220 27040 article Path: news.gmane.org!not-for-mail From: Carl Cook Newsgroups: gmane.comp.lang.c++.isocpp.proposals Subject: Re: Proposal - non allocating std::function Date: Fri, 15 Jul 2016 02:12:58 -0700 (PDT) Lines: 79 Approved: news@gmane.org Message-ID: References: Reply-To: std-proposals@isocpp.org NNTP-Posting-Host: plane.gmane.org Mime-Version: 1.0 Content-Type: multipart/mixed; boundary="----=_Part_190_1624127528.1468573978381" X-Trace: ger.gmane.org 1468573985 13912 80.91.229.3 (15 Jul 2016 09:13:05 GMT) X-Complaints-To: usenet@ger.gmane.org NNTP-Posting-Date: Fri, 15 Jul 2016 09:13:05 +0000 (UTC) To: ISO C++ Standard - Future Proposals Original-X-From: std-proposals+bncBD27VEPGSEGBBG6SUK6AKGQEZYBPVIA@isocpp.org Fri Jul 15 11:13:04 2016 Return-path: Envelope-to: gclcip-std-proposals@m.gmane.org Original-Received: from mail-pf0-f199.google.com ([209.85.192.199]) by plane.gmane.org with esmtp (Exim 4.69) (envelope-from ) id 1bNzB7-0007mG-SH for gclcip-std-proposals@m.gmane.org; Fri, 15 Jul 2016 11:13:03 +0200 Original-Received: by mail-pf0-f199.google.com with SMTP id p64sf205166937pfb.0 for ; Fri, 15 Jul 2016 02:13:01 -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=XMXJJy4zejOB7rln4zLPsmjb2+iza9xpScFik7VWzQ0=; b=VxN2tQm1a8hXULSkVeNnzkUjYDITDAnM9q9Dq/rO1CTLJapoqlJ+mzUoWCO+mGmxzx bp3XqzShsdTxfGvk+7OTpReON0pedw92182Yvm/DY0W5hQqhFT+B0jxUPbtR+qQB+5Yq XYkvI3R/F/dwEE7Ji1743PqD5j1WBHpX594qEtVaq1kK2vpm/WqSdGUpWc5cOxq4m/sU EkzB8zBjC8NR5Vhm4WlsB9xpFLVZZtRd6FaAlIoorP6ouogLBlyWz7u9hXj4367PedYw TGFn+vkB9yyq3vGzdd+k9XWymkk6w43oyRe3+zht3bBIWgT+85Ld/Jy2Zujy6FtlGYex J3EQ== 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 :x-spam-checked-in-group:list-post:list-help:list-archive :list-subscribe:list-unsubscribe; bh=XMXJJy4zejOB7rln4zLPsmjb2+iza9xpScFik7VWzQ0=; b=mZhMeddhfsqBR1tjwoPhRjkqffcU+nOtItXOWvSUMr0wv4YpuvyEeaQz95Hq3XwhHA SBH2uqzS3HlBi5tU02Pxc+GH3CJBqMyo+/uFA0aSbSNkGFw/S1ftcoMWq1CESiWFBDNt YOjL6oYlJLP230VMleh6ndaAaBgKSVtq71mC6rPW7ByppZBDXY1SFvetuPB6cIoeAPcS IH//hGrMxMvEbzfRxTxinafVQmcu+LHzvBsYzfXnx2VeHYb7SfhLPAcFki+VLdJOxqKE n0N7FRhgMS4zsKjp6N42cvRpz2YwRGMYBrywUTeXlbYZWm4VRxNqCC91eGDww5l3sQXS DhTw== 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:x-spam-checked-in-group:list-post:list-help :list-archive:list-subscribe:list-unsubscribe; bh=XMXJJy4zejOB7rln4zLPsmjb2+iza9xpScFik7VWzQ0=; b=SXwd49reHk7DbBgZNuHn6/sgycMjzzDMQ1rMWOmNJDsDuoXSoB9JbsrdmNFalSeDZY H9014JtpfgZkQ1PYjbSEAS7nB5dZB58iTLjz6JzZB4VvuCiRbQP4KHORLWCAEAJ8elq6 drIrbivDEgU9iSQ5wtAiiyBlxSsEM0K3KB+4HSQk3mj5UYK4osiLaB2+KbpNHPoqbZM6 8DPqhDOsyD5d4k0FKMl2PG8AyU36q7VzUzH7592B7IWHK0w7vlvZ1qdmAdw3NYSq4oZ2 1QM1fX/A5Rv1wfDklonvqORMPyoPaWlOMbsuq3VIZREZqwhM5YKQZaxC++9b1L0Vc2II 4+gg== X-Gm-Message-State: ALyK8tKCZD9c4Da+iXw45zWP6fsIg/QixeTxlVwLRiu9HlJ6IJfWLf1ziah03FJk9g0HCg== X-Received: by 10.67.24.33 with SMTP id if1mr7937406pad.29.1468573980775; Fri, 15 Jul 2016 02:13:00 -0700 (PDT) X-BeenThere: std-proposals@isocpp.org Original-Received: by 10.107.15.25 with SMTP id x25ls1297494ioi.5.gmail; Fri, 15 Jul 2016 02:12:59 -0700 (PDT) X-Received: by 10.36.210.213 with SMTP id z204mr1207109itf.0.1468573979461; Fri, 15 Jul 2016 02:12:59 -0700 (PDT) In-Reply-To: X-Original-Sender: carl.cook@gmail.com Precedence: list Mailing-list: list std-proposals@isocpp.org; contact std-proposals+owners@isocpp.org List-ID: X-Spam-Checked-In-Group: std-proposals@isocpp.org 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:27040 Archived-At: ------=_Part_190_1624127528.1468573978381 Content-Type: multipart/alternative; boundary="----=_Part_191_69710619.1468573978382" ------=_Part_191_69710619.1468573978382 Content-Type: text/plain; charset=UTF-8 On Friday, 15 July 2016 02:35:42 UTC+2, Richard Smith wrote: > > llvm::function_ref doesn't capture anything, and is not supposed to -- > it's a *non-owning* handle to a callable that outlives the handle. > (llvm::function_ref is to std::function as std::string_view is to > std::string.) This is a feature and a design goal of llvm::function_ref, > but I think it means it's addressing a fundamentally different problem than > the one you're tackling here (which seems to be essentially, "let me > control the size and alignment in std::function's small function > optimization" > Understood. What caught me out is that compilers can aggressively limit the scope of lambdas. Hence I believe the following is not legal usage: int non_const_var = 0xf; function_ref f_ref = [&]() { return non_const_var;}; return f_ref(); -- 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/cd6e299d-7cec-4d8e-8a55-f25fd88d1b91%40isocpp.org. ------=_Part_191_69710619.1468573978382 Content-Type: text/html; charset=UTF-8 Content-Transfer-Encoding: quoted-printable
On Friday, 15 July 2016 02:35:42 UTC+2, Richard Smith wro= te:
llvm::function_ref doesn't capture anything, and = is not supposed to -- it's a *non-owning* handle to a callable that out= lives the handle. (llvm::function_ref is to std::function as std::string_vi= ew is to std::string.) This is a feature and a design goal of llvm::functio= n_ref, but I think it means it's addressing a fundamentally different p= roblem than the one you're tackling here (which seems to be essentially= , "let me control the size and alignment in std::function's small = function optimization"

Understood. What caught me out is that compilers can aggressively limit = the scope of lambdas. Hence I believe the following is not legal usage:

int non_const_var =3D 0xf;
function_ref<int()> f_ref =3D [&]() { return non_const_va= r;};
return f_ref();
<= /div>


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