220 29856 article Path: news.gmane.org!.POSTED!not-for-mail From: "D. B." Newsgroups: gmane.comp.lang.c++.isocpp.proposals Subject: Re: Default constructor for lambdas Date: Fri, 16 Dec 2016 23:15:13 +0000 Lines: 61 Approved: news@gmane.org Message-ID: References: <13497310-30de-4542-9ba4-fb1fbd730cb6@isocpp.org> Reply-To: std-proposals@isocpp.org NNTP-Posting-Host: blaine.gmane.org Mime-Version: 1.0 Content-Type: multipart/alternative; boundary=001a114ccb68fe113a0543cebdf9 X-Trace: blaine.gmane.org 1481930118 20309 195.159.176.226 (16 Dec 2016 23:15:18 GMT) X-Complaints-To: usenet@blaine.gmane.org NNTP-Posting-Date: Fri, 16 Dec 2016 23:15:18 +0000 (UTC) To: std-proposals@isocpp.org Original-X-From: std-proposals+bncBCWNZ4ECS4GBBAXL2HBAKGQEXQEK3GI@isocpp.org Sat Dec 17 00:15:11 2016 Return-path: Envelope-to: gclcip-std-proposals@m.gmane.org Original-Received: from mail-lf0-f71.google.com ([209.85.215.71]) by blaine.gmane.org with esmtp (Exim 4.84_2) (envelope-from ) id 1cI1iY-0003ln-LT for gclcip-std-proposals@m.gmane.org; Sat, 17 Dec 2016 00:15:10 +0100 Original-Received: by mail-lf0-f71.google.com with SMTP id b14sf10151429lfg.6 for ; Fri, 16 Dec 2016 15:15:15 -0800 (PST) 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=woAEli+DHVz/JWNIr02IIOLBvEsCgcCM3etTIqs86ic=; b=zd/9n0N3DCybNdN1PXlYMtVe0/BASUM+dM1pG4ClUwLxv/GPGfvlwj4UwjR7f/AsFl 4E5G2sOh9ZAu5DDEtiEDCeRAzrSnZqByF5iXZeXUqWtvjN7aNRG5RZV9xRYlunXi8Gro N2dodHwIw4j37UOBIRaKw1BQynwMDgMxDSt+CngS5ygm/gfDJWeSahQPOvGOrUPRsMy6 yPwmu7Ap/kzeOP3n9Ken2bYxkV6YnaADmcaiLBRV1kBV6DjB4Eh3uS9F7MA/Pkx87fDY ZwhY7SICM8QdQVCY9SBM/jPHnFULKg/Nty5eMORbCxVZQizs8P251pWP7ZnCIlla0iL/ vT0A== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20161025; 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=woAEli+DHVz/JWNIr02IIOLBvEsCgcCM3etTIqs86ic=; b=AJapUfgCAUcjgyZj0H/0kmXMsGKJ2oxHPAR/rB+V+HvSoYU7CuIwAPYyCC2nKn2Hnb /2+jH9v7h2H+F73t1jXIA8Ckl1EyfnC+WvIV5Xb/BfEmx1As7K7euMK8h0AQKlOe8rH8 CjFIM+ShJJ23LCf4QCmlKY9vM0ot4+pq31nfLTekhrVvrHcqse18rPrr5rFiBGJnV/ox zuDoT5XeNHN6jl2MUjySRCDw5nX7AZSrXo3EltdJhTa0x4TX6wMS6Bm+1qxJNuvvfQN3 +v5HGDKXU4+5OhMeKUUy8uXU4bNBzwHsVKgQ4OYjV5eVrrTHh2fKNPxpA28oYrHDPD/X AFkQ== X-Gm-Message-State: AKaTC03tKnyHqmm+/E2gT7xtFGjvvkpAg1k3jfAOr3SqCwb7cqzLFyJsY/1NubVp/7sU7Q== X-Received: by 10.25.202.26 with SMTP id a26mr435926lfg.26.1481930114965; Fri, 16 Dec 2016 15:15:14 -0800 (PST) X-BeenThere: std-proposals@isocpp.org Original-Received: by 10.28.203.73 with SMTP id b70ls519299wmg.3.canary-gmail; Fri, 16 Dec 2016 15:15:13 -0800 (PST) X-Received: by 10.28.209.7 with SMTP id i7mr5319910wmg.62.1481930113769; Fri, 16 Dec 2016 15:15:13 -0800 (PST) Original-Received: from mail-wm0-x235.google.com (mail-wm0-x235.google.com. [2a00:1450:400c:c09::235]) by mx.google.com with ESMTPS id l128si5636291wml.79.2016.12.16.15.15.13 for (version=TLS1_2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128/128); Fri, 16 Dec 2016 15:15:13 -0800 (PST) Received-SPF: pass (google.com: domain of db0451@gmail.com designates 2a00:1450:400c:c09::235 as permitted sender) client-ip=2a00:1450:400c:c09::235; Original-Received: by mail-wm0-x235.google.com with SMTP id a197so47867484wmd.0 for ; Fri, 16 Dec 2016 15:15:13 -0800 (PST) X-Received: by 10.28.168.137 with SMTP id r131mr4904351wme.16.1481930113420; Fri, 16 Dec 2016 15:15:13 -0800 (PST) Original-Received: by 10.28.144.66 with HTTP; Fri, 16 Dec 2016 15:15:13 -0800 (PST) In-Reply-To: <13497310-30de-4542-9ba4-fb1fbd730cb6@isocpp.org> X-Original-Sender: db0451@gmail.com X-Original-Authentication-Results: mx.google.com; dkim=pass header.i=@gmail.com; spf=pass (google.com: domain of db0451@gmail.com designates 2a00:1450:400c:c09::235 as permitted sender) smtp.mailfrom=db0451@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:29856 Archived-At: --001a114ccb68fe113a0543cebdf9 Content-Type: text/plain; charset=UTF-8 My uninformed guess is that it's because lambdas are primarily intended to be called and passed around as opaque entities, and the fact they have types is a kind of unavoidable baggage, rather than a design goal or something to exploit. But I'm quite likely to be wrong :) Could you elaborate on where an ability to construct another instance of the templated type would be useful? As written, I can't see why you wouldn't just stash it as a member in the ctor and call it again later. it seems wasteful, constructing a lambda initially, only to discard it and rebuild on each execute(); the one in the ctor is merely a surrogate for type deduction. If the type had mutable or static members, that could cause different behaviour, but then why would you pass such a type into the above pattern? There must be motivations this doesn't illuminate (or maybe it's just too late in the day for me to be thinking about things like this!) -- 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/CACGiwhHpOT%2BZ-gM7ypjxTVvBA6%3DL0R-j1DFx6PsQdVWA1Rg%3DoQ%40mail.gmail.com. --001a114ccb68fe113a0543cebdf9 Content-Type: text/html; charset=UTF-8 Content-Transfer-Encoding: quoted-printable
My uninformed guess is that it's because lam= bdas are primarily intended to be called and passed around as opaque entiti= es, and the fact they have types is a kind of unavoidable baggage, rather t= han a design goal or something to exploit. But I'm quite likely to be w= rong :)

Could you elaborate on where an ability to construct a= nother instance of the templated type would be useful? As written, I can= 9;t see why you wouldn't just stash it as a member in the ctor and call= it again later. it seems wasteful, constructing a lambda initially, only t= o discard it and rebuild on each execute(); the one in the ctor is merely a= surrogate for type deduction. If the type had mutable or static members, t= hat could cause different behaviour, but then why would you pass such a typ= e into the above pattern? There must be motivations this doesn't illumi= nate (or maybe it's just too late in the day for me to be thinking abou= t things like this!)

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