March 2014 - Boost - lists.preview.boost.org

Boost summer of formal reviews
by Borislav Stanimirov 12 Mar '14

12 Mar '14

Hello, This is a (half-)joke suggestion. There are currently 19 libraries in the review schedule ( http://www.boost.org/community/review_schedule.html ) which need a review manager (yes, including mine). Some of them have been there for years. Instead of focusing on getting people to write new libraries, which could potentially end up stuck in the review schedule (like AFIO), why don't we focus on getting the reviews for the ones that are already there. Or at least revising the review process. For example, I would be willing to review some of these libraries, but I am not qualified to be a review manager (since I am not very active in the community). I am not saying that most (or any) of the libraries stuck in review limbo, should pass the process, but some of them at least deserve a look (again, like AFIO). -- Borislav

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[GSoC 2014] [ Hypergeometric functions ] [ Complex Numbers Calculations ]
by Cosmin Boaca 11 Mar '14

11 Mar '14

Hello, I am Cosmin Boaca and I want to work during GSoC 2014 at the hypergeometric functions project. The project aims to approximate some hypergeometric functions for real values of their parameters. Even though the final result of the computation will be a real floating point number, some intermediate results would require complex numbers calculations such as the real power of a negative number, the square root of a negative number and also basic operations with complex numbers. My first question is : is there a way to do this operations using boost::multiprecision types such as cpp_dec_float and cpp_bin_float in order to store the real and the imaginary part of the complex number ? The second question is : Can I use the complex functions from the cstdfloat branch of Boost.math ? Thank you, Cosmin Boaca

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Boost.Align review manager approved
by Glen Fernandes 11 Mar '14

11 Mar '14

On February 25, 2014 Glen Fernandes wrote: >Ahmed, many thanks. :-) > >Some information about the role of a review manager: >http://www.boost.org/community/reviews.html#Review_Manager > >The next step, after you verify the submission code/documentation is >complete, would be to get in touch with the review wizard, Ron, > and finalize a date for the review. Ahmed, Ron just listed you as the review manager for Align. :-) Thanks again for volunteering. Glen

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Fwd: Regarding GSoc'14 Boost.odeint idea
by Rishav Agrawal 11 Mar '14

11 Mar '14

Sir/Mam, I, Rishav Agarwal, am a sophomore studing at the Indian Institute of Technology, Kanpur, India. I am interested in the working on implementing implicit routine for solving ODEs. I have done a semeser long on Numerical Methods in my third semester and am quite familiar with the algorithms used. Although I do not have much experience working with the Boost library, I am well aquaited with C++ and Python and can pick up the libraries easily. I would appreciate if the probable mentor could guide me through the application process and tell me about any pre-requisite/tests that I need to clear which could strengthen my proposal. A list of my previous projects can be found here <http://github.com/rra94>. Sincerely, Rishav Raj Agarwal I.I.T.Kanpur

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Standard C++ [Boost.Document] API
by pritesh vikram 11 Mar '14

11 Mar '14

Hello guys, As of having interested in Participating this year's Google Summer of Code Program. I am interested in developing Library which allow integration with spreadsheet application. Situation: As there is need for an API which understands all currently available formats of office applications running in different platforms. So API has to be aware of all formats available to all the platforms. There will be support for interconversion between these document formats.As well as classes and functions supporting to these operations.Conversion to portable formats like PDF. Proposed Solution: Separate components withing the library would be needed for Word processor, Spreadsheet, Presentation application.And also conversion code for each of these components with respect to different formats. Steps Involved: 1. Design all necessary components needed for the proposed solution. 2. Keeping informed to the mentor for the proposed design. 3. Implement using C/C++ as a language for the integration with the existing boost library. 4. Testing the Implemented model. 5. Getting the implemented code approved with the mentor. 6. Proceeding with the full implementation of the API. Benefits: 1. Help existing boost library users to take advantage of the creation, modification,conversion features for office documents. 2. No need for the users to look for another API for getting support for manipulation with office documents. As there is no existing work going on relating to this API.I am aware that all the libraries and components must be developed from scratch. I will move foreword with my above specified proposal for the project. If there is any more details to be included in the API i would like to informed for the additional details needed for this project to be fully integrated with all necessary components. If my proposal is effective then i would like to be appreciated that i am good to go for proposed layout with google summer of code program. Thanks, Pritesh Vikram

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boost::iterator_range does not work in boost::variant in boost 1.55
by Jon Biggar 10 Mar '14

10 Mar '14

If I try to put a boost::iterator_range into a boost::variant, it breaks the variant, because something in boost::iterator_range doesn't allow variant to use SFINAE deduction. My best guess at the problem is the declarations in boost/range/iterator_range_core.hpp that have a 'class ForwardRange' template argument are insufficiently constrained and accept almost anything as a possible ForwardRange type. I'm guessing that putting the correct enable_if<> template constraints on the templates that use 'ForwardRange' will fix the issue, but I'm having trouble identifing the correct metafunction test to use, since concept FowardRange concept doesn't have too many good targets. I'd like to test a candidate FowardRange type to see if boost::begin() and boost::end() can be successfully called on it, but I haven't figured out how to do that yet. Any suggestions? Known fixes or workarounds? I know about the has_range_iterator metafunction, but it can't be used here due to circular definition issues... Exmaple: #include <boost/variant.hpp> #include <boost/range.hpp> #include <boost/mpl/vector.hpp> using namespace boost; enum E { e1, e2, e3 }; typedef mpl::vector<E, std::string > args; typedef boost::make_variant_over<args>::type OkVariant; typedef mpl::vector<boost::iterator_range<std::string::iterator>, args> args1; typedef boost::make_variant_over<args1>::type BrokenVariant; int main(int argc, char **argv) { OkVariant ok; ok = e1; ok = ""; BrokenVariant broken; std::string s; broken = boost::iterator_range<std::string::iterator>(s.begin(), s.end()); broken = e2; broken = ""; } Yields errors on the last two assignments to 'broken' in g++4.8.2: test.cpp:27:12: required from here ./boost/mpl/eval_if.hpp:60:31: error: no type named 'type' in 'boost::mpl::eval_if_c<true, boost::range_const_iterator<E>, boost::range_mutable_iterator<const E> >::f_ {aka struct boost::range_const_iterator<E>}' typedef typename f_::type type; I've attached the full error log and my project-config.jam. -- Jon Biggar jon(a)floorboard.com jon(a)biggar.org jonbiggar(a)gmail.com

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Boost.Thread project for GSoC 2014
by Haoyue Wang 10 Mar '14

10 Mar '14

Hi, I am Haoyue, a PhD student in geophysics at MIT. I used C++11 to write parallel finite element codes in my research and had some coursework on concurrent programming. Boost is such a powerful and efficient library. I sincerely hope I could contribute to it this summer and beyond. I am interested in the standalone GSoC Projects under Boost.Thread. Particularly, the Work-Stealing-Thread-Pool project is a great one that I expect to learn a lot from. I understand that there could be much more to discuss once I have a preliminary proposal. Here I just want to ask if I am heading in the right direction. I think a good point to start is chapter 6, 7, and 9 of the book C++ Concurrency in Action: Practical Multithreading and the Executors and Schedulers revision 3 from http://www.open-std.org/. I haven't used Executor before but I am ware of its existence in Java for a while. Maybe I could go through some Executor and fork/join Java examples to see how they are used in practice. Finally, I will read and understand the executors codes on GitHub. I hope I could put up a good first draft proposal next Monday. If there is any advice, please let me know. Haoyue Wang

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Review Request: Convert V2
by Vladimir Batov 10 Mar '14

10 Mar '14

I think I've addressed all comments/suggestions received so far. So, to keep things moving I would like to request a formal review of the library. Location: https://github.com/yet-another-user/boost.convert.git Short Description: The main purpose of the framework is to unify and to deploy various conversion facilities through one consistent interface, to provide generic consistent behavior -- one of the factors in improving productivity and code-correctness in commercial s/w development environment. / Boost.Convert/ builds on the /boost::lexical_cast/ experience and takes those conversion/transformation-related ideas further * to be applicable to a wider range of conversion-related deployment scenarios, * to provide a more flexible, extensible and configurable type-conversion framework. Thank you.

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speed of light from universal_constants Boost.Units
by Roger Martin 10 Mar '14

10 Mar '14

Hi, I've tried and tried and just not understanding or can't muddle my way through the boost units(looks powerful though). For a start, just trying to get at the speed of light in boost/units/systems/si/codata/universal_constants.hpp boost::units::si::constants::codata::c boost::units<boost::units::si>::constants::codata::c.value() and massive errors; especially if I try to multiplying with something. I use boost::math::constants::pi<double>() from #include "boost/math/constants/constants.hpp" But the universals allude me; and example? where is my brain stuck?

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Regression test failures on the develop branch
by Neil Groves 10 Mar '14

10 Mar '14

Hi! I've been doing some work on Boost.Range and have been ignoring complete failures from the following machines: teeks99* *jc-bell jasonr-Ubuntu13.04-intel-13.0.1 I'm concerned that the errors have been present for a couple of weeks. We are almost without MSVC coverage on the develop branch. I have taken to going off-process and after cycling the other platforms pushing to master to get coverage of MSVC. Of course I completely understand the difficulties balancing our busy schedules to devote time to Boost. This isn't a complaint. I wondered if there was already a plan to fix these and if there was anything I could do to help. Do we need more machines covering Microsoft compilers and platforms? Should we be approaching companies that use Boost with Microsoft that might be willing to donate some equipment and/or time? I don't think the risk is unacceptable at present since the new branching model means that at this stage of the schedule a hiccup on master can be quickly reverted without a total train wreck. I think we should probably get on top of this before we reach the final phase of the next release. Please let me know if I can help in any way. Regards, Neil Groves

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[GSOC] Mentors for a C++11 TMP-related project
by Louis Dionne 09 Mar '14

09 Mar '14

Hi, I am a student considering to apply for GSOC 2014. Short story =========== I would like to know if someone is interested to mentor a project whose aim is boldly to: - Document the current state of the art in C++11 template metaprogramming. - Propose modifications to the current Boost.MPL or perhaps write a TMP library as a successor to the MPL. Full story ========== I have been working on a C++11 TMP library[1] for a while now, and I will present the state of my work at C++Now 2014. In the process of writing the library, I experiment with several TMP techniques, which I document and benchmark. The goal is to propose a new library that improves over the current MPL in a measurable way (i.e. it's not just my preference). That library could be seen as a C++11 successor to the MPL and new code could use that instead of the MPL. Now, while I expect the library to be fairly advanced by the beginning of the summer, there will certainly be criticism when I present it publicly. I see two possibilities here: (1) Input is negative enough that the idea to propose it is dropped. In that case, I could work on improvements to the current MPL during the summer. The kind of improvements I'm talking about range from documentation to bugfixes to support for C++11 when available. (2) Input is generally positive and the library is proposed circa the beginning of the summer. If the library is refused, then I'm back to (1). Otherwise, I can work on improvements and modifications required for the library to officially make it in. In both cases, the scope of the project seems reasonable to me. There is nothing similar in the list of proposed GSOC projects, so if someone is interested in mentoring this project, please speak up. I will then go through the normal process for proposing GSOC projects and include a more detailed description of it, and we'll see what happens. Regards, Louis Dionne [1]: http://github.com/ldionne/mpl11

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[thread] Address sanitizer failures on marshall-mac
by Andrey Semashev 09 Mar '14

09 Mar '14

Hi, I'm observing Boost.Log and Boost.Atomic test failures on marshall-mac with AddressSanitizer enabled. http://www.boost.org/development/tests/develop/developer/output/marshall-ma… http://www.boost.org/development/tests/develop/developer/output/marshall-ma… The error messages don't contain function names but the backtraces have Boost.Thread on top. I can also see similar failures in Boost.Thread: http://www.boost.org/development/tests/develop/developer/output/marshall-ma… Is this a known problem in Boost.Thread? Can the backtraces be deciphered so that function names are shown?

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[thread, async] Mini design review requested for a generic extensible Boost monadic continuations framework
by Niall Douglas 09 Mar '14

09 Mar '14

Dear Boost, I've been working on a Boost generalisation framework for N3857 "Improvements to std::future<T> and Related APIs" (Jan 2014). It's also an extension of Vicente's N3865 "More Improvements to std::future<T>" (Jan 2014), though slightly incompatible with it. I would appreciate the Boost community's feedback on what is essentially pure exploratory prototype code before I commit any major design flaws in a proper implementation. The proposed design is specifically intended to allow proposed Boost.AFIO's async_io_op future-like object to seamlessly interoperate with any other future-like object e.g. std::future<T> or boost::future<T>. The design is intended to be extensible to any other third party future-like object, even including ones whose implementation is completely external (e.g. Qt). I would like to thank some people whose off-list discussions helped inform this design: to Bjorn Reese who has done so much to help me knock the kinks out of AFIO; to Vicente J. Botet Escriba for engaging with me pitching this proposal to him (he disagrees with it by the way); to Artur Laksberg and Niklas Gustafsson for continuing to reply to my criticisms and thoughts of the papers which precede N3857. What N3857 proposes for reference: * future<T> and shared_future<T> gain a .then(R(prec_future_type<T>)) method. Callable will be called with the signalling future after the future signals. Return type is a future<R>. * A new when_all(...) can be used to compose a future which signals when all input futures are signalled. Inputs can be futures of heterogeneous types, in which case a future<tuple<...>> is returned. * A new when_any(...) composes a future which signals when any of its input futures signals. Inputs can be futures of heterogeneous types, in which case a future<tuple<...>> is returned. To avoid the linear scan on return, for a homogeneous types a when_any_swapped(...) swaps the last item in the return value with the ready item. Note there is no way in N3857 to avoid a when_any() linear scan when input types are heterogenous (something I feel is a deficiency, all you need to return is an index!). * A new executor base class, with subclass thread_pool are added. Executors allow adding a std::function<void()> for asynchronous execution. These are detailed by N3785 "Executors and schedulers, revision 3" (Oct 2013). I haven't mentioned in detail here, but N3857 specifies overloads for .then(executor, ...) to send some continuation to some executor. You will note the below framework makes it possible to use tag dispatch instead which looks much cleaner and is easier to write, nevertheless this explicit form is intended to be preserved. I won't mention executor support again for brevity. Where I find issue with a naïve implementation of N3857 (and Vicente's N3865 mentions some of these same issues): * N3857 only understands std::future<> and std::shared_future<>. That means the following code will not compile: std::future<int> &a; boost::future<int> &b; boost::afio::async_io_op &c; std::future<std::tuple<int, int, std::shared_ptr<async_io_handle>>> f=when_all(a, b, c); This is unhelpful for interoperation. It doesn't just affect Boost: imagine mashing up Qt async objects and C++17 objects for example, or even WinRT Task<T> objects and C++17 objects. Most C++ (and C) libraries of any complexity supply their own async notification objects, and this problem of writing never ending boilerplate to get some async object from library X to work with library Y is very tedious considering the compiler can do it for you. * As I mentioned earlier, when_any() is suboptimal when called with heterogenous types. I don't particularly like the when_any_swapped() hack either - a better solution would solve when_any() of all kinds optimally. * The .then(R(prec_future_type<T>)) is not tremendously useful in practice because it's too limited. Witness the very common use pattern of this form: auto ret=openedfile .then(write({ "He", "ll", "o ", "Wo", "rl", "d\n" }, 0)) .then(sync()); .then(write({ "He", "ll", "o ", "Wo", "rl", "d\n" }, 12)) .then(sync()); This sequence of code is clearly a *transaction* i.e. the programmer intends the set of continuations as a contained group of operations, and indeed some async i/o providers may guarantee atomic rollback (hint: forthcoming TripleGit does exactly this). A big additional problem is the lack of error handling logic: if say the second write() fails, you may wish to undo the first write, or do something custom. The problem with N3857 is that only the state of the first sync() is passed into the second write, and it may be the case that in generic code sync() needs to always sync irrespective of its preceding operation and therefore might pass through a garbage state. N3857 provides no easy method for a later .then() to inspect preceding .then()'s and do something about them (e.g. rewinding until it finds a valid open file handle rather than error states), other than by declaring special wrapper lambdas to pass through state. I personally think that is ugly. * Vicente mirrors my point above in N3865 by pointing out that having .then(R(prec_future_type<T>)) push the error handling into the callable makes your callables unnecessarily boilerplate. N3865 proposes adding .next(R(prec_future_type<T>)) for when a preceding operation succeeds and .recover(R(exception_ptr)) for when a preceding operation fails, with .fallback_to(value) as a way of default setting the return from an errored future. I think Vicente's argument here is a good one: but it's not generic enough in my opinion. I think continuations should be able to _filter_ outputs from preceding continuations in a really generic and customisable way. What I'd really like is this: continuations::thenable_get_placeholder<-1> last; auto ret=openedfile .then(write({ "He", "ll", "o ", "Wo", "rl", "d\n" }, 0)) .then(if_error(last, [](future<...> f){ do something with last; })) .then(sync()); .then(write({ "He", "ll", "o ", "Wo", "rl", "d\n" }, 12)) .then(if_error(last, [](thenable<...> t){ do something more with everything; })) .then(sync()); Which treats the continuation as a functional transformation. In other words, Vicente's .recover(R(exception_ptr)) becomes tag dispatched instead of explicitly specified, so it's very easy for the programmer to transform state according to state. What I am proposing instead: a generic extensible Boost monadic continuations framework which via metaprogramming lets the compiler assemble the right code from N3857 like syntax. A quick summary of the proposed generic extensible Boost monadic continuations framework follows: * Future-like behaviours such as .valid(), .then(), .get(), .wait() and .share() have functional mixin classes of the form (simplified for brevity, but you get the picture): namespace boost { namespace continuations { // Indicates the derived type provides a future compatible valid() template<class I> struct validable : public I { bool valid() const; }; // Indicates the derived type provides a future compatible then() template<class I, class... Types> struct thenable : public I { template<class F> thenable<decltype(F(...))>, Types..., I> then(F &&f); }; // Indicates the derived type provides a future compatible get() template<class T, class I> struct gettable: public I { T get(); }; // Indicates the derived type provides a future compatible wait() template<class I> struct waitable: public I { void wait() const; template<class Rep, class Period> std::future_status wait_for(const std::chrono::duration<Rep,Period> &timeout_duration) const; template<class Clock, class Duration> std::future_status wait_until(const std::chrono::time_point<Clock,Duration> &timeout_time) const; }; } } To mark up a type as being future-like, one might use: namespace boost { namespace continuations { template<class T> using monad = thenable<waitable<gettable<T, validable<std::future<T>>>>>; // Do all the partial specialisations of the internal machinery // for this type to hook it into the metaprogramming } } // Voila, boost::continuations::monad<T> is now an interoperable // form of std::future<T> * .then() can now take callables of the following forms: 1. R() and R(prec_future_type<T>) for compatibility with N3857. 2. R(..., continuations::thenable_get_placeholder<idx>, ...) inserts an item from the continuation chain into the call. thenable_get_placeholder can be fed a negative number to wrap from the bottom, so thenable_get_placeholder<-1> is the most recently preceding operation. Therefore R(prec_future_type<T>) from above is actually implemented as R(continuations::thenable_get_placeholder<-1>). This can be used to insert error processing filters as illustrated earlier which can view a preceding chunk of chain at once, and act. 3. R(thenable<...> &&) which gives a continuation access to the entire continuation chain, just for those people who really need it. You saw this in the example above. 4. Any specially treated prototype depending on what the metaprogramming has extended for some future_type. For example, if one does async_io_op.then(void(const boost::system::error_code& error, size_t bytes_transferred)) - which is the ASIO callback spec - then AFIO would emulate the ASIO callback calling convention for the completion of some i/o. This only happens if and only if the item being .then() is an async_io_op i.e. such custom extensions are type specific. * future_type<T>.then(R()) now returns a thenable<future_type<R>, future_type<T>> which auto decays to a future_type<R> on demand for compatibility with N3857. Similarly a future_type<T>.then(R()).then(S()) would return a thenable<future_type<S>, future_type<T>, future_type<R>> and so on. You can convert a thenable<T, ...> into a std::tuple<..., T> using an overload of the make_tuple() function. * when_all() and when_any() gain overloads for thenable<...>. These simply convert the tuple taken out of a thenable chain into a future with the results - AFIO will implement this generically using its closure engine, but a more intelligent solution might decompose all inputs into HANDLEs and do an asynchronous WaitForMultipleObjects() for example. Note this is a BREAKING CHANGE from N3857: If you do a when_all() under N3857 on a .then() chain, you will get a future to the last then() return, whereas under this proposal you will get a future to all the returns from all the then()s. This breaking change may still actually compile and work as expected - however when_any() actually now has completely different behaviour: when_any() under N3857 will be the same effect as when_all() on a .then() chain under N3857, whereas under this proposal when_any() will signal when any of the then() chain signals (I would assume the first item). I personally doubt this breaking change would affect any real world code, but it's worth noting. Note the following: 1. The proposed continuations framework, despite being monadic, is separate from the mooted Boost.Functional/Monads framework. This continuations framework could be implemented using such a Boost.Functional/Monads framework, but I suspect there wouldn't be much gain except interoperability with other monadic patterns. Continuation monads are a very limited specialisation of general monads, especially under the tight constraints of the N3857 requirements, so reuse of any Boost.Functional/Monads I suspect would be minimal. 2. The proposed framework is 100% compatible with N3857 apart from the when_all()/when_any() breakages which I would assume shouldn't turn up in real world code, and it should be viewed as a Boost-specific extension which may get standardised later if it proves popular. Here is the very rough prototype code: https://github.com/BoostGSoC/boost.afio/blob/monadic_continuations/lib s/afio/test/tests/monadic_continuations_test.cpp. It compiles using VS2013 only. It probably doesn't work, but it's simply there to demonstrate the viability of the concept and to help those confused by my unclear explanation above. Thoughts regarding the design much appreciated! My thanks in advance. Niall -- Currently unemployed and looking for work in Ireland. Work Portfolio: http://careers.stackoverflow.com/nialldouglas/

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Segment Tree Implementation for GSoC 2014
by Kevin Zuniga Garate 08 Mar '14

08 Mar '14

Hello everyone, I'm Kevin and I'd like to contribute to Boost in this SoC. I enjoy coding in C++ and participate a lot in competitive programming sites such as TopCoder, Codeforces, etc. A data structure I have learn from participating in those contests is segment tree. A segment tree is a data structure for storing data and querying and updating it in intervals, I haven't found a segment tree library in C++, so I thought it may be a good data structure for Boost. Do you think that would be a good addition for Boost? If not, what other data structure would you like to see implemented? Greetings. -- Kevin

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Multi-methods and type switch
by Camille GILLOT 08 Mar '14

08 Mar '14

Hello, SoC2014 page on trac mentions interest for an implementation of type-switch for C++. For now, I have implemented a toy library for open multiple dispatch. It is based on compressed dispatch tables. It still just supports single inheritance and needs to attach integer tags to the dispatched class hierarchy. Is there any interest for further development of this library ? What would be the typical use cases ? Note : Although I opened with a reference to SoC2014, I do not intend to write a GSoC proposal for this work. Best regards, Camille Gillot

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[tuple] any interest in a unique_tuple<...>?
by Hui Li 08 Mar '14

08 Mar '14

Testing the water, see if anyone might find this useful. Any comments/suggestions are absolutely welcome and appreciated! unique_tuple<T...>, where types in <T...> may themselves be other unqiue_tupe<...>'s, contains exactly one copy of each of the "finally nested" element types in <T...>, regardless of how many times a type appears in the type parameter pack, or how deeply it is nested inside one or more unique_tuple's in <T...>. unique_tuple<T...> differs from std::tuple<T...> and boost::fusion::set<T...> etc in that nested unique_tuple's are effectively "flattened", and elements contained are unique no matter how complex the nesting gets, or how many times or how deeply nested the element type is in <T...>. unique_tuple<T...> in a way emulates virtual inheritance, but at compile time. The implementation does NOT use virtual inheritance. implementation is available at: https://www.dropbox.com/sh/f7ur7j6jetabovj/MuhhhNWU0K/unique_tuple.h and some demonstration of uses at (tested with "clang-3.5 -std=c++1y" on mac osx/macport) https://www.dropbox.com/sh/f7ur7j6jetabovj/cy_cvpPIYc/main.cpp In the following example, t1,t2,t3 all contain exactly one A, and exactly one B: struct A{}; struct B{}; unique_tuple<A,B,A,B> t1(A{},B{}); unique_tuple<A,unique_tuple<B>,unique_tuple<A,B>> t2{B{},A{}}; // order doesn't matter in constructor // B is default constructed, empty unique_tuple (possibly nested) doesn't matter unique_tuple<A,unique_tuple<unique_tuple<>>,unique_tuple<A,B,unique_tuple<A,B,unique_tuple<A,B>>>> t3{A{}}; // unique_tuple<A,B> t4(A{},B{},A{}); // doesn't compile because more than one A is supplied // unique_tuple<A,B> t5(A{},B{},1.0); // doesn't compile because double doesn't belong There are helper classes and functions, e.g.: A& a = get<A>(t0); auto x = make_unique_tuple(A{},B{},1,1.0); // unique_tuple<A,B,int,double> static_assert( is_unique_tuple<decltype(t0)>::value, "t0 is a unique_tuple type" ); static_assert( is_element_of<A,decltype(t1)>::value, "A is an element in t1" ); static_assert( is_subset_of<decltype(t1),decltype(x)>::value, "<A,B> is a subset of <A,B,int,double>" ); static_assert( unique_tuple_size<decltype(t3)>::value == 2, "there are 2 elements in t3: A and B" ); Equality comparason exists for two unique_tuple<...>s that contain the same element types, e.g., t0 == t2 && t1 != t3; Mixed operations with std::tuple are available if std::get<typename>(std::tuple<...>) exists (c++14), which effectively requires that the element types are all unique in the std::tuple<...>. synopsis: template < typename... T > struct unique_tuple { template < typename... U > explicit constexpr unique_tuple(U&&...); template < typename... U > explicit constexpr unique_tuple(const std::tuple<U...>&); template < typename... U > explicit constexpr unique_tuple(std::tuple<U...>&&); // allocator extended constructors template < typename Alloc, typename... U > unique_tuple(std::allocator_arg_t, const Alloc& a, U&&...); template < typename Alloc, typename... U > unique_tuple(std::allocator_arg_t, const Alloc& a, const unique_tuple<U...>&); template < typename Alloc, typename... U > unique_tuple(std::allocator_arg_t, const Alloc& a, unique_tuple<U...>&&); template < typename Alloc, typename... U > unique_tuple(std::allocator_arg_t, const Alloc& a, const std::tuple<U...>&); template < typename Alloc, typename... U > unique_tuple(std::allocator_arg_t, const Alloc& a, std::tuple<U...>&&); // assign template < typename... U > unique_tuple& operator=(const unique_tuple<U...>&); template < typename... U > unique_tuple& operator=(unique_tuple<U...>&&); template < typename... U > unique_tuple& operator=(const std::tuple<U...>&); template < typename... U > unique_tuple& operator=(std::tuple<U...>&&); // swap template < typename... U > void swap(unique_tuple<U...>&); template < typename... U > void swap(std::tuple<U...>&); }; // helpers template < typename... T > unique_tuple<typename std::decay<T>::type...> make_unique_tuple(T&&... t); template < typename... T > struct unique_tuple_size<unique_tuple<T...>>; // number of unique elements template < typename T > struct is_unique_tuple; template < typename T, typename... U > struct is_element_of<T,unique_tuple<U...>>; template < typename... T, typename... U > struct is_subset_of<unique_tuple<T...>,unique_tuple<U...>>; // element access template < typename T, typename... U > T& get<T>(unique_tuple<U...>&); template < typename T, typename... U > const T& get<T>(const unique_tuple<U...>&); template < typename T, typename... U > T&& get<T>(unique_tuple<U...>&&); // equality compare template < typename... T, typename... U > bool operator==(const unique_tuple<T...>&, const unique_tuple<U...>&); template < typename... T, typename... U > bool operator==(const unique_tuple<T...>&, const std::tuple<U...>&); template < typename... T, typename... U > bool operator==(const std::tuple<T...>&, const unique_tuple<U...>&); template < typename... T, typename... U > bool operator!=(const unique_tuple<T...>&, const unique_tuple<U...>&); template < typename... T, typename... U > bool operator!=(const unique_tuple<T...>&, const std::tuple<U...>&); template < typename... T, typename... U > bool operator!=(const std::tuple<T...>&, const unique_tuple<U...>&); // swap template < typename... T, typename... U > void swap(unique_tuple<T...>&, unique_tuple<U...>&); template < typename... T, typename... U > void swap(unique_tuple<T...>&, std::tuple<U...>&); template < typename... T, typename... U > void swap(std::tuple<T...>&, unique_tuple<U...>&);

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Re: [boost] testing potential GSOC students
by Ganesh Prasad 08 Mar '14

08 Mar '14

( (c) TM (R) Will Smith) --> (The man in BLACK ) ... The actor one ??? I love that guy. Not sure if I would go competitive against him. :D

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Re: [boost] testing potential GSOC students
by Ganesh Prasad 07 Mar '14

07 Mar '14

As this year the main focus of UBLAS will be compile time optimizations, and I wish to submit a proposal for this project, I would like to show the compile time library Gns::META_LISCPP , written by me. In reference to *Boost Digest, Vol 4288, Issue 3, Message :3 ,* I am sending this library by me for evaluation. Though I have not implemented a minimal Vector library over it yet , still it demonstrates, I optimally guess, my understandings of the generic meta programming paradigm. And I guess, I might come up with some vector processing features for it soon. Here is the github url to the repository : *https://github.com/GnsP/GNS--META_LISCPP/ <https://github.com/GnsP/GNS--META_LISCPP/>* Looking forward to your responses. Best Wishes Ganesh Prasad

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Re: [boost] [Re] [Re] JSON Parsing Library for GSoC 14
by Sebastian Theophil 07 Mar '14

07 Mar '14

There are many libraries that parse JSON to maps and vectors. IIRC Microsoft’s REST SDK includes a JSON library as well (http://casablanca.codeplex.com) There are at least 15 other C++ libraries like that and we don’t need to write another one. But there are only two libraries AFAIK that parse JSON to C++ structs using serialization adaptors: - https://github.com/Loki-Astari/ThorsSerializer - http://fossil.wanderinghorse.net/repos/nosjob/index.cgi/index I consider the ability to read and write C++ structs essential for any library admitted to boost. Shouldn't such a library be an extension to boost.serialization? Boost.Serialization already defines a way for each data structure to define which data should be written/read. The Boost.Serialization docs say that the library even offers methods & macros to output a class member together with its member variable name as a name value pair. Exactly what a JSON library would need. There has been a discussion about last year’s GSoC mentioning further desirable properties of a JSON library: http://boost.2283326.n4.nabble.com/JSON-Parser-GSoC-2013-td4645117.html Regards Sebastian -- Dr. Sebastian Theophil | stheophil(a)think-cell.com Senior Software Engineer We are looking for C++ Developers: http://www.think-cell.com/career think-cell Software GmbH | Chausseestr. 8/E | 10115 Berlin | Germany http://www.think-cell.com | phone +49 30 666473-10 | US phone +1 800 891 8091 Amtsgericht Berlin-Charlottenburg, HRB 85229 | European Union VAT Id DE813474306 Directors: Dr. Markus Hannebauer, Dr. Arno Schödl

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[GSoC] pipelines questions
by Thaler Benedek 06 Mar '14

06 Mar '14

Hi, I'm interested in the Boost.Pipelines proposal of GSoC 2014. [0] I'd like to ask the stakeholder (Vicente J. Botet Escriba ?) the following: * Is this supposed to be built from scratch or rather to be some kind of improvement over the already existing google implementation? [1] * If the former is true, should be n3534 [2] considered as a strict requirement or as a vague suggestion? * If the later is true, which features should be the main distinctive ones? I think about things like using Boost libraries (e.g: Boost.Atomic) instead of custom solutions, cross platform support, comply to Boost coding standard, etc. Are there any areas of improvement identified in the reference implementation? * I understand it might take quite a long time for a proposal to make it to Boost, therefore it's not a requirement. Is there any objective milestone that a successful project should reach anyway? Thanks, Benedek [0]: https://svn.boost.org/trac/boost/wiki/SoC2014#Boost.Pipelines [1]: https://code.google.com/p/google-concurrency-library/source/browse/include/… [2]: http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2013/n3534.html#Proposal

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[uuid] sequential_generator / comb_generator / utc_generator / timestamp_generator
by Adam Walling 05 Mar '14

05 Mar '14

For personal use, I've created a few generators that create sequential and time-based uuids. However there does not seem to be a single standard for these kinds of algorithms. While tidying up this code, I've run into some obstacles with generalization of the logic. Although some applications like SQL Server will use GUIDs and lexicographically compare based on the least significant bytes of Data4 for boost::uuids' purposes we can simply assume a block of 16 bytes. The generic approach is to combine (basic_comb_generator) a number of bytes from a sequential source, filling the rest of the bytes with random data. What concerns me is the choice of source and the number of bytes to use. And additionally the value which specifies the variant / version. The usual choices seem to be 8 or 6 bytes. The source is also usually UTC Unix time. However the original uuid version used nanosecond intervals and the MAC address. Am I worrying too much about extensibility? As it is now my basic_comb_generator has a template param for a source, a number of bytes of the source to use, and a UniformRandomNumberGenerator to fill the rest. Since resolution may be a second if using Unix time they may not be consistently sequential but generally so, hence my hesitation to name the generator typedef as sequential. Of course it is possible to use even higher resolution. I suppose I am gauging interest in this feature, as well as asking if there are any thoughts or suggestions on how others would likely use this, and alternative or standard algorithms defined. Once I have some feedback I intend to complete the code and bounce it back on here for any further comments before lobbying to include anything within the library. It seems like commonly needed functionality at least! Nilsson article here for SQL Server: http://www.informit.com/articles/article.aspx?p=25862&seqNum=7 CouchDB's uuid generation algorithms: https://wiki.apache.org/couchdb/HttpGetUuids

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[signals2] Test failure in C++11 (trivial fix for incorrect usage of boost::optional)
by Ben Pope 05 Mar '14

05 Mar '14

I have the following errors: "clang++-3.4" -c -x c++ -std=c++11 -stdlib=libc++ -O0 -g -fno-inline -Wall -g -DBOOST_ALL_NO_LIB=1 -DBOOST_TEST_NO_AUTO_LINK=1 -I".." -o "/home/ben/development/boost/test/build/results/boost/bin.v2/libs/signals2/test/signal_test.test/clang-linux-3.4~c11_libc++/debug/link-static/signal_test.o" "../libs/signals2/test/signal_test.cpp" ../libs/signals2/test/signal_test.cpp:32:16: error: invalid operands to binary expression ('boost::optional<int>' and 'int') if(max == false) max = *first; ~~~ ^ ~~~~~ "clang++-3.4" -c -x c++ -std=c++11 -stdlib=libc++ -O0 -g -fno-inline -Wall -g -DBOOST_ALL_NO_LIB=1 -DBOOST_TEST_NO_AUTO_LINK=1 -I".." -o "/home/ben/development/boost/test/build/results/boost/bin.v2/libs/signals2/test/track_test.test/clang-linux-3.4~c11_libc++/debug/link-static/track_test.o" "../libs/signals2/test/track_test.cpp" ../libs/signals2/test/track_test.cpp:36:14: error: invalid operands to binary expression ('boost::optional<int>' and 'int') if(max == false) Richard smith explains the problem here: http://llvm.org/bugs/show_bug.cgi?id=18180#4 "OK, I see what's happening -- in Clang 3.3 and GCC 4.8, 'false' is being treated as a null pointer constant. boost::optional implicitly converts to an "unspecified-bool-type" that happens to be a pointer-to-member type, and thus can be compared against a null pointer constant via the built-in operator!=(pointer-to-member, pointer-to-member) overload. In C++11 onwards, 'false' isn't a null pointer constant any more, so this comparison is no longer valid. Clang 3.3 and GCC 4.8 don't implement that rule; Clang 3.4 does." The trivial fix is to change the if statements at: ../libs/signals2/test/signal_test.cpp:32:16: ../libs/signals2/test/track_test.cpp:36:14: to if(!max) rather than if(max == false). Ben

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[range][documentation] - best practice for generating documentation?
by Neil Groves 05 Mar '14

05 Mar '14

Hi, I'm currently the suitably ashamed owner of numerous documentation trac issues for Boost.Range. I would like to address these issues but I'm unclear about what our strategy is for generating documentation since our move to modular Boost. I anticipate that if I continue to commit the generated html as I had done previously that I will be in for a "world of pain" when it comes to merge to master. I've searched and found several pages about document best-practice but the pages contain references to the subversion repository which leads me to believe that this must be out-of-date. I'd like some advice to ensure that my commits are aligned with what is wanted. If there is a temporary workflow I can use that will not end in a merge disaster then I'd like to put small documentation fixes in quickly before major re-factoring of the documentation generation process. I apologise in advance if my search skills have been deficient. Sending a link accompanied with abuse is entirely acceptable! Thanks, Neil Groves

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[offtopic] Wonders of C++ syntax
by Andrey Semashev 05 Mar '14

05 Mar '14

Maybe this experience will be interesting to someone... I'm currently trying to write a simple parser for function signatures for Boost.Log and collecting different curious use cases. The parser is supposed to extract the function name from the compiler-generated string with the signature (i.e. BOOST_CURRENT_FUNCTION). Now the interesting case I've stumbled upon is a conversion operator to a function pointer: namespace namespc { struct my_class2 { typedef char (*pfunc_t)(double); operator pfunc_t () const { std::cout << BOOST_CURRENT_FUNCTION << std::endl; return 0; } }; } I first tried to imagine how this could be written without the typedef, but my brain broke soon enough. Then I decided to ask the compiler, and naturally different compilers gave different answers. GCC nicely sidestepped the problem altogether: namespc::my_class2::operator pfunc_t() const MSVC was more creative: __cdecl namespc::my_class2::operator char (__cdecl *)(double)(__cdecl *(void) const)(double) Frankly, my brain can't parse this one either and it looks incorrect to me since the function pointer type is duplicated. So it seems, there's no syntax for expressing the operator without a typedef, is that right? In that case, I wonder what to do with MSVC output...

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changelog for 1.56
by Oliver Kowalke 05 Mar '14

05 Mar '14

I tried to add comments to the change log of 1.56 - but I've no permission to push the commit. is feed/history/boost_1_56_0.qbk the correct place and can I get permission to push commits?

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