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

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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Re: [boost] [interprocess] boost::hash - different values for the same input?
by Daniel James 17 Jan '16

17 Jan '16

I altered the subject to include interprocess, since this is relevant there. On 9 December 2015 at 20:13, trafdev <trafdev(a)mail.ru> wrote: > > As per hash_range docs > (http://www.boost.org/doc/libs/1_59_0/doc/html/hash/reference.html#boost.has…): > > "This hash function is not intended for general use, and isn't guaranteed to > be equal during separate runs of a program - so please don't use it for any > persistent storage or communication." > > As per code > (http://www.boost.org/doc/libs/1_59_0/boost/functional/hash/hash.hpp) it > uses hash_combine_impl which doesn't use any random, process_id etc values > which might change during new process launches. > > At the same time, in an example describing container usage in the shared > memory > (http://www.boost.org/doc/libs/1_59_0/doc/html/interprocess/allocators_conta…), > boost::hash is being used: > > typedef boost::unordered_map > < KeyType , MappedType > , boost::hash<KeyType> ,std::equal_to<KeyType> > , ShmemAllocator> > MyHashMap; > > My question is: is it safe to use boost::hash in a shared (persistent) > storage or it's safe only for a particular (non-pointer) types? > > In this case, boost::hash docs should be changed to mention this exceptions, > because otherwise no one could use boost::hash in a shared memory > containers. Sorry about the very slow reply. I'm afraid the answer is that it depends. The reason why I originally wrote that note was because it can generate different hash values when compiled for different platforms or architectures, e.g. a 32-bit executable might generate a different hash value to a 64-bit executable. Also, I occasionally change the algorithm in new versions of boost (and probably will in the next version). For interprocess this currently won't be an issue if all the processes are using the same executable, or using executables built with same version of boost and the same architecture, but could be a problem if that isn't the case. So maybe the Interprocess documentation needs to explain this. But there's another problem coming up. The last proposal I saw for a standard generic hash function will support randomized hash functions (such as siphash) which will only work with interprocess if they are somehow seeded identically. I'll want to support whatever is accepted to the standard (although maybe as a separate library). I'll need to catch up with how that is progressing, as I haven't kept up to date.

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Any-Range containing transformed range fails when compiled with optimizations
by Auer, Jens 17 Jan '16

17 Jan '16

Hi, I have a program which produces different results based on the compiler options. The program uses a boost::any_range containing a transformed range where the transformation function just returns a new object of a simple struct: #include <vector> #include <boost/range.hpp> #include <boost/range/any_range.hpp> #include <boost/range/adaptor/transformed.hpp> #include <iostream> template<typename T1, typename T2> void ASSERT_EQ(T1 x,T2 y) {assert(x == y);}; struct SourceEvent { std::uint32_t event; void* ptr; }; int main() { using boost::adaptors::transformed; using R = boost::any_range<SourceEvent, boost::forward_traversal_tag, SourceEvent, std::ptrdiff_t>; std::vector<std::int32_t> v(100); R r = v | transformed( [](auto const&) {return SourceEvent{0u, nullptr};} ); auto t = v | transformed( [](auto const&) {return SourceEvent{0u, nullptr};} ); ASSERT_EQ( 100u, boost::size(r) ); ASSERT_EQ( 100u, boost::size(t) ); for (auto const& i: t) { ASSERT_EQ(0u, i.event ); ASSERT_EQ(nullptr, i.ptr); } for (auto const& i: r) { ASSERT_EQ(0u, i.event ); ASSERT_EQ(nullptr, i.ptr); } std::cout << "OK" << std::endl; return 0; } When compiled without optimization, it just prints ok. The same source compiled with optimizations asserts, and prints some interesting warnings: In file included from /usr/local/boost-1.60.0/include/boost/range/detail/any_iterator.hpp:22:0, from /usr/local/boost-1.60.0/include/boost/range/any_range.hpp:17, from prog.cc:3: /usr/local/boost-1.60.0/include/boost/range/detail/any_iterator_wrapper.hpp: In member function 'boost::range_detail::any_forward_iterator_wrapper<WrappedIterator, Reference, Buffer>::reference boost::range_detail::any_forward_iterator_wrapper<WrappedIterator, Reference, Buffer>::dereference() const [with WrappedIterator = boost::iterators::transform_iterator<boost::range_detail::default_constructible_unary_fn_wrapper<main()::<lambda(const auto:1&)>, SourceEvent>, __gnu_cxx::__normal_iterator<int*, std::vector<int> >, boost::iterators::use_default, boost::iterators::use_default>; Reference = SourceEvent; Buffer = boost::any_iterator_buffer<64ul>; boost::range_detail::any_forward_iterator_wrapper<WrappedIterator, Reference, Buffer>::reference = SourceEvent&]': /usr/local/boost-1.60.0/include/boost/range/detail/any_iterator_wrapper.hpp:302:57: warning: function may return address of local variable [-Wreturn-local-addr] return dereference_cast<reference>(*m_it); ^ /usr/local/boost-1.60.0/include/boost/range/detail/any_iterator_wrapper.hpp:302:52: note: declared here return dereference_cast<reference>(*m_it); ^ prog.exe: prog.cc:7: void ASSERT_EQ(T1, T2) [with T1 = unsigned int; T2 = unsigned int]: Assertion `x == y' failed. Aborted The example is compiled with gcc 5.2 and boost 1.60 (http://melpon.org/wandbox/permlink/QF1qyw5bWHKwyKJ8). Is there an error in my code? I would guess that transforming a range into a range of new objects of another type is quite common, so it should work. I am also curious why the warning is only emitted when compiling with optimizations. Best wishes, Jens -- Jens Auer | CGI | Software-Engineer CGI (Germany) GmbH & Co. KG Rheinstraße 95 | 64295 Darmstadt | Germany T: +49 6151 36860 154 jens.auer(a)cgi.com<mailto:jens.auer@cgi.com> Unsere Pflichtangaben gemäß § 35a GmbHG / §§ 161, 125a HGB finden Sie unter de.cgi.com/pflichtangaben<http://de.cgi.com/pflichtangaben>. CONFIDENTIALITY NOTICE: Proprietary/Confidential information belonging to CGI Group Inc. and its affiliates may be contained in this message. If you are not a recipient indicated or intended in this message (or responsible for delivery of this message to such person), or you think for any reason that this message may have been addressed to you in error, you may not use or copy or deliver this message to anyone else. In such case, you should destroy this message and are asked to notify the sender by reply e-mail.

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Re: [boost] [gsoc16] Can I quickly check if the below really is the best approach?
by Shangtong Zhang 16 Jan '16

16 Jan '16

Hi, > // At global scope, allocates no memory whatsoever > static const constexpr static_map<int, const char *> map { > { 5, "apple" }, > { 8, "pear" }, > { 0, "banana" }, > ... > }; > // Works, constexpr "apple" > constexpr const char *what_is_5 = map[5]; > // Works > assert(map[5] && !strcmp(map[5], "apple"); > // Works > map[5]="orange"; > assert(map[5] && !strcmp(map[5], "orange"); > // Throws exception as there is no key 6 > map[6]; > map.at <http://map.at/>(6); I have difficulty understanding this, As variable map is const and constexpr, how can map[5]=“orange” work? I don’t know how to implement this, where to store the “orange”. Could anyone help me? Thanks, Shangtong Zhang, Senior Student, School of Computer Science, Fudan University, PRC.

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[gsoc16]Interest in static map
by Shangtong Zhang 15 Jan '16

15 Jan '16

Hi Niall Douglas, I’m interested in the project static map and want to contribute to it in gsoc 2016. And I try to start with the programming competency test. Following is what I have done, https://github.com/ShangtongZhang/StaticMap/blob/master/main.cpp <https://github.com/ShangtongZhang/StaticMap/blob/master/main.cpp> Could you please give me some advice? In addition, I’m a little confused with // This should fail elegantly and usefully ... //constexpr std::array<unsigned, 0> string_hashes_fail = hash_strings(5); My understanding is that it will raise a run-time exception, is it right? Thanks, Shangtong Zhang, Senior Student, School of Computer Science, Fudan University, PRC.

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Is there interest in Computable Calculus?
by Damian Vicino 15 Jan '16

15 Jan '16

Hi, I’m interested in developing basic support of “real numbers” for computable calculus applications. In computable calculus, reals have infinite precision (certain restrictions may apply). The usual approach is representing numbers as functions producing digits. An arithmetic operation produces a new function using the functions in the operands and some simple expression manipulations. When a number needs to be evaluated (e.g., for comparisons where expression rules are unknown), enough digits for reaching an answer are generated using the functions. For example, 3.14 < pi requires generating 3 digits to answer “true”. The algorithms for arithmetic operations and evaluation are well known, and multiple implementations were developed (mostly in the 90s). However, I couldn’t find an open source implementation and had to come up with my own for working in a project during the last 2 years. My preferred reference for the required algorithms is the book: Aberth, Oliver. Computable Calculus. Academic Press, 2001. In particular, my initial scope would be the 4 arithmetic operations (+, -, *, /), and the comparison operators (<, =) for reals. Someone is interested in such a library in boost?

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IS THERE A WAY TO FIND IF A CERTAIN TYPE HAS A CERTAIN MEMBER?
by Juan Dent 15 Jan '16

15 Jan '16

> HI, > > > I have read that via enable_if and other constructs, one can declare a member of a type conditionally. > > What I need is a way to be able to test whether a certain type has a certain method or member data, so that I can call it or use it accordingly. > > Does boost have something like this?? > > > Regards, > Juan

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a safe integer library
by Robert Ramey 14 Jan '16

14 Jan '16

Arithmetic operations in C++ are NOT guaranteed to yield a correct mathematical result. This feature is inherited from the early days of C. The behavior of int, unsigned int and others were designed to map closely to the underlying hardware. Computer hardware implements these types as a fixed number of bits. When the result of arithmetic operations exceeds this number of bits, the result will not be arithmetically correct. I have crafted a library to address this issue once and for all. You can find out more about this by checking out the page for Safe Numerics at the boost library incubator. www.blincubator.com I hereby request that this library be added to the boost review queue. I've also made a proposal for the C++ Standards committee to include a simplified version of this library as part of he C++ standard. You can see the proposal at http://www.rrsd.com/software_development/safe_numerics/proposal.pdf Robert Ramey

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ATTENTION: Library requirements..
by Rene Rivera 13 Jan '16

13 Jan '16

Last Summer I brought up the subject of library organization requirements to make it easier to write the development and release tools needed to keep the Boost machine going. See this thread < http://lists.boost.org/Archives/boost/2015/06/223027.php> for a refresher. This morning I committed the first part of the above.. A new set of library requirements that take into account existing practices. Adds some additional integration requirements. And puts in limits to reduce some integration burdens. Please read the new requirements carefully < http://www.boost.org/development/requirements.html#Requirements>. It would be wonderful if authors start making changes as needed immediately. But at some point I, and possible others, will start making changes to all libraries to follow the requirements. So that the release, build, and testing teams can move forward with better support. And of course, more cleanups and such will follow. Hopefully before the next release is out the door. -- -- Rene Rivera -- Grafik - Don't Assume Anything -- Robot Dreams - http://robot-dreams.net -- rrivera/acm.org (msn) - grafikrobot/aim,yahoo,skype,efnet,gmail

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[BPM] Supporting an alternative to meta/libraries.json
by Louis Dionne 13 Jan '16

13 Jan '16

Dear list, Currently, all Boost libraries are required to have a meta/libraries.json file at their root, which contains some meta-data describing the library. As I understand it, this meta-data is then used to generate the list of all libraries with their description when a release is done. I find having such a directory at the root of every library annoying, since it clutters it. Furthermore, for metaprogramming libraries, the name can be slightly confusing since meta/ might be expected to contain something different. I propose that we allow libraries to specify their metadata in a `.boost` file located at their root. Using a dotfile is the most common way of providing information for an external service (for example .travis.yml), and dotfiles are usually more discrete when viewing the project in an editor. Furthermore, making `boost` part of the filename is more descriptive. I have submitted a pull request to BPM [1] adding the ability to fetch the meta data in a .boost file. The meta-data can still be provided in meta/libraries.json, so this should not affect existing libraries. Related questions that we might want to consider: - Should it be .boost.json instead of .boost? - Perhaps we could store the meta-data for all the libraries in the same place, and get rid of the individual meta-data files? - If this suggestion is accepted, is there more to modify than BPM? Regards, Louis [1]: https://github.com/boostorg/bpm/pull/1

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[test] BOOST_TEST macro and std::max
by Benedek Thaler 13 Jan '16

13 Jan '16

Hi, I'd expect the following cheks to pass: BOOST_TEST(3u == (std::max)(0u, 3u)); BOOST_TEST(3u == ((std::max)(0u, 3u))); But both fails with: check 3u == ((std::max)(0u, 3u)) has failed [3 != 7095312] Did I miss something regarding BOOST_TEST usage? Platform: Linux, GCC 5.3, Boost 1.60 Thanks, Benedek

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Re: [boost] asio config.hpp macro redefinition - mistake?
by Curdeius Curdeius 13 Jan '16

13 Jan '16

> > ---------- Wiadomość przekazana dalej ---------- > From: "John M. Dlugosz" <mpbecey7gu(a)snkmail.com> > To: boost(a)lists.boost.org > Cc: > Date: Tue, 12 Jan 2016 17:32:48 -0600 > Subject: [boost] asio config.hpp macro redefinition - mistake? > In file boost_1_59_0\boost\asio\detail\config.hpp line 227 gives a macro > redefinition warning. > (...) > It seems that this is missing a guard or has the if/else things mixed up. > This was fixed some time ago. See https://github.com/boostorg/asio/commit/b9cb61416e1972d7490d91da91df549703f… . Regards, Marek Kurdej

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[fusion]enabler.hpp junk character at start of file
by Aparna Kumta 13 Jan '16

13 Jan '16

All accumulator tests fail when compiled with Oracle Solaris Studio in 'dev' branch as follows: "../boost/fusion/support/detail/enabler.hpp", line 1: Error: A declaration was expected instead of "???". 1 Error(s) and 1 Warning(s) detected. See http://www.boost.org/development/tests/develop/developer/output/oracle-spar… It appears that in file boost/fusion/support/detail/enabler.hpp, there is some junk character at the start of file. This cannot be observed via vi editor, but with ' head -1 enabler.hpp', this can be seen. % head -1 enabler.hpp ��/*===================================== Perhaps these characters should be removed? When I view the file on github, I do not see the issue, however when I try to edit the file, I see it. Will submit a PR. Thanks, Aparna

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[regression] Regression tests for 'develop' has error
by Edward Diener 13 Jan '16

13 Jan '16

Trying to open the regression test results for 'develop' page gives: "Error extracting file: Error code 3 - A severe error in the zipfile format was detected." This has happened numerous times before. Can this be fixed, not only now but permanently ? Surely there must be some way of determining why the zipfile format has a severe error and preventing this in the future.

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asio config.hpp macro redefinition - mistake?
by John M. Dlugosz 13 Jan '16

13 Jan '16

In file boost_1_59_0\boost\asio\detail\config.hpp line 227 gives a macro redefinition warning. // Compliant C++11 compilers put noexcept specifiers on error_category members. #if !defined(BOOST_ASIO_ERROR_CATEGORY_NOEXCEPT) # if (BOOST_VERSION >= 105300) # define BOOST_ASIO_ERROR_CATEGORY_NOEXCEPT BOOST_NOEXCEPT # elif defined(__clang__) # if __has_feature(__cxx_noexcept__) # define BOOST_ASIO_ERROR_CATEGORY_NOEXCEPT noexcept(true) # endif // __has_feature(__cxx_noexcept__) # elif defined(__GNUC__) # if ((__GNUC__ == 4) && (__GNUC_MINOR__ >= 7)) || (__GNUC__ > 4) # if defined(__GXX_EXPERIMENTAL_CXX0X__) # define BOOST_ASIO_ERROR_CATEGORY_NOEXCEPT noexcept(true) # endif // defined(__GXX_EXPERIMENTAL_CXX0X__) # endif // ((__GNUC__ == 4) && (__GNUC_MINOR__ >= 7)) || (__GNUC__ > 4) # endif // defined(__GNUC__) # if defined(BOOST_ASIO_MSVC) # if (_MSC_VER >= 1900) # define BOOST_ASIO_ERROR_CATEGORY_NOEXCEPT noexcept(true) // ****** here ****** # endif // (_MSC_VER >= 1900) # endif // defined(BOOST_ASIO_MSVC) # if !defined(BOOST_ASIO_ERROR_CATEGORY_NOEXCEPT) # define BOOST_ASIO_ERROR_CATEGORY_NOEXCEPT # endif // !defined(BOOST_ASIO_ERROR_CATEGORY_NOEXCEPT) #endif // !defined(BOOST_ASIO_ERROR_CATEGORY_NOEXCEPT) To paraphrase, the block reads # if (BOOST_VERSION >= 105300) // it is: 105900 >= 105300 *# define BOOST_ASIO_ERROR_CATEGORY_NOEXCEPT BOOST_NOEXCEPT* ⋮ # if defined(BOOST_ASIO_MSVC) # if (_MSC_VER >= 1900) *# define BOOST_ASIO_ERROR_CATEGORY_NOEXCEPT noexcept(true)* # endif // (_MSC_VER >= 1900) # endif // defined(BOOST_ASIO_MSVC) It seems that this is missing a guard or has the if/else things mixed up.

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[property_tree] Still being maintained?
by Gavin McNiff 12 Jan '16

12 Jan '16

Hi, I was wondering if the Property_Tree library is still being actively maintained. There are 9 GitHub pull requests stacked up since the summer? Best regards Gavin McNiff

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[err] RFC
by Domagoj Saric 11 Jan '16

11 Jan '16

https://github.com/psiha/err README.md copy-paste: --------------------------------------------- err - yet another take on C++ error handling. We have throw and std::error_code, what more could one possibly want? --------------------------------------------- std::error_code&co tried to solve or at least alleviate the problem of overhead of using exceptions (in terms of both source code verbosity and binary code size&speed) with functions which need to report failures that need not be 'exceptional' depending on the context of the call (thereby requiring try-catch blocks that convert exceptions to 'result codes'). Unfortunately, the way it was finally implemented, std::error_code did not quite accomplish what it set out to do: • in terms of runtime efficiency: 'manual'/explicit EH (try-catch blocks) is no longer needed but the compiler still has to insert hidden EH as it has to treat the functions in question as still possibly throwing (in fact the implementation/codegen of functions which use std::error_code for error reporting becomes even fatter because it has to contain both return-on-error paths and handle exceptions) • in terms of source code verbosity: again, try-catch blocks are gone but separate error_code objects have to be declared and passed to the desired function. Enter boost::err: 'result objects' (as opposed to just result or error codes) which can be examined and branched upon (like with traditional result codes) or left unexamined to self-throw if they contain a failure result (i.e. unlike traditional result codes, they cannot be accidentally ignored). Thanks to latest C++ language features (such as r-value member function overloads) incorrect usage (that could otherwise for example lead to a result object destructor throwing during a stack-unwind) can be disallowed/detected at compile time. Discussions where the concept (or a similar one) was first concieved of and/or so far discussed: • http://boost.2283326.n4.nabble.com/system-filesystem-v3-Question-about-erro… • http://cpptips.com/fallible • https://github.com/ptal/std-expected-proposal • https://github.com/ptal/expected • https://github.com/adityaramesh/ccbase/blob/master/include/ccbase/error/exp… • http://stackoverflow.com/questions/14923346/how-would-you-use-alexandrescus… • https://svn.boost.org/trac/boost/wiki/BestPracticeHandbook#a8.DESIGN:Strong… • http://2013.cppnow.org/session/non-allocating-stdfuturepromise **************************************************************** For starter's, to reduce the length of the first post, I'll assume that everyone as at least somewhat familiar with similar/related proposals from Andrei Alexandrescu (std::expected) and Niall Douglas (std::monad) to which I gave links above. What, primarily, makes (Boost.)Err different from other proposals is the ability to (using latest C++ features) detect/distinguish between temporaries and 'saved' return values by using two different class templates (result wrappers), fallible_result (for rvalues) and result_or_error (for lvalues) and thus minimise or often completely eliminate any extra verbosity: If we had a function foo() that produces bar_t objects but can fail with an err_t, up till now we had two options: * bar_t foo() throw( err_t ); * optional<bar_t> foo( err_t & ); Err enables the library writer to write a single API and a single implementation: err::fallible_result<bar_t, err_t> foo(); where fallible_result is the class template that wraps temporaries/rvalues returned from functions and its member functions are all declared with && (i.e. callable only on rvalues) so you get a compiler error if you save it to an auto value and try to do anything with it. The two exceptions are the implicit conversion operators to: - bar_t, which will either return bar_t or throw err_t and which is used for the 'EH code path' bar_t my_bar( foo() ); - err::result_or_error<bar_t, err_t> which is used for the 'oldsk00l nothrow error code path' err::result_or_error<bar_t, err_t> maybe_bar( foo ); if ( maybe_bar ) { print( *maybe_bar ); } else { log( maybe_bar.error() ); } Also, if the fallible_result rvalue is left uninspected and contains an error its destructor will throw (which AFAICT should be safe considering it is an rvalue and no other exception can possibly be active at the same time) - this makes code that uses Err enabled libraries/APIs but relies on EH almost indistinguishable from 'classic EH' APIs (almost because the one difference that remains is with the immediate use of the return value: because of the wrapper class one can no longer write foo().do_something() but has to implicitly use the -> operator and write foo()->do_something() where the -> operator will check-and-throw if foo() did not succeed). To wrap up, this approach gives the user the immediate and fine grained control over which error handling mechanism he/she wants to use while allowing the developer to write a single API and implementation - AFAICT it is a no brainer replacement for <system_error>, it is less verbose and much more efficient ;-) ps. the small library @ https://github.com/psiha/err is by no means a finished product, it contains no tests or documentation but 'it works' (i.e. it is used in the, also upcoming, https://github.com/psiha/mmap)...I'm bringing it to public view for scrutiny, discussion and guidance lest I steer in the wrong direction ;) -- "What Huxley teaches is that in the age of advanced technology, spiritual devastation is more likely to come from an enemy with a smiling face than from one whose countenance exudes suspicion and hate." Neil Postman

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Add Boost.Convert to the Trac
by Vicente J. Botet Escriba 11 Jan '16

11 Jan '16

Hi, I have requested this (https://svn.boost.org/trac/boost/ticket/11814) 6 weeks ago without response. Is anyone maintaining the Trac component? I see Doug Gregor, but I believe he is not actively working on Boost. Best, Vicente

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[trac] boost 1.61
by Raffi Enficiaud 11 Jan '16

11 Jan '16

Hi all, Would it be possible to add 1.61 to the roadmap? Thanks, Raffi

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want to contribute in boost c++ organisation
by Aman Varshney 11 Jan '16

11 Jan '16

As I am a 2nd year computer Science student at IIIT-Hyderabad. Being a beginner I have some idea about C++ and want to start contributing to open source. I found the boost c++library. It would be great if I get some directions from you as to where to start from. Thank You

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[regression] Summary for develop is unavailable
by Antony Polukhin 08 Jan '16

08 Jan '16

Hi, At http://www.boost.org/development/tests/develop/developer/summary.html you'll find "Error extracting file: Error code 3 - A severe error in the zipfile format was detected." Please, could someone fix that? -- Best regards, Antony Polukhin

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