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

Status on Travis
by Raffi Enficiaud 18 Aug '16

18 Aug '16

Hi dear list, Hi Rene, I would like to know more about Travis and its status. From what I understand, a lot of efforts have been made recently for making things running per commit on Travis and have a quick feedback. * Naturally the first question is: is the status given by Travis the "official" one? so we consider the status given by Travis an official source of information, especially wrt. to its competing regression dashboard. * What are the development plans for Travis? Right now I see 3 types of builds, and I do not fully understand what they cover (platform, compiler) nor their differences. * For boost.test, I am testing each feature branch before merging to develop, by 1. cloning boost superproject on develop 2. switching only boost.test to the feature branch This is for preventing the breakages on develop that we observed in the past since several libraries are depending on boost.test. Would it be possible to have that as well on Travis or any continuous CI? That would be per library then. Would it also be possible to have like a template .travis.yml coming from the boost.superproject which can partly be overiden by a library? (if we want to build things slightly differently) * The CI I am using is able to parse the junit files generated by the test framework, and summarizes the information of each build nicely (also tracks the tests history). Is there anything similar in Travis? Right now, apart from looking at the full logs (which is hard), is there any intermediate information than red/green overall status? * I can see many project under the boostorg of Travis https://travis-ci.org/boostorg/ . How do we do that? Thanks, Raffi

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[Beast] Status: HTTP+WebSocket for Boost
by Vinnie Falco 17 Aug '16

17 Aug '16

I’m reporting on the status of Beast, a C++11 header-only library implementing HTTP and WebSocket which is submitted to the boost incubator. The official repository for Beast is at: https://github.com/vinniefalco/Beast It has been a few months since the last update and the number of users measured on GitHub has grown steadily. There is robust, active development with bug fixes and improvements. Unfortunately there hasn’t been much of in terms of attention from the Boost community, no feedback from the incubator was provided. If anyone would like to help out by checking out Beast in the incubator and leaving some comments that would be a tremendous help. Incubator link: http://blincubator.com/bi_library/beast-2/?gform_post_id=1579 The most exciting news is that Beast HTTP and WebSockets have been deployed in the production server environment for the company I work for, Ripple (http://ripple.com) On a side note, my co-worker David Schwartz is giving a CppCon 2016 Keynote speech on the relationship of C++ to public blockchain systems and cryptocurrencies: http://cppcon.org/schwartz-keynote-turner-plenary/ You can see the Beast integration in “rippled”, an open source server application that implements Ripple’s decentralized ledger: https://github.com/ripple/rippled/tree/develop/src/ripple/server/impl I will be doing a 15 minute lightning talk introducing CppCon 2016 conference attendees to Beast. The talk will have 8 minutes of presentation with the remainder of the time allocated for questions (if there are no questions I have additional materials which can be presented). At the conference I would love to meet anyone who is interested in the library or wants to have their questions answered - feel free to reach out to me through my email address vinnie.falco(a)gmail.com (also listed on my GitHub profile) if you’d like to get in contact. Thanks! -- Follow me on Github: https://github.com/vinniefalco/Beast

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[contract] Contracts for constexpr functions
by Lorenzo Caminiti 16 Aug '16

16 Aug '16

Hello all, A couple of the proposals I read on adding Contract Programming to the C++ standard raise the question if contracts should be supported for constexpr functions or not. I tough about this question a bit... but I am still not sure of the answer. I wanted to discuss this topic with this mailing list, especially with respect to what Boost.Contract can currently do. My general impression is that preconditions, postconditions, and class invariants should useful for constexpr functions but noting that: * Probably old values will not be useful in constexpr functions because constexpr prevents its functions from having side-effects (so it seems there will no variable visible outside of the function that the function body can change, and those variables are usually the candidates for making old copies). * Subcontracting will never apply to constexpr functions because they cannot be virtual. For example: struct conststr { // No virtual function so no subcontracting. [[invariant: empty() == (size() == 0)]] // Useful class invariants. [[invariant: data() != nullptr]] template<unsigned N> constexpr conststr(char const (&s)[N]) [[requires: s != nullptr]] // Useful preconditions. : data_(s), size_(N - 1) {} constexpr char back() const [[ensures(result): result == data()[size() - 1]]] // Useful postconditions. // Old values never useful because constexpr has no side-effects? { return data_[size_ - 1]; } constexpr unsigned size() const { return size_; } constexpr bool empty() const { return size_ == 0; } constexpr char const* data() const { return data_; } private: char const* data_; unsigned size_; }; That said, if I understand it correctly, the following are not allowed from within constexpr functions: 1. (Literal) type local variables with non-trivial constexpr destructors (see N3597 and subsequent proposals). 2. Try-catch statements (see N3597 and subsequent proposals). 3. Lambda functions (see N4487). Reading a few proposals, it seems that supporting the above from constexpr functions would be technically possible, but difficult to implement (see N3597 and its subsequent proposals, N4487, etc.). I'm not really familiar with these constexpr restrictions and plans/discussions to relax them in future revisions of the standard... Boost.Contract implementation uses all the above 1-2-3 respectively to: a. Check class invariants and postconditions at function exit (using RAII). b. Catch assertion failures as well as any other exception that might occur while evaluating an asserted conditions and then call the appropriate contract failure handler. c. Conveniently program functors that check pre- and postconditions within the contracted function. Therefore Boost.Contract implementation does not currently support contracts for constexpr functions. --Lorenzo

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'is_palindrome' and 'const char*'
by Зайцев Александр 14 Aug '16

14 Aug '16

Hello. I have some question about some case for 'is_palindrome' algo. 'is_palindrome' algorithm checks a sequence - if sequence is a palindromeor empty, function returns true, in other cases returns false. But in case e.g. "a" (is_palindrome("a")) result is false, because "a" = {'a', '\0'}. And maybe this behaviour is unexpected for users. So... what do you think about it? Should I implement special version for const char* or not? -- Best regards, Zaitsev Alexander

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filesystem 1.61.0 and cygwin: Windows assumed, posix expected
by Frédéric Bron 12 Aug '16

12 Aug '16

Hi, On cygwin, the following program #include <iostream> #include <boost/filesystem.hpp> int main() { auto p = boost::filesystem::path{"foo"}; p /= "bar"; std::cout << p.string() << '\n'; return 0; } outputs: foo\bar but cygwin is a posix system and I expect: foo/bar I read in the doc that "User-defined BOOST_POSIX_API and BOOST_WINDOWS_API macros are no longer supported." So how can I have posix support on cygwin? Thanks, Frédéric

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[graph] Sync develop with master?
by Murray Cumming 12 Aug '16

12 Aug '16

Now that Boost 1.61 is out, it would be great if the various fixes in boost graph's develop branch could be merged/cherry-picked/whatever to master, please. There seem to be a couple of years of fixes that have not appeared in a release. -- Murray Cumming murrayc(a)murrayc.com www.murrayc.com

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[thread][circular_buffer] Unmerged changes for 1.62
by Andrey Semashev 12 Aug '16

12 Aug '16

Hi, There are a couple of my PRs hanging for quite some time that I'd like to be merged before 1.62 is released: https://github.com/boostorg/circular_buffer/pull/9 Changes the default implementation of circular_buffer in debug mode to the thread-safe by default. https://github.com/boostorg/thread/pull/92 Fixes compilation of Boost.Thread with MSVC-8. There is also https://github.com/boostorg/thread/pull/94, which is not mine but it looks like it fixes a genuine problem. Could someone have a look at them and merge? Thanks.

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[interprocess] weirdest bug with offset_ptr equality comparison
by Joaquin M López Muñoz 11 Aug '16

11 Aug '16

The following is a distilled testcase after the ticket reported at https://svn.boost.org/trac/boost/ticket/12367 #include <boost/interprocess/allocators/allocator.hpp> #include <boost/interprocess/managed_shared_memory.hpp> template<typename Allocator> struct node_base { using allocator_type=Allocator; }; template<typename Allocator> struct node_impl { using value_type= typename Allocator::template rebind<node_impl>::other::value_type; }; template<typename Super> struct trampoline:node_impl<typename Super::allocator_type>{}; template<typename Super> struct node:Super,trampoline<Super>{}; int main() { using node_type= node< node< node_base< boost::interprocess::allocator< int, boost::interprocess::managed_shared_memory::segment_manager > > > >; using pointer=boost::interprocess::offset_ptr<node_type>; pointer p=nullptr; bool b=(p==p); // here's the problem } This works fine with GCC. When compiled with Visual Studio 2015, we get: 1>------ Build started: Project: borrame2015, Configuration: Debug x64 ------ 1> sandbox.cpp 1>d:\usr\joaquin\proyectos\boost-repo\trunk\boost\interprocess\detail\mpl.hpp(74): error C2594: 'argument': ambiguous conversions from 'node<node<node_base<boost::interprocess::allocator<int,boost::interprocess::segment_manager<CharType,MemoryAlgorithm,IndexType>>>>> ' to 'node_impl<boost::interprocess::allocator<int,boost::interprocess::segment_manager<CharType,MemoryAlgorithm,IndexType>>> ' 1> with 1> [ 1> CharType=char, 1> MemoryAlgorithm=boost::interprocess::rbtree_best_fit<boost::interprocess::mutex_family,boost::interprocess::offset_ptr<void,ptrdiff_t,size_t,0x00>,0x00>, 1> IndexType=boost::interprocess::iset_index 1> ] 1> d:\usr\joaquin\proyectos\borrame2015\sandbox.cpp(39): note: see reference to class template instantiation 'boost::interprocess::ipcdetail::is_convertible<node_type *,PointedType *>' being compiled 1> with 1> [ 1> PointedType=node_impl<boost::interprocess::allocator<int,boost::interprocess::segment_manager<char,boost::interprocess::rbtree_best_fit<boost::interprocess::mutex_family,boost::interprocess::offset_ptr<void,ptrdiff_t,size_t,0x00>,0x00>,boost::interprocess::iset_index>>> 1> ] ========== Build: 0 succeeded, 1 failed, 0 up-to-date, 0 skipped ========== Note that it is the line bool b=(p==p); // here's the problem that triggers the problem; if removed, compilation goes fine. Almost anything in the testcase program is needed for the problem to arise: - using node_type=node<node<...>> --> using node_type=node<...> (just one node level): compilation OK - remove using value_type=... in node_impl: compilation OK - rebind<node_mpl> --> rebind<char>: compilation OK - use std::allocator rather than boost::interprocess::allocator: compilation OK Ion, I'm totally puzzled by this and unable to navigate through the internals of Boost.Interprocess. Totally at your disposal if you need further info or assistance running tests etc. Thank you, Joaquín M López Muñoz

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[contract] noexcept and throwing handlers
by Lorenzo Caminiti 10 Aug '16

10 Aug '16

Hello all, I would like to discuss contracts and exception specifications (e.g., noexcept) specifically with respect to what Boost.Contract does. On one hand, it seems silly to allow a contract failure handler to throw an exception to only translate such an exception into a call to terminate() for noexcept functions. However, noexcept can be considered part of the function contract (namely, the contract that says the function shall not throw) and contract failure handlers should not be allowed to break such contract, not even when they are allowed to throw. For example consider a noexcept function fclose() that is called from a destructor without a try-catch statement (correctly so because fclose is declared noexcept). If fclose() is now allowed to throw when its preconditions fail, that will cause the destructor ~x() to throw as well?! void fclose(file& f) noexcept [[requires: f.is_open()]] ... class x { ~x() noexcept { fclose(f_); // f_ might not be open because of some bug... ... } file f_; }; (A point similar to the above is also made in N4160, in contrast with what argued in N4110.) Functions should honor their exception specifications (noexcept, etc.) even when their contracts fail and contract failure handlers are configured to throw. That is what Boost.Contract does (given that contract checking code appears within the function definition so it is subject to the exception specifications that appear in the enclosing function declaration): void fclose(file& f) noexcept { // This will call terminate()... boost::contract::guard c = boost::contract::function() .precondition([&] { BOOST_CONTRACT_ASSERT(f.is_open()); // ...even if this throws. } ; ... } int main() { boost::contract::set_precondition_failure( [] (boost::contract::from where) { // Re-throw exceptions (assertion_failure, user-defined, etc.). if(where != boost::contract::from_destructor) throw; std::terminate(); // But destructors never throw. } ); ... } Also note that a contract framework that allows to install failure handlers that throw exceptions should also pass some sort of parameter to the handler function to indicate if the contract failure happened in a destructor or not. That is so the failure handlers can choose to never throw for destructors, not even if class invariants (or postconditions) fails when checked by destructors. --Lorenzo

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[release] Continuous release archives.
by Rene Rivera 09 Aug '16

09 Aug '16

Starting with this release the archives for the prospective beta and release candidates are continuously built from the master branch and uploaded to SourceForge [1] (and to Bintray [2]). The release team would really appreciate if authors would download the archives and check the contents. In particular that the archives contain all the content you expect of your library, or libraries. And if you can also try building in your system that would stupendous. The more eyes we have on the final release products the smoother the process will be. And result in more time that the master branch is not blocked. Please report any problems sooner rather than later. So that we can try and address them before it's took late. Thank you, The Release Team [1] <https://sourceforge.net/projects/boost/files/boost/snapshots/master/> [2] <https://bintray.com/boostorg/master/snapshot#files> -- -- 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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