July 2019 - Boost - lists.preview.boost.org

CMake Announcement from Boost Steering Committee
by Jon Kalb 13 Aug '24

13 Aug '24

The libraries produced by the Boost community have had a greater impact on the way that the C++ community writes code than any other library implementation. The focus of the Boost community will always be on the libraries, but it is undeniable that we are dependent on and often limited by the infrastructure of our trade. Years ago, the move to Git was contentious; yet, it was required to improve development. In a similar vein our build system has become an impediment for many developers and users, existing and prospective. Therefore, we, the Steering Committee, announce to the Boost community our desire and intent to move Boost’s build system to CMake for users and developers alike. We are soliciting comments and proposals from the community to guide the process and the goals. Our desire is that the community can come to consensus by the end of the calendar year with a vision of supporting users and developers. We understand that the actual process of achieving the end goal will be long, time consuming, and not without its share of conflict. We also recognize that the Boost community is comprised of bright and passionate individuals that are eager to get involved and help get work done. The members of the Steering Committee have been encouraged by the discussions and activity surrounding CMake on the mailing lists over the years and know that many people have voiced visions. We hope that each of you rejoins the discussion to support this initiative and contributes to the common goal of improving Boost’s integration into the broader C++ ecosystem. For the Boost Steering Committee, Jon Kalb, Chair jonkalb(a)boost.org

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Result of out_ptr review.
by Zach Laine 07 Aug '19

07 Aug '19

I've compiled the results of the reviews of out_ptr during its recent review. Unfortunately, out_ptr is NOT ACCEPTED, though many of the reviewers indicated interest in seeing it come back in some future form. I counted these formal reviews: Andrey Semashev: reject Louis Dionne: accept David Sankel: reject Phil Endecott: reject Glen Fernandes: reject Gavin Lambert: reject Thanks to all of the above reviewers, and to all those who contributed to the ongoing discussions surrounding out_ptr, even if they did not have time for a full review. Points against out_ptr raised during the review: - Many reviewers indicated their puzzlement that this library was proposed at all, since they had never seen enough calls to C APIs in their own code to motivate the need for out_ptr. - Some reviewers who did find the motivating cases of the library compelling, still said that they would prefer to write wrappers instead of using something like out_ptr. - Multiple reviewers want the library to provide error-reporting help (it currently does not). In particular, for c_func(out_ptr(p)), there was a concern about whether p is assigned a value, when c_func() returns a failure-status. - There was concern from several reviewers about the fact that out_ptr's types' dtors may throw, though this is only limited to the use of out_ptr with shared_ptr and similar smart pointers. In particular, non-unique_ptr uses will never throw in out_ptr's types' dtors, unless the user provides a throwing deleter. - Multiple reviewers disagreed with the use of template specialization as a customization mechanism. - There was widespread concern about the use of potentially UB-invoking tricks to get max performance out of the implementation. - Many reviewers wanted a more typical Boost tutorial introduction in the documentation. Now please permit me a digression. The library attempts to take a call that looks like this (simplest call possible): // CASE 0 foo * new_foo; TODO if (!create_foo(&new_foo)) { // etc. ... } And turn it into something as close as possible to this: // CASE 1 std::unique_ptr<foo> new_foo; if (!create_foo(new_foo)) { // etc. ... } out_ptr does a great job of this lexically: // CASE 2 std::unique_ptr<foo> new_foo; if (!create_foo(out_ptr(new_foo))) { // etc. ... } If you have not written thousands of lines of code that look like case 0, stop for a second and consider what it would be like to drop those thousands of raw pointers into your code, and how much you would like to replace them all with unique_ptrs. Now consider what it would take you to write all the wrapping functions necessary to make those thousands of calls look like case 1. You may make tooling to generate the wrappers, and that's time consuming. Writing it by hand is even more so. out_ptr also has the nice property that using it as I have above with unique_ptr does not change the meaning of the code, except to ensure that new_foo is guaranteed to be treated in a RAII manner. Thus we get increased exception safety, memory leak mitigation, etc. -- y'know, all that RAII stuff. If out_ptr is implemented well, case 2 should produce nearly identical object code to case 0, except that case 2 handles calling new_foo's dtor at the right time. Note that because of this, you have the same relationship to the C API in all three cases. That is, you need to check for the success value returned from create_foo(), and you need to know what create_foo()'s contract is in the face of errors -- did it write to new_foo or not? out_ptr is how you get from raw pointers to RAII ones, not how you solve all programming problems related to calling functions. Hopefully that motivates the use case for out_ptr, even if you don't need it in your own code. Hopefully that also allays concerns that out_ptr is not doing enough -- doing more is outside the library's scope. Now, on to exceptions in out_ptr's types' dtors. I heard a lot of discussion about this during the review. To me, concerns about what happens when an out_ptr or an inout_ptr throws in its dtor misses the point entirely, because it is concerned with fixing corner cases we should not even care to support. Instead of worrying about the semantics of exceptions in those kinds of situations, we should instead be asking why we want to support user code like this: ... } catch { create_foo(in_out_ptr(my_shared_ptr_to_a_foo)); ... } In other words, we don't really care about the dtor exceptions, unless: - there is an active exception already, and - we are also calling a C API to create a new object (a possible, but certainly atypical thing to do when handling an exception), and - we're catching this new object in a shared_ptr-like smart pointer that might throw on construction. Who writes code like that? Few people, perhaps none. It's not impossible to see code like that, but until there are well-motivated cases for this, maybe leave it for a later version of the library. In other words, the question should have been "Why support anything other than nothrow-constructible RAII types like unque_ptr?" Note that I find this argument compelling for the WG21-facing version of this work too. To summarize: I think the first four bullet points listed at the beginning of this post are, or could easily be made to be, irrelevant. So, that leaves some issues still outstanding: - figure out how to provide customization points (I'm actually fine with the current approach...), - eliminate the UB-dangerous code, or make it opt-in, - rework the tutorial portion of the docs, and - many assorted doc cleanups. That does not seem like an unreasonable amount of stuff to resolve in post-review acceptance readiness. I bring all this up because I do in fact hope that JeanHeyd brings this back for a future review, and I hope that my arguments here will convince some of you that this library is a useful thing to have around. I waited until now to say any of these things in an attempt to remain impartial during the review; I've been bothered by seeing previous review managers clearly represent a pro-acceptance position from the start. Thanks to JeanHeyd for his submission. A no-vote from this group is a tough thing, and I hope that the feedback he has received takes some of the sting out. Zach

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[asio][coroutine] forbid_suspend blocks
by Vinícius dos Santos Oliveira 07 Aug '19

07 Aug '19

I've implemented a dumb linter using Python + clang API that allows you to mark certain blocks as “atomic in respect to coroutines” using C++11 attributes. Usage example follows: void f() { int yield; g(yield); [[bt::forbid_suspend]] { // Comment this call to make linter accept the code g(yield); t(); } } You can change bt::forbid_suspend to another identifier by tuning settings on the beginning of the script. The prefix forbid was inspired by Rust's linters[1] as you cannot disallow the linter from inside the forbid_suspend block. Some limitations follow: - A suspend point is identified by looking references to any id equals to yield in the last argument passed to function calls. It means that yield[ignored_ec] and alike will be correctly identified, but it needs to be named yield and it needs to be the last argument to the function call. - I haven't found a way to extract attributes related to COMPOUND_STMT nodes with clang API, so I manually look for token gaps and do a simple regex. It means you cannot use macros to [[bt::forbid_suspend]] as the macro won't be expanded. - You better call the script with '-x c++' and also ' -I/usr/lib/clang/5.0.1/include'. Like I've said in the beginning of the email, it's a *dumb* linter, which means it doesn't try to handle all cases. Therefore, I don't hope to do many changes to it or maintain it to work against newer releases of clang and I'm only uploading it to gist (not fullblow Github): < https://gist.github.com/vinipsmaker2/d930fbe5b7597432b021effe618da171>. It should also be easy to hack as it is very small. I'm releasing the linter under public domain. Enjoy. I have been using fibers in a daily basis on the last months of my job to solve networking problems on a gateway project. Some of the technologies I use are: - Boost.Asio and its spawn function. - A few custom synchronization primitives for the fibers (e.g. mutex, semaphore). - Eventually I'll have to write a custom spawn function that returns a joinable handle so I can kill the usage of a fiber::barrier in a few places. I've been using the linter for about a week already and looks fine. My use case are: - To prevent iterator invalidation in regions accessing shared variables. - To guarantee events order in algorithms that handle races (cannot yield while task YYY hasn't finished). The project I use it in is not an open source project, so I cannot talk much more about it. Also, I don't claim my solution is original. I wouldn't be surprised if the very same solution exists in the wild (please let me know if you know of a similar approach). This is not a new problem. It is know for some time. For instance, in P0171, Gor Nishanov noted this same problem: “In coroutines the suspend point is clearly marked with await, which tells the reader that something unusual happens in this function and allows the reader, for example, to confirm whether the lifetimes of the objects of interest align with the lifetime of the coroutine or not, whether some locks need to be acquired to protect some concurrently accessed data, and whether some locks need to be released before the execution reaches the suspend point.” — <http://open-std.org/jtc1/sc22/wg21/docs/papers/2015/p0171r0.html>, 2015 However, the solution he presented was to manually examine whole blocks of code without help from the compiler. I argue that the solution he presented is as error-prone as manually looking for exit paths that don't free acquired resources in languages lacking RAII. And I've been spoiled too much by RAII. Furthermore, I take this comment of his with highly suspicious look: “Since we are on the subject of maintenance nightmares, we would like to offer a conjecture that the absence of the await in P0114 is a likely source of many maintenance nightmares. Without a syntactic marker to signal to the person reading the code that something funny is going on, it is impossible to tell whether the following code is correct or not” — http://open-std.org/jtc1/sc22/wg21/docs/papers/2015/p0171r0.html If I had to give a vote to the proposal he was defending or Chris' proposal, I'd probably have chosen Chris'. [1] https://doc.rust-lang.org/reference/attributes.html# lint-check-attributes -- Vinícius dos Santos Oliveira https://vinipsmaker.github.io/

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Making copyright holders easier to parse
by Giovanni Mascellani 07 Aug '19

07 Aug '19

Dear Boost developers, I am one of the Debian developers maintaining the Boost package in Debian. As part of packaging policy, we want the copyright status of each file in Debian packages to be documented, which includes at least the name of the copyright holders and the license of that particular file. As you can believe, this is rather complicated for Boost, since there are a lot of files with many copyright holders. I started to use the tool bcp, which among other things is able to collect such copyright information. My clone is available here[1]. However, bcp often is confused by the inconsistent style of how copyright holders are listed in different files, so it required a lot a manual fixing. For example, sometimes copyright years are written before the name, sometimes after, sometimes they're absent; names are sometimes separated by commas, sometimes by newlines, maybe even sometimes by nothing. Sometimes there are spelling mistakes or casing inconsistencies between names, or inconsistent institutions' names. Bcp has some complicated regular expression to overcame all these differences, but the result is brittle at its best. [1] https://salsa.debian.org/gio/boost-copyright Since I am doing this manual work anyway, I might as well update the Boost files so that their copyright headers are more consistent and easy to parse, and then I could submit you patches for having them fixed in the Boost official repositories. My question is: are you interested in this kind of patches? Of course I would still go through the ordinary patch submission procedure. I am just asking if this kind of patches would be well received or not. To better illustrate what I mean, let me consider a few examples (the chosen files are completely random); file libs/log/include/boost/log/exceptions.hpp currently has: > /* > * Copyright Andrey Semashev 2007 - 2015. > * Distributed under the Boost Software License, Version 1.0. > * (See accompanying file LICENSE_1_0.txt or copy at > * http://www.boost.org/LICENSE_1_0.txt) > */ I might change this to: > /* > * Copyright: 2007-2015 Andrey Semashev > * License: Boost Software License, Version 1.0 > * (See accompanying file LICENSE_1_0.txt or copy at > * http://www.boost.org/LICENSE_1_0.txt) > */ File libs/atomic/include/boost/atomic/fences.hpp has: > /* > * Distributed under the Boost Software License, Version 1.0. > * (See accompanying file LICENSE_1_0.txt or copy at > * http://www.boost.org/LICENSE_1_0.txt) > * > * Copyright (c) 2011 Helge Bahmann > * Copyright (c) 2013 Tim Blechmann > * Copyright (c) 2014 Andrey Semashev > */ I might change this to: > /* > * Copyright: 2011 Helge Bahmann > * Copyright: 2013 Tim Blechmann > * Copyright: 2014 Andrey Semashev > * License: Boost Software License, Version 1.0 > * (See accompanying file LICENSE_1_0.txt or copy at > * http://www.boost.org/LICENSE_1_0.txt) > */ I hope these examples illustrate my intention. I think that having more easily parsable copyright holders could be useful for Debian, for Boost and for Boost adopters which should properly care about the licensing of the libraries they use. Thank you, Giovanni. -- Giovanni Mascellani <g.mascellani(a)gmail.com> Postdoc researcher - Université Libre de Bruxelles

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[release] 1.71.0 post-beta merges
by Michael Caisse 05 Aug '19

05 Aug '19

The master branch is is now open for post-beta merges, but only as described in the Post-Beta Merge Policy. See <https://github.com/boostorg/boost/wiki/Releases%3A-Beta-Merge-Policy> Thanks, -- The Boost Release Team

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Norton blocking Appveyor?
by John Maddock 01 Aug '19

01 Aug '19

Hi all, I see that my browser is just started blocking ci.appveyor.com which is a bit of a problem for CI to say the least. Is anyone else seeing this? Any ideas whether it's justified or spurious? Thanks, John. --- This email has been checked for viruses by Avast antivirus software. https://www.avast.com/antivirus

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Final Call for Submissions: International Conference on Information Society (i-Society 2019)
by International Conference on Information Society 29 Jul '19

29 Jul '19

If you are not able to see this mail, click http://r.confinfosoc.org/mk/mr/dNqT-1si6HE5qHDv5cV6nrZEGnVvH63myFIAZaMHhWb9… Final Call for Submissions: International Conference on Information Society (i-Society 2019) The i-Society is a global knowledge-enriched collaborative effort that has its roots from both academia and industry. The conference covers a wide spectrum of topics that relate to information society, which includes technical and non-technical research areas. Submission Instructions: * You can submit your extended abstract or paper online at [ http://www.i-society.eu/paper-submission/ ]( http://r.confinfosoc.org/mk/cl/f/cKABES_5mIGAo8Mgp-cuui5DCd9DYYIrOsBvLgtLLN… )or email it to papers(a)i-society.eu * You can submit your poster via email at posters(a)i-society.eu * You can submit your workshop or tutorial proposal at workshop(a)i-society.eu or tutorial(a)i-society.eu * You can submit your speaker's proposal at speakers-2019(a)i-society.eu [ Submit ]( http://r.confinfosoc.org/mk/cl/f/FhV5CG1-0Pk8UtOQVyS5RSUsGqCAVXq-AH1LIwQW9t… ) This email was sent to boost(a)lists.boost.org You received this email because you are registered with Infonomics Society [ Unsubscribe here ]( http://r.confinfosoc.org/mk/un/07f-n0ocPpExwtzrl_PeKAeTG4ctupFicTSTp-RuT97r… ) [ ]( http://r.confinfosoc.org/mk/cl/f/j-a-1n1z1XvvyX_L5iaFp6R3gGFhBceWdCdqP1QnZF… ) © 2019 Infonomics Society

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MSVC 2019
by Cg K 27 Jul '19

27 Jul '19

I recently installed Visual Studio 2019 and then Boost and Quantlib. I tried to compile Quantlb with the precompiled 1.70 boost. I go the error message: LINK : fatal error LNK1104: cannot open file 'libboost_unit_test_framework-vc142-mt-gd-x64-1_70.lib' It appears that compatibility with Visual Studio/MSVC 2019 has not been worked out in 1.70 given its release date was so close to the release date of Visual Studio 2019. I also noted the the beta for 1.71 was closed. Wondering if the beta fixes this or is there a workaround or is this a user error?

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RSS1/RSS2/ATOM + P2P
by Ggh 27 Jul '19

27 Jul '19

Dear All, I invite you all to a debate/brainstorming on implementing an RSS library for boost, as well as an RSS+p2p protocol on the application layer on the TCP/IP stack. I do not claim that RSS should have an implementation in boost, however I think it might be a good idea. Lots of activity on http/application layer of the web and perhaps we/boost developers should consider an RSS extention to boost of RSS/Atom, with P2P capabilities. As always, comments and critisism is velcome. Thank you, Cheers Greg Tell me, and I forget. Ask me, and I discover...

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proposals
by VALERIU SMERICA 27 Jul '19

27 Jul '19

Hello. Is it possible to propose some data structures to be part of Boost that use code under the Apache 2.0 license? Are there any legal issues with this? I heard Apache 2.0 license was pretty permissive. Thanks.

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[release] Boost 1.71.0 Beta 1
by Michael Caisse 26 Jul '19

26 Jul '19

Boost release 1.71.0 beta 1 is now available at: <https://dl.bintray.com/boostorg/beta/1.71.0.beta1.rc1/source/> The SHA256 checksums are as follows: 451adc4f199c73e995e541f38c4dbd51faf4ce0db15537136ffd5213a1be5e55 boost_1_71_0_b1_rc1.7z a93d7066fc1514995aec0e726532a219447dd39b0ffa7cb97ca5736f16b0488b boost_1_71_0_b1_rc1.tar.bz2 34743b80466463e0c1b7fc71b677f326bdc242fe0b87a9c1599b6f7ea6e5c0cb boost_1_71_0_b1_rc1.tar.gz 5cd448bddc8394469391306e0ccada0a8f88c5c6cf8ec775ddf8e56adef8bbc2 boost_1_71_0_b1_rc1.zip For details of what's in the release, see <http://www.boost.org/users/history/version_1_71_0.html>. Note: Having some trouble getting the web page updated... check back with it soon. Please download the beta, give it a try, and report any problems you encounter. Thanks, -- The Boost Release Team

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Boost proposals
by VALERIU SMERICA 26 Jul '19

26 Jul '19

Hello. Is it possible to propose some data structures to be part of Boost that use code under the Apache 2.0 license? Are there any legal issues with this? I heard Apache 2.0 license was pretty permissive. Thanks.

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boost::serialization optional does not use boost::serialization::access
by Janek Kozicki 25 Jul '19

25 Jul '19

Hi, this simple program will not compile. The only way to make it work is to make a public default constructor. This defeats the purpose of boost::serialization::access. I tried to fix <boost/serialization/optional.hpp> but I couldn't get it to correctly call the access::construct(); Please help. // g++ -o serialize_optional /tmp/serialize_optional.cpp -lboost_serialization #include <fstream> #include <iostream> #include <boost/serialization/nvp.hpp> #include <boost/serialization/serialization.hpp> #include <boost/archive/xml_iarchive.hpp> #include <boost/archive/xml_oarchive.hpp> #include <boost/serialization/access.hpp> #include <boost/archive/text_oarchive.hpp> #include <boost/archive/text_iarchive.hpp> #include <boost/serialization/optional.hpp> #include <boost/optional.hpp> class Foo { public: Foo(int k) : i(k) {} friend std::ostream& operator<<(std::ostream& os, Foo const& foo) { return os << "Foo { " << foo.i << " }"; } private: Foo() : i(-1) {}; friend class boost::serialization::access; template<class Archive> void serialize(Archive & ar, const unsigned int){ #define N(a) BOOST_SERIALIZATION_NVP(a) ar & N(i); #undef N }; int i; }; int main() { using Data = boost::optional<Foo>; std::cout << "Boost version: " << BOOST_VERSION << "\n"; { auto f = Data(133); std::ofstream os("test.xml"); boost::archive::xml_oarchive oa(os); oa << boost::serialization::make_nvp("f", f); } { Data g; std::ifstream is("test.xml"); boost::archive::xml_iarchive ia(is); ia >> boost::serialization::make_nvp("f", g); std::cout << g.get() << "\n"; } } best regards Janek Kozicki

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[gil] Missing doc/html/ files from Boost 1.70
by Mateusz Loskot 24 Jul '19

24 Jul '19

Hi, I'm following up this old report of mine [1] about missing GIL docs. Apparently, GIL documentation was not generated during the release process, so no files were copied wherever they should be. The documentation is missing from: - boost_1_70_0 source archives - https://www.boost.org/doc/libs/1_70_0/libs/gil/ Is it possible to fix the website at least, redirect it to valid URL? Can I fix it myself? How? [1] https://lists.boost.org/Archives/boost/2019/04/245985.php Best regards, -- Mateusz Loskot, http://mateusz.loskot.net

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[locale] Loss of precision (C4244) warnings in MSVC 64-bit build
by Kenneth Porter 24 Jul '19

24 Jul '19

Building with MSVC compilers for 64-bit results in several C4244 warnings in api.hpp, due to passing the difference of two pointers (ptrdiff_t) to Win APIs expecting an int. Patch here: <https://github.com/boostorg/locale/issues/42> Using this command with the recent 1.71.0 beta: call .\bootstrap.bat --without-python .\b2 --without-python toolset=msvc-14.2,msvc-14.0,msvc-12.0,msvc-10.0 runtime-link=shared,static address-model=32,64

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[release] Boost 1.71.0 Beta 1 - déjà vu
by Michael Caisse 23 Jul '19

23 Jul '19

Note: The previous email announcement still had the rc1 tag in the filenames. This version of beta1 is identical in content to beta1 rc1. Boost release 1.71.0 beta 1 is now available at: <https://dl.bintray.com/boostorg/beta/1.71.0.beta1/source/> The SHA256 checksums are as follows: 451adc4f199c73e995e541f38c4dbd51faf4ce0db15537136ffd5213a1be5e55 boost_1_71_0_b1.7z a93d7066fc1514995aec0e726532a219447dd39b0ffa7cb97ca5736f16b0488b boost_1_71_0_b1.tar.bz2 34743b80466463e0c1b7fc71b677f326bdc242fe0b87a9c1599b6f7ea6e5c0cb boost_1_71_0_b1.tar.gz 5cd448bddc8394469391306e0ccada0a8f88c5c6cf8ec775ddf8e56adef8bbc2 boost_1_71_0_b1.zip For details of what's in the release, see <http://www.boost.org/users/history/version_1_71_0.html>. Note: Having some trouble getting the web page updated... check back with it soon. Please download the beta, give it a try, and report any problems you encounter. Thanks, -- The Boost Release Team

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[BOOST] Boost fusion testcase fails with llvm and gcc when optimization enabled
by Jaydeep Chauhan 22 Jul '19

22 Jul '19

Hi Devs, consider below boost testcase, boost_1_70_0/libs/fusion/test/functional/invoke.cpp when compiles with optimization enabled, $g++ -O2 -I./boost_1_70_0 boost_1_70_0/libs/fusion/test/functional/invoke.cpp $./a.out ./boost_1_70_0/libs/fusion/test/functional/invoke.cpp(391): test 'that.data == fusion::invoke(& members::data, fusion::join(sv_obj_c_ctx,seq))' failed in function 'void test_sequence_n(Sequence&, mpl_::int_<0>) [with Sequence = boost::fusion::vector<>]' ./boost_1_70_0/libs/fusion/test/functional/invoke.cpp(401): test 'that.data == fusion::invoke(& members::data, fusion::join(sv_obj_c_d_ctx,seq))' failed in function 'void test_sequence_n(Sequence&, mpl_::int_<0>) [with Sequence = boost::fusion::vector<>]' ./boost_1_70_0/libs/fusion/test/functional/invoke.cpp(391): test 'that.data == fusion::invoke(& members::data, fusion::join(sv_obj_c_ctx,seq))' failed in function 'void test_sequence_n(Sequence&, mpl_::int_<0>) [with Sequence = boost::fusion::list<>]' ./boost_1_70_0/libs/fusion/test/functional/invoke.cpp(401): test 'that.data == fusion::invoke(& members::data, fusion::join(sv_obj_c_d_ctx,seq))' failed in function 'void test_sequence_n(Sequence&, mpl_::int_<0>) [with Sequence = boost::fusion::list<>]' 4 errors detected. And When compiled without any optimization $g++ -O0 -I./boost_1_70_0 boost_1_70_0/libs/fusion/test/functional/invoke.cpp $./a.out No errors detected. $g++ --version Target: x86_64-pc-linux-gnu Configured with: ../gcc-9.1.0/configure -- --enable-languages=c,c++ --disable-libquadmath --disable-libquadmath-support --disable-werror --disable-bootstrap --enable-gold Thread model: posix gcc version 9.1.0 (GCC) Here we demonstrated the test case with g++ but same can be seen with clang++. When analyzed further we have seen that this is [ boost_1_70_0/boost/fusion/functional/invocation/invoke.hpp:139 ] trying to return local address, which is undefined behavior. And that lead to above test-case failure. So either we have to modify test-case to pass as reference or disable it.But before going ahead like to know your thought/suggestions? Thanks, Jaydeep

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Innocent but annoying warning in Boost QVM library
by Luigi Castelli 19 Jul '19

19 Jul '19

Hi Emil and all, when compiling Boost QVM, compilation succeeds but I get this warning: filename: quat_operations.hppwarning: Declaration shadows a typedef in function 'boost::qvm::axis_angle' A declaration in line 1438 shadows one in line 1414 Could this be solved for the next update?Thanks - Luigi

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Boost log to limit log file maximum file size
by JH 19 Jul '19

19 Jul '19

H Andrey and all, Can the log file be configured to set up the file size cap, when the log file reaches to the maximum file size, it deletes it and starts a new log file not rotates it? Thank you. - jupiter

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Lambda testcase fails when optimization enabled in gcc and llvm
by navya deepika garakapati 19 Jul '19

19 Jul '19

Hi Devs, consider below reduced testcase from boost lamda. $cat result_of_tests.cpp #include <boost/lambda/lambda.hpp> #include <stdio.h> template<class A, class F> typename boost::result_of<F(A)>::type apply1(F f, A b) { return f(b); } using namespace boost::lambda; int main(int, char *[]) { int one = 1; int d= (apply1<int>(_1 ,one) == 1); printf("\n%d\n",d); return 0; } when compiled with optimization O2 $g++ result_of_tests.cpp -I ./boost_1_70_0 -O2 $./a.out 0 And,when we compile same testcase with O0 $g++ result_of_tests.cpp -I ./boost_1_70_0 -O0 $./a.out 1 The above testcases is demonstrated with g++ compiler but behavior is same on clang as well. so we thought that this may be boost testcase issue. When we replace , int d= (apply1<int>(_1 ,one) == 1); with int d= (apply1<int&>(_1 ,one) == 1); testcase gives correct result with or without optimization. Wanted to confirm here,is it valid testcase or we have to modify testcase as per above? Thanks, Navya

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Review request for LEAF, review manager needed
by Emil Dotchevski 19 Jul '19

19 Jul '19

I'm requesting a formal review for LEAF, a C++11 error-handling library: https://zajo.github.io/leaf. Features: * Header-only, no dependencies. * No dynamic memory allocations. * Compatible with std::error_code, errno and any other error code type. * Can be used with or without exception handling. LEAF comes complete with its own result<T> type, but it is compatible with any other type with value-or-error variant semantics (like outcome::result<T>) as long as .error() returns a std::error_code. https://travis-ci.org/zajo/leaf https://ci.appveyor.com/project/zajo/leaf

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Re: [boost] [release] 1.71.0 closed for Beta
by Kenneth Porter 19 Jul '19

19 Jul '19

I'm seeing the following block of warnings repeated with several MSVC compiler versions. I'd suggest changing int to ptrdiff_t or size_t for the target type. f:\devel\Boost\boost_1_71_0\libs\locale\src\win32\api.hpp(149): warning C4244: 'argument': conversion from '__int64' to 'int', possible loss of data f:\devel\Boost\boost_1_71_0\libs\locale\src\win32\api.hpp(153): warning C4267: 'argument': conversion from 'size_t' to 'int', possible loss of data f:\devel\Boost\boost_1_71_0\libs\locale\src\win32\api.hpp(153): warning C4244: 'argument': conversion from '__int64' to 'int', possible loss of data f:\devel\Boost\boost_1_71_0\libs\locale\src\win32\api.hpp(170): warning C4244: 'argument': conversion from '__int64' to 'int', possible loss of data f:\devel\Boost\boost_1_71_0\libs\locale\src\win32\api.hpp(245): warning C4244: 'argument': conversion from '__int64' to 'int', possible loss of data f:\devel\Boost\boost_1_71_0\libs\locale\src\win32\api.hpp(249): warning C4244: 'argument': conversion from '__int64' to 'int', possible loss of data My build command: call .\bootstrap.bat --without-python .\b2 --without-python toolset=msvc-14.2,msvc-14.0,msvc-12.0,msvc-10.0 runtime-link=shared,static address-model=32,64

1 0

[release] 1.71.0 closed for Beta
by Michael Caisse 19 Jul '19

19 Jul '19

The master branch is now closed for all changes except by permission for the Beta release. Also, remember to add your libraries' changes to the release notes at: <https://github.com/boostorg/website/blob/master/feed/history/boost_1_71_0.q…> Thanks, -- The Boost Release Team

5 8

Any sample code to configure boost log for syslog?
by JH 18 Jul '19

18 Jul '19

Hi, I am using boost log to write log file in the disk of the desktop, but for an embedded system application where the NAND flash is used, to prolong the flash service life time, I try not to write log files in flash, but use journalctl to view the log in RAM. Are there any simple example to configure boost log for syslog? Thank you. - jh

2 2

Something off my chest about Boost
by Maarten Verhage 18 Jul '19

18 Jul '19

Dear Boost people, Sorry but I need to get something off my chest regarding the Boost culture. To start of with something nice: I’m convinced Boost provides really useful facilities for C++ and some of them even make it into the standard C++ library. I do believe I can also contribute in a reasonable way. But the terse documentation keeps me from advancing. How it is currently stated on https://www.boost.org/users/faq.html “What about documentation? A very simple library might be accepted with only a well commented header file. For more substantial libraries, some form of documentation is certainly going to be expected. HTML is the preferred form.” To make Boost more accessible to people I believe Boost should ask more on this from current and new library authors. Speaking for myself. I think the first bits to get started with a library are on a sufficient level. You know the tutorial and the example code. But I get lost when I want to use the library for my own application domain. Then I do need library facilities not covered in the example code and sometimes the documentation mentions only the syntax. As I would imagine the library author working on his/her library judging whether to add a facility or not. Finally decided to add something: *the thought/motivation that goes along with that*, that would be so valuable for me to read that in the documentation!! Yes, I’m annoyed that I cannot read that in the documentation. Another issue is when example code introduces three or more facilities at once. Then it is very hard for me to see how these bits relate to each other to make it useful for myself. Ok, a few examples for what I would like to ask the Boost community to demand from the library authors: 1) In general, for the classes/functions where the user should directly deal with documentation like cppreference.com. So, with function prototypes showing the argument- and return types and a complete list of members along with what they do. 2) Specifically for Spirit X3, a part on Parser Directives: https://www.boost.org/doc/libs/develop/libs/spirit/doc/x3/html/spirit_x3/qu… I would very much like that the reason why each directive is added along with a minimal example that shows how to use just that directive. Anyway, I hope people are also interested to discus documentation policies on this mailing list. I do believe it is important. Best regards, Maarten Verhage

10 17

ASIO socket termination crashed at boost::asio::async_read
by JH 17 Jul '19

17 Jul '19

Hi, I use boost TCP socket for months, it works well until I call a termination of smart pointer which is running at boost::asio::async_read. Could anyone explain what could be the cause for the following errors? void Comms::HandleReadBody(const boost::system::error_code &error, const uint32_t length) { ................ boost::asio::async_read(this->mHandler->Socket(), boost::asio::buffer(this->mHeader, sizeof(this->mHeader)), [=](const boost::system::error_code &status, const uint32_t length) {this->HandleReadHeader(status, length);}); ............... } (gdb) run 2019-07-15 11:47:32.396184: Sanity check socket connection and terminate it when it is inactive ............. pure virtual method called terminate called without an active exception Program received signal SIGABRT, Aborted. (gdb) backtrace #0 __GI_raise (sig=sig@entry=6) at ../sysdeps/unix/sysv/linux/raise.c:51 #1 0x00007ffff7a24801 in __GI_abort () at abort.c:79 #2 0x00007ffff5565957 in ?? () from /usr/lib/x86_64-linux-gnu/libstdc++.so.6 #3 0x00007ffff556bab6 in ?? () from /usr/lib/x86_64-linux-gnu/libstdc++.so.6 #4 0x00007ffff556baf1 in std::terminate() () from /usr/lib/x86_64-linux-gnu/libstdc++.so.6 #5 0x00007ffff556c8bf in __cxa_pure_virtual () from /usr/lib/x86_64-linux-gnu/libstdc++.so.6 #6 HandleReadHeader(boost::system::error_code const&, unsigned int) () #7 0x00007ffff679a116 in boost::asio::detail::read_op<boost::asio::ssl::stream<boost::asio::basic_stream_socket<boost::asio::ip::tcp, boost::asio::stream_socket_service<boost::asio::ip::tcp> > >, boost::asio::mutable_buffers_1, boost::asio::detail::transfer_all_t, HandleReadBody(boost::system::error_code const&, unsigned int)::{lambda(boost::system::error_code const&, unsigned int)#1}>::operator()(boost::system::error_code const&, unsigned long, int) () #8 0x00007ffff6799c20 in boost::asio::ssl::detail::io_op<boost::asio::basic_stream_socket<boost::asio::ip::tcp, boost::asio::stream_socket_service<boost::asio::ip::tcp> >, boost::asio::ssl::detail::read_op<boost::asio::mutable_buffers_1>, boost::asio::detail::read_op<boost::asio::ssl::stream<boost::asio::basic_stream_socket<boost::asio::ip::tcp, boost::asio::stream_socket_service<boost::asio::ip::tcp> > >, boost::asio::mutable_buffers_1, boost::asio::detail::transfer_all_t, HandleReadBody(boost::system::error_code const&, unsigned int)::{lambda(boost::system::error_code c---Type <return> to continue, or q <return> to quit--- onst&, unsigned int)#1}> >::operator()(boost::system::error_code, unsigned long, int) () #9 0x00007ffff679b547 in boost::asio::detail::reactive_socket_recv_op<boost::asio::mutable_buffers_1, boost::asio::ssl::detail::io_op<boost::asio::basic_stream_socket<boost::asio::ip::tcp, boost::asio::stream_socket_service<boost::asio::ip::tcp> >, boost::asio::ssl::detail::read_op<boost::asio::mutable_buffers_1>, boost::asio::detail::read_op<boost::asio::ssl::stream<boost::asio::basic_stream_socket<boost::asio::ip::tcp, boost::asio::stream_socket_service<boost::asio::ip::tcp> > >, boost::asio::mutable_buffers_1, boost::asio::detail::transfer_all_t, HandleReadBody(boost::system::error_code const&, unsigned int)::{lambda(boost::system::error_code const&, unsigned int)#1}> > >::do_complete(boost::asio::detail::task_io_service*, boost::asio::detail::task_io_service_operation*, boost::system::error_code const&, unsigned long) () #10 0x000055555559f5c0 in boost::asio::detail::task_io_service::do_run_one(boost::asio::detail::scoped_lock<boost::asio::detail::posix_mutex>&, boost::asio::detail::task_io_service_thread_info&, boost::system::error_code const&) () #11 0x000055555559f747 in boost::asio::detail::task_io_service::run(boost::system::error_code&) ()

4 5

Useful Release Notes
by James E. King III 13 Jul '19

13 Jul '19

I'd suggest we make sure our release notes are useful to end users; I found some examples that are in the 1.71 that are not useful when reading the notes: * [phrase library..[(a)/libs/flyweight/index.html Flyweight]:] * Maintenance work. * [phrase library..[@/libs/poly_collection/ PolyCollection]:] * Maintenance work. Thanks, Jim

2 1

meeting today
by Robert Ramey 12 Jul '19

12 Jul '19

I was impressed with your presentation today. you can find current renderings at this link: https://we.tl/t-TDoBHgw9AF Robert Ramey

1 1

The out_ptr review is now over
by Zach Laine 11 Jul '19

11 Jul '19

Thanks to all that participated. A review result with be posted sometime in the next couple of weeks (the upcoming C++ standards meeting next week will delay it a bit). Zach

1 0

Failed reconnection
by JH 11 Jul '19

11 Jul '19

Sorry for keeping posting questions about ASIO TCP socket reconnection regarding to network interface changes, I am very much stuck at the moment. As I described in other emails, when one network interface WiFi failed, the network interface Ethernet takes over, the client application using boost ASIO TCP socket cannot detect the broken of WiFi, it continually sent messages to the remote server via the broken WiFi interface without triggering errors but obviously the server could not receive messages any more. So my solution is prior to send message, it ping to 8.8.8.8 via the network interface WiFi, if it failed, it called the SetConnection again to close the socket binding to WiFi interface and to start reconnection to bind to Ethernet interface: void SetConnection(void) { if (this->mSocket.lowest_layer().is_open()) { std::cout << "Set connection close socket" << std::endl; this->mSocket.lowest_layer().close(); } boost::asio::ip::tcp::resolver resolver(this->mIoService); boost::asio::ip::tcp::resolver::query query(this->mHost, this->mPort); this->mIterator = resolver.resolve(query); this->mContext.load_verify_file("ssl/ca.pem"); this->mSocket.set_verify_mode(boost::asio::ssl::verify_peer); this->mSocket.set_verify_callback(boost::bind(&client::verify_certificate, this, _1, _2)); boost::asio::async_connect(mSocket.lowest_layer(), this->mIterator, boost::bind(&client::handle_connect, this, boost::asio::placeholders::error)); } But it did not work, the error: handle_connect connect failed: Network is unreachable What I am missing here? How can I make the TCP socket reconnection? Thank you. Kind regards, - jupiter

2 3

Link problem with graph and pending still appears unresolved?
by pbristow＠hetp.u-net.com 10 Jul '19

10 Jul '19

I have been bitten by this problem, again ☹ error: Cannot create link boost\pending\detail\disjoint_sets.hpp to libs\graph\include\boost\pending\detail\disjoint_sets.hpp. error: Link previously defined to another file, libs\disjoint_sets\include\boost\pending\detail\disjoint_sets.hpp. that was discussed https://lists.boost.org/Archives/boost/2019/04/246083.php I have got going again by deleting the contents of boost/boost/ containing the symlinks. But I note that a folder pending still exists, but not graph. Is this unresolved? Should it be fixed for the next release? Paul Paul A. Bristow Prizet Farmhouse Kendal, Cumbria LA8 8AB UK

5 14

[releaase] 1.71.0 closed for major changes
by Marshall Clow 09 Jul '19

09 Jul '19

The master branch is now closed for new libraries and breaking changes, and will be closing for the beta in one week. Also, if you're ready, you can also add your libraries' changes to the release notes at: < https://github.com/boostorg/website/blob/master/feed/history/boost_1_71_0.q… > After editing the release notes, you should get a form to create a pull request, remember to submit it, otherwise I won't see your change. As always, the calendar for the release cycle is available at: https://www.boost.org/development/ Thanks, -- The Boost Release Team

3 2

Beast repo history changed?
by Tom Kent 09 Jul '19

09 Jul '19

Did something get re-written in the beast repo? I was getting some weird errors on my cron mirror job: error: object file ./objects/3c/5bd5d909ee9b71f2b28d002dfe9d98355766c9 is empty error: object file ./objects/3c/5bd5d909ee9b71f2b28d002dfe9d98355766c9 is empty fatal: loose object 3c5bd5d909ee9b71f2b28d002dfe9d98355766c9 (stored in ./objects/3c/5bd5d909ee9b71f2b28d002dfe9d9835576 6c9) is corrupt error: object file /mnt/fs2/boostorg/beast.git/objects/3c/5bd5d909ee9b71f2b28d002dfe9d98355766c9 is empty error: object file /mnt/fs2/boostorg/beast.git/objects/3c/5bd5d909ee9b71f2b28d002dfe9d98355766c9 is empty fatal: loose object 3c5bd5d909ee9b71f2b28d002dfe9d98355766c9 (stored in /mnt/fs2/boostorg/beast.git/objects/3c/5bd5d909e e9b71f2b28d002dfe9d98355766c9) is corrupt Deleting and re-creating the repo worked fine: git clone --mirror git@github.com:boostorg/beast.git Cloning into bare repository 'beast.git'... remote: Enumerating objects: 296, done. remote: Counting objects: 100% (296/296), done. remote: Compressing objects: 100% (158/158), done. remote: Total 48131 (delta 142), reused 210 (delta 110), pack-reused 47835 Receiving objects: 100% (48131/48131), 35.50 MiB | 24.22 MiB/s, done. Resolving deltas: 100% (33475/33475), done. Not an issue for my just curious/suspicious. Tom

2 1

Contributing to Boost. Astronomy
by Siddhartha Sen 09 Jul '19

09 Jul '19

Hello, I want to get started in contributing to Boost. Astronomy. Could anyone help me out here? This is the first time I will be contributing to open source. Hence I don't have any idea how this works. I am proficient in C and C++ and have a keen interest in Astronomy. Could anyone tell me what all things I need to learn first before I am able to contribute? What documentation should I read or what issues should I be aware of, before I can start contributing? Any help would be appreciated.

3 2

out_ptr formal review
by Gavin Lambert 05 Jul '19

05 Jul '19

My apologies in advance for the light novel. # Do you think the library should be accepted as a Boost library? Not in its current form, although I encourage cleaning it up and resubmitting it. # Your knowledge of the problem domain I've used COM smart pointers (usually CComPtr) a few times, and more rarely wrapped some other C or C-like APIs. (Although mostly pre-C++11, requiring something more hand-rolled than unique_ptr.) # What is your evaluation of the library's: ## Design The API seems reasonable for both out_ptr and inout_ptr. (Although also see the end of this post.) Actual uses for inout_ptr outside of a "realloc" type function seems a bit rare to me (and such APIs also seem rather rare), but perhaps there are other justifying cases I am not aware of, or it's more common in a particular domain. I do like that unspecified function argument evaluation order was considered, and I agree that it is better to try to maintain safety regardless of evaluation order rather than simply telling users to not access the smart pointer in other arguments -- it is a very easy trap for users to fall into, especially where the same code that has been working forever may suddenly fail with a different compiler version or different compiler settings. (Sequencing of destructor execution with additional && conditionals is admittedly a similar problem with no good solution within this design, as is explained in the caveats.) I don't like that it is left unspecified whether release() is called on construction or destruction (as that decision is left to the custom specialisations), as this potentially reintroduces that problem. I think it should be required that all specialisations behave in the following manner: For out_ptr: - construction initialises a raw ptr to nullptr and does not alter the smart ptr. - destruction resets the smart pointer to the raw ptr (in all cases). - this provides a useful guarantee that the smart ptr is always reset to nullptr if the called method returns nullptr, even if it had some other value previously. For inout_ptr: - construction get()s the current value of the smart ptr in two separate raw ptrs (one passed as the function argument, one cached for the destructor to use for comparison), but does not release() it. - destruction will (only if the raw ptr now has some different value) release()s the smart ptr and then reset()s it to the new raw ptr. - this makes it safe to use the smart ptr's value in other arguments of the method call; unspecified release() timing would have made that unsafe. (There is a slightly dodgy step in there where technically the smart pointer could be pointing at something which it thinks it owns, but that the called function has already deleted. However given that any normal or exceptional exit path would then call the inout_ptr destructor [guaranteed before the smart pointer destructor], which would safely release() the pointer without double-deleting it, this seems sufficiently safe, and worth it to permit safe argument usage. The only caveat is that usage of the smart pointer sequenced after the method call but before the destructor execution [as in additional && conditions] is not safe, as it may access deleted memory; however that code would never have the correct behaviour anyway and the documentation already warns to avoid doing that.) Perhaps there are some types of smart pointer for which this contract wouldn't work (eg. if it is possible for release() to fail, or to release a different pointer from what get() returns)? But then if so I'm not convinced it's safe to give them a uniform interface with pointers where it is safe, because otherwise inevitably someone is going to hit the unspecified-parameter-evaluation-order problem (or assuming that it will be nullptr on failure). Especially given these suggested constraints, I would prefer that a simple ADL or traits-type customisation point were added, so that you can adapt to smart pointers which merely have different spellings of the reset and release methods and don't require deeper customisation -- though the existing customisation point could be retained for especially weird smart pointer types if needed. (ADL customisation points are superior because, if designed correctly, they would not introduce a dependency on Boost.OutPtr, and if named well could theoretically also be used by other libraries, as with non-member begin and swap.) Similarly, while the static_assert check in base_out_ptr_impl specifically for std::shared_ptr and boost::shared_ptr seems valuable to prevent a significant class of bugs, I question whether it might be better handled by checking a type trait or other customisation point rather than checking directly for those types, such that it would be possible for a user-defined smart pointer type to also participate if it has a similar concern. Or perhaps it should just discourage use of shared_ptr at all; there should be little performance difference between using shared_ptr directly and using a unique_ptr which is later moved to a shared_ptr. (Since neither can take advantage of the make_shared optmisation, and by definition ownership must be unique at that point.) ## Implementation I haven't verified whether the current implementation exactly follows my suggested contract above, as there are a few too many layers of indirection and inheritance for me to easily parse. Simplifying the implementation would be nice if possible, especially for out_ptr, to improve readability. (However I think that my description is close at least.) I am strongly opposed to both of the "clever" implementations in the library. They should be completely removed. I can think of absolutely no justification (performance or otherwise) for a "clever" out_ptr. Due to both the requirement to pass in nullptr and to not delete the original smart pointer on construction (as it might be used in other parameters), the raw pointer can never have the same storage as the smart pointer anyway. (At least not unless you absolutely promise to never use a non-nullptr smart pointer, which reduces usefulness, albeit admittedly for a slightly peculiar use case [which would have been unsafe when used with raw pointers directly].) (In theory you could pass in an uninitialised raw pointer and then conditionally reset or do nothing depending on whether it still has the same uninitialised value after the call, but this both requires capturing the actual value at construction and providing a weaker contract to the C API, so it seems like a bad idea and a pessimisation to me. Another option is to unconditionally reset() on construction, but this sacrifices use in other parameters.) There is a possible justification for the clever inout_ptr, in that you can save two raw pointer copies if you reuse the smart pointer's storage, and this does not have the same caveats as with out_ptr. I am not convinced that anyone should care about that (especially in code paths also including memory allocation), although it is possible that the savings may be more significant with a smart pointer more complex than unique_ptr. Having said that, this "clever" implementation should absolutely never be used for any existing smart pointer, especially including std::unique_ptr or boost::movelib::unique_ptr. If there is sufficient justification for its existence at all, then you should instead create a new smart pointer (bikeshed: boost::out_ptr::fast_ptr) which behaves equivalent to std::unique_ptr except that you can steal its raw pointer storage when using inout_ptr. This could be made move-compatible with std::unique_ptr for the people who want to keep that type in their interfaces -- although that would presumably also remove any dubious performance benefit. As previously brought up in a separate thread, the current review implementation also leaks public inheritance of std::tuple, which is presumably intended as an empty-base optimisation, but must not be public or it will allow inappropriate slicing (and Very Bad Things™). ## Documentation The documentation seems decent, although being split into many short pages as at present can at times make it harder to locate something specific. I would prefer longer single pages divided into sections, but that's a matter of taste and not a review condition. I dislike the assertion that a "well-designed" C API would always set the parameter to nullptr on failure. That is certainly one option (and typically a preferred one), but leaving the parameter unchanged is another entirely reasonable option, and does not signify "poor design". It is only reasonable to claim poor design if the API allocates and sets the value, internally deletes it, and then reports failure (while still returning the altered and deleted pointer), as this condition cannot be handled by out_ptr (or indeed by anything that doesn't understand the failure return semantics of the API). The time axis scale in the benchmarks seems not entirely helpful as a lot of the time the difference between two implementations is within one axis division of each other. And again, the magnitude of performance difference sitting in the <1ns range in code which inherently implies memory allocation suggests a severe case of premature optimisation to me. (Though perhaps that might be more justifiable when used in non-memory handle contexts -- but then that might be an abuse of calling it a "pointer".) ## Usefulness I think that this library or something like it could be quite useful to help unify and improve safety when interacting with C-style T** APIs (or T* output arguments for some opaque handle type that requires cleanup), without requiring exploitation of operator& tricks like CComPtr does. (Sure, it's trivial to write an RAII wrapper around such APIs, but this can become cumbersome when there are hundreds or thousands of such APIs, unless you're using a code generator. And it's easy to accidentally forget subtle but important things such as deleting copy operations.) # Did you try to use the library? With what compiler? Did you have any problems? I did not try it. However the "clever" implementation is highly compiler-and-library-specific and quite aside from its design issues I think it would also produce significant portability issues. # How much effort did you put into your evaluation? I spent several hours on this review over the course of several days, and some related prior discussion in the mailing list. I read through all the documentation and most of the code (though not the tests). ============================ Having said all of the above, I wonder whether the library author has considered a different design for this functionality? Rather than the given example code: using bop = boost::out_ptr; boost::shared_ptr<mll_driver> axis_driver(nullptr); mll_errno err = mll_driver_init( bop::out_ptr(axis_driver, mll_driver_free), /* additional args ...*/); if (err != MLL_SUCESS) { // ... } A wrapping lambda syntax could be used instead: boost::shared_ptr<mll_driver> axis_driver(nullptr); mll_errno err = bop::invoke( [&](mll_driver** p) { return mll_driver_init(p, /* additional args ...*/); }, bop::out_ptr(axis_driver, mll_driver_free)); if (err != MLL_SUCESS) { // ... } Here, rather than its current meaning, bop::out_ptr just defines a parameter grouping which is then turned into a raw pointer-pointer argument for the lambda; it has no destructor-based shenanigans. (This could also be used for other non-pointer argument types -- there just needs to be a way for invoke to query the expected API argument type from the out_ptr or from the lambda itself.) This is admittedly more verbose than the current design (although bop::invoke could be written as just "invoke" due to ADL, for a slight simplification); but it would allow you to more safely control the sequencing between the API call and the reassignment of the smart pointer -- in particular all of the existing caveats with order of evaluations and with if-statement and composite conditional ordering no longer apply. (You can safely "&& axis_driver" above as long as you do it outside of the invoke call.) The API would be called (via the lambda) from a try-catch block inside of bop::invoke (or instead of the try-catch an RAII helper can be used to perform a try-finally action), and either the existing guarantee of not calling reset() or release() until after the call can be maintained (thereby allowing the smart pointer to be used by reference within the lambda), or it could be forbidden to use the smart pointer inside the lambda and the caller could lambda-capture the necessary arguments by value instead. Either way, the caller should be less surprised about lifetime issues across a lambda "border", and would quickly discover if they did it "wrong" (because the reset/release would either always occur before or always occur after argument evaluation, never in mixed order). invoke would normally be called with only one out_ptr or inout_ptr argument (and consequently one argument to the lambda), but could in principle be extended to any number of arguments either by nested invoke calls or by supporting a variadic form which does the equivalent within the library. It could possibly also be extended to support user-defined argument types to do something more complex, by defining a concept interface that it uses to interact with the argument, rather than explicit overloads or specialisations on those specific types. This could leave the decision of when to reset/release up to the smart-pointer-specific specialisation (if that's useful for performance reasons), and without leaving any time bombs for the caller.

1 0

Mother of all Variants
by Robert Ramey 05 Jul '19

05 Jul '19

I'm way out of my depth in the variant discussion. Seems to me it revolves around all the trade offs regarding design choices. Could we perhaps decide not to decide. Suppose we create a type which looks like: template< bool BasicGuaranteeSupported, bool StrongGuaranteeSupported, bool EmptyStateProhibited, bool AssignmentSupported, bool MoveSupported, class T ... > struct mother_of_variants{ // some trivial mp11 code }; Now we could define: using boost_variant = mother_of_all variants< bool true, //BasicGuaranteeSupported, bool true, //StrongGuaranteeSupported, bool true, //EmptyStateProhibited, bool true, //AssignmentSupported, bool true, //MoveSupported, >; std_variant, std_optional, std_expect, boost_outcome, etc. would be similarly defined. And some "extras" like no_except_variant, trivial_variant, etc. would be added. and of course my favorite candidate: using safe_variant = mother_of_all variants< bool true, //BasicGuaranteeSupported, bool true, //StrongGuaranteeSupported, bool true, //EmptyStateProhibited, bool false, //AssignmentSupported, bool false //MoveSupported, >; In addition, we'd have some type traits: mother_of_all_variants::no_runtime_allocation<mov>; mother_of_all_variants::no_double_instancen<mov>; mother_of_all_variants::is_mother_of_all_variants<mov>; etc. Just think that of all the time we've spent on discussions about optional, expected, std::variant, boost::variant, etc. At this rate, these discussions will keep hounding us forever. Of course I realize that the main purpose of having these variants of variants is to justify the discussions - but perhaps we might be ready for a new topic. Robert Ramey

17 57

Boost Version 1.47 not building with 2017.
by nunna, sarath babu (GE Healthcare) 03 Jul '19

03 Jul '19

Hello, 1.47 boost is not being built with VS2017. We want to get boost 1.47 built with VS2017, So that we can integrate them with our VS2017 code base. Please guide us, it will be a great help. Thanks, Sarath.

4 9

Boost compatibility/communication issue with 1.47 to 1.7
by nunna, sarath babu (GE Healthcare) 03 Jul '19

03 Jul '19

Hello All, So far we have used Boost 1.47 VS2010 built binaries integrated with our VS2010 Code Base . But now we are upgrading VS2010 to VS2017 of our product code base, also we tried Boost 1.70 boost built using VS2017 and integrated with our VS2017 code base. Our product should be compatible with older versions of all tools including boost. We have not faced any issues except boost. Issue: 1.7 boost is not able to communicate to 1.47 boost and giving "SERIALIZATION ERRORS". 1.47 boost is not able to communicate with 1.7 boost and giving "SERIALIZATION ERRORS". Please help us and let us know which boost version we could upgrade that can be compatible with 1.47. Note: The customer is already using 1.47 2010 boost binaries with built VS2010 product which we can't change. Please suggest us the resolution or the version that we should use. Thanks, Sarath.

4 4

Construction of /defaultlib:XXX for boost::python
by Kacvinsky, Tom 01 Jul '19

01 Jul '19

I discovered while using boost 1.69 with Python 2.7 that a /defaultlib:XXX directive for the boost::python import library is injected into each object file that uses boost::python header files. What I have not been able to figure out is the magic for doing this. I presume it is a macro that makes a #pragma for default libs based on the threading model, the address model, the version of Python in use, and the _MSC_VER compiler macro. Am I am on the right track? Where would this code be? I could find it via searching for #\w?pragma in the code base. Thanks, Tom

2 1