January 2016 - Boost - lists.preview.boost.org

Interest in library for nested containers?
by Alberto Marnetto 28 Jan '16

28 Jan '16

Hello, is there interest in adding a library for nested containers (including a flattening view, a function counting the scalar elements etc.) to Boost? A working version is available at https://github.com/AlbertoMarnetto/multidim . If the concept and the interface are suitable for a submission – in particular if the requirement of a C++11 compiler is acceptable and the small number of functionalities is not a problem – I can proceed to restructure the library to meet Boost's style guidelines. Regards, Alberto Marnetto

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QuickBook generate table of references?
by Nat Goodspeed 27 Jan '16

27 Jan '16

I have a biggish document consisting of a number of different .qbk files -- big enough to make it unreasonable to start over with a different toolchain. I would like to mark up particular methods of particular classes in such a way that QuickBook will produce a consolidated list of links to those methods. I read a little about DocBook being able to generate tables of figures, etc., but between QuickBook syntax and the final output document, my mental model has a big "then a miracle occurs" cloud. Will someone please show me how this is achieved? Thank you!

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Query regarding time complexity requirements of iterators in custom container
by Soul Studios 26 Jan '16

26 Jan '16

Hi there- currently working on Colony, last version I'm working on has achieved constant-time(amortised) time-complexity for iterator operations, except for the random-access operators (+, -, +=, -=, [], >, <, >=, <=). It's not possible to make these constant-time due to the nature of the algorithms and structure of container. Ion pointed out to me that there is an obscure C++ requirement for iterators that all operations be constant-time. Given this, is it worth keeping these in Colony before submitting to Boost, or would it be best to remove them and make the iterator bidirectional-only prior? Cheers, Matt

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[serialization] Custom archive and arrays
by Bjorn Reese 23 Jan '16

23 Jan '16

I am currently adding support of C++ arrays to a custom oarchive. My archive inherits from boost::archive::detail::common_oarchive and implements save_override(), which will pass any unknown type to boost::archive::save(). This enables me to implement non-intrusive serialization. When I pass an array to boost::archive::save(), it detects that this is an array and then calls detail::save_array_type. This is where my problem starts, as the function is hardcoded to always store a prefixed array count, which is illegal in the format that my custom archive uses. Would it be possible to lift this restriction? My current workaround is to add an overload for arrays to my custom archive, i.e. template <typename T, std::size_t N> void save_override(const T (&data)[N]);

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[type_traits] Tests for implicit convertibility?
by John Maddock 22 Jan '16

22 Jan '16

Folks, I suspect we may have unintentionally backed ourselves into a corner with is_convertible/is_constructible. While trying to fix https://svn.boost.org/trac/boost/ticket/11922 I found I needed to SFINAE-out some conversion operators when the conversion already exists (as an implicit constructor in the target type). So far so easy, but consider: class Int { public: Int(const int& i) {}; Int(const Int& i) = delete; }; static_assert(is_convertible<int, Int>::value, "Ooops"); Now you would think this would pass right? But it doesn't (at least on GCC and clang), and this is true for both boost:: and std:: type_traits and appears to be an unintended side effect of the way is_convertible is defined, that a valid copy constructor is required on the target type. Of course: is_constructible<Int, int>::value is true, but that also catches explicit constructors. So... have we backed ourselves into a corner or do we still have a way to test for implicit-constructibilty that doesn't also require copy-constructibility on the target type? Thanks, John.

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test matrix messages
by Robert Ramey 22 Jan '16

22 Jan '16

I have a certain number of failures for the tests of the serialization library on the test matrix. If I go to get the messages associated with the failure, I rarely get any helpful information. Here are a couple of common cases: http://www.boost.org/development/tests/develop/developer/output/teeks99-08c… http://www.boost.org/development/tests/develop/developer/output/igaztanaga-… Can anything be done about this? Robert Ramey

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[gsoc16] Attn: We need 2016 mentors and project ideas for Boost!
by Niall Douglas 21 Jan '16

21 Jan '16

Dear Boost community, We are now within one month of the beginning of Google Summer of Code 2016! Last year's GSoC was a particularly momentus one as we witnessed the approval by the community for Boost.Hana to enter Boost - congratulations to Louis and his mentor Joel for bringing to Boost a very exciting new C++ library which pushes C++ compilers to their limits. We have also seen greatly improved retention of GSoC students in the community thanks to the improved student selection procedures introduced last year, and the fresh blood brought into Boost has been very evident on the mailing list this year. As part of filling in our application for 2016, we must supply to Google a list of potential GSoC mentors and potential GSoC projects for summer 2016 in order to be approved as an organisation this year. Therefore a lengthy page of awesome project ideas at https://svn.boost.org/trac/boost/wiki/SoC2016 before *February 8th* would be an enormous help to getting us approved again this year and bringing to Boost another US$35,000 of Google funding. If you think yourself able to mentor a student doing some work on Boost this summer, *please* consider adding a description of the proposed work item and your name to the list. Last year we had more slots awarded to us by Google than we had good combinations of student and mentor, so we had to return slots which I believe has not happened here at Boost GSoC in at least a decade. That means that your project ideas have a better chance than ever of receiving funding if you can find a good student, and that is best done by getting project ideas floated *early*. If you want to know more about mentoring a Google Summer of Code funded student work before you nominate yourself, please feel free to ask on the main Boost developers mailing list boost(a)lists.boost.org or via gsoc-admin(a)boost.org. Thank you in advance for your time. --- Boost C++ Libraries Google Summer of Code 2016 admin https://svn.boost.org/trac/boost/wiki/SoC2016

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please add safe numerics to the review queue
by Robert Ramey 21 Jan '16

21 Jan '16

Any chance I could get safe numerics added to the Boost Review queue? THe link to the incubator is here: http://rrsd.com/blincubator.com/bi_library/safe-numerics/?gform_post_id=426 documention here: http://htmlpreview.github.io/?https://github.com/robertramey/safe_numerics/… and github repo here: https://github.com/robertramey/safe_numerics Robert Ramey

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[gsoc16] Can I quickly check if the below really is the best approach?
by Niall Douglas 19 Jan '16

19 Jan '16

Dear Boost, In the prototype https://svn.boost.org/trac/boost/wiki/SoC2016 at https://goo.gl/1CQAuQ I claim "Even with all of Boost's facilities [1] and using C++ 14, this program represents the currently best available method of implementing a static constant associative map of keys to values" and you can find either the code at the link or pasted below. Can I quickly check here if that claim is true? Is there a better way than my example program? BTW by static constant associative map of keys to values I mean the thing me and Tony van Eerd were speaking about here last year and the year before, and indeed frequently at BlackBerry! Niall [1]: I believe Boost.Hana could implement a static constan associative map quite easily, but I'd be fairly sure Hana will likely be beyond most students. --- cut --- #include <initializer_list> #include <experimental/string_view> #include <map> #include <unordered_map> #include <iostream> using std::experimental::string_view; enum class weekday { sunday, monday, tuesday, wednesday, thursday, friday, saturday }; // initializer_list, pair and string_view are constexpr, so this list can be constexpr // (i.e. lives in the mind of the compiler only and has zero representation in generated code) #define STRING_VIEW(str) { str, sizeof(str)-1 } constexpr std::initializer_list<std::pair<const string_view, weekday>> string_to_weekday { { STRING_VIEW("sunday"), weekday::sunday }, { STRING_VIEW("monday"), weekday::monday }, { STRING_VIEW("tuesday"), weekday::tuesday }, { STRING_VIEW("wednesday"), weekday::wednesday }, { STRING_VIEW("thursday"), weekday::thursday }, { STRING_VIEW("friday"), weekday::friday }, { STRING_VIEW("saturday"), weekday::saturday } }; int main(void) { { // Calls malloc() at least 7 times static const std::map<string_view, weekday> to_weekday1 = string_to_weekday; std::cout << "'monday' maps to " << static_cast<int>(to_weekday1.at("monday")) << std::endl; std::cout << "'friday' maps to " << static_cast<int>(to_weekday1.at("friday")) << std::endl; // Calls free() at least 7 times } { // Calls malloc() at least 8 times static const std::unordered_map<string_view, weekday> to_weekday2 = string_to_weekday; std::cout << "'monday' maps to " << static_cast<int>(to_weekday2.at("monday")) << std::endl; std::cout << "'friday' maps to " << static_cast<int>(to_weekday2.at("friday")) << std::endl; // Calls free() at least 8 times } return 0; } -- ned Productions Limited Consulting http://www.nedproductions.biz/ http://ie.linkedin.com/in/nialldouglas/

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whatever happened to the constrained value library?
by Robert Ramey 18 Jan '16

18 Jan '16

I just stumbled upon the following announcement. http://lists.boost.org/boost-announce/2010/09/0265.php But I don't see any such library as part of boost. What's up with this? Robert Ramey

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