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[62.158.237.238]) by mx.google.com with ESMTPSA id 2sm584768lai.36.2014.10.08.01.25.41 for (version=TLSv1 cipher=ECDHE-RSA-RC4-SHA bits=128/128); Wed, 08 Oct 2014 01:25:41 -0700 (PDT) In-Reply-To: <5434AAA1.1090507@gmail.com> X-Mailer: Apple Mail (2.1878.6) X-Original-Sender: miro.knejp@gmail.com X-Original-Authentication-Results: mx.google.com; spf=pass (google.com: domain of miro.knejp@gmail.com designates 2a00:1450:4010:c03::22b as permitted sender) smtp.mail=miro.knejp@gmail.com; dkim=pass header.i=@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:13752 Archived-At: On 08 Oct 2014, at 05:08 , John Bytheway wrote: > On 2014-10-07 15:20, Daniel Kr=FCgler wrote: >> 2014-10-07 21:14 GMT+02:00 Marc Mutz : >>> Hi, >>>=20 >>> I've recently had use of default-constructing a range of T's into >>> uninitialized memory. When I was filling the range with copies of a T, >>> std::uninitialized_fill() was a good fit, esp. since it is strongly exc= eption >>> safe. >>>=20 >>> But there's no uninitialized_ algorithm for default-constructing a rang= e. >>>=20 >>> The nearest there is, >>> std::uninitialized_fill(first, last, T()); >>> has slightly different semantics, as it invokes the copy contructor ins= tead >>> (and that one could be deleted). >>>=20 >>> The same issue plagues the use of raw_memory_iterator. >>>=20 >>> I ended up writing a loop and a try-catch block :( >>>=20 >>> So I think there's a place for >>> std::uninitialized_default(ForwardIterator first, ForwardIterator last= ); >>> (better names welcome). >>=20 >> No better name suggestion at the very moment at my hand, but the >> general idea looks reasonable and safe to me. >>=20 >>> Since I don't much like the name 'uninitialized_default', I looked for = a more >>> general name / algorithm, and I found "emplace". Emplace without argume= nts >>> default-constructs, with one argument or type T, it is a replacement of= _fill >>> (with no intention to deprecate _fill): >>> std::uninitialized_emplace(ForwardIterator first, ForwardIterator las= t, >>> Args&&...args); >>>=20 >>> Does that make sense? >>=20 >> I have strong concerns in regard to emplace in that context. Basically >> everywhere "emplace" means a potential move of the provided arguments >> to construct a single object. This won't work for a potential >> multi-construction operation except for special cases (like empty >> packs or packs of lvalues to const). People will easily get that >> wrong. If you insist on copying the arguments, you could name it >> emplace_copy and ensure that the argument pack refers to references to >> const. In the context of the standard library functions labeled "emplace" simply d= o in-place construction at the destination location. What happens to the ar= guments is solely the responsibility of the invoked constructor. If you con= struct multiple objects with the same arguments you better use constructors= that behave well in that scenario. But you probably do want to receive arg= uments as lvalue references in this case just to be safe. --=20 ---=20 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 e= mail 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-proposa= ls/. .