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[operators] The Dangling Reference Polarization
by Daniel Frey 05 May '13

05 May '13

I see some good discussion going on, thanks to everyone participating! Rest assured that I value both side's contributions, it is important for me (and those agreeing with my perspective) to be able to defend this position and also to keep looking for improvements. If our side can not be defended, it's probably not good enough :) That said, here's what I hope can serve as a first summary, let's first look at it from a technical perspective: If an operator returns an rvalue reference (T&&), it is safe for all use-cases except binding the result to an rvalue- or const-lvalue-reference: T r = a + b + c; // no problem const T r = a + b + c; // no problem T& r = a + b + c; // compile-time error const T& r = a + b + c; // problem (P1) T&& r = a + b + c; // problem (P2) It seems that this is consistent behavior across at least GCC, Clang and VC++. If a compiler shows a different behavior, its likely a compiler-bug. Technically, there is no doubt that the above is a bug, but that doesn't answer the question of whether this is a bug of the user who wrote the above code or if it's a bug of the operator to return an rvalue reference instead of an rvalue. This is where we leave the technical-aspects-land and enter the minefield of opinions, expectations and decisions. I am of the opinion that the above problematic use-cases are a bug on the users side, my line-of-thoughts and my arguments are: a) The above code is explicit, you can spot it in the users code. It's not something that happens silently. b) The above code always looked suspicious to me anyways, it has a code-smell that I just don't like. c) It rely's on the fact that it extends the lifetime of a returned temporary value. The rules of the C++ standard that allow this are quite clear, and hence it's the users responsibility to make sure that there actually is a temporary value whose lifetime can be extended. It has always been an error if the expression returned a reference and not a value. Consider const std::string& oops = std::vector<std::string>(1, "hello, world" ).front(); This compiles are creates a dangling reference, as the standard says that front() returns a reference and not a value. It's not 100% comparable as in this case the standard guarantees a bug, but the main point for C++ has always been which guarantees are given and not about a certain expectation one might have. As an example: static_assert( std::is_empty< std::tuple<> >::value, "Expectation 1 broken" ); static_assert( std::is_empty< std::array< T, 0 > >::value, "Expectation 2 broken" ); // with any valid T The first case is certainly a reasonable expectation and it currently works for all implementations of std::tuple that I know of, but it is not guaranteed! If your code relies on it and it breaks in the future, you can not blame the person who modified std::tuple. The second case is also a reasonable expectation, but it breaks everywhere and AFAIK there is no standard-conforming way to implement std::array so that std::array<T,0> is empty. For the curious, here's the StackOverflow question I asked about it: <http://stackoverflow.com/q/15512827/2073257>. Another example about how to properly handle expectations vs. guarantees: <http://stackoverflow.com/q/14882588/2073257>. d) I fail to see any valid use-case for binding the result of the expression to a reference. Can someone please provide a convincing example of why (P1) or (P2) are needed/useful? Keep in mind that in the context of operator+ (or any other operator in question), we already require that the type T is copy-/moveable and that copy-elision most likely takes place if you use "T r = …" instead of "const T& r = …". e) The alternative needs to prove its claimed/theoretical efficiency in practice. Too often I have heard about "sufficiently smart compilers", but I'm more the prove-it-in-the-real-world type. So summarizing it once again: For a) and b), this is just an observation and my personal opinion. c) means it's important to talk about guarantees, not just about expectations (no matter how reasonable they are). d) poses the question if we loose something if we don't guarantee that (P1) and (P2) are allowed. I currently have several ideas/option of how we could improve Boost.Operators, some of which I already mentioned, some which only recently occurred to me. Before I will discuss these, I'd like to resolve (if possible) the Dangling Reference Polarization and gather more opinions/feedback. So far, I found the discussion both challenging and very helpful, again thanks to everyone participating! Best regards, Daniel

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[gsoc] Boost.Multiprecision Proposal
by Saurav 04 May '13

04 May '13

Hi, I have attached my proposal for the Boost.Multiprecision project. It has been provided in PDF format for better readability. Please have a look and give your feedback. Best regards, Saurav

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[Boost.ThreadPool] GSOC 2013 Proposal
by Ian Forbes 04 May '13

04 May '13

Hi, I am submitting my Google Summer of Code proposal for review. My proposal is for the Boost.ThreadPool library. It will be based on work done here: https://svn.boost.org/trac/boost/wiki/SoC2013#Boost.ThreadThreadPool The current proposal can be found at: http://cs.mcgill.ca/~iforbe/gsoc2013.html The original proposal can be found here: http://www.google-melange.com/gsoc/proposal/review/google/gsoc2013/en4bz/1 , although it has broken HTML tags and is ill formatted. Thanks goes to Vicente J. Botet Escriba for pointing out that Boost does in fact has LockFree concurrent data structures. Please feel free to respond with any questions or criticism. I will try to respond to the best of my ability. Thanks, Ian Forbes

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[chrono/date] year/day/week literals
by Vicente J. Botet Escriba 04 May '13

04 May '13

Hi, on the GSoC discussion about Boost.Chrono/Date proposal we were discussing about date construction. Some of us think that we need to use named types for day, month, year and week so that the date constructors are not ambiguous. Everyone agree with the constant object for month. date dt(year(2013), may, day(3)); But having to use day(3) or year(2013) seems to wordy. I was wondering if we can not add some literals for day, year and week so that we can just write date dt(2013y, may, 3d); The advantage I see in addition to been less wordy, is that we will have a compile error when the year, day or week is out of range. What do you think? Vicente

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Live read-only GIT mirrors of Boost trunk SVN
by Niall Douglas 04 May '13

04 May '13

The live GIT mirrors of Boost trunk SVN have become a bit stale in recent months: https://github.com/ryppl/boost-svn, long time favourite of many, now 4 months stale. https://github.com/Beman/boost-trunk-git-svn is now 2 months stale. https://github.com/alexanderkjeldaas/boost-mirror is fresh, but has no branches nor tags. They all generally use git-svn, which tends to be brittle and not translate commits perfectly unfortunately e.g. SVN eol properties and other such metadata. So I decided to try out a new Subversion <=> Git mirroring tool, SubGit v2.0 EAP (http://subgit.com/eap/) whose author very kindly gave me a free open source licence and the result is at: https://github.com/ned14/boost-trunk All branches and tags, as far as I can tell, are mirrored correctly. I've set a cron job every 24 hours. Theoretically if we had an authors mapping file it would work in the opposite direction too i.e. be read-write. My next task is to live mirror a github repo into Boost Sandbox. Currently SubGit segfaults on this due to the complex SVN properties auto-translation which requires a specially marked up .gitattributes, but the author is very keen to fix the problem. In theory then it ought to just work. Any mistakes in my Boost mirror, or any problems, or even thoughts are gratefully received. Niall

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Specific-Width Floating-Point Typedefs
by Paul A. Bristow 04 May '13

04 May '13

There has recently been some discussion on improving portability of programs using floating-point. Drawing on the benefits from definition of typedefs for int32_t, int64_t, int128_t . we have drawn up a proposal to add similar typedefs for floating-point. Our draft document (in both html and pdf) is at https://svn.boost.org/svn/boost/sandbox/precision/libs/precision/doc/html/i… https://svn.boost.org/svn/boost/sandbox/precision/libs/precision/doc/precis… We hope to propose this to the SG6 Numerics subgroup of WG21 ISO C++ standards body. But would welcome comments from Boosters to help us improve this proposal. Thank you. Paul --- Paul A. Bristow, Prizet Farmhouse, Kendal LA8 8AB UK +44 1539 561830 07714330204 pbristow(a)hetp.u-net.com

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date libary construction
by Shamsher Siddiqui 04 May '13

04 May '13

i am deeply regretting for not responding your Question and for not posting the google summer of code Proposal . my pre semester exams are going on so i was busy in preparing which is ending on 7 may which is coming tuesday so i will be always not active during this period but i will try to respond to discussion which happening on the mailing list . i am finally sending only the proposal part . Proposal for DATE LIBRARY 1)Construction of Date: According to paper [2] there were many benchmark set but date should be represented in both ways i.e field and serial .Field and serial representation have their advantage over each other under certain operation . No invalid dates can be entered considering range cheaking ,non existent date if entered bad_date exception is thrown during the time of constructing the date. Constructing constant object for day,week_day. Date construction concrete structure <template class date_concrete> class date_pre { //year, month,week day //constructors //basic accessors declaration //conversion accessors //airthematic operation //camparison operator for date camparison } 2) Arithematic Operation On date Date airthematic can be done on three units i.e day,month,year.In chrono date ::calendar(Gregorian calendar) length of month and year is not fixed : day arithematic Adding number of days to date until range doesn’t exceed Implementing last day arithmetic to avoid the bad date excepti Eg. aug/last/2011 +months(1)= sep/30/2011 aug/31/2000 +months(1)=sep/31/2000 //invalid date bad date excep thrown month arithmetic Month arithmetic is quite complex compared to day arithmetic since number of are not fixed . (month day <=28 || month day =last day ) always add month month day =29 cheak for leap year and than add month Month day>=30 add but don’t add if resulting month is feb Using constant objects for month arithmetic. year arithematic Always add year to date considering the condition of leap year Reversal of date back to original date Usage of last day during year arithematic 3) InterConversion field representation & serial representation Some operation are quite fast on field but airthematic operation are much faster on serial campared field representation .So it is necessary to provide the inter-coversion so that it can be easily converted from one representation to another. Constructing bi-directional conversion of serial and field by making use of memoization optimization techinique. 4)Gregorian calendar implementation This Gregorian calendar will be a hybrid calendar that support both Julian and Gregorian calendar with a single discontinuity(the day on which Gregorian calendar was adopted ).The only difference between gregorian and julian is leap year calculation and before day of adoption of Gregorian calendar ,Julian calendar is implemented in this date library. The concrete draft for implementation for calendar template< typename ymd_type ,type name date _int _type > class gregorian_calendar { public : typedef ymd_type ymd _ type ; typedef typename ymd_type : : month_type month_ type ; typedef typename ymd_type : :day_type day_type ; typedef typename ymd_type : : year_type year_type ; typedef date_ int _type date_int_type ; static unsigned short day_of_week (const ymd _type &ymd ) ; static int week_number (const ymd_type &ymd ) ; static date_int_type day_number(const ymd_type &ymd ) ; static ymd_type from_day_number(date_int_type) ; static date_int_type julian_day_number(const ymd_type &ymd) ; static bool is_leap_year(year_type) ; static unsigned short end_of _month_day( year_type y ,month_type m ) ; static ymd _ type epoch() ; static unsigned short days _ i n _week(); }; 5)Building date iterator ,date output and date input Date Iterator will generate the date based on initial condition and end.Bidirectional iterator will do all the generation of series of date.Various iterators which will be implemented are day ,week ,month ,year Iterator. date output same as H. Hinnant. Questions: 1)could you explain us why do you think a class template date is a good alternative? i am using the template class since it will implement the user extensibility .This is very important feature for developer but not for normal user because developer likes to customise code it will give them to add or modify without removing features. 2) What is the expected service of the concrete classes? Which concrete representations would you provide? i have made the concrete class to show some of details of the date library which i am going to implement . <template date_concrete> class date_pre { /*year, month,week day construction of date_field i.e serial and field based reprasentation*/ /*details of constructor 1)date_pre(); //default constructor to initialise the date with the initial default value set 2)date_pre(year_type year,month_type month,day_type day); /*this constructor will initialize the date with values given by the user . but the constructor argument arrangement can be differ according to user or the country date format used */ 3)date_pre(year_type year,month_type month,week_of_month_type week_number,weekday_type wd); //this will constructs the date like monday in week 20 of 2013 4)date_pre(special day sp); //this will day construct the date with the special values like mothers day ,christmas in year //basic accessors declaration //conversion accessors //airthematic operation //camparison operator for date camparison //Coversion of calendar }; these all same as in H. Hinnant proposal except the conversion of Julian calendar to gregorian calendar . 3) How would you implement the memoizer for conversions? Would it be thread safe? Could you post an example how your date_pre and gregorian claendar classes are used? in summary, how your proposal improc-ves H.H implementation or my prototype? since pre semester are going so can i answer to this 2 question after coming tuesday ie 7 may 2013 sorry again for not answering ur questions i will try to be active on the mailing list during my pre semester xam Thanking You Shamsher Ahmed

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[gsoc-2013] Physics Library Abstraction Layer
by Preston Hamlin 04 May '13

04 May '13

Attached is my current proposal in PDF format, as I am a bit wary of pasting several pages worth of formatted text into an email. Well wishes, -Preston

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GSoC 2013 Boost mentors discussions
by Vicente J. Botet Escriba 04 May '13

04 May '13

Hi, I would like to share privately some comments with the GSoC 2013 Boost mentors. How can we do it? How to know who is a mentor? Do we have a know e-mail for all of them? Best, Vicente

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Re: [boost] [operators] moving forward use return by reference for compilers with proper support?
by Niall Douglas 04 May '13

04 May '13

> Operators returning rvalue references are NOT safe. The C++98/03/11/14+ rules > apply to this scenario: > > X temporary(); > const X& r = temporary(); // ok, lives as long as r does > X&& r2 = temporary(); // ok, lives as long as r2 does > > They do NOT apply to this scenario: > > X&& func(X&& x) { return std::move(x); } > const X& r3 = func(temporary()); // DANGLING REFERENCE > X&& r4 = func(temporary()); // DANGLING REFERENCE > > The Standardization Committee made this mistake when applying rvalue > references to string's operator+(), which was fixed before C++11 was released. I completely agree. 99.9% of the time the only reason to *ever* return rvalue refs from an operator() is when you're passing through a parameter. Otherwise, return by value and leave the compiler's optimizer do its job. Niall --- Opinions expressed here are my own and do not necessarily represent those of BlackBerry Inc.

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GSoC 2013 Bernoulli Numbers
by David Joy 03 May '13

03 May '13

Hi, I'm an Open University student completing my Open degree this summer (CompSci / Pure- & Applied Maths / Classical History) and am very interested in the Bernoulli numbers project for the Google Summer of Code. As well as the OU I've done quite a bit of mathematics elsewhere (Durham and KCL). Enclosed is my (naive) response to your challenge to implement the Akiyama–Tanigawa algorithm. I use the Boost framework for rational numbers, so as not to lose precision (though haven't yet adapted the solution for arbitrary precision numbers). [It would be more aesthetically pleasing if I could write the main algorithm in a STL-style so that it iterates of the vector, rather than explicitly using an index.] I have yet to get to grips with Boost.Test, but the enclosed shell script can generate a list of results, which matches the table found on the Bernoulli Number Page <http://www.bernoulli.org/> out to B_20. All code criticism gratefully accepted, David Bernoulli.cpp <http://boost.2283326.n4.nabble.com/file/n4646219/Bernoulli.cpp> Bernoulli_test.sh <http://boost.2283326.n4.nabble.com/file/n4646219/Bernoulli_test.sh> -- View this message in context: http://boost.2283326.n4.nabble.com/GSoC-2013-Bernoulli-Numbers-tp4646219.ht… Sent from the Boost - Dev mailing list archive at Nabble.com.

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Re: [boost] GSoC Boost.Multiprecision project
by Jyotesh Choudhari 03 May '13

03 May '13

Hello, > Hi Jyotesh. >> Thank you for your valuable feedback. I have written >> project proposal for the first time in my life. So, I did >> not know what details to include. I have made some >> changes to my proposal as per your suggestions. > The proposal is a lot better. Now you need to submit > it to Google's melange site. > Please note that the proposal must be submitted > to Googles melange site. Some candidates have > been sending the proposals directly to us, and > this is incomplete. I have uploaded my proposal on http://www.google-melange.com/gsoc/proposal/review/google/gsoc2013/jyoteshr… >> I was studying the code for cpp_bin_float and I >> have some doubts in my mind. >> 1. What are eval_ops_signed_type, eval_ops_unsigned_type and >> eval_ops_float_type? > Eval-ops are the global binary arithmetic operatory, > and the eval_ops-types are those types that will be > supported for global binary math with the radix-2 > back-end. >> 2. What is the use of following lines? >> typedef mpl::list<eval_ops_signed_ type>? signed_types; >> typedef mpl::list<eval_ops_unsigned_type> unsigned_types; >> typedef mpl::list<eval_ops_float_type>? ? float_types; > It's Boost's way of creating a list of built-in types. > Again, these are the types that will be supported for > global binary math. >> These are not used in the class elsewhere. Similar lines >> are present in cpp_dec_float.hpp also and not used >> elsewhere in the class. > They are used by the multiprecision::number front-end > to actually implement global binary math ops. >> 3. In the function from_float_type, I think the variable >> number_of_digits should be initialized to zero before >> using it in while loop. > cpp_bin_float is in a rudimentary state right now. > It is not even close to working. That's the point of > the GSoC project. So stuff might not be quite right > yet. Thank you solving my doubts. I will see the code multiprecision::number also to see how above types are used. >> Lastly, I have seen on mailing list, that some of the >> students are submitting code samples. > It's too late for code. Get your best shot at a good > proposal onto melange. If you would like to submit > code sample, you can do it after your proposal is up. > Good luck. > Sincerely, Chris. Thanks and regards, Jyotesh Choudhari

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Voronoi benchmark update
by Sebastien Loriot 03 May '13

03 May '13

Hello, I'm involved in the CGAL Project, and saw the Voronoi benchmark. It would be nice if you could change the CGAL code slightly, as it is not as bad as it currently seems. Attached is the diff to the trunk of boost. Concerning the Voronoi diagram of points, a CGAL user, would use the Delaunay_triangulation_2 class. Concerning the Voronoi diagram of segments (that do not intersect) one would make a better choice for number types and traits classes. Also one better first inserts the endpoints and then the segments (I agree, this should definitely go into a member function). Admittedly our examples could be better. Cheers, Sebastien

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[gsoc-2013] Physics Library Abstraction Layer
by Preston Hamlin 03 May '13

03 May '13

On Sun, Apr 21, 2013 at 9:37 PM, Michael Marcin <mike.marcin(a)gmail.com>wrote: > On 4/19/2013 8:59 PM, Preston Hamlin wrote: > >> >> I have completed a draft proposal and would appreciate some feedback: >> >> https://www.dropbox.com/s/**7xhha0a3ahk5p6r/preston_** >> hamlin_gsoc_proposal_draft.pdf<https://www.dropbox.com/s/7xhha0a3ahk5p6r/preston_hamlin_gsoc_proposal_draf…> >> >> >> > Seems like a fine proposal. > > Do take note of boost coding guidelines. > > -- > Use the naming conventions of the C++ Standard Library (See Naming > conventions rationale): > > * Names (except as noted below) should be all lowercase, with words > separated by underscores. > * Acronyms should be treated as ordinary names (e.g. xml_parser instead of > XML_parser). > * Template parameter names begin with an uppercase letter. > * Macro (gasp!) names all uppercase and begin with BOOST_. > -- > > http://www.boost.org/**development/requirements.html#**Guidelines<http://www.boost.org/development/requirements.html#Guidelines> > > Prefer object interfaces to pointers. > > For example instead of: > bxPhysics* physics(___); > > prefer: > boost::physics::physics physics_(____); > > Although on second thought naming might need some more thought here. > > What exactly is it that PxCreatePhysics creates? Is it a physics context > like an OpenGL context? Is it more like a physics service like a > boost::asio::io_service? Is it a physics simulation? Is it physics object > factory? > > I'm not sure but I think it's almost certainly not just a physics. > > > In any event it looks good to me. > > My apologies for the belated response. With ACM duties and finals week I have had no more than a few minutes to sit down. I typically try to follow the Google style guide for coursework and the like, so changing naming conventions is but a minor change. The PxPhysics object is used to create and maintain a "realm" of physics. It keeps track of collision methodologies and is essentially the backbone of how edges and vertices interact with one-another. It is build on top of a PxFoundation object which provides the "foundation" of the program, including callback management and some behind-the-scenes memory allocation. The PxScene object manages the elements of a particular "scene" or "world" including pointers to the various objects and gravity. I am not sure how (other than routing messages between objects) boost::asio::io_ would provide much of anything in terms of physics. It is similar to a context like a Device Context or OpenGL Rendering Context but is not used directly and instead used in the creation of more modular objects which are linked to it upon creation. There are no built-in emitters (something that could be provided in this project) and the documentation states that the non-fluid particle system uses rigid bodies that interact with the world but not eachother, which makes sense. I was unsure how prefixes should/would be used in a project like this, which is why I used the "bx" prefix. One thing to note is that PhysX uses a 3-vector class to hold vector data. It is pretty basic but also moderately fleshed out in the source. Would compatibility with the uBLAS matrices (as vectors are to be consolidated) be desirable? The PhysX design uses pointers for just about everything, so that could mean some interesting design considerations. I will be spending the Summer assisting one of my professors with his research project (half-time) and will update my proposal accordingly. Also, if I have some free time this weekend, I can crank out some *rough* proof of concept code if it is desired. Many thanks, -Preston

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[GSOC 2013]Boost.Math Proposal
by Nikhar Agrawal 03 May '13

03 May '13

Hi everyone, I have been in touch with mentors for the project "Boost.Math Bernoulli Numbers and Applications to Special Functions" for the past three weeks. And after regular interactions and assignments and suggestions from them, I have finally posted my proposal. I was a little late because in submitting the proposal because of my end semester examinations. But that now they are over, I have all the free time to completely concentrate on the project. Here's the link to the proposal. http://www.google-melange.com/gsoc/proposal/review/google/gsoc2013/nikhar/1 I'd be really grateful if you guys could review it and suggest improvements. Thanks a lot. :) Nikhar P.S.:- If anyone wants I could also forward the conversations I've had with the mentors until now and I could upload the assignments I've done if anyone's interested.

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[gsoc-2013] proposal for approximate string matching
by Yu Jiang 03 May '13

03 May '13

Hi, I'm a student from Tsinghua University in china and interested in the idea about "approximate string matching". Below is my proposal for this. Could you please view it and give me any kinds of suggestions on it? Thanks! (1) Personal Details * Name: Yu Jiang * College/University: Tsinghua University, China * Course/Major: Computer Science and Technology * Degree Program: M.Sc. * Email: sunlightt07(a)gmail.com * Homepage: do not have one * Availability: - How much time do you plan to spend on your GSoC? Since I have a long summer holiday, I can spend 30 hours a week. - What are you intended start and end dates? I will follow the calendar of GSoC. I have plenty of time from June to September. - What other factors affect your availability (exams, courses, moving, work, etc.)? I have some courses this term which will end before June. 15th. However, these courses don't have heavy workload, I still have enough time to work on GSoC. (2) Background Information * Please summarize your educational background (degrees earned, courses taken, etc.). I majored in Computer Science and got my bachelor degree in Tsinghua University from 2008 to 2012. I learned some basic courses such as algorithm, data structure, algebra and logic. I also learned many advanced courses such as database, operating system, network, formal language, compiler, computer architecture. Currently I'm working for my master degree. My research interest is database. * Please summarize your programming background (OSS projects, internships, jobs, etc.). This is the first time I plan to take part in an OSS projects. I have worked as an intern in Hulu, an online video website, for one year, mainly focus on frontend webpages. I have used C++ to finish many course projects, such as a simple ftp server and client, completing a tiny os and so on. Recently I am learning the new features in C++11 and get to know much more about the C++ language. * Please tell us a little about your programming interests. I really love to optimize on the implantation of an algorithm by making full use of the compiler and the architecture(e.g. cache, SIMD). Besides, I like to write webpages using different kinds of excellent frameworks. * Please tell us why you are interested in contributing to the Boost C++ libraries. Boost is the most famous C++ libraries. It is powerful and can be used in many different kinds of programs. It's my honor to add some new features into it. * What is your interest in the project you are proposing? It's related to my research interest. Nowadays data are produced rapidly. To clean or integrate them so that we can get a better view, "Approximate string matching" is rather a powerful tool. I'd like to see such functions in boost library. * Have you done any previous work in this area before or on similar projects? Yes. My lab has focused on researching on such algorithms for 3-5 years. The "best" algorithm for general string similarity search and join is called "passjoin", which is invented by our lab. I have implemented it and done a lot of optimizations. Early this year we attended a string similarity search & join competition[1] and achieved champion. The code is mainly written by me. [1] http://www2.informatik.hu-berlin.de/~wandelt/searchjoincompetition2013/Resu… * What are your plans beyond this Summer of Code time frame for your proposed work? I will make efforts to make it accepted by the boost library. If it can be released someday, I will maintain it. * Please rate, from 0 to 5(0 being no experience, 5 being expert), your knowledge of the following languages, technologies, or tools: -C++: 3 -C++ Standard Library: 3.5 -Boost C++ Libraries: 2 -Subversion: 3 * What software development environments are you most familiar with? Eclipse. I use it in both windows and linux. * What software documentation tool are you most familiar with? Doxygen. (3) Project Proposal Approximate string matching is a "hotspot" in recent years. It's widely used in big data processing such as search engine, DNA matching. It also can be used in simple tasks like spell checking. However, there isn't a high performance and well-designed library in such area. I wish to see such algorithms in boost so that many people can benefit from this! My proposal contains two parts: A. To implement basic similarity metrics. Edit distance and Jaccard may be the most popular ones. Well, I'll implement more similarity metrics, such as Hamming distance, dice and cosine. B. To implement the fastest algorithm for string similarity search and join. Similarity metrics will be edit distance only since it is most commonly used. Similarity search is to find out all the strings in a given set S, which are "similar" to a query string. Similarity join is to find out all the string pairs<r,s>, where r is in set R and s is in set S and r is similar to s. They are the most useful operators in large data processing. However, the brute-force method for such problem is too slow. And it's not easy to write a correct and high performance algorithm without reading the details in many research papers and debugging them for a long time. To avoid reinventing the wheel, I strongly propose to implement it in boost library. Here is a prototype for the interface: Part A. basic similarity metrics (use edit distance as an example) (1) int edit_distance(const Range1T&, const Range2T&); // return edit distance. (2) int edit_distance(const Range1T&, const Range2T&, int threshold); // return edit distance if it is no larger than threshold, else return -1 or threshold + 1. (3) int edit_distance(const Range1T&, const Range2T&, equal_func); // use uqual_func to determine whether two elements are equal or not. (4) int edit_distance(const Range1T&, const Range2T&, insert_cost_func, delete_cost_func, substitute_cost_func); // use three cost functions to calculate the cost for one insert/delete/substitute operation. (5) some functions to return the sequence of operations? Version (1) may be the most common case. Version (2) can use the given threshold to do optimization for the speed (O(m*n) -> O(threshold * min(m, n))). It's useful since sometimes we only care about the exact edit distance if it is small. Version (3) and (4) extend the flexibility of this utility algorithm. I'm not sure whether to support (5) or not. Part B. string similarity search and join algorithms, focus on edit distance class searcher { void insert(IDType id, const string &word); // insert a word to the index, id is used as an identifier of this word. void erase(IDType id); // erase a word from the index, id should be the same one used in insertion process. vector<Result> search(const string &query, int threshold); // performing similarity search, which will return all the strings which are similar to the query string. Result may be a pair of the id and real edit distance. }; class joiner { vector<PairResult> join(const string_and_id_container &R, const string_and_id_container &S, int threshold); // performing similarity join. Usually we are doing on-line join, which means we cannot pre-build the index. So we only need this one function. It will return all the <r,s> pair where r is in R and s is in S and r is similar to s. PairResult may be a tuple of r's id, s's id and real edit distance. }; (4) Proposed Milestones and Schedule Now – June 15 To be more familiar with the Boost library. Discuss the details and interfaces with my mentor and on the develop mail list. June 15 – July 15 Develop a beta version of the approximate matching library. Most functions will be done at this time. July 15 – August 1 Review my code and improve its performance and quality. Discuss with my mentor for mid-term evaluation and future works. August 1 – September Write documentation, test code for my library. Make it "boost" like.

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[GSoC 2013] Proposal Boost.Math Bernoulli Numbers and Applications to Special Functions
by Łukasz Marecik 03 May '13

03 May '13

Hi, I would like to introduce my proposal to project "Boost.Math Bernoulli Numbers and Applications to Special Functions". It is available at https://google-melange.appspot.com/gsoc/proposal/review/google/gsoc2013/luk… Please note that HTML version is not the best one: the formatting is not very nice, there is also lack of equations and source codes (there are provided in external files). So please take a look at PDF-version of my proposal (follow the link at Google Melange site). Kind regards, Lukasz Marecik

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GSoC: Data structures and algorithms for integer ranges.
by Jeremy Murphy 03 May '13

03 May '13

Hello Boost community, I realized almost too late (two days ago) that GSoC 2013 is happening, and that Boost is in. Obviously I have missed the boat on "engaging with the community" early, but I still plan to submit a proposal. The one thing I would love to get some brief feedback on in these last hours is scope: how much should I expect to get done in 12 weeks? Unsurprisingly, it is one of the hardest questions for an inexperienced worker in any field to answer. The core of my proposal is to implement i) a van Emde Boas tree and ii) three counting sort algorithms: "counting", radix and bucket. Is that enough? Too much? Any advice would be helpful, thanks. Cheers. Jeremy

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Google summer of code 2013
by Jawad Elomari 03 May '13

03 May '13

Hi everyone, I want to join the Google summer of code this year, for the PaGMO/PyGMO<http://www.google-melange.com/gsoc/org/google/gsoc2013/pagmo> library. I'm interested in the Racing projects, but I'm not sure which Boost library is most suitable for it. Any ideas? Regards,

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[GSoC 2013] Implicit routines in boost.odeint
by Artem Serov 03 May '13

03 May '13

Hello again! I have been working on proposal since aproximately 15 of April, investigating boost odeint, some theory of numeric methods of solving ODE and implementing a draft of the design of implicit routines. I discussed some issues privately with mentors of odeint project Mario Mulansky and Karsten Ahnert and have taken into account all the points. Here is the 1st version of the proposal for Boost.odeint implicit routines. Note: The main idea i kept in mind was to describe steps how i will do the project as clear and detailed as possible. I tried to show my acquired experince of odeint structure and concepts, my understanding of the issue and concrete ways of tackling it. Note: The proposal entirely lacks introduction, list of literature and sources! i will settle it as soon as possible. Here is the link to the proposal: https://docs.google.com/file/d/0B-2QwVSmhDBIYTB0eVZxdHhsNUE/edit?usp=sharing -- Thanks, Artem Serov

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GSoC: Student application deadline in less than 24 hours
by Boris Schaeling 02 May '13

02 May '13

Students interested in applying for a GSoC project should submit their application as soon as possible. The deadline is in less than 24 hours. Click here to apply: <https://google-melange.appspot.com/gsoc/homepage/google/gsoc2013> Boris

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[gsoc-2013] Boost.Expected
by Pierre T. 02 May '13

02 May '13

Hello, My name is Pierre Talbot, I participated to GSoC 2011 and began the implementation of the Boost.Check library (for checking the validity of any number having a check digit — credit card number, ISBN, …). It was two years ago and the design is still evolving due to many variation points in the code. One of the function looks like : template <typename check_algo, typename range> boost::optional<typename check_algo::checkdigit_type> compute_checkdigit(const range &x); Using boost::optional tell us that: "A check digit should be computed if 'x' is a valid sequence". Since 'x' has many reasons to be incorrect, many errors could be raised. Based on a policy template class, it launches exception or returns with an empty optional . Then I though a lot about a better way to do it, allowing the user to get an exception or an error code. But it was quite complex for a so little part of my library… I decided that the policy "throw exception or nothing" should be enough. Yesterday, I watched the video of Mr. Alexandrescu on Boost.Expected and I think it would be a very useful library. It could mainly be useful in system programming (where many error codes can arise from a single call), but in any code where many exception errors can be thrown (like in Boost.Check). As you suspected, I'm interested in coding Boost.Expected during the summer as a GSoC student. Firstly, it could be very useful to list the resources on the subject (aside the talk), I have several articles that I will talk about later. Secondly, and hoping you'll debate, I would like to ask your opinion about several ideas and facts: 1) In the Boost project description, we can read: "adding a class expected-or-error_code". Obviously, the main design decision made by Alexandrescu is to consider that error code are exception. Do we need an abstraction of exception/error code ? Why do you think a "expected-or-error_code" class is interesting ? 2) Consider this code (from Alexandrescu slides) : // Caller string s = readline(); auto x = parseInt(s).get(); // throw on error auto y = parseInt(s); // won’t throw if (!y.valid()) { // handle locally if (y.hasException<std::invalid_argument>()) { // ------------------ < The flagged line. // no digits ... } y.get(); // just "re"throw } The flagged line has some tastes of "return to the past" flavor. Back to the C procedural language, the basic error code handling system was a lot criticized because: * Readability of the code decrease ; * Error handling occurs in the middle of the execution flow ; * <Add your favourite reason here>. Several links on the subjects (if you have others, I'm interested) http://www.joelonsoftware.com/articles/Wrong.html http://www.joelonsoftware.com/items/2003/10/13.html http://blogs.msdn.com/b/oldnewthing/archive/2005/01/14/352949.aspx http://nedbatchelder.com/text/exceptions-vs-status.html Basically, only the last one is clearly for exception. The main argument against the procedural approach is the readability. I would say that the Expected approach just differ by allowing to rethrow exception. But if you want to handle it, you must code multiple if-than-else statements. So I considered a complementary approach working with Expected to handle multiple error cases: string visa_number = readline(); expected<char> expected_checkdigit = compute_checkdigit<visa>(visa_number); if(expected_checkdigit.valid(visa_error_resolver)) { visa_number += expected_checkdigit.get(); std::cout << visa_number << std::endl; } With this code, there is only a if statement, and no more multiple error cases handles. But what is this error_resolver ? It may be declared as : // Somewhere in visa.hpp. A type list. typedef error_list<size_error_exception, unknown_character_exception, checkdigit_encoding_exception, …> visa_errors; // Somewhere in the user code. error_resolver<visa_errors, expected_type> visa_error_resolver; // in this case, expected_type is a char. // Initialize error handler on specific exception/errors. visa_error_resolver.on<size_error_exception>(size_error_handler) .on<unknown_character_exception>(unknown_character_exception) ... Now we are agree that visa_error_resolver can be reused everywhere we want to resolve an error on a visa number. What are the handlers ? There are [Function|Functor|Lambda] (pick up your favourite) with this form : expected<ExpectedType> size_error_handler(const size_error_exception&) expected<ExpectedType> unknown_character_exception(const unknown_character_exception&) Now you can understand for what the type list "error_list" stands for, we can store these handlers into the error_resolver and call them without any virtual cost. Why the return type of error handler is expected<ExpectedType> ? Consider this size_error_handler code : expected<ReturnType> size_error_handler(const size_error_exception& e) { std::cout << "The number you gave has a bad size." << std::endl; std::cout << "Enter it again : " << std::endl; return read_visa_checkdigit(); } read_visa_checkdigit can call recursively valid() until it's valid. Though there are some ways to make this treatment iterative. A basic treatment could be to print an warning message and just returns (in this case, valid returns false): expected<ReturnType> size_error_handler(const size_error_exception& e) { std::cout << "Warning: the VISA field is incorrect." << std::endl; return expected<ReturnType>::fromException(e); } Results: * The error code handling is delegated to specific functions ; * The readability is still excellent ; * You can easily re-use your error handler function ; * If you don't like it, you can still throw exception on failure with "get()". I can code a "proof of concept" if you think this is a good idea. Do not hesitate to comment it, point out programming pitfalls, request further clarification, or anything you judge useful. Thank you for reading it ! Pierre Talbot

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Re: [boost] [gsoc-2013] Boost.Thread/ThreadPool project
by Niall Douglas 02 May '13

02 May '13

> > I have just read N3388 - Using Asio with C++11 and a think I start to > > understand the ASIO design. > > Could we say the completion handlers are continuations? > > And that the user use to master which thread executes the continuation by > > calling the io_service::run() function? > > Pretty much, except that multiple threads can call io_service::run > concurrently. Basically Boost.Asio is a work sharing queue plus a > collection of waitqueues to wait for specific events. Far clearer than my explanation. Thanks. > That's orthogonal. Boost.Asio provides the funding blocks. A nicer > interface that doesn't require an explicit continuation passing style > transformation can be built with Boost.Context or a similar library. > But it probably needs a future implementation that integrates with > ASIO, which is one of the point of Niall Douglas. Spot on. Especially as parts of ASIO are due to enter with TR2. I worry that a thread pool designed without ASIO in mind would become an orphan isolate. Niall --- Opinions expressed here are my own and do not necessarily represent those of BlackBerry Inc.

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[testing] run.py and cross compilation
by Antony Polukhin 02 May '13

02 May '13

Hi, Is there some possibility to compile sources on one platform (x86) and then run compiled tests on other platform (ARM/Android) using run.py script? This is required, because Android SDK exists only for x86 so there is no way to compile tests on ARM Android device. -- Best regards, Antony Polukhin

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[GSoC2013] My updated proposal to the XML library project
by Amos Ji 02 May '13

02 May '13

Hi, I have updated my proposal to the XML library project. If you're interested in it, you can review it at http://www.google-melange.com/gsoc/proposal/review/google/gsoc2013/amosji/3… And there is also a pdf version: https://www.dropbox.com/s/3zgxkpb9bx45auo/Boost_XML_library.pdf Any comments are appreciated. Thanks a lot. Regards, Mingchao

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