- Boost - lists.boost.org

[variant] awkward recursion
by Dave Abrahams 03 Nov '12

03 Nov '12

I've been playing around with variant a bit and decided to try to build a data structure for storing json. I came up with several different approaches but none are super-satisfying. I'd like some feedback. (If you need a refresher on what's in json, the front page of http://json.org tells all). In the abstract, json looks like: struct null {}; typedef std::map<std::string, value> object; typedef std::vector<value> array; typedef variant< null, std::string, double, object, array, bool > value; Naturally, this code isn't legal C++, so I set about making it be. The first thing I tried was to use recursive_wrapper<>, as the documentation implies it is the most flexible way to do this sort of thing. Unfortunately, there's no clean way to reformulate this type in a way that allows recursive_wrapper work, because the type that needs to be wrapped in recursive_wrapper includes "value" in its name, and I can't forward-declare it. The only way to forward-declare a type X, as far as I know, is: struct X; // or class X; So to try to get recursive_wrapper to work, I tried a couple of formulations that started with that, but it turns out that when you do this, you end up not needing recursive_wrapper at all struct value; typedef std::map<std::string, value> object; typedef std::vector<value> array; typedef variant< null, std::string, double, object, array, bool > value_base; struct value : value_base { value() {}; template <class T> value(T const& x) : base(x) {} // no move; I'm in C++03-land value& operator=(value const& x) { base::operator=(x); return *this; } } }; I don't know if I've missed some things that should be in that "value" class. I know that a recursive variant, in principle, requires a pointer indirection somewhere, so I was wondering if, had I wrapped object and array in recursive_wrapper as below, I would have been adding an unnecessary inefficiency. typedef variant< null, std::string, double, reference_wrapper<object>, reference_wrapper<array>, bool > value_base; I also wondered whether that would give me different results from typedef std::map<std::string, value> object; typedef std::vector<value> array; typedef variant< null, std::string, double, std::map<std::string, reference_wrapper<value> >, std::vector<reference_wrapper<value> >, bool > value_base; and which one was better. Does anyone know? I think that should be in the docs. Using recursive_variant_ works out quite nicely, except that it doesn't allow me to separately declare "object" and "array" and re-use them in the definition of "value": typedef boost::make_recursive_variant< null , std::string , double , std::map<std::string, boost::recursive_variant_> , std::vector<boost::recursive_variant_> , bool >::type value; I also wonder if I'm getting an unnecessary inefficiency in that case. Lastly, what flexibility am I sacrificing by using this approach? -- Dave Abrahams BoostPro Computing Software Development Training http://www.boostpro.com Clang/LLVM/EDG Compilers C++ Boost

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[1.52.0] Release candidates available
by Marshall Clow 03 Nov '12

03 Nov '12

Release candidate files for 1.52.0 are available at http://boost.cowic.de/rc/ As always, the release managers would appreciate it if you download the candidate of your choice and give building it a try. Please report both success and failure, and anything else that is noteworthy. This helps ensure the candidates build OK before we push them out to SourceForge. Thanks, -- Marshall

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New Stepanov lecture videos released by A9
by Mat Marcus 02 Nov '12

02 Nov '12

http://www.youtube.com/user/A9Videos/videos?flow=grid&view=1

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[string_algo] Documentation Complaint
by Dave Abrahams 02 Nov '12

02 Nov '12

Wow, I found this documentation hard to use! I wanted to translate various 1-character substrings into new strings, e.g. translate the TAB character ('\t') to its textual escaped representation "\\t", and I went looking for an algorithm to do it. After 5 minutes of searching, I *think* the algorithm isn't there, but I'm still not sure. I nearly went blind (well, not really, but it felt that way) looking at http://www.boost.org/doc/libs/1_51_0/doc/html/string_algo/reference.html#he… because there's no vertical whitespace. More importantly, there's *no description of what any of these algorithms actually do*! ... calming down ... Heh, very terse descriptions are in the "Quick Reference": http://www.boost.org/doc/libs/1_51_0/doc/html/string_algo/quickref.html These might be good enough for me, but I always figure I'm going to get complete detail from the non-quick reference, and this one is just a dump of all the declarations, so I had to go around in a big circle and begin writing this documentation complaint before I found it. Can this situation be improved? -- Dave Abrahams BoostPro Computing Software Development Training http://www.boostpro.com Clang/LLVM/EDG Compilers C++ Boost

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[Variant] Documentation Questions/Notes
by Dave Abrahams 02 Nov '12

02 Nov '12

- What does this mean? Full value semantics, including adherence to standard overload resolution rules for conversion operations. Seems to me that it's impossible *not* to adhere to any standard rules. Is the part after the comma vacuous? - The "temporary heap backup" technique seems to have a hole: 1. Copy-construct the content of the left-hand side to the heap; call the pointer to this data backup. 2. Destroy the content of the left-hand side. 3. Copy-construct the content of the right-hand side in the (now-empty) storage of the left-hand side. 4. In the event of failure, copy backup to the left-hand side storage. 5. In the event of success, deallocate the data pointed to by backup. What happens in the event of a failure in step 4? - I note the section on motivation doesn't mention the new capabilities of C++11 unions. Now some of the constructs are possible... *if* you do all the bookeeping yourself. - I note that the implementation has at least some support for move semantics and yet the docs require all elements to be "bounded types", which in turn are required to be CopyConstructible. Is that accurate, or outdated? - "completeness at the point of template instantiation" is a rather odd thing to put in a concept. I suggest that that should be just part of the requirements on the variant template rather than on BoundedType. - Do the semantics for are_strict_equals at http://www.boost.org/doc/libs/1_51_0/doc/html/variant/tutorial.html differ from those of the built-in equality operator? - it might be worth making the point that recursive variants offer the ability to define complex linked data structures *as value types* in a type- and memory-safe manner. I.e. no explicit handling of pointers; copy construction and assignment "just work," etc. -- Dave Abrahams BoostPro Computing Software Development Training http://www.boostpro.com Clang/LLVM/EDG Compilers C++ Boost

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[optional] Doc Nit
by Dave Abrahams 01 Nov '12

01 Nov '12

> A typical approach is to consider the existence of a > valid return value as a postcondition, so that if the > function cannot compute the value to return, it has > either undefined behavior (and can use assert in a > debug build) or uses a runtime check and throws an > exception if the postcondition is violated. This is a > reasonable choice for example, for function (A), This is possibly technically correct, but confusing. Undefined behavior results from precondition violations, not postcondition violations. I'd suggest: One approach is to make a non-negative argument a precondition, so when violated the function has undefined behavior (and can use assert in a debug build). Alternatively, one can use a runtime check and specify that an exception is thrown if the postcondition cannot be satisfied. These are a reasonable choice for example, for function (A), I'm not sure the first sentence is quite right for your needs, but I'm out of time to improve it further. -- Dave Abrahams BoostPro Computing Software Development Training http://www.boostpro.com Clang/LLVM/EDG Compilers C++ Boost

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Re: [boost] make_shared_array and allocate_shared_array
by Glen Fernandes 01 Nov '12

01 Nov '12

On Thu Nov 1 2012 at 1:48 PM, Olaf van der Spek <ml(a)vdspek.org> wrote: > Does Glen's make_shared_array have variants for both initialized and uninitialized allocations (for builtin types)? Hi Olaf, I just updated the code to only have initialization for non POD types: https://github.com/glenfe/glenfern/commit/05ea1f429bddfe7f07e4bb392db248492… Glen

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Review: Code Review: allocate_shared_array and make_shared_array
by Glen Fernandes 01 Nov '12

01 Nov '12

A big thank you to Peter Dimov who has been kind enough to review my code. The open question we both have is whether these functions should continue to return shared_ptr<T> or be changed to return shared_array<T> after some modification to shared_array (both to support construction from (or conversion to) a shared_ptr and to have things like a no-throw constructor). Updated code: https://github.com/glenfe/glenfern/tree/master/boost Original blog post: http://glenfernandes.wordpress.com/ Some context from our discussion: Peter Dimov wrote: > Providing two separate sets of functions doesn't appeal to me much. > make_shared_array should return whatever we decide they should return. You > are right about shared_array's default constructor though, and maybe we can > use this opportunity to fix it (and add move support), and perhaps provide a > way for people to get a shared_ptr from a shared_array, if they have to work > with other people who only use that in their APIs. :-) > > Let's see what the Boost list will say. > > Glen Fernandes wrote: > > 1. I keep the functions returning shared_ptr but rename them to > > allocate_shared_sequence and make_shared_sequence. I think they are still > > useful for people who would want to avoid shared_array in their APIs for > > various reasons (e.g. its default constructor can throw). > >

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C++ Now 2013 Call for Submissions
by Hartmut Kaiser 31 Oct '12

31 Oct '12

---------------------------------------------------------------------------- C++ NOW CONFERENCE 2013 - Aspen CO, USA, May 13-17, 2013, www.cppnow.org ---------------------------------------------------------------------------- CALL FOR SUBMISSIONS -------------------- We invite you to submit session proposals to the 2nd annual C++ Now Conference (Aspen CO, USA, May 13-17, 2013). Building upon the resounding success of C++ Now 2012 and five years of BoostCon, C++ Now 2013 will present leading speakers from the whole C++ community. The C++ Now Conference is dedicated to discussion and education about C++, an open and free language and standard. Our Conference will focus on discussion and education about open source software usage and developments in the C++ developer and user community. To reflect the breadth of the C++ and Boost communities, the conference includes sessions aimed at three constituencies: C++ and Boost end-users, hard-core Boost library and tool developers, and researchers pushing the boundaries of computation. The program fosters interaction and engagement within and across those groups, with an emphasis on hands-on, participatory sessions. As a multi-paradigm language, C++ is a melting pot where the most compelling ideas from other programming communities are blended in powerful ways. Historically, some of the most popular sessions at C++ Now have highlighted these concepts, from DSLs to functional programming to transactional memory and more. Bring your C#, Python, Ruby or Haskell influences to bear in an environment that will broaden their exposure. At C++ Now 2013 we would like to focus on parallel and distributed computing with C++. However, by no means this is intended to restrict the topics of proposals we hope to see. Any other topic related to C++ as outlined below is perfectly fine for submission. IMPORTANT DATES --------------- New proposal submissions due: December 15th, 2013. Proposals decisions sent (tentative program available): January 30th, 2013. Fully scheduled program available: February 24th, 2013. BEST PRESENTATION AWARDS ------------------------ We know how much effort it takes to prepare talks for our conference. For this reason we will award the best presentations in the following categories: Best Presentation, Best Short Presentation, Best Tutorial, and Best Workshop. The awards will be given based on the audience's voting. Each award will include the author's name listed on the cover of the C++ Now website for that year and a plaque containing all the C++ Now conference information. SESSION TOPICS -------------- Topics of interest include, but are not restricted to, the following: * Parallelism in the new C++11 standard * Parallel, distributed and GPGPU topics relating to C++ * C++11 and how it changes life for users and library writers * General tutorial sessions on C++11, the C++11 Standards library, and one or more Boost libraries * In-depth sessions on using specific Boost libraries * Case studies on using Boost * Experts panels * Advanced sessions on implementation techniques used within Boost libraries * Development workshops to extend or enhance existing Boost libraries * Workshops on design process * Infrastructure workshops such as Build tools, Website, Testing * Concepts and Generic Programming * Hardware and infrastructure presentations focused on how libraries can make better use of the technology * Software development tools and their application to C++ and or Boost * Other topics likely to be of great interest to C++ users and developers Interactive and collaborative sessions are encouraged, as this is the style of learning and participation that has proven most successful at such events. Sessions can be tutorial based, with an emphasis on interaction and participant involvement, or workshop based, whether hands-on programming or paper-based, discussion-driven collaborative work. SESSION FORMATS --------------- Presentations Presentations focus on a practitioner's ideas and experience with anything relevant to C++11, Boost and users. Panels Panels feature three or four people presenting their ideas and experiences relating to C++11 and Boost's relevant, controversial, emerging, or unresolved issues. Panels may be conducted in several ways, such as comparative, analytic, or historic. Tutorials Tutorials are sessions at which instructors teach conference participants specific skills relevant to C++11 and Boost. Workshops Workshops provide an active arena for advancements in Boost-relevant topics. Workshops provide the opportunity for experienced practitioners to develop new ideas about a topic of common interest and experience. Author's Corner Presentations These were introduced at BoostCon 2008, and were a great success. They are short (30 minute) sessions, focusing on tips on usage and design. In addition, we're looking to uncover the hidden design gems in Boost libraries. Tool Vendors Presentations We actively encourage tool vendors and ISP's to submit proposals for a special Tool Vendors Session Track aimed at products related to Boost and C++ (compilers, libraries, tools, etc.). Other formats may also be of interest. Don't hold back a proposal just because it doesn't fit into a pigeonhole. SUBMITTING A PROPOSAL --------------------- Standard Sessions are 90 minutes. You may submit a proposal for fractions Or multiples of 90-minutes. Fractional proposals will be grouped into 90 Minute sessions covering related topics. Longer sessions, such as tutorials and classes, will be assigned three hour (i.e. half day), or six hour (i.e. full day) time slots. Please include: * The working title. * Type of session: presentation, panel, tutorial, workshop, authors corner, vendor track, other. * A paragraph or two describing the topic covered, suitable for the conference web site. * Proposed length: 10-20 minute short talks, 45 minutes, 90 minutes, half day, full day. * Alternate lengths, if you are willing to make adjustments: 10-20 minute short-talks, 45 minutes, 90 minutes, half-day, full day. * Audience: users, developers, both. * Level: basic, intermediate, advanced. * A biography, suitable for the conference web site. * Your contact information (will not be made public). SUBMISSION DETAILS ------------------ All submissions should be made through the EasyChair conference management system: http://www.easychair.org/conferences/?conf=cppnow2013. If you have not already registered at EasyChair, you will need to do so in order to submit your proposal. All submissions will go through a peer review process. Authors are invited (but are not required) to submit PDF versions of full papers of up to 10 pages in ACM conference proceedings format (see http://www.acm.org/sigs/publications/proceedings-templates) The full papers are not required unless you want them published in the proceedings. All accepted proposals will be made available in the Association for Computing Machinery (ACM) Digital Library (approval pending). Best papers, after further reviews, will be considered to be book chapters or journal articles in a renowned journal. The session materials go on the C++ Now website and will be available to attendees. For general information on the C++ Now 2013 paper submission or the scope of technical papers solicited; please refer to the conference website at www.cppnow.org. For any other questions about the submission process or paper format, please contact the Program Committee at cppnow2013(a)easychair.com. If you have any technical problems with EasyChair, please contact EasyChair for help. Note: Presenters must agree to grant a non-exclusive perpetual license to publish submitted materials, either electronically or in print, in any media related to C++ Now. Hartmut Kaiser, email: hartmut.kaiser(a)gmail.com (Program Committee Chair) Dave Abrahams, email: dave(a)boostpro.com (Conference Chair) On behalf of the conference organizers

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[chrono][ratio][boost_1_52_0_beta1] warning in user code
by Jeff Flinn 31 Oct '12

31 Oct '12

I've just downloaded boost_1_52_0_beta1 and get the warning below in my user code on VC11(I'm using thread which evidently brings in the above libs). I didn't see mention of this in trac. I'm moving forward from 1.47 and from VC8 so I'm not sure if this is an indication of some project setting[s] of mine, or if it should be corrected in the lib? Thanks, Jeff 6>D:\boost_1_52_0_beta1\boost/ratio/detail/overflow_helpers.hpp(136): warning C4293: '<<' : shift count negative or too big, undefined behavior 6> D:\boost_1_52_0_beta1\boost/ratio/detail/overflow_helpers.hpp(282) : see reference to class template instantiation 'boost::ratio_detail::br_mul<X,Y>' being compiled 6> with 6> [ 6> X=0x01, 6> Y=0x01 6> ] 6> D:\boost_1_52_0_beta1\boost/ratio/ratio.hpp(155) : see reference to class template instantiation 'boost::ratio_detail::ratio_divide<R1,R2>' being compiled 6> with 6> [ 6> R1=boost::ratio<0x01,0x0989680>, 6> R2=boost::ratio<0x01,0x03e8> 6> ] 6> D:\boost_1_52_0_beta1\boost/chrono/duration.hpp(305) : see reference to class template instantiation 'boost::ratio_divide<R1,R2>' being compiled 6> with 6> [ 6> R1=boost::ratio<0x01,0x0989680>, 6> R2=boost::ratio<0x01,0x03e8> 6> ] 6> D:\boost_1_52_0_beta1\boost/chrono/duration.hpp(784) : see reference to class template instantiation 'boost::chrono::detail::duration_cast<FromDuration,ToDuration>' being compiled 6> with 6> [ 6> FromDuration=boost::chrono::duration<int_least64_t,boost::ratio<0x01,0x0989680>>, 6> ToDuration=boost::chrono::milliseconds 6> ] 6> D:\boost_1_52_0_beta1\boost/chrono/ceil.hpp(27) : see reference to function template instantiation 'boost::chrono::duration<Rep,Period> boost::chrono::duration_cast<To,int_least64_t,boost::ratio<N,D>>(const boost::chrono::duration<Rep,boost::ratio<N,D>> &)' being compiled 6> with 6> [ 6> Rep=int_least64_t, 6> Period=boost::milli, 6> To=boost::chrono::milliseconds, 6> N=0x01, 6> D=0x0989680 6> ] 6> D:\boost_1_52_0_beta1\boost/thread/win32/basic_timed_mutex.hpp(199) : see reference to function template instantiation 'To boost::chrono::ceil<boost::chrono::milliseconds,int_least64_t,boost::ratio<N,D>>(const boost::chrono::duration<Rep,Period> &)' being compiled 6> with 6> [ 6> To=boost::chrono::milliseconds, 6> N=0x01, 6> D=0x0989680, 6> Rep=int_least64_t, 6> Period=boost::ratio<0x01,0x0989680> 6> ]

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