March 2025 - Boost - lists.preview.boost.org

Pretty printer module
by Дмитрий Архипов 14 Apr '25

14 Apr '25

Recently Niall Douglas posted about his idea to embed GDB pretty printers into binaries using a header. At the time I was thinking about a good way to deploy pretty printers for JSON that facilitates their autoloading. After Niall's post I experimented a little bit more, and I came to the conclusion that indeed nothing beats embedding via a C++ header in terms of convenience. At the same time I was also thinking about testing that pretty printers do in fact work. Given that pretty printers (usually) are implemented as a Python module, it initially looked like one could just run a Python program and import GDB Python modules. But actually you cannot. It turns out, though, you can run a Python script with GDB as the interpreter. After several iterations I arrived at this setup: https://github.com/boostorg/json/blob/develop/test/printers.cpp. A script converts this file into a Python script that uses GDB to break on certain lines and check if a particular expression produces a particular output when printed. While doing all this I thought that most of this work can be useful to other libraries. So, I moved the reusable parts into a separate directory (https://github.com/boostorg/json/tree/develop/pretty_printers) and added both a b2 module, and a CMake module. For B2. Importing: https://github.com/boostorg/json/blob/develop/build.jam#L8-L9 https://github.com/boostorg/json/blob/develop/build/Jamfile#L13 (Re)generating the header: https://github.com/boostorg/json/blob/develop/build/Jamfile#L88-L95 Testing: https://github.com/boostorg/json/blob/develop/test/Jamfile#L96-L101 For CMake: Importing: https://github.com/boostorg/json/blob/develop/CMakeLists.txt#L54-L55 (Re)generating the header: https://github.com/boostorg/json/blob/develop/CMakeLists.txt#L56-L63 Testing: https://github.com/boostorg/json/blob/develop/test/CMakeLists.txt#L80-L88 My questions to the community: do you find this useful? Would you use it in your Boost or non-Boost library? If you do, the module should be moved to tools rather than stay in libs/json.

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boost::python and Python 3.12
by Tom Kacvinsky 13 Apr '25

13 Apr '25

While working on a project to upgrade an embedded Python interpreter (to Python 3.12), which uses boost::python, I noticed the structs from the Python C API now have more members and those extra struct members were not populated in the boost::python code. In particular I was bit by the enum module crashing our application startup. I noticed this with boost 1.78, but I found the same problematic code in the release that was current as of two months ago (1.87.0, I think). I got things to compile and run, but my approach was to just make the code Python 3.12 compliant. I can prepare a patch that has the appropriate macro guards for populating the structs as they relate to different Python versions. I'll read the boost developers guide and follow the necessary steps to submit a fix. Regards, Tom

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[release] Master branch is now open for bug fixes
by Marshall Clow 02 Apr '25

02 Apr '25

Hi, The master branch is now open for bug fixes, test and documentation changes, but please follow the policy described in: https://github.com/boostorg/wiki/wiki/Releases%3A-Beta-Merge-Policy The next deadline: On April 2nd, master closes for all changes. As always, the calendar is at https://www.boost.org/development/ — The release managers

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Boost::MQTT5 and boost 1.82.0?
by Georg Gast 31 Mar '25

31 Mar '25

Hi Boost, i read here [1] that boost::mqtt5 needs boost 1.82.0 but it is published with 1.88.0 Beta1 How to use boost::mqtt5 with boost 1.82.0? > Boost.MQTT5 is a header-only library. To use Boost.MQTT5 it requires the following: > > C++17 capable compiler > Boost 1.82 or later. In addition to Asio, we use other header- >only libraries. > OpenSSL. If you require an SSL connection by using boost::asio::ssl::stream. [1] https://www.boost.org/doc/libs/1_88_0_beta1/libs/mqtt5/doc/html/mqtt5/intro…

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Issue fixed in context library that is not included in 1.88 beta release?
by Anders Axelsson 29 Mar '25

29 Mar '25

Hi, I stumbled upon a problem found in the 1.87.0 release (and also 1.88 beta1) The issue seems to have been resolved on the develop branch in the actual submodule repo quite some time ago by another developer, but it is yet not included in the top/super project. The ticket: https://github.com/boostorg/context/issues/297 I am very new to the community, so I don't really know what is the typical way of working here. it would be sad if we miss to include an important build issue in the next release just because of some administrative issues, so I am happy to help but like I said, I am not familiar with how I can do that. Any ideas?

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Asio Beta changes are missing on the 1.88 Beta page
by Dennis Luehring 27 Mar '25

27 Mar '25

Asio is missing on the beta release page https://www.boost.org/users/history/version_1_88_0.html but there seem to be changes available for the beta https://www.boost.org/doc/libs/1_88_0_beta1/doc/html/boost_asio/history.html

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Reminder: Master branch closes for the 1.88.0 release NEXT WEDNESDAY
by Marshall Clow 26 Mar '25

26 Mar '25

Also, if you have release notes, now’s the time to write them. — Marshall

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release] Boost 1.88.0 beta 1 released
by Marshall Clow 16 Mar '25

16 Mar '25

Boost release 1.88.0 beta 1 is now available at: https://archives.boost.io/beta/1.88.0.beta1/source/ The SHA256 checksums are: bc4948bc664fde0c2142badae2679a42124b464dc58019250afe0ef57fd7763e boost_1_88_0_rc1.zip 3c334a9a743b68a35452b0223be8932fb39f26a6938382f9b9e625c4df99602c boost_1_88_0_rc1.tar.gz 9e42c0611500151d795d66a07ef0a21036c02d24678e2e887caf6d97fcbc25ca boost_1_88_0_rc1.tar.bz2 7faf60c4cb12ee90270e41716cf3735a8739016d7346983ce9f5e899e510b26d boost_1_88_0_rc1.7z Release notes (still need updates): https://www.boost.org/users/history/version_1_88_0.html Please try the beta and report any problems you encounter. Thanks to everyone who contributed to the release. -- Boost Release Team

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[release] Boost 1.88.0 Release Candidate 1 is available
by Marshall Clow 14 Mar '25

14 Mar '25

Available at: https://archives.boost.io/beta/1.88.0.beta1/source/ The SHA256 checksums are as follows: bc4948bc664fde0c2142badae2679a42124b464dc58019250afe0ef57fd7763e boost_1_88_0_b1_rc1.zip 3c334a9a743b68a35452b0223be8932fb39f26a6938382f9b9e625c4df99602c boost_1_88_0_b1_rc1.tar.gz 9e42c0611500151d795d66a07ef0a21036c02d24678e2e887caf6d97fcbc25ca boost_1_88_0_b1_rc1.tar.bz2 7faf60c4cb12ee90270e41716cf3735a8739016d7346983ce9f5e899e510b26d boost_1_88_0_b1_rc1.7z 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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[proposal] OpenMethod library
by Jean-Louis Leroy 11 Mar '25

11 Mar '25

Hello Boost developers! I would like to propose my open-method library for inclusion in Boost. Open-methods are an elegant solution to the Expression Problem: > Given a set of types, and a set of operations on these types, is it possible > to add new operations on the existing types, and new types to the existing > operations, without modifying existing code? Open-methods solve the Expression Problem by making it possible to define free virtual functions, i.e. virtual functions that exist outside of a class. They also help reduce coupling. Open-methods are often called "multi-methods", because they typically make it possible to select an overrider on the basis of more than one argument (as this library does). Nice, but this is a distraction. Observations show that single dispatch largely outnumbers multiple dispatch in real systems, even in languages that natively support multi-methods (Common Lisp, Clojure, Julia, Dylan, TADS, Cecil, Diesel, Nice, etc). "Multi" is just the cherry on the "open" cake. Bjarne Stroustrup wanted open-methods in C++ almost from the beginning. In D&E he writes: > I repeatedly considered a mechanism for a virtual function call based on more > than one object, often called multi-methods. [...] Since about 1985, I have > always felt some twinge of regret for not providing multi-methods. > Stroustrup, 1994, The Design and Evolution of C++, 13.8. Circa 2007, he tried to bring open-methods into the standard, unfortunately without success, to his enduring regret. Decades later he writes: > In retrospect, I don’t think that the object-oriented notation (e.g., x.f(y)) > should ever have been introduced. The traditional mathematical notation f(x,y) > is sufficient. As a side benefit, the mathematical notation would naturally > have given us multi-methods, thereby saving us from the visitor pattern > workaround. > Stroustrup, 2020, Thriving in a Crowded and Changing World: C++ 2006–2020. This is what this library is all about: f(x, y), and getting rid of visitors. It closely follows the design described in the papers by Stroustrup and his PhD students Peter Pirkelbauer and Yuriy Solodkyy. Method dispatch is *fast*. It uses v-tables similar to native virtual functions, and it can match their performance. The library also provides additional features: a mechanism to call the next most specialized overrider, support for smart pointers, customization points for alternative RTTI systems, error handling, tracing, etc. The library requires C++17 or above. It supports virtual and multiple inheritance, excluding repeated inheritance. For evaluation purposes, I prepared a repository with a library adapted to Boost naming conventions: https://github.com/jll63/Boost.OpenMethod. The documentation is here: https://jll63.github.io/Boost.OpenMethod. Here are a few examples from the tutorial on Compiler Explorer: * Hello World: https://godbolt.org/z/9hv8oE8zd * AST - combining virtual_ptr and std::unique_ptr: https://godbolt.org/z/cPjzfanc8 * Intrusive vptr: https://godbolt.org/z/87h9zv7dK * Policy for throwing exceptions: https://godbolt.org/z/nEYWGsPc5 If you like what you see, please consider endorsing the library. Thanks, Jean-Louis Leroy

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