.kohlhoff@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:14040 Archived-At: ------=_Part_403_1565842355.1413751801166 Content-Type: text/plain; charset=UTF-8 On Monday, October 20, 2014 4:35:16 AM UTC+11, Ville Voutilainen wrote: > > On 19 October 2014 01:36, > wrote: > >> Then again, I don't quite see how to return a future with N4244 - I > >> would > >> expect I need to return a future& and have the future as a capture. > > It's a similar principle to when you write "async(f)". The function f > > doesn't return the future; instead std::async wraps it in the necessary > > machinery to run f and make the result available as a future. So, we > could > > Blargh, I was confused for a moment. The gist of the matter is sharing the > state, and the lifetime of it. From the state of a resumable lambda, the > lambda can quite easily generate futures that are not necessarily > associated > with the state of the lambda. The lifetime of the state itself > is bound to the lambda, and sharing the state itself via the return type > is not really important, although it could theoretically be done. Neither > resumable lambdas nor resumable functions can move the state itself > out of themselves(*). Experience with the macro-based equivalent of resumable lambdas shows that they can. For example: []() resumable { ... yield async_something(std::move(*[]this)); ... } is roughly equivalent to: __state = __LINE__; \ async_something(std::move(*this)); \ return; \ case __LINE__: Any state is moved along into the operation and the only thing the moved-from lambda does is exit following the yield. This works very nicely as a truly lightweight way to chain async operations. The return type of a resumable function takes care > of the lifetime of the state, whereas in a resumable lambda, the lambda > itself takes care of it. > I prefer to think that the resumable lambda itself is the state, but yes. Cheers, Chris -- --- 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. Visit this group at http://groups.google.com/a/isocpp.org/group/std-proposals/. ------=_Part_403_1565842355.1413751801166 Content-Type: text/html; charset=UTF-8 Content-Transfer-Encoding: quoted-printable


On Monday, October 20, 2014 4:35:16 AM UTC+11, Vil= le Voutilainen wrote:
On 19 Oct= ober 2014 01:36,  <chris.k...@= gmail.com> wrote:
>> Then again, I don't quite see how to return a future<T> = with N4244 - I
>> would
>> expect I need to return a future<T>& and have the fu= ture as a capture.
> It's a similar principle to when you write "async(f)". The functio= n f
> doesn't return the future; instead std::async wraps it in the nece= ssary
> machinery to run f and make the result available as a future. So, = we could

Blargh, I was confused for a moment. The gist of the matter is sharing = the
state, and the lifetime of it. From the state of a resumable lambda, th= e
lambda can quite easily generate futures that are not necessarily assoc= iated
with the state of the lambda. The lifetime of the state itself
is bound to the lambda, and sharing the state itself via the return typ= e
is not really important, although it could theoretically be done. Neith= er
resumable lambdas nor resumable functions can move the state itself
out of themselves(*).

Experience with t= he macro-based equivalent of resumable lambdas shows that they can. For exa= mple:

  []() resumable
  {
    ...
    yield async_something(std:= :move(*[]this));
    ...
  }
<= br>
is roughly equivalent to:

  __s= tate =3D __LINE__; \
  async_something(std::move(*this)); \<= /div>
  return; \
  case __LINE__:

Any state is moved along into the operation and the only thing the= moved-from lambda does is exit following the yield.

This works very nicely as a truly lightweight way to chain async operati= ons.

The r= eturn type of a resumable function takes care
of the lifetime of the state, whereas in a resumable lambda, the lambda
itself takes care of it.

I prefer t= o think that the resumable lambda itself is the state, but yes.
<= br>
Cheers,
Chris

--

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