220 5767 article Path: news.gmane.org!not-for-mail From: inkwizytoryankes@gmail.com Newsgroups: gmane.comp.lang.c++.isocpp.proposals Subject: Re: Uniform intialization with std::intializer_list is not uniform. Date: Fri, 23 Aug 2013 10:14:50 -0700 (PDT) Lines: 270 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/alternative; boundary="----=_Part_890_28558716.1377278091051" X-Trace: ger.gmane.org 1377278093 24874 80.91.229.3 (23 Aug 2013 17:14:53 GMT) X-Complaints-To: usenet@ger.gmane.org NNTP-Posting-Date: Fri, 23 Aug 2013 17:14:53 +0000 (UTC) To: std-proposals@isocpp.org Original-X-From: std-proposals+bncBDDLTAGNTIBBBC5R32IAKGQE7XZGQZQ@isocpp.org Fri Aug 23 19:14:54 2013 Return-path: Envelope-to: gclcip-std-proposals@m.gmane.org Original-Received: from mail-vc0-f198.google.com ([209.85.220.198]) by plane.gmane.org with esmtp (Exim 4.69) (envelope-from ) id 1VCuwn-00027n-Ew for gclcip-std-proposals@m.gmane.org; Fri, 23 Aug 2013 19:14:53 +0200 Original-Received: by mail-vc0-f198.google.com with SMTP id ht10sf687270vcb.5 for ; Fri, 23 Aug 2013 10:14:52 -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=xryncyupB8+bm3HjbpL85pDmfBJBGNTri43h7lAZD4M=; b=kcPvXaBNyxcLpBzfs8lHMCEZo8m/ERrZ7zSnrjR6DVi7cn5PXKgQRF+EyOXPHmQmwz AwFaJo6AEf/qjBDacGZ9qBlhadNARxplS/z/e2nPspNZj4VFV5OouJ4g19DvU0hkpoBx LciCyB3tHMN6I5vm3gzk6iMYDK78xDQWWcKE/TllFJCXZXjrcqkH4Duf30qM85S6orsP bT9hrXmtqJG0lvJhMrHjYlhbQzcb4A8ZvnVYJe/Gb15d4NbLEfSQVwyEvCmwCemRFz5j Y1lInc4MdGNVhzYC+7shyq9F2mBU8QDH+H5oDVSycV9l/icD48D6lfS52PNXYVtODjZU CekA== X-Received: by 10.236.174.232 with SMTP id x68mr247384yhl.42.1377278092504; Fri, 23 Aug 2013 10:14:52 -0700 (PDT) X-BeenThere: std-proposals@isocpp.org Original-Received: by 10.49.119.9 with SMTP id kq9ls1706386qeb.48.gmail; Fri, 23 Aug 2013 10:14:51 -0700 (PDT) X-Received: by 10.49.28.97 with SMTP id a1mr47183qeh.0.1377278091634; Fri, 23 Aug 2013 10:14:51 -0700 (PDT) In-Reply-To: X-Original-Sender: inkwizytoryankes@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:5767 Archived-At: ------=_Part_890_28558716.1377278091051 Content-Type: text/plain; charset=ISO-8859-1 On Wednesday, August 14, 2013 12:50:47 PM UTC+2, toma...@gmail.com wrote: > > The std::initializer_list is defined as a non-owning handle to a const > array of the T elements placed probably on stack, with requires from > containers constructor to copy the elements into container. This lead for > usability problem, especially in generic programming. > > The most common example of usage of std::initializer_list is to write: > std::vector v{1,2,3,4}; > instead of: > std::vector v; v.reserve(4); > v.emplace_back(1); > v.emplace_back(2); > v.emplace_back(3); > v.emplace_back(4); > There is not difference between this two codes, because the copy and move > constructor of int does not differ. > > It can be easy fixed by helper class: template class make_vector { std::vector data; public: template inline make_vector(A&&... a) { data.reserve(sizeof...(A)); auto f = {(data.emplace_back(std::forward(a)), 0)...}; //hack to reduce code size } operator std::vector() { return std::move(data); } }; int main() { std::vector> v = make_vector> { std::unique_ptr(new int{1}), std::unique_ptr(new int{2}), std::unique_ptr(new int{4}), }; for(auto& i : v) std::cout<< *i << "\n"; } -- --- 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_890_28558716.1377278091051 Content-Type: text/html; charset=ISO-8859-1 Content-Transfer-Encoding: quoted-printable


On Wednesday, August 14, 2013 12:50:47 PM UTC+2, t= oma...@gmail.com wrote:
The std::initializer_list<T> is defined as a non-owning han= dle to a const array of the T elements placed probably on stack, with requi= res from
 containers constructor to copy the elements into containe= r. This lead for usability problem, especially in generic programming.
<= br>The most common example of usage of std::initializer_list is to write:  std::vector<i= nt> v{1,2,3,4};
instead of:
  std::vector<int> v; v.reserve(4);
 = v.emplace_back(1);
  v.emplace_back(2);
  v.emplace_back(3= );
  v.emplace_back(4);
There is not difference between t= his two codes, because the copy and move constructor of int does not differ= ..

It can be easy fixed by helper class:
<= div class=3D"prettyprint" style=3D"background-color: rgb(250, 250, 250); bo= rder-color: rgb(187, 187, 187); border-style: solid; border-width: 1px; wor= d-wrap: break-word;">

template<typename T>
class make_vector
{
    std::vector<T> = data;
public:
    template<typename... A>
    inline make_vector(A&&... a)
&n= bsp;   {
&nb= sp;       data.reserve(si= zeof...(A));
      &nb= sp; auto f =3D {(data.emplace_back(std::forwa= rd<A>(a)), 0)...}; //hack to reduce code size
    }
   
    operator std::vector<T>() { return std::move(data); }
<= span style=3D"color: #660;" class=3D"styled-by-prettify">};

int main()
{
    std::vector<std:= :unique_pt= r<int&g= t;> v =3D make_vector<std::unique_ptr<int>>
    {
        std::unique_ptr<int>(new int{1}),
  &nbs= p;     std::unique_ptr<int>(new int{2}),
        std::unique_ptr<int>(new int{4}),
  &nbs= p; };
  &nbs= p; for(auto& i : v)
        std::cout<< *= i <<= "\n";
}


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