220 14493 <706b7c7d-2bc2-4281-b534-848763d0657e@isocpp.org> article Path: news.gmane.org!not-for-mail From: Bengt Gustafsson Newsgroups: gmane.comp.lang.c++.isocpp.proposals Subject: Re: Range-based if Date: Tue, 11 Nov 2014 14:26:05 -0800 (PST) Lines: 131 Approved: news@gmane.org Message-ID: <706b7c7d-2bc2-4281-b534-848763d0657e@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_1183_390031277.1415744765776" X-Trace: ger.gmane.org 1415744797 27693 80.91.229.3 (11 Nov 2014 22:26:37 GMT) X-Complaints-To: usenet@ger.gmane.org NNTP-Posting-Date: Tue, 11 Nov 2014 22:26:37 +0000 (UTC) Cc: mw_triad@users.sourceforge.net To: std-proposals@isocpp.org Original-X-From: std-proposals+bncBCRIRSPDTQIRB7UZRKRQKGQEH6BNGQQ@isocpp.org Tue Nov 11 23:26:30 2014 Return-path: Envelope-to: gclcip-std-proposals@m.gmane.org Original-Received: from mail-ig0-f199.google.com ([209.85.213.199]) by plane.gmane.org with esmtp (Exim 4.69) (envelope-from ) id 1XoJt1-0003qn-9a for gclcip-std-proposals@m.gmane.org; Tue, 11 Nov 2014 23:26:07 +0100 Original-Received: by mail-ig0-f199.google.com with SMTP id hn18sf9268870igb.2 for ; Tue, 11 Nov 2014 14:26:06 -0800 (PST) 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:cc: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=KALlt3sPJDc/Iu95SsGfdjBWypqCNpTcaIFA8NPnDgc=; b=cjPLwSLuXHuPOb7cyo/E5+TM9xuycDj2cg5ijKNp3qre2TrU2m3i7ddL++51vCIdw/ iRUW1AgKiu2jqx4p4VLRHWs8HxqSjUKopPnAs2xnK6nCT6jUUqYdOm8FByN3yukmKNcZ vvEEbxVGa8cgnCvoAAHL17UlAM4sSrusuwOqnElaikWUiTDHN0fgCjgbYjypVlIImb+3 UZzTrozKD4oSbRqDJW9CGeVSNFuKQcnjPB7u3ql6xW91rNdaWqmmGtqxwpkaaLg14Lf7 SxnkZk8QohjTHxdcxqDzOMBIojDoYB/894VntWt3TbC2uTEHXeY1mLDQwrSznVIZ7Ecv ecRg== X-Gm-Message-State: ALoCoQmV3lupu0Fhe1EnzaaiTqb2ludzMKaTjHfmgWH5Cp4zslOMcQmfhB/JIobCX+R1QaZn3JFt X-Received: by 10.50.111.131 with SMTP id ii3mr27270816igb.6.1415744766650; Tue, 11 Nov 2014 14:26:06 -0800 (PST) X-BeenThere: std-proposals@isocpp.org Original-Received: by 10.140.93.225 with SMTP id d88ls2575704qge.91.gmail; Tue, 11 Nov 2014 14:26:06 -0800 (PST) X-Received: by 10.140.101.227 with SMTP id u90mr60106qge.18.1415744765962; Tue, 11 Nov 2014 14:26:05 -0800 (PST) In-Reply-To: X-Original-Sender: bengt.gustafsson@beamways.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:14493 Archived-At: ------=_Part_1183_390031277.1415744765776 Content-Type: text/plain; charset=UTF-8 Or use the new free function size, count or whatever it is eventually called, or maybe there is an empty() too in the works: if (!std::empty(range)) DoSomething(*begin(range)); Den tisdagen den 11:e november 2014 kl. 22:34:39 UTC+1 skrev Matthew Woehlke: > > On 2014-11-11 16:12, Brent Friedman wrote: > > I've noted in our codebase that we lean heavily on the convenience of > > range-based for even when it's not perhaps the best way to express an > idea. > > > > //do something to the first item > > for (auto& Item : range) > > { > > DoSomething(Item); > > break; > > } > > auto first_or_null(auto range) -> decltype(&range.begin()) > { > auto begin = range.begin(); > auto end = range.end(); > return (begin == end ? nullptr : &(*begin)); > } > > if (auto item = first_or_null(range)) > > Basically you want that, right? :-) > > I'm not sure if that actually works, and it requires an additional > dereference when you go to use 'item', but OTOH it wouldn't require a > language change... > > That said, how often can you not write: > > if (!range.empty()) > DoSomething(*range.begin()); > > ...? > > -- > Matthew > > -- --- 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_1183_390031277.1415744765776 Content-Type: text/html; charset=UTF-8 Content-Transfer-Encoding: quoted-printable
Or use the new free function size, count or whatever it is= eventually called, or maybe there is an empty() too in the works:

=
if (!std::empty(range))
    DoSomething(*beg= in(range));



Den tisdagen den 11:e november= 2014 kl. 22:34:39 UTC+1 skrev Matthew Woehlke:
On 2014-11-11 16:12, Brent Friedman wrote:
> I've noted in our codebase that we lean heavily on the convenience= of
> range-based for even when it's not perhaps the best way to express= an idea.
>=20
> //do something to the first item
> for (auto& Item : range)
> {
>     DoSomething(Item);
>     break;
> }

    auto first_or_null(auto range) -> decltype(&range.= begin())
    {
        auto begin =3D range.begin();
        auto end =3D range.end();
        return (begin =3D=3D end ? nullptr : &(= *begin));
    }

    if (auto item =3D first_or_null(range))

Basically you want that, right? :-)

I'm not sure if that actually works, and it requires an additional
dereference when you go to use 'item', but OTOH it wouldn't require a
language change...

That said, how often can you not write:

    if (!range.empty())
        DoSomething(*range.begin());

...?

--=20
Matthew

--

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