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boost::throw_exception potential changes
by Peter Dimov 07 Feb '22

07 Feb '22

Currently, `boost::throw_exception(x)` automatically throws an exception derived from `x` that (1) injects a boost::exception base class if there's none, and (2) injects a base class that enables boost::exception_ptr support (boost::current_exception and boost::rethrow_exception.) This is convenient, but the downside is the amount of generated code, e.g. https://godbolt.org/z/5T8T8GEqP (422 lines) compared to https://godbolt.org/z/1zr1odf7n (36 lines.) This is not the end of the world as this code is only generated once per exception type, not on every call to throw_exception, but it's still unpleasant to see. It so happens that boost::exception_ptr has recently acquired the ability to work under C++11 without the need for the supporting base class, by using the standard std::exception_ptr infrastructure. So if we also remove the automatic injection of boost::exception as a base class, and ask users to derive their exceptions from it if they desire having it as a base, it's possible to simplify boost::throw_exception considerably. The normal call now can be almost the same as the naked throw, https://godbolt.org/z/WssWzfrfW (47 lines.) And if BOOST_THROW_EXCEPTION is used, which still adds the source location (file/line/function) to the exception, the result is 97 lines. (https://godbolt.org/z/nETnqrsx8) However, there is a downside. Due to the way std::exception_ptr works under GCC/Clang (and all compilers using the same ABI), the exception is never copied, not when it's captured with std::current_exception (and consequently boost::current_exception), nor when it's rethrown with boost/std::rethrow_exception. This causes problems if an exception is captured, rethrown, caught and modified, then rethrown again using the same exception_ptr. The second rethrow throws the modified exception. This problem can be seen in https://godbolt.org/z/K9eh71ovP. So... what do we do? Should I go ahead with these changes to throw_exception (having a macro to revert to the old behavior, of course)? Or is that too much of a break? We can of course offer the same functionality as part of Boost.Exception, like boost::exception::raise, or similar, but would that be enough to offset the inconvenience?

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[concept_check][ublas] Fixing deprecated copy warnings
by Antony Polukhin 07 Feb '22

07 Feb '22

Hi, There are two PR that fix deprecated copy warnings for GCC and Clang: * https://github.com/boostorg/concept_check/pull/35 * https://github.com/boostorg/ublas/pull/153 Please review those. They make the intent explicit and the code becomes more portable. Trivial sample that causes the warning https://godbolt.org/z/YaPvGfedv -- Best regards, Antony Polukhin

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Primary test compilers in Boost release notes
by Peter Dimov 01 Feb '22

01 Feb '22

We have an issue, https://github.com/boostorg/boost/issues/610, that points out that the "Primary test compilers" section in the Boost 1.78 release notes is misleading, because it doesn't actually reflect whether a Boost library works with a specific compiler or not. The specific example cited is Multiprecision. The release notes say that on Linux, the following C++11 GCC compilers are "primary": GCC, C++11: 4.7.3, 4.8.5, 11 However, Multiprecision doesn't work with GCC 4.7.3 or 4.8.5, and likely never will, because these compilers do not actually implement the C++11 standard. (They don't implement reference qualified member functions and don't have a conforming <type_traits> header.) It would be better for everyone involved if the primary test compilers are somewhat aligned with (a) what Boost libraries actually support or require, and (b) what Boost libraries actually test with. The section historically lists what's in our test matrix, but nowadays most libraries depend on CI for testing, specifically on Github Actions (after the untimely death of open source Travis) and Appveyor. There's a fair bit of discussion in the linked issue above, but what I think is reasonable to list as primary test compilers as far as GCC is concerned is something like C++03: 4.8, 4.9, 5 C++11: 4.8(*), 4.9(*), 5 I would start with 4.8, because this is what GHA has on its 18.04 image. C++03 needs to have GCC up to 5 because this is the default -std level for these versions (GCC 6 is -std=c++14 by default), and the system- provided Boost is compiled with the default. 4.8 has enough of C++11 so it's possible for C++11 libraries to support it without much heroics, but we could go either way on this one, hence the asterisk.

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[GSoC 2022] [Graph] Potential mentors
by Dev Jain 15 Jan '22

15 Jan '22

Hello everyone. I am Dev Jain, a sophomore student pursuing a Bachelors in Computer Science and Engineering from IIT Jammu. I am passionate about discrete mathematics, and in particular graph theory and graph algorithms. I would like to contribute to the Boost Graph Library. I can't find any project ideas for the BGL in recent years of GSoC. Are there any people active with BGL, and any prospective mentors? I understand that, it is recommended to come to the mailing list asking for mentors by describing an idea, but I wanted to ask this since for many years a BGL project hasn't been proposed in the ideas list. Thanks.

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Does anybody know why boost::array does not support multiple dimensions?
by Ivan Matek 10 Jan '22

10 Jan '22

I don't know much about library development, but with variadic templates does not seem so hard, although every library development is much harder than regular user code. Sure boost::array probably wants to support ancient compilers, but variadic version could exist only for "modern"(I do not consider >10y old standards modern) C++. I found this std:: proposal http://www.open-std.org/JTC1/SC22/WG21/docs/papers/2013/n3794.html#Ch05 from 9 y ago, also author seemed to have some working impl on github https://github.com/CTMacUser/ArrayMD/tree/master/include/boost/container But I guess none of it ever progressed. Does anybody knows more about this? It is not trivial since there are probably a ton of edge cases, typdefs, semantics(what should size return?, I would say array of dims) to deal with, but I think it would be a nice extension since I find nested std::array hideous (with current syntax), e.g.: std::array<std::array<int,3>, 4> arr; I would like to have this boost::array<int,4,3> arr; P.S. I know I can use Eigen or some other library, but I think if not std then at least boost should support simple way to have multidim arrays.

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Error with geometry buffer?
by KL 10 Jan '22

10 Jan '22

Hi, Boost Geometry 1.78, linux Â I was getting bad results with my calculations so I decided to narrow down the implementation up to the point I got the following problematic code: Â typedef boost::geometry::model::point <double, 2, boost::geometry::cs::cartesian> Vector2d; Â int main (){ Â Â Â Â Â Â Â Â multi_polygon <polygon <Vector2d> > mp; Â Â Â Â Â Â Â Â /*{ Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â polygon <Vector2d> poly; Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â poly.outer().push_back( {0, 0} ); Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â poly.outer().push_back( {0, 4} ); Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â poly.outer().push_back( {4, 4} ); Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â poly.outer().push_back( {4, 0} ); Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â correct( poly ); Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â mp.push_back(poly); Â Â Â Â Â Â Â }*/ Â Â Â Â Â Â Â { Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â polygon <Vector2d> poly; Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â poly.outer().push_back( {10, -1} ); Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â poly.outer().push_back( {14, -1} ); Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â poly.outer().push_back( {10, -2} ); Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â poly.outer().push_back( {14, -2}Â ); Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â correct( poly ); Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â mp.push_back(poly); Â Â Â Â Â Â Â } Â Â Â Â Â Â Â Â Â boost::geometry::strategy::buffer::join_miter join_strategy; Â Â Â Â Â Â Â boost::geometry::strategy::buffer::end_flat end_strategy; Â Â Â Â Â Â Â boost::geometry::strategy::buffer::side_straight side_strategy; Â Â Â Â Â Â Â boost::geometry::strategy::buffer::point_square point_strategy; Â Â Â Â Â Â Â Â boost::geometry::strategy::buffer::distance_symmetric <double> distance_strategy( 2 ); Â Â Â Â Â Â Â boost::geometry::model::multi_polygon <polygon <Vector2d> > result; Â Â Â Â Â Â Â Â boost::geometry::buffer( mp, result, distance_strategy, side_strategy, join_strategy, end_strategy, point_strategy ); Â Â Â Â Â Â Â Â cout << dsv( result ) << endl; Â Â Â Â Â Â Â Â return 0; Â } Â and the result I get is: ((((13.7169, -3.13232), (13.5149, -3.94029), (12, -3.56155), (10.4851, -3.94029), (10.2831, -3.13232), (9.51493, -2.94029), (0.0749244, 0.221833), (10, 1), (14, 1), (23.9251, 0.221833), (14.4851, -2.94029), (13.7169, -3.13232)))) Â Notice the two points: (0.0749244, 0.221833) and (23.9251, 0.221833) Â I have multiple complex (concave) shapes which behave worse than that simple rectangle. But it is a starting point here. Â Did I do something wrong? I need to get my job done, any alternative or helping code massaging ? Â Thanks --Â MKL Â

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[ASIO] Need help reading the documentation
by Andrzej Krzemienski 01 Jan '22

01 Jan '22

Hi Everyone, I need some help in reading the ASIO docs. I am looking at the following example from the docs https://www.boost.org/doc/libs/1_78_0/doc/html/boost_asio/example/cpp17/cor… It calls one of the overloads of async_write in line co_await async_write(socket, boost::asio::buffer(data, n), use_awaitable); The reference section lists eight overloads: https://www.boost.org/doc/libs/1_78_0/doc/html/boost_asio/reference/async_w… But it is still impossible for me to figure out which one it is. `use_awaitable` is documented as "completion token" in https://www.boost.org/doc/libs/1_78_0/doc/html/boost_asio/reference/use_awa… There is some mention of completion token at https://www.boost.org/doc/libs/1_78_0/doc/html/boost_asio/reference/asynchr… So I would expect the name `CompletionToken` to appear in the documentation of `async_write`. Am I missing something? Regards, &rzej;

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[ASIO] Do I have to use shared_ptrs with ASIO?
by Andrzej Krzemienski 29 Dec '21

29 Dec '21

Hi Everyone, I am looking at an example implementation of an asynchronous TCP echo server in Boost.ASIO library: https://www.boost.org/doc/libs/1_77_0/doc/html/boost_asio/example/cpp11/ech… It uses a shared_ptr in the implementation to store the things related to session: socket handle, data buffers. I tried to modify it in a number of ways to avoid the usage of shared_ptr (and any form of shared ownership), but they all failed. It looks like I have to use a shared_pointer (or equivalent) when I use ASIO sockets. But conceptually, there is never a point in time where two tasks have to access members of this `session` concurrently: they are always sequenced. So, at least conceptually, there should be a way to do this with a session type that is only movable, with unique ownership: a task does its job with the session and then moves it to the subsequent task. So is this necessity to use a shared pointer an unnecessary and suboptimal design choice? Or is there something fundamental that prevents the unique ownership of buffers and socket handles? Or maybe is there a way to do it in ASIO that I overlooked? I am not trying to solve any specific problem. It just strikes me that a shared_ptr is used in a demo example for the library. I was always of the opinion that a shared_ptr is often abused as a way of doing an ad-hoc GC. Regards, &rzej;

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Seeking help for kickstart
by Rahul Sharma 23 Dec '21

23 Dec '21

Hello everyone, I read all the information given on the blog pages and websites sent to me via email which I received when I subscribed to this mailing list, but I am too confused and I am not able to figure out from where to start and how to find some beginner friendly issues and projects to work on. Hoping for help and guidance to kickstart this journey. Accept my apologies if this is not the proper way to communicate about such problems. Sent from [1]Mail for Windows References 1. https://go.microsoft.com/fwlink/?LinkId=550986

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To contribute to this community.
by Rahul Sharma 22 Dec '21

22 Dec '21

Hello everyone, I am Rahul Sharma currently a sophomore at IIT Guwahati pursuing my B.Tech with major in Civil Engineering. I am very much enthusiastically inclined towards technology and want to pursue my carrier in the field of technology. And also I am very much interested in the open source communities and would really like to be part of such a community and to work with other peers with the same vision and to work with dedication on some really cool real world projects. My tech stack comprises of programming languages like c and c++ and am also a front end web developer and currently learning the back end web development with react. Seeking for the guidance from the other experienced peer developers and mentors. Sent from [1]Mail for Windows References 1. https://go.microsoft.com/fwlink/?LinkId=550986

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