220 29855 <13497310-30de-4542-9ba4-fb1fbd730cb6@isocpp.org> article Path: news.gmane.org!.POSTED!not-for-mail From: Vincent Reverdy Newsgroups: gmane.comp.lang.c++.isocpp.proposals Subject: Default constructor for lambdas Date: Fri, 16 Dec 2016 14:47:45 -0800 (PST) Lines: 129 Approved: news@gmane.org Message-ID: <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/mixed; boundary="----=_Part_2411_169816189.1481928465523" X-Trace: blaine.gmane.org 1481928467 29518 195.159.176.226 (16 Dec 2016 22:47:47 GMT) X-Complaints-To: usenet@blaine.gmane.org NNTP-Posting-Date: Fri, 16 Dec 2016 22:47:47 +0000 (UTC) To: ISO C++ Standard - Future Proposals Original-X-From: std-proposals+bncBCYPFAORZMKRBEW62HBAKGQEQEQC5LY@isocpp.org Fri Dec 16 23:47:43 2016 Return-path: Envelope-to: gclcip-std-proposals@m.gmane.org Original-Received: from mail-qk0-f199.google.com ([209.85.220.199]) by blaine.gmane.org with esmtp (Exim 4.84_2) (envelope-from ) id 1cI1Hy-0006nf-I5 for gclcip-std-proposals@m.gmane.org; Fri, 16 Dec 2016 23:47:42 +0100 Original-Received: by mail-qk0-f199.google.com with SMTP id m67sf74981751qkf.0 for ; Fri, 16 Dec 2016 14:47:47 -0800 (PST) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=isocpp-org.20150623.gappssmtp.com; s=20150623; h=date:from:to:message-id: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=RSWLECWMINlvZWnKUtfYYV8BGGfxi/st17ZYaknAnhE=; b=0M8g2fXVXeofiP0InH5O721kXMIgwabxA3/0/dbrWFh/iVQ/ZWnGoDhvbawcgZvG8y HGaJNs5tofA7qV/tpGxKfe4a5GYfdxb5gScHWFSLkYZjf385HbOn7SU5Qp3mIrIkmwic MY4LXWj1+aeVxwL9dCxBEkMi7w8CycjYsYpWO07UiC1x60DMKX83tyq7aEu0lqsPYDCa ca7K7Zj79qqzl0JeEtbtPJXvN4Wywc/8iGm0XY/myscH8DkHzkC0uVD4b7JcGEOWtp7/ Q593Ocepe6vAy8ekhQl8XOEaHqPcQC7UINxqHuvAoGkGM1Oqv+HuTWz0a1p98kmN2dWD 8AiQ== DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gmail.com; s=20161025; h=date:from:to:message-id: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=RSWLECWMINlvZWnKUtfYYV8BGGfxi/st17ZYaknAnhE=; b=cJYDDseJt79jqaZBMJwIqQjx6lzgTEnc/Cg8jS8jGldXxApSbwMVjRsbm5Ko/CCVAs pfq9LmwOw5v/2NkmieO+iSvokffwHa4z4ItE8nwZ/jkfUFmlUjUtZ+cFJJ/3PcX/cJN+ RmT4BN7i9FJkAvrty2dnMGMMlTXmb42y93OZOISkiFnkVuNiFRk3MTHCu5oxN0x1/JSC z/GxxPs5QfA24eiyc6cysJK/llI6xdoppDYajP0bFHy7b/aL36Cyr7m4/kO2ziJLf41q yEpjvZPaooega7YDnApQo5OZWat9Li78Tmgzf+GfiwqVlcKe0jDrUDDZezse95aYCBMW AemQ== 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: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=RSWLECWMINlvZWnKUtfYYV8BGGfxi/st17ZYaknAnhE=; b=MMQoTpGuMTDF5uaRNow0fI+Bb20twvGPD7hxDmJVIaKQAyv/kklevSVlpHdXemCCXI Z7hGeqE5k4pNXnsAutaCooeX0zfGJXvTpXpwvoXZAM400xHUX5vtlSKlvrjNTjJ7TyF0 Bz21wwPj++KsRZmyRSPlzGlEFEjXJe68m2YsroH36KoYpduMVdbyFrCErarz/zVDdTit LrnPeJMnF0Dih4Lwh3Pxg+TYqitUeSudGo0AnAjBDH2EXw+P8oujBY81PTpCv/CkEfdf VnXb667NhpFYbvPHAxJyswKRAxvEuc6j+ABcJonDhgSvTybZBaqv6eSz8EqQNndelTRz IFGw== X-Gm-Message-State: AIkVDXKlh4c6I2a0l6ZqLQ7RaCERvNiQKzw+nmq58TKvoY+gnwT64uAX+2sa29lNLFR/Aw== X-Received: by 10.237.36.163 with SMTP id t32mr1130514qtc.22.1481928466803; Fri, 16 Dec 2016 14:47:46 -0800 (PST) X-BeenThere: std-proposals@isocpp.org Original-Received: by 10.157.23.193 with SMTP id j59ls9701350otj.24.gmail; Fri, 16 Dec 2016 14:47:46 -0800 (PST) X-Received: by 10.157.18.211 with SMTP id g77mr353706otg.14.1481928466056; Fri, 16 Dec 2016 14:47:46 -0800 (PST) X-Original-Sender: Vince.Rev@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:29855 Archived-At: ------=_Part_2411_169816189.1481928465523 Content-Type: multipart/alternative; boundary="----=_Part_2412_2115786499.1481928465524" ------=_Part_2412_2115786499.1481928465524 Content-Type: text/plain; charset=UTF-8 Hello. What is the reason why lambdas have no default constructor? Is there any technical reason behind that, or is it a pure design decision? I have a use case where not having a default constructor for lambda is annoying. Given C++17 class template deduction, I would like to be able to do: template class object { constexpr object(F) {} // Constructor constexpr void execute() {F()();} // Default-construct the lambda, and run it }; object myobject([](){std::cout<<"Hello world!"<Hello.

What is the reason why lambdas have no defau= lt constructor? Is there any technical reason behind that, or is it a pure design decision?

I ha= ve a use case where not having a default constructor for lambda is annoying= ..

Given C++17 class template deduction, I would like to be able to d= o:

template <class F>
class object
{
=C2=A0 =C2=A0 constexpr object(= F) {} =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0// Constructo= r
=C2= =A0 =C2=A0 constexpr= void execute= () {F()();} // Default-construct the lambda, and run it
};

object myobject([](){std::cout&= lt;<&qu= ot;Hello world!"<<std::endl;});<= span style=3D"color: #000;" class=3D"styled-by-prettify">
myobject.execute();

W= hat do you think? Remarks? Comments?

Thank you very much.
Best,Vincent Reverdy

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