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

[OpenMethod] review starts on 28th of April
by Дмитрий Архипов 12 May '25

12 May '25

Dear Boost community. The peer review of the proposed Boost.OpenMethod will start on 28th of April and continue until May 7th. OpenMethods implements open methods in C++. Those are "virtual functions" defined outside of classes. They allow avoiding god classes, and visitors and provide a solution to the Expression Problem, and the banana-gorilla-jungle problem. They also support multiple dispatch. This library implements most of Stroustrup's multimethods proposal, with some new features, like customization points and inter-operability with smart pointers. And despite all that open-method calls are fast - on par with native virtual functions. You can find the source code of the library at https://github.com/jll63/Boost.OpenMethod/tree/master and read the documentation at https://jll63.github.io/Boost.OpenMethod/. The library is header-only and thus it is fairly easy to try it out. In addition, Christian Mazakas (of the C++ Alliance) has added the candidate library to his vcpkg repository (https://github.com/cmazakas/vcpkg-registry-test) The library is also available in Compiler Explorer under the name YOMM2. As the library is not domain-specific, everyone is very welcome to contribute a review either by sending it to the Boost mailing list, or me personally. In your review please state whether you recommend to reject or accept the library into Boost, and whether you suggest any conditions for acceptance. Other questions you might want to answer in your review are: * What is your evaluation of the design? * What is your evaluation of the implementation? * What is your evaluation of the documentation? * What is your evaluation of the potential usefulness of the library? * Did you try to use the library? With what compiler? Did you have any problems? * How much effort did you put into your evaluation? A glance? A quick reading? In-depth study? * Are you knowledgeable about the problems tackled by the library? Thanks in advance for your time and effort! Dmitry Arkhipov, Staff Engineer at The C++ Alliance.

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A proposal for a modern build-system
by Hassan Sajjad 07 May '25

07 May '25

Hi. I compiled 25 Boost libraries with C++20 header-units, including examples and Tests of a few. This resulted in a 1.44x speed-up if we exclude the scanning. Scanning was as slow as the header-unit build. I have a solution for that. I am sending this paper (Making some final edits) https://htmlpreview.github.io/?https://github.com/HassanSajjad-302/iso-pape… , which allows for a build-system to use a scanning-less approach to build header-units.This method requires only minimal modifications to the compiler and enables memory-mapped file sharing, which significantly reduces filesystem overhead and further boosts speed. My proposal for a scanning-less approach will allow HMake to have another amazing feature, monolithic Big header-units. BigHu will allow you to map all the headers from a directory to a single header-unit. This header-unit includes all these header-files and consumes them as header-files. Now, whenever the compiler requests a header-unit from this directory, the build-system instead sends this consolidated BigHu. This will not only improve the clean build speed, because of fewer process launches. But also massively boosts the rebuild speed as few header-units need to be read instead of lots of files. No source-code editing will be needed to use this feature. And you will have the option to either build a library as BigHu (if you don't mean to edit it) or as small header-units (if you are working on it). HMake will soon support compile_commands.json, which I guess can work fine with header-units. Thus you can benefit from both, faster compilation and working intelliscence. The API shown in hmake.cpp is a work in progress. HMake build-system benefits are numerous, even if we leave out the header-units support. This makes it a perfect replacement for B2. I believe we can complete the switch in the next 2 months. And if some compiler supports my paper, we get >3x faster compilation as well. Best, Hassan Sajjad

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In 1.88.0, BCP creates project that doesn't build
by Mason Loyet 04 May '25

04 May '25

Hi, I am attempting to use BCP to put boost into a different namespace as below: mkdir myboost_1_88_0 curl -L https://archives.boost.io/release/1.88.0/source/boost_1_88_0.tar.bz2 | tar -xvjf - cd boost_1_88_0 && ./bootstrap.sh && ./b2 tools/bcp && ./dist/bin/bcp --namespace=myboost . ../myboost_1_88_0 cd ../myboost_1_88_0 ./b2 This results in: … error: Unable to find file or target named error: '/boost/align//boost_align' error: referred to from project at error: '/home/mloyet/external/boost-test/myboost_1_88_0/libs/atomic/build' The snippet appears to work for 1.84.0. Has something changed? Am I invoking BCP incorrectly? ________________________________ Note: This email is for the confidential use of the named addressee(s) only and may contain proprietary, confidential, or privileged information and/or personal data. If you are not the intended recipient, you are hereby notified that any review, dissemination, or copying of this email is strictly prohibited, and requested to notify the sender immediately and destroy this email and any attachments. Email transmission cannot be guaranteed to be secure or error-free. The Company, therefore, does not make any guarantees as to the completeness or accuracy of this email or any attachments. This email is for informational purposes only and does not constitute a recommendation, offer, request, or solicitation of any kind to buy, sell, subscribe, redeem, or perform any type of transaction of a financial product. Personal data, as defined by applicable data protection and privacy laws, contained in this email may be processed by the Company, and any of its affiliated or related companies, for legal, compliance, and/or business-related purposes. You may have rights regarding your personal data; for information on exercising these rights or the Company’s treatment of personal data, please email datarequests(a)jumptrading.com.

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Library submission, checking out the interest
by Artem Shapovalov 04 May '25

04 May '25

Hello Boost dev community. Hope you are doing well and I'm doing right. I want to make my small contribution with my small library. It's a minimalistic implementation of a message bus that may connect together the pieces of code inside the same binary. Idea is: bring a microservices-like approach and the Publish-Subscribe pattern into a micro-level and allow all of the people not to reinvent the bicycle. Several times, I've re-implemented it because it's useful and had no reference implementation, and this is why I finally decided to make it, and I did. Here, you may check it out, it's generally satisfy some standards of Boost: https://github.com/Artem-Shapovalov/Independency Thanks for your attention. I hope you'll like it and find it useful and worth for Boost Libraries' family. Sincerely,Artem Shapovalov.

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[OpenMethod] A pre-release feedback
by Andrzej Krzemienski 03 May '25

03 May '25

Hi Everyone, The library review starts still in two weeks, but I wanted to give some early feedback. First, I wanted to thank Jean-Louis for exploring the subject, writing and sharing the library, and for submitting it for the Boost Review. My feedback is based on the reading of the documentation, I haven't played with the library just yet. [1]. Animals as examples There are already a number of things in the library that suggest it might not be suitable for production use (I describe them below), but using class Animal as explanatory examples amplifies the impression that this is going to be a toy library. Half of the books I have read on OO use the Animal (or Employee) example, but never in my C++ career did I have to use OO to model something close to "animal". I know they are just examples, but picking one so detached from programming reality is in my estimation harmful. The arithmetic expression example is way better. I, for one, use OO for representing dynamically-configurable parts of the applications, such as plugins or user-selectable sorting or selection predicates. [2]. The motivation In C++ we already have a dynamic-dispatch tool for "closed set of methods with open set of types": virtual functions. We also have a dynamic-dispatch tool for "open set of methods with closed set of types": the visitation of std::variant. You need to provide a motivating example (more convincing than the zoo) that needs exactly this: "open set of methods with the open set of types". The arithmetic expression example doesn't do the job: there is a fixed and well known list of concrete types. Also, the fact that Bjarne Stroustrup wanted to add open methods long ago is insufficient a motivation. [3]. Are open methods compatible with static type checking? It looks that when one of the two things -- number of types, number of methods -- is known statically, the compiler can verify if the programmer didn't forget to take some type or method into account. (Well, sometimes we get the "pure virtual function call" error, but these are very rare cases.) The same seems not to be the case for open methods. What this library advertises as flexibility would be the source of many programmer bugs detected only at runtime, possibly by end users. Imagine that programmer Alice is adding her new type A and plugs it into open methods known to her, and at the same time programmer Bob in another file adds a new open method B known only to him. Bob doesn't know about class A, and Alice doesn't know about open method B. The ISO C++ proposals quoted in the docs mentioned solving this by a mandated or encouraged linker error. Is it possible for this library to diagnose the incomplete specification of an open method in the `initialize()` function? The docs use an expression, "when an error is encountered [...]". But note that in C++ we often use the term "error" to express the situation where a _correct_ program encounters a hostile situation in the environment (lack of resources, bad user input). But openmethod docs actually mean something different: a programmer bug. It is very easy for a programmer to plant a bug in this flexible design. [4] In a similar vein, the decision to select an arbitrary specialization of an open method upon a tie, is another runtime surprise: not even a reported error. For multi methods it is not even clear how a static check for exhaustive unambiguous specialization should work. [5] It is concerning that so many things are defined in the global namespace. The docs say, "First we need to include the library’s main header. It defines a few macros, and injects a name - virtual_ptr - in the global namespace." But then the reference part says that virtual_ptr is in the namespace boost::openmethod. Who is right? The fact that as common a name as `next` is reserved inside open methods is also uncomfortable. Why not use a namespace-scoped name? Next, the docs use the using-directive: `using namespace boost::openmethod;`. This is a bad idea: both for real programs and for the documentation: it is not clear if the library was designed with namespaces in mind. Also, all the examples define open methods in the global namespace. I instead would like the docs to show how to declare open methods in my namespace, as this is a far more probable use case. [6] Friendship It puzzles me how the notion of friendship can be combined with this idea of flexibility in open methods. It is my understanding that open methods are added on top of the existing classes. That is: classes do not have to know that some open method will be added in the future. In other words, open methods are non-intrusive, right? So how would a class know who to grant the friendship to? Also, the examples use the declaration `friend struct`, even though we are talking about methods. I think docs should mention the existence of these structs more prominently. [7] Function signatures Some macros in the library use function types in declarations: `BOOST_OPENMETHOD_OVERRIDERS(poke)<void(std::ostream&, virtual_ptr<Cat>)>` Others specify the type separately: `BOOST_OPENMETHOD_OVERRIDE(value, (virtual_ptr<Plus> node), int)` Is there a reason for this? Can the clever use of macros not offer the same function signature syntax? [8] Passing virtual pointers to const objects If `virtual_ptr<Cat>` is an analogue of this pointer, could we see an example in the docs that shows a virtual pointer to const objects? It would be `virtual_ptr<const Cat>`, I guess? [9] Is this library intended for production use? The library comes with a lot of clever macros, a lot of pointer type templates, a lot of new syntax and runtime surprises (mentioned earlier). I am concerned about how the debugging would look if something goes wrong with the usage of this library. Would you recommend it for use in production systems? Or is it for experimentation? [10] Minor things Section Custom RTTI has sentence: > Now we can include the "core" header and then header `boost/openmethod/core.hpp` is not included. Is it a bug? Regards, &rzej;

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[OpenMethod] Questions about custom policies.
by Ivan Matek 01 May '25

01 May '25

Hello, I just started with review and I have a cluster of questions, but it is not clear what the root cause of my issues is so apologies if ordering of questions is wrong. 1. I wanted to get hash map stats, but they are not printed in debug policy, even when env variable is set, I must hack release policy like this: - vptr_vector<release>, vectored_error_handler<release>> {}; + vptr_vector<release>, vectored_error_handler<release>, basic_trace_output<release>> {} Is this expected? IDK why debug prints some trace, but not hash info 2. While playing with this I get crashes when I just c/p release policy and rename it, e.g. +struct my_release : basic_policy< + my_release, std_rtti, fast_perfect_hash<my_release>, + vptr_vector<my_release>, vectored_error_handler<my_release>> {}; crashes in template<bool Indirect> inline auto box_vptr(const vptr_type& vp) { if constexpr (Indirect) { return &vp; } else { return vp; } } but when I switch boost::openmethod::initialize<boost::openmethod::policies::my_release>(); to boost::openmethod::initialize<boost::openmethod::policies::release>(); it works fine. It also exibits some other weird behavior, e.g. if I switch debug inheritance from release to my_release crash goes away, even when not using debug... Looks to me I am doing something that is not allowed, but it is not clear what I am doing wrong. regards, Ivan

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[OpenMethod] Some questions
by Andrzej Krzemienski 30 Apr '25

30 Apr '25

Hi Everyone, I have concerns with the design philosophy of OpenMethod library. Giving this flexibility that one person can add new open methods to a class hierarchy in one file and another person can add classes to a class hierarchy in another file independently, this is asking for miscommunication problems (programmer bugs) discovered only at runtime. I tried to recreate this situation that I expect would be common. My first question, even before I run tests is what will happen when I have a class hierarchy: struct Node { virtual ~Node(); }; struct XNode : Node {}; I declare an open method `value()` and override it for XNode in one file, adn in another file I extend the hierarchy with: struct YNode : Node {}; And then in main(), in yet another file, I will call `value()` with `YNode`. The documentation does not give me a clear answer. Section Error Handling says, > When an error is encountered, the program is terminated by a call to abort. And then in the next sentence it talks about different debug and release policies, and ultimately, I do not know if by default abort() is called or not. But that is not the only problem. The docs use the term " When an error is encountered". What is considered "an error" here? How many situations constitute "an error"? The docs should enumerate all these situations. I need to know when my program will be calling `abort()`. So, I dun a Compiler Explorer test: https://godbolt.org/z/3fW8j4eTM And indeed, I get something that looks like abort() But when I wrap the call into a try-catch block, all of a sudden, the implementation seems to pick the wrong overrider and return a value, clearly not the intended one. And the program goes on: https://godbolt.org/z/Y6z3o56h5 This is the worst thing that can happen: a random runtime behavior. Is this a bug? Or am I missing something? Next question that naturally arises: how do I declare `noexcept` open methods with this library? Regards, &rzej;

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Proposal: Abandoning monolithic Boost documentation.
by René Ferdinand Rivera Morell 23 Apr '25

23 Apr '25

Today, in slack, we had a discussion on problems with building the monolithic docs. For context what I'm calling the monolithic docs are these <https://www.boost.org/doc/libs/1_88_0/doc/html/libraries.html>. The main problem that was raised is that a failure in one library causes all the docs to disappear. That problem is due to the nature of DocBook, XSLT, and the single monolithic generation. This is not something that can be resolved at the build system leve. The one solution is to abandon the monolithic build. And instead move to only having per library documentation builds. Hence.. I am proposing we abandon the monolithic documentation build. The benefits: * No longer missing docs from problems in individual libraries. * It's modular. I.e. libraries would build, and include, their docs in the modular layout. Do note that most libraries, more than 2/3, already use modular documentation. So technically this would be completing the modular transition that has already been happening. Thoughts? -- -- René Ferdinand Rivera Morell -- Don't Assume Anything -- No Supongas Nada -- Robot Dreams - http://robot-dreams.net

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Review Manager Volunteers
by Matt Borland 23 Apr '25

23 Apr '25

Hi All, Recently, we've seen a shortage of review managers: Joaquin has been looking for one for his bloom-filters library for a few weeks (now solved), and Dmitry recently withdrew his GDB debugging tools due to lack of review manager. Looking at the review schedule for the last few years[1] you'll find a number of repeated names and long-time contributors. In an effort to find new volunteers for review managers I would like to ask what are the showstoppers that keep you from wanting to be a review manager? Time, Training, Recognition, none of the above? I am genuinely curious in an effort to find new volunteers so we can continue to add great libraries to the project. Thank you, and Happy Easter to those that celebrate. Matt [1] https://www.boost.org/community/review_schedule.html

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Printf library suggestion
by Aaron Graham 22 Apr '25

22 Apr '25

I'd like to gauge the interest in adding the following library to boost: https://github.com/rokudev/rostd/blob/main/include/rostd/printx.hpp It's a simple library that checks and rewrites the format string at compile time in order to fortify it for use with printf, leaving the object code with only a call to the underlying C-standard printf-family function. It's a single header and requires C++20 or above (for cNTTP support). It contains these four functions: printf, sprintf, snprintf, fprintf These functions are used like so: printf<"Hello %s\n">("World!"); char buf[20]; sprintf<"Hello %s\n">(buf, "World!"); // yes, it's safe char buf[20]; snprintf<"Hello %s\n">(buf, sizeof buf, "World!"); fprintf<"Hello %s\n">(file, "World!"); Features/rationale: * It provides old-style printf (supports all standard printf specifiers). * Fully type-safe. No format string attacks. Issues are found at compile time. * Length modifiers are deduced; these format strings are portable. (No PRIu64 inttypes stuff needed anymore, just use %u) * Adds %? format specifier (print whatever type is there). * Compiles to std::printf (much smaller object code than std::format). * Provides a way for developers to easily adapt this printf formatting capability to their own functions (logging, etc.) More detailed rationale is here: https://github.com/rokudev/rostd/blob/main/doc/printx.adoc

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