220 14506 <70a52592-8f61-4fc2-855e-f65d73af9be8@isocpp.org> article Path: news.gmane.org!not-for-mail From: Olaf van der Spek Newsgroups: gmane.comp.lang.c++.isocpp.proposals Subject: Re: Re: Range-based if Date: Wed, 12 Nov 2014 11:33:29 -0800 (PST) Lines: 101 Approved: news@gmane.org Message-ID: <70a52592-8f61-4fc2-855e-f65d73af9be8@isocpp.org> References: Reply-To: std-proposals@isocpp.org NNTP-Posting-Host: plane.gmane.org Mime-Version: 1.0 Content-Type: multipart/alternative; boundary="----=_Part_898_1511322349.1415820809109" X-Trace: ger.gmane.org 1415820818 4348 80.91.229.3 (12 Nov 2014 19:33:38 GMT) X-Complaints-To: usenet@ger.gmane.org NNTP-Posting-Date: Wed, 12 Nov 2014 19:33:38 +0000 (UTC) To: std-proposals@isocpp.org Original-X-From: std-proposals+bncBC5NB45SSABBBCPMR2RQKGQELBVVIBA@isocpp.org Wed Nov 12 20:33:32 2014 Return-path: Envelope-to: gclcip-std-proposals@m.gmane.org Original-Received: from mail-ie0-f197.google.com ([209.85.223.197]) by plane.gmane.org with esmtp (Exim 4.69) (envelope-from ) id 1XodfW-0004AU-Ps for gclcip-std-proposals@m.gmane.org; Wed, 12 Nov 2014 20:33:30 +0100 Original-Received: by mail-ie0-f197.google.com with SMTP id rd18sf69704573iec.8 for ; Wed, 12 Nov 2014 11:33:30 -0800 (PST) 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=LLfxepIaAnrmlMqAKZjpib/fbdkeFoO5RikmtaUNto0=; b=HH5UBkKVxZ9emrJ8dVO9mGc+QHanZ3kkoTxIpHqon95J2X/NZokyGANt9D/tCLxjVi YLUfMDa3uZWdk7Fxe5sT1KxJ/UBsTUjeN9mzuTqfD3/69OIjqwTp3lVxQ6B77sKP6GYA C7l8IRrFz0hsXaKktLBglmS2bWSFX5YyWNbDb961mJQuUc6SwzcnohIxPvgIa9mR45KQ 6xeW+kMpt6IGeCtjpG71snEv+hoU7ooCBe/Ajv+6oB2cy3RhzNloCPIyzCRWTPHJjCSY rMXCOWaMA/Ikqz8Izd4FJ0uOW8A0d7duEe1Y3Owcbowh3QC9GiRtlb1wv79eWumrnSH1 AOew== 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=LLfxepIaAnrmlMqAKZjpib/fbdkeFoO5RikmtaUNto0=; b=cp2+3d86vvAh0QfWEIO0K08fNPBKtsNMK1yJj0IMLcd62cqxb3Dr16t6DoutVQokMm EFEiB6eAjWzTD5zmTutcm277UZs8+K4nSjNteTPsHhLTvmSmt8uxiHeqM8g+kRNbDpyX 43gCQVlecBbJe7LXJnMVg0GvAR81bLVOubEDh5E0FkBNSP9sMIJXl7vXdJQ/9eUfFMTU KU9TXmftsUSD2uLnURjTjTb3TR5lbPp6El8CRiBL/Smvx2FG3X/2cbtXOEBqeWSExXAN RYHLHoV3k/af9SBWBaUmT7+rwuA6+ZeVpcaWeAf5ggHNpoKv9vHMSKPNJlAMGRWjOXP6 FT4Q== X-Gm-Message-State: ALoCoQkCkRIuhhP9xi27YCnAXHHGy4ixrmB6WX/TH5XywzuXm9GgCpqzcTfDr4MqA8uNzxsSsno7 X-Received: by 10.182.89.136 with SMTP id bo8mr735850obb.7.1415820810179; Wed, 12 Nov 2014 11:33:30 -0800 (PST) X-BeenThere: std-proposals@isocpp.org Original-Received: by 10.140.85.101 with SMTP id m92ls3079758qgd.51.gmail; Wed, 12 Nov 2014 11:33:29 -0800 (PST) X-Received: by 10.140.20.108 with SMTP id 99mr59581qgi.15.1415820809463; Wed, 12 Nov 2014 11:33:29 -0800 (PST) In-Reply-To: X-Original-Sender: olafvdspek@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:14506 Archived-At: ------=_Part_898_1511322349.1415820809109 Content-Type: text/plain; charset=UTF-8 On Wednesday, November 12, 2014 3:39:34 AM UTC+1, Brent Friedman wrote: > > > auto first_or_null(auto range) -> decltype(&range.begin()) > > This assumes pointers, which while addressing some use cases it isn't > sufficient for the general case. > > > if (!range.empty()) > > DoSomething(*range.begin()); > > This is more or less what we're doing currently. If you need to do more > than one something, then it becomes > > if (!range.empty()) > { > auto&& front = *range.begin(); > DoSomething( front ); > //etc > } > > 'range' may of course be an rvalue, perhaps the result of a function call. > We do this a lot. Currently, we'll have to create a variable to store > 'range'. So introducing an additional scope would be wise to contain > 'range'. > > { > auto& range = GetTheRange(); > if (!range.empty()) > { > auto& front = *range.begin(); > DoSomething( front ); > //etc > } > } > > IMO it'd be nice if this was possible: if (auto& range = GetTheRange()) -- --- 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_898_1511322349.1415820809109 Content-Type: text/html; charset=UTF-8 Content-Transfer-Encoding: quoted-printable
On Wednesday, November 12, 2014 3:39:34 AM UTC+1, Brent Fr= iedman wrote:
= > auto = first_or_null(auto range) -> decltype(&range.begin())
This assumes pointers, which while addressing some use cases it= isn't sufficient for the general case.

>    if (!ra= nge.empty())
>        DoSomething(*range.begin());

This is more or less what we're doing currently. If y= ou need to do more than one something, then it becomes

=
if (!range.empty())
{
    auto&&= front =3D *range.begin();
    DoSomething( front );
    //etc
}

'range' ma= y of course be an rvalue, perhaps the result of a function call. We do this= a lot. Currently, we'll have to create a variable to store 'range'. So int= roducing an additional scope would be wise to contain 'range'.
{
  auto& range =3D GetTheRange();
  if (!range.empty())
  {
    &nb= sp; auto& front =3D *range.begin();
      DoSo= mething( front );
      //etc
  }
}


IMO i= t'd be nice if this was possible:
if (auto& range =3D GetTheR= ange())

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