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union support in describe
by Gero Peterhoff 12 Nov '21

12 Nov '21

Hello, first of all, thank you very much for the great work. But I miss the support for unions. Is that correct? namespace boost { namespace describe { #define BOOST_DESCRIBE_UNION(C, Public) \ static_assert(std::is_union<C>::value, "BOOST_DESCRIBE_UNION should only be used with union types"); \ BOOST_DESCRIBE_PUBLIC_MEMBERS_(C BOOST_DESCRIBE_PP_UNPACK Public) \ BOOST_DESCRIBE_PROTECTED_MEMBERS_(C) \ BOOST_DESCRIBE_PRIVATE_MEMBERS_(C) } // describe } // boost This version only supports public members. I also miss the support for std::get. Is that correct? namespace boost { namespace describe { #define BOOST_DESCRIBE_GET(C) \ template <std::size_t Index> \ inline constexpr const auto& get(const C& arg) noexcept \ { \ static_assert(std::is_class<C>::value || std::is_union<C>::value, "BOOST_DESCRIBE_GET should only be used with class, struct or union types"); \ using members = boost::describe::describe_members<C, boost::describe::mod_any_access>; \ static_assert(Index < boost::mp11::mp_size<members>()); \ return arg.*boost::mp11::mp_at_c<members, Index>().pointer; \ } \ template <std::size_t Index> \ inline constexpr auto& get(C& arg) noexcept \ { \ static_assert(std::is_class<C>::value || std::is_union<C>::value, "BOOST_DESCRIBE_GET should only be used with class, struct or union types"); \ using members = boost::describe::describe_members<C, boost::describe::mod_any_access>; \ static_assert(Index < boost::mp11::mp_size<members>()); \ return arg.*boost::mp11::mp_at_c<members, Index>().pointer; \ } } // describe } // boost However, the access rights are not taken into account. E.g.: struct A { int i; float f; }; BOOST_DESCRIBE_STRUCT(A, (), (i, f)) namespace std { BOOST_DESCRIBE_GET(A) } // std This also solves a very special problem, provided the compiler supports it: active member of a constexp union. Problem: union U { int64_t i; double d; }; constexpr U u{.d{3.1415}}; constexpr auto i=u.i; -> error In short: namespace std { template <typename Type> inline constexpr bool is_constant_initialized(const Type& arg) noexcept { #if __has_builtin(__builtin_constant_p) return __builtin_constant_p(arg); #elif defined(BOOST_MSVC) ??? #else static_assert(false, "is_constant_initialized not supportet"); return false; #endif } template <typename Type> inline constexpr bool is_constant_initialized_front(const Type& arg) noexcept { return is_constant_initialized(arg); } template <typename Type, size_t Size> inline constexpr bool is_constant_initialized_front(const Type(&arg)[Size]) noexcept { static_assert(Size > 0); return is_constant_initialized(arg[0]); } template <typename Type, size_t Size> inline constexpr bool is_constant_initialized_front(const std::array<Type, Size>& arg) noexcept { static_assert(Size > 0); return is_constant_initialized(arg[0]); } } // std namespace boost { namespace describe { template <typename Type> inline constexpr std::size_t active_index(const Type& arg) noexcept { static_assert(std::is_union_v<Type>); using any = describe_members<Type, mod_any_access>; std::size_t result{0}, index{0}; bool first{true}; boost::mp11::mp_for_each<any>([&](const auto& desc) constexpr noexcept { const auto& elem{arg.*desc.pointer}; if (std::is_constant_initialized_front(elem)) { if (first) { first = false; result = index; } } ++index; }); return first ? 0 : result; } template <auto Value> inline constexpr std::size_t active_index_v = std::integral_constant<std::size_t, active_index(Value)>::value; } // describe } // boost union __mm128_emu { float m128_f32[4]; double m128_f64[2]; int64_t m128_i64[2]; int32_t m128_i32[4]; int16_t m128_i16[8]; int8_t m128_i8[16]; uint64_t m128_u64[2]; uint32_t m128_u32[4]; uint16_t m128_u16[8]; uint8_t m128_u8[16]; }; BOOST_DESCRIBE_UNION(__mm128_emu, (m128_f32, m128_f64, m128_i64, m128_i32, m128_i16, m128_i8, m128_u64, m128_u32, m128_u16, m128_u8)) namespace std { BOOST_DESCRIBE_GET(__mm128_emu) } // std constexpr __mm128_emu m128{.m128_u32{4711}}; constexpr auto arr = std::to_array(std::get<boost::describe::active_index_v<m128>>(m128)); // works with gcc, clang, intel Do you have an idea how to implement __builtin_constant_p for all compilers? thx Gero

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Update on the 1.78.0 beta
by Marshall Clow 11 Nov '21

11 Nov '21

The beta was supposed to be released yesterday. It’s done, but there’s an issue on Jfrog that seems to make it hard to download. I’m talking to the JFrog folks to get this resolved, and when that’s done, I’ll announce that the beta is released. — Marshall

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[release] Boost 1.78.0 Beta 1 Release Candidate 1 is available
by Marshall Clow 09 Nov '21

09 Nov '21

The first release candidates for the 1.78.0 beta release are now available at: <https://boostorg.jfrog.io/ui/native/main/beta/1.78.0.beta1/source <https://boostorg.jfrog.io/ui/native/main/beta/1.78.0.beta1/source>> The SHA256 checksums are as follows: 7a3a025451dfa2923129214eef7d16b03c02310a353d02158a549f6caa4284b0 boost_1_78_0_b1_rc1.tar.bz2 c491b1dcb916195598aa6581d6708d57fcc750516641c22511c088d572de9c07 boost_1_78_0_b1_rc1.tar.gz 35e7a3b0eb412a3933e57c72ba96374eb7d88ff1f89dbec62a16d67ffea2105a boost_1_78_0_b1_rc1.7z e6b68feb2f63401c96ca9fe25e939b409189fbe526a6e784e4bd69832c8f09cb boost_1_78_0_b1_rc1.zip As always, the release managers would appreciate it if you download the candidate of your choice and give building it a try. Please report both success and failure, and anything else that is noteworthy. -- The Release managers

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How to get started with contribution
by Anmol Singh 09 Nov '21

09 Nov '21

Respected Sir/Madam, I am Anmol Singh, an Information Technology undergrad. I have just entered my second year at ADGITM, IP University. I am new to open source contributions but I am well aware of C++,C and javascript. I would love to contribute to your organisation but could you please tell me how to get started? Regards Anmol

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conversion of catched exception to shared_ptr
by rajesh daggumati 08 Nov '21

08 Nov '21

rajesh daggumati <rajeshdaggumati9999(a)gmail.com> 09:59 (4 hours ago) to boost-users HI, please help me to solve below issue. Shared pointers are used in my code. class Exception : public virtual std::exception,public virtual boost::exception { --- }; class ExceptionTestException : public Exception { --- }; boost::shared_ptr<Exception> exceptionptr_t; try { Boost_Throw_function(ExceptionTestException("Hiii")); } catch(...) { boost::exception_ptr exceptionptr = boost::current_exception(); try { boost::rethrow(exceptionptr) } catch(boost::exception &e) { //here i need to assign this 'e' to shared pointer but this e is not in heap so then how to assign this e to sharedptr(exceptionptr_t). 1 way is : boost::exception *ep = new ExceptionTestException(e); exceptionptr_t(ep); here we know that exception_ptr is having ExceptionTestException but in some cases, we dont know which type of excepiton we have in exception_ptr in runtime. then how to assign to shared_ptr

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Library category error handling
by Emil Dotchevski 07 Nov '21

07 Nov '21

Should we add a formal category for error handling libraries in https://www.boost.org/development/library_metadata.html?

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Does boost have a way to get type name at compile time?
by Ivan Matek 04 Nov '21

04 Nov '21

I am aware of hacks/magic with __PRETTY_FUNCTION__ <https://stackoverflow.com/questions/69624128/parameter-pack-sorting-or-equi…>but I wonder if there is a portable boost way to do that?

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Header-only libraries linking to compiled libraries...
by Peter Dimov 03 Nov '21

03 Nov '21

... create problems (at least) for CMake users, because a project using a header-only library must link to its compiled dependencies by hand. (Important Note: this is not about the CMake build of Boost. It's about the b2 build of Boost, and the CMake configuration files it generates.) Compiled libraries don't have this problem, because they have CMake targets, and linking to the library target automatically links to the dependencies. For instance, linking to Boost::filesystem would automatically link to Boost::atomic (and on Windows, to bcrypt.lib) as needed. However, as pointed out in https://github.com/boostorg/boost_install/issues/54, header-only libraries such as Process or UUID have no CMake targets. Consequently, it's not possible for the CMake project to link to Boost::uuid and automatically inherit the dependency to bcrypt.lib, or to link to Boost::process and automatically acquire a dependency to Boost::filesystem. Since the CMake configuration files that are generated by `b2 install` define CMake targets based on the b2 targets, it's not possible to fix this just on the boost-install side. If we want Boost::process to appear as a target in CMake, we need boost_process to appear as a target in b2, that is, we need libs/process/build/Jamfile to exist. The easiest way to fix it - if we decide to do something about it - is to create dummy compiled libraries for each such header-only library that isn't really header-only because of dependencies. A number of Boost libraries are already header-only with a stub library for backward compatibility (System, DateTime, Regex), so this wouldn't be something novel.

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Reminder: The master branch will be closing for the 1.78.0 beta release TOMORROW
by Marshall Clow 02 Nov '21

02 Nov '21

If you have changes for the beta, they need to be merged to master before the end of day tomorrow. See https://www.boost.org/development/index.html <https://www.boost.org/development/index.html> for the full calendar — The Release managers

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Boost libraries packaged for build2
by Boris Kolpackov 02 Nov '21

02 Nov '21

We have added support for the build2 build systems to 136 out of 145 Boost libraries and version 1.77.0 is now available from the cppget.org package repository. For details, see: https://build2.org/blog/build2-boost.xhtml Folks on this mailing list may be particularly interested in the "Implementation Details" section where we go deeper into how this conversion was accomplished: https://build2.org/blog/build2-boost.xhtml#impl-details (There is also the README-DEV file in the repository linked from this section which has even more details.) Also, let me add that this is not a call to convert Boost to build2. While we would gladly assist with this effort if the Boost community so wishes, we are also happy to continue our work out of tree.

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