September 2018 - 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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[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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Re: [boost] [ Interest? ] [ out_ptr ] Tiny C++ Abstraction for C-Style Output Pointers
by Bjorn Reese 12 May '19

12 May '19

On 06/28/18 21:03, ThePhD via Boost wrote: > out_ptr is a small abstraction for making types such as > std::unique_ptr, std::shared_ptr, boost::shared_ptr, and the upcoming > std::retain_ptr > <http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2016/p0468r0.html> work > work C-Style output functions as a parameter, addressing the need of > wanting to be able to do "my_c_api_init( foo, bar, &my_smart_ptr );". It's Does out_ptr have other use-cases than C interoperability?

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[test] unit test command-line handling
by Stefan Seefeld 22 Mar '19

22 Mar '19

Hello, this is a question concerning the Boost.Test framework. I'd like to pass command-line arguments to my tests, and I'm unsure of how to proceed. I have found https://www.boost.org/doc/libs/1_68_0/libs/test/doc/html/boost_test/adv_sce…, which shows how to access the command-line programmatically, but that's declared obsolete, and it's also lacking some important info, such as how I should handle the argv vector. Are there any examples that demonstrate this use case ? Specifically: * What (non-deprecated) API can I use to access command-line arguments during test initialization ? * How does my own handling of command-line arguments interact with Boost.Test's own command-line argument handling ? Thanks, Stefan -- ...ich hab' noch einen Koffer in Berlin...

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clang-win, again
by Peter Dimov 31 Oct '18

31 Oct '18

Has anyone succeeded in getting clang-cl.exe working under b2? I've installed llvm-6.0.1, added it to PATH, put using clang-win : : : <compatibility>vc14 ; in my user-config, and what I get is: C:\boost-git\develop\libs\smart_ptr\test>b2 toolset=clang-win sp_interlocked_test warning: mismatched versions of Boost.Build engine and core warning: Boost.Build engine (b2) is 2015.07.00 warning: Boost.Build core (at C:/boost-git/develop/tools/build/src) is 2018.02-git C:/boost-git/develop/tools/build/src/tools\msvc.jam:1087: in set-setup-command *** argument error * rule virtual-target.from-file ( file : file-loc : project ) * called with: ( : /C:/boost-git/develop/libs/smart_ptr/test : object(project-t arget)@129 ) * missing argument file C:/boost-git/develop/tools/build/src/build\virtual-target.jam:970:see definition of rule 'virtual-target.from-file' being called C:/boost-git/develop/tools/build/src/tools\msvc.jam:652: in clang-win.compile.c+ + C:/boost-git/develop/tools/build/src/kernel\modules.jam:107: in modules.call-in C:/boost-git/develop/tools/build/src/util\indirect.jam:105: in indirect.call C:/boost-git/develop/tools/build/src/build\virtual-target.jam:902: in execute C:/boost-git/develop/tools/build/src/build\virtual-target.jam:821: in class@acti on.actualize C:/boost-git/develop/tools/build/src/build\virtual-target.jam:332: in actualize- action C:/boost-git/develop/tools/build/src/build\virtual-target.jam:518: in actualize- no-scanner C:/boost-git/develop/tools/build/src/build\virtual-target.jam:142: in class@virt ual-target.actualize C:/boost-git/develop/tools/build/src/build\configure.jam:258: in try-find-build C:/boost-git/develop/tools/build/src/build\configure.jam:396: in find-builds-raw C:/boost-git/develop/tools/build/src/build\configure.jam:455: in configure.find- builds C:/boost-git/develop\boostcpp.jam:734: in boostcpp.deduce-address-model C:/boost-git/develop/tools/build/src/kernel\modules.jam:107: in modules.call-in C:/boost-git/develop/tools/build/src/util\indirect.jam:105: in indirect.call C:/boost-git/develop/tools/build/src/build\property.jam:144: in property.evaluat e-conditionals-in-context C:/boost-git/develop/tools/build/src/build\targets.jam:1087: in evaluate-require ments C:/boost-git/develop/tools/build/src/build\targets.jam:1121: in common-propertie s2 C:/boost-git/develop/tools/build/src/build\targets.jam:1017: in targets.common-p roperties C:/boost-git/develop/tools/build/src/build\targets.jam:1313: in class@basic-targ et.generate C:/boost-git/develop/tools/build/src/build\targets.jam:812: in generate-really C:/boost-git/develop/tools/build/src/build\targets.jam:784: in class@main-target .generate C:/boost-git/develop/tools/build/src\build-system.jam:797: in load C:\boost-git\develop\tools\build\src/kernel\modules.jam:295: in import C:\boost-git\develop\tools\build\src/kernel/bootstrap.jam:139: in boost-build C:\boost-git\develop\boost-build.jam:17: in module scope

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[test] How to execute shell commands
by Mike Dev 18 Oct '18

18 Oct '18

As an extension to my previous question: Does the boost test framework provide an integrated mechanism to get the binary directory (the directory where the currently running test executable is placed) and/or the source directory (where the jam-file resides that defined the test)? Best Mike

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[RFC] unique_val (handles, IDs, descriptors...)
by Miguel Ojeda 15 Oct '18

15 Oct '18

Hi all, While working on a medium-sized project, I had to wrap quite some handles, IDs, descriptors, etc. into RAII classes. Somehow, writing those and making them movable seemed more verbose than needed. I searched in the STL and Boost for something already implemented, but nothing seemed to come up. I decided to write my own prototype to see whether I was missing something important; but actually using it in my project felt quite natural and simple. At this point, I asked for a second opinion from a well-known expert (thanks Scott!) and he agreed that it seemed like a reasonable idea but, of course, he would also be surprised if others haven't come up with something similar. So I polished it up a bit and uploaded it to: https://github.com/ojeda/unique_val Below you have the introduction inlined [1]. If you have the time, please take a look (specially to the Rationale) and let me know your comments. The code itself is very short and straightforward. If you already have this class/template in Boost somewhere that I missed, please let me know! Otherwise, if you think this could be interesting to put into Boost in some existing library (not sure which) or as a new tiny library, I would be glad to make the effort to expand it, clean it up, etc. Thank you! Miguel [1] """ A single-header header-only library for representing unique values (handles, IDs, descriptors...) that default to a value on move for C++11, C++14 and C++17. It simplifies writing resource-owning classes (RAII) with move semantics support for resources with handles, IDs or descriptors that are supposed to be used as unique values, not as unique pointers. For instance, it can be used with non-pointer handlers (like the `int` file/socket descriptors in POSIX) and with opaque pointer handlers (like the `HWND` handles in the Win32 API). As such, it can be used as an alternative to `std::unique_ptr` with or without custom deleter, specially for resources that use a non-pointer type or resources that are not simply heap-allocated. It does not have any overhead compared to using the original type. It supports booleans, integers, pointers and enumerations. The default value can be different than the default-constructed value (i.e. different than 0, nullptr, etc.). """

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Boost xxhr ? High level http client library
by Damien Buhl 13 Oct '18

13 Oct '18

Dear Boost, I've built an header-only library based on Boost.Beast which allows you to perform HTTP requests. It is implememented with two backends : * Boost.Beast for native builds. * XmlHttpRequest for WebAssembly (plans to migrate to fetch API which is richer) Actually Boost.Beast is a great lib, however it's API is thought to build HTTP centric app not just to make some simple HTTP call ( as for example urdl was ). xxhr on the other hand is about making it simple to call an HTTP service. Usage example : GET <https://nxxm.github.io/xxhr/html/namespacexxhr.html#a69bafa24d7c33b004a7de8…>( "http://httpbin.org/anything"s, on_response = [](auto&& resp) { std::cout << resp.text; }); I would be really interested in a pre-review or some feedback about it's API. The implementation merits more attention and can significantly be improved but this email is to grab a first feedback from the community. Documentation : https://nxxm.github.io/xxhr/ GitHub : https://github.com/nxxm/xxhr Example code relying on it : nxxm/gh <https://github.com/nxxm/gh>: partial GitHub API implementation Thanks for your time :) -- Damien Buhl Software Developer +33 6 77 43 10 05 https://nxxm.github.io/

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Tools to manage multiple repositories effectively?
by James E. King III 09 Oct '18

09 Oct '18

Hello, I am looking for tools that would allow me to create a portal and/or monitor the following properties of boost repositories. I am in the CMT and at least one fix that was in develop never made it into master for the 1.68.0 release, so I want to be able to see, at a glance, information about the boost repositories I care about in one place. There are about 20 repositories I regularly participate in now so a portal to show what I need to worry about would be useful. 1. How far behind is master (with respect to develop)? This would help identify which repositories are behind develop. Useful for ensuring things get into a release. 2. How many open pull requests? 3. How many new pull requests (within the last week)? 4. How many updated pull requests (within the last week)? 5. How many open issues? 6. How many new issues (within the last week)? 7. How many updated issues (within the last week)? "week" could be configured, perhaps month, or "since I last visited". Anybody know of any good tools or perhaps an existing site that can do this for a multi-repository solution? Thanks, Jim

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Formal Review of Proposed Boost.Histogram Library is FINISHED
by Mateusz Loskot 05 Oct '18

05 Oct '18

Dear Boost Community, The formal review of Hans Dembinski's Histogram library has been completed. Here is the quantitative summary of feedback received: * Reviews: 1. Klemens David Morgenstern 2. Jim Pivarski (off-list via e-mail to Hans) 3. Björn Reese 4. Steven Watanabe 5. Alex Hagen-Zanker * Non-review participations: 1. degski 2. Gavin Lambert 3. Seth 4. Mateusz Loskot I believe I've collected the names/numbers right, but please let me know ASAP if you think otherwise. I'd like to thank all the participants for their time and efforts. I'm sure Hans received lots of valuable comments and suggestions. FYI, the discussion threads are still open for new posts. Those won't be taken into consideration towards the review result though. I will do my best to announce the review results next week. Mateusz Review Manager for the proposed Boost.Histogram -- Mateusz Loskot, http://mateusz.loskot.net

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Twenty years and time to retire
by Beman Dawes 04 Oct '18

04 Oct '18

The idea behind Boost was hatched in March, 1998, and the proposal document <https://www.boost.org/users/proposal.pdf> was released May 6, 1998. That makes Boost twenty years old, and makes me twenty years older. It is high time I retire from Boost; I haven't been able to contribute for some time now. Thanks to all of you who made Boost such an overwhelming success in the past and will drive Boost forward into a bright future! --Beman

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[histogram] Variance
by Bjorn Reese 02 Oct '18

02 Oct '18

The variance of individual bins can be obtained when using the adaptive_storage (via h.at(i).variance().) I am trying to understand the overhead of this feature. If I interpret the code correctly, there is a space overhead because each counter has to keep track of both the count and the sum of squares. The computational overhead is that the sum of squares has to be calculated for each insertion. Is this correct? If so, is there any way to use the adaptive storage policy without variance? Furthermore, why does variance() return the sum of squares? Should this not be divided by the sample size?

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[histogram] Formal review
by Bjorn Reese 01 Oct '18

01 Oct '18

Boost.Histogram contains useful and well-designed features, like excess (over/underflow) bins, and axis transforms to name a few. As this is a review, I am going to spent most time below on critical scrutiny. I. DESIGN --------- Iterators are const. This prevents us from bootstrapping the histogram with a prior distribution using STL algorithms like std::fill(), std::generate(), or std::sample(). The adaptive_storage does not work well with STL algorithms, because weight_counter is not an arithmetic type. See the Implementation section below for more detail. I therefore propose that the default storage policy is changed to something without weight_counter. The adaptive_storage has two responsibilities: data compaction and weights. Would it be possible to split this into two separate storage policies? I have no real use for arrival variance. I am not too fond of using operator() for insertion. The code looks like a function call with side-effect. I prefer an explicitly named member function. The axis::ouflow_type is oddly named. I suggest that this is renamed to something like axis::excess_type. II. IMPLEMENTATION ------------------ The implementation is generally of high quality. However, I did encounter the three problem areas listed below. (A) Integration with STL algorithms can be improved. Here are some examples: First, std::distance() does not work on a histogram with array_storage. This means that other STL algorithms, like std::any_of(), fails to compile. I solved this problem by copying the distance_to() function from the axis iterator to the histogram iterator. Second, std::max_element (and brethren) cannot be used on a histogram. Consider the following example: auto element = std::max_element(h.begin(), h.end()); Compilation fails for adaptive_storage because weight_counter has no less-than operator. Furthermore, compilation fails for array_storage because iterator_over<H>::operator= fails. It attempts to re-assign a reference, but accidentally triggers a copy-constructor instead. Letting the iterator store a pointer instead of a reference solves the problem. Apropos, iterator_over<H>::operator= does not return *this. Consider adding the -Werror=return-type compiler flag and a unit-test to that calls this operator. Third, std::inner_product fails to compile for adaptive_storage because weight_counter does not have a binary operator*. The inner product of two histograms is useful for calculating the cosine similarity, which can be used to compare two distributions. std::inner_product works for array_storage though. (B) Indexing and size use different types (int versus std::size_t.) I assume that this is because of the underflow bin, which is indexed by -1. I am not certain whether or not this is a real problem, but it does cause some oddities when stressed to the limit. For example, if we need a histogram that counts each unsigned int, then we get an "lower < upper" exception during construction: using range_type = unsigned int; auto h = make_static_histogram_with( array_storage<int>(), axis::integer<>(0, std::numeric_limits<range_type>::max())); It works if we reduce the end by 2, but then we are not collecting all values (unless we shift the range left by 1 and misuse the excess bins for the two missing values.) A possible solution could be to replace the -1 and N excess indices with an "enum struct excess { lower, upper }" and let operator[] et al use overloading on this enum. (C) Sometimes the compilation errors are nonsensical. For example: // Forgot to use make_static_histogram_with() auto h = make_static_histogram(array_storage<int>, axis::regular<>(10, 0, 1)); triggers an incomprehensible static_assert plus an error about a missing .shape() function. III. DOCUMENTATION ------------------ User guide is clear and pedagogical. I would like to see more examples that uses STL algorithms, such as calculating the CDF using std::partial_sum(), or calculating the cosine similarity of two histograms using std::inner_product(). Most examples use std::cout plus a comment to document the results of operations. Consider using assert() instead. Consider using a tabular layout similar to that of the C++ standard (or cppreference.com for that matter) on the Concepts page. Reference documentation is rather meager and shows implementation details. The documentation contains both a "Reference" and a "References" chapter which are completely different. Consider renaming the latter to something like "External references" , "Literature references", or "Bibliography". IV. MISC -------- I have spent around 15 hours on the review, mainly writing small examples that uses STL algorithms on Boost.Histogram. I am well-versed in the topic. I work with statistical distributions for real-time analysis of data, although I mainly dabble around in one dimension. I have written a library for online/streaming statistical algorithms. V. VERDICT ---------- While Boost.Histogram is a small niche library, it has a wide range of practical applications to warrant the inclusion into Boost. Boost.Histogram should be ACCEPTED into Boost, provided: 1. Reference documentation is finalized. I furthermore strongly recommend that the default storage policy is changed to something without weight_counter because of the various problems with STL algorithms. This recommendation is not a prerequisite for acceptance.

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Median in Boost.Accumulators
by Lakshay Garg 30 Sep '18

30 Sep '18

Hello Boost Some time ago, I needed to compute the exact median for a stream of elements and after using Boost.Accumulators, realized that it only provides an approximation of the median and not the exact number. I rolled up my custom implementation of the algorithm and used it for my project. I wanted to check if people on this list might be interested in such an implementation for Boost.Accumulators in which case I can try to adapt my implementation and send a PR. Performance characteristics: For a stream of n numbers, the memory required is O(n). Median can be queried at any point of time in O(1) and adding all the elements costs O(nlog(n)) Lakshay

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Will boost support DTLS / UDP?
by jupiter 29 Sep '18

29 Sep '18

It seems to me that Boost does not support DTLS so far, any plan and time line for boost to support DTLS?

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CMake in Boost
by Robert Ramey 29 Sep '18

29 Sep '18

Many have expressed the desire that Boost support CMake. The Boost Board of Directors has emitted some sort of resolution to this effect - it's been a year. I would like to see progress in this direction. To this end I propose the following: a) Boost announce that a review of proposals to incorporate CMake into boost will be held in January 2019. This will follow customary Boost practices. b) Those who are willing and able to submit code/documentation and whatever else in necessary should do so before this date. I would anticipate at least two such submissions. As is the case with other reviews, I would not exist such submissions to be totally complete. But I would expect that they include enough for reviewers to test and practice with the proposed system. c) Prior to this discussions can be held on the list regarding the scope of such an effort. The review manager will distill these discussions to a statement of scope. This will be posted around 30 October 2018. I nominate myself (Robert Ramey) as review manager in this instance. Why would I do this? a) Boost needs this b) I've never been a review manager c) I'm a masochistic idiot. Robert Ramey

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[test] How to execute shell commands
by Mike Dev 28 Sep '18

28 Sep '18

Does the boost unit test frame work provide a way to write a test that executes a couple of shell commands? Specifically, I want to write a test that compiles a cmake project: https://github.com/boostorg/vmd/pull/4 https://github.com/boostorg/preprocessor/pull/20 what I need to do for that is essentially (on Linux): - mkdir <build_dir> - cd <build_dir> - cmake <source_dir> - cmake --build . Of course I can write a cpp program that uses std::system to execute those commands but I was wondering if there was a more direct way to do it. Best Mike

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contract work
by Ggh 28 Sep '18

28 Sep '18

Hi, Sorry to pollute but: Available for contract work, code samples here: http://www.multi.fi/~ghaga/bak1 Cheers Greg

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stufff
by Ggh 28 Sep '18

28 Sep '18

I don't know what I am up to: http://www.multi.fi/~ghaga/bak1/ http://www.multi.fi/~ghaga/ Thank you, Greg

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Re: [boost] [cmake] Pull request announcement
by Bjorn Reese 28 Sep '18

28 Sep '18

On 09/14/18 13:44, Mike Dev via Boost wrote: > This will not address > - Testing [...] > In short: all the difficult stuff is left out ;) > The goal is not to present a solution that can replace b2 but to have > a minimal starting point upon which individual library authors or the > community as a whole can make iterative improvements. If and when BCM > (or an alternative) is accepted into boost, individual libraries can > then easily switch to this full-fledged solution and of course any > author can create a more complete CMake solution for his library at > any time (as some already have). In my experience, we want to have both an integration and standalone CMake file. This split is necessary to avoid problems with multiple instances of enable_testing() when using one library from another. * The integration file builds only what is necessary for integration into other projects. This is similar to what you are proposing. * The standalone file builds everything including test and documentation. This reuses the integration file to build the library itself. If we place your proposed CMake file in the library root, and dependent libraries start using that location, then it becomes difficult to later have the standalone CMake file in the library root, which is the more natural choice. So we should be cautious about where we place these files.

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Formal Review of Proposed Boost.Histogram Library Starts TODAY
by Mateusz Loskot 27 Sep '18

27 Sep '18

Dear Boost Community, The formal review of Hans Dembinski's Histogram library starts TODAY, the September 17th, and lasts until September 26th, unless an extension occurs. =========== What is it? =========== Histogram is a header-only C++11 library, provides multi-dimensional histogram template class for counting, statistics and data exploration. The histogram class interface has been carefully designed to make the library * offer simple and convenient default behaviour * easy to learn and safe to use * convenient to use for one- as well as multi-dimensional analysis * compatible with STL algorithms * dependant only on C++11 standard library and optionally on Boost The author followed the "Don't pay for what you don't use" principle. The histogram class is customisable through policy classes, but the default policies were carefully crafted so that most users do not need to customize anything. The default policies guarantee the histogram to be safe to use as a black box, memory efficient, and very fast, where safety is related to overflow prevention and large values capping. This guarantees is one of unique features of the library in comparison to other implementations. The histogram class comes in two variants, which share a common interface: * static variant is optimised at compile-time to provide maximum performance, at the cost of reduced runtime flexibility and potentially larger executables; * dynamic variant is a bit slower, but configurable at run-time. Both variants of the histogram class provide optional serialization support implemented with Boost.Serialization. The library itself is header-only and the tests as well as examples can be built using both, Boost.Build and CMake. There are no dependencies required other than C++11 compiler. Optional dependencies include the GNU Scientific Library (GSL) and the ROOT framework from CERN which are needed the corresponding speed test programs used for performance comparison. A note on history: The library was first announced to the Boost community in May, 2016 [1] and the author received extensive feedback. Then, after a year of work posted second request for comments in April, 2017 [2]. =================== Getting the library =================== Checkout the `master` branch from the library git repository: https://github.com/HDembinski/histogram/ NOTE: The author follows the library submission process [3]: the master branch remains frozen for the period of the formal review, modifications in response to feedback should go to `develop` branch and big items may be worked and discussed via opening an issue on GitHub. Documentation: http://hdembinski.github.io/histogram/doc/html/ Website: http://hdembinski.github.io/histogram/ ================ Writing a review ================ Please, follow the official Boost formal review procedure [4]. If you feel this is an interesting library, then please submit your review to the Boost developer list (preferably), or the review manager to mateusz (at) loskot (dot) net. Here are some questions you might want to answer in your review: - 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 problem domain? And finally, every review should answer this question: - Do you think the library should be accepted as a Boost library? Be sure to say this explicitly so that your other comments don't obscure your overall opinion. If needed, refer to the Boost Library Requirements and Guidelines [5]. Please, give constructive criticism! [1] https://lists.boost.org/Archives/boost/2016/05/229389.php [2] https://lists.boost.org/Archives/boost/2017/04/234410.php [3] https://www.boost.org/development/submissions.html#Review [4] https://www.boost.org/community/reviews.html [5] https://www.boost.org/development/requirements.html Mateusz Review Manager for the proposed Boost.Histogram -- Mateusz Loskot, http://mateusz.loskot.net

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[GitHelp] release version of boost from GitHub?
by Kostiantyn Ponomarenko 26 Sep '18

26 Sep '18

Hi, guys. What is the right place for getting the last/or-any (released) version of boost? This page provides the last release as well as others: https://www.boost.org. But I've got the impression that after Boost moved to GitHub and became "modular", the releases can be downloaded right from the GitHub "releases" page. So it looks like it is not the case, and my assumptions is wrong because when I go to the "releases" page on GitHub (https://github.com/boostorg/boost/releases) and download a release (let's say "boost-1.68.0") I don't get any libs inside. Could you please help me to understand this situation. Is the only place to get a release of boost is https://www.boost.org, but not GitHub? Is GitHub used only for development, or getting the latest changes which are not released yet? --- Kostia Kyiv, Ukraine

3 3

Formal Review of Proposed Boost.Histogram Library - LAST DAY
by Mateusz Loskot 26 Sep '18

26 Sep '18

Dear Boost Community, According to the review schedule, the formal review of Hans Dembinski's Histogram library lasts until the end of TODAY. Please, anyone who is aiming to post a review, hurry up! If there are members who have planned to post a review and still wish to do it but require more time, please speak up now indicating how much time you'd need. [1] https://www.boost.org/community/review_schedule.html Best regards, -- Mateusz Loskot, http://mateusz.loskot.net

1 0

Making Boost invisible
by John Maddock 25 Sep '18

25 Sep '18

Folks I have a bug report against Boost.Config that I don't know what (if anything) I should do about: https://github.com/boostorg/config/issues/243 The issue is this: lets say I build boost as static libraries with -fvisibilty=hidden because I want my application or shared library to *hide all boost symbols*. But there are some parts of boost which unconditionally make things visible - throw_exception is one particular culprit, but there are others, probably anything which uses BOOST_SYMBOL_VISIBLE in fact. Question: should we support this? If so how? The only thing I can think of is a user-defined macro which when set, disables symbol visibility. Thoughts? Thanks, John. --- This email has been checked for viruses by Avast antivirus software. https://www.avast.com/antivirus

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Re: [boost] Formal Review of Proposed Boost.Histogram Library Starts TODAY
by Klemens David Morgenstern 25 Sep '18

25 Sep '18

- What is your evaluation of the design? The design is excellent, in that is geared towards readability and performance. - What is your evaluation of the implementation? It looks highly optimized with a focus on only being as cheap as possible on CPU. I.e. only pay for what you use. - What is your evaluation of the documentation? Detailed, good examples, I understood everything. - What is your evaluation of the potential usefulness of the library? It's not my domain, but for anyone interested in data analysis this seems super useful. I think there should be more libraries from that domain, even tough it's not my primary one. - Did you try to use the library? With what compiler? Did you have any problems? Yes, I did last year, when it was still in development, I used MinGW 5 and MSVC 2017. No problems. - How much effort did you put into your evaluation? A glance? A quick reading? In-depth study? I looked into the library in depth last year and gave the author my feedback on several implementation details. - Are you knowledgeable about the problem domain? Not in depth, but I know the basics. And finally, every review should answer this question: - Do you think the library should be accepted as a Boost library? Yes, definitely.

2 1

Interest in Unicode library for Boost?
by Zach Laine 23 Sep '18

23 Sep '18

I've been working on a Unicode library for submission to Boost, with an eye toward standardizing robust Unicode support for C++. It started as a better string library for namespace "std2", with minimal Unicode support. Though "std2" may never happen, those string types are still in there, and the library has grown to also include all the Unicode features most users will ever need. You can find the Github page here: https://github.com/tzlaine/text You can find the online docs here: https://tzlaine.github.io/text If you care about portable Unicode support, or even addressing the embarrassment of being the only major production language with next to no Unicode support, please have a look and provide feedback. I gave a talk about this at C++Now in May, though it's a bit out of date, as the library was not then finished. It's three hours, so, y'know, maybe skip it. For completeness' sake: https://www.youtube.com/watch?v=944GjKxwMBo&index=7&list=PL_AKIMJc4roVSbTTf… https://www.youtube.com/watch?v=GJ2xMAqCZL8&list=PL_AKIMJc4roVSbTTfHReQTl1d… Zach

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Re: [boost] Median in Boost.Accumulators
by Lakshay Garg 23 Sep '18

23 Sep '18

On Sun, 23 Sep 2018 at 12:53, Zach Laine <whatwasthataddress(a)gmail.com> wrote: > > On Sun, Sep 23, 2018 at 2:45 PM Lakshay Garg <lakshayg373(a)gmail.com> wrote: >> >> On Sun, 23 Sep 2018 at 11:59, Zach Laine <whatwasthataddress(a)gmail.com> wrote: >> > Also, what if I don't actually call get() very often? >> >> If get() is not called very often, then I guess just using a plain vector and >> calling nth_element on it would be the best approach. >> >> > Is there any way to take advantage of make_heap()'s O(n) characteristics, >> > and avoid doing an O(n) push_heap() n times? I can't think of one offhand, >> > just curious. >> >> The complexity of push_heap is actually O(log(n)) and not O(n) > > [make.heap] says: > > Complexity: At most 3 * (last - first) comparisons. > Correct! complexity for make_heap is O(n) and complexity for push_heap is O(logn). https://en.cppreference.com/w/cpp/algorithm/make_heap https://en.cppreference.com/w/cpp/algorithm/push_heap

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Re: [boost] Median in Boost.Accumulators
by Lakshay Garg 23 Sep '18

23 Sep '18

On Sun, 23 Sep 2018 at 11:59, Zach Laine <whatwasthataddress(a)gmail.com> wrote: > > On Sun, Sep 23, 2018 at 10:59 AM Lakshay Garg <lakshayg373(a)gmail.com> wrote: >> >> On Sun, 23 Sep 2018 at 08:39, Zach Laine via Boost >> <boost(a)lists.boost.org> wrote: >> > >> > Could you compare and contrast this with the standard library's way of >> > computing a median, std::nth_element()? Yout just give it N/2 for 'n', and >> > it computes the median. >> >> The reason for not using std::nth_element was because I wanted >> to be able to query the median at any point of the sequence very >> efficiently. Had I used std::nth_element, I would have needed O(n) >> time for obtaining the median. For a case where I need to compute >> median after every single element, this would have required O(n^2) >> time for a sequence of length n. Here is my implementation in case >> you would like to have a look: >> >> https://gist.github.com/lakshayg/d27f29b4634cbfea3fc48c21b7b608ef > > I missed that the first time, thanks. > > Your implementation does not seem to support a windowed working set > (one element at a time is added and the oldest one removed). Is that right? Yes, that is correct. This approach does not support a window. > Also, what if I don't actually call get() very often? If get() is not called very often, then I guess just using a plain vector and calling nth_element on it would be the best approach. > Is there any way to take advantage of make_heap()'s O(n) characteristics, > and avoid doing an O(n) push_heap() n times? I can't think of one offhand, > just curious. The complexity of push_heap is actually O(log(n)) and not O(n)

1 0

Re: [boost] Median in Boost.Accumulators
by Bjorn Reese 23 Sep '18

23 Sep '18

On 09/23/18 04:21, Lakshay Garg via Boost wrote: > I rolled up my custom implementation of the algorithm and > used it for my project. I wanted to check if people on > this list might be interested in such an implementation > for Boost.Accumulators in which case I can try to adapt my > implementation and send a PR. Boost.Accumulators does not seem to be actively maintained. > Performance characteristics: For a stream of n numbers, the > memory required is O(n). Median can be queried at any point > of time in O(1) and adding all the elements costs O(nlog(n)) Sounds like you keep two ordered lists (e.g. std::set) of equal size. Then the median is the first element in the second list.

2 1

Formal Review of Proposed Boost.Histogram Library is HALFWAY through
by Mateusz Loskot 22 Sep '18

22 Sep '18

Dear Boost Community, We've reach half-way through the formal review of Hans Dembinski's Histogram library. The review lasts until the end of September 26th. If you are interested in applications for mathematics, statistics graphics, image analysis, and such, or in the Histogram library itself, please consider reviewing the Histogram library by the end of September 26th. Best regards, -- Mateusz Loskot, http://mateusz.loskot.net

1 0

[filesystem] Library maintainers needed
by Beman Dawes 22 Sep '18

22 Sep '18

I'm retiring, so Boost.Filesystem needs one or more maintainers. This is a high complexity library, further complicated by (1) requiring both Windows and non-Windows implementation code and (2) needing a major upgrade for compatibility with the new standard library version shipped in C++17. Furthermore, there are constant Pull Requests and Issues that arise, and these almost invariably take a lot of time for the maintainer to process. My personal opinion is that Boost should deprecate the Boost library in favor of the standard library implementations, and do only minimal maintenance for several years until most users have migrated to C++17 or later. But that's up to the new maintainers to decide. Thanks, --Beman

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[endian] Library maintainer needed
by Beman Dawes 22 Sep '18

22 Sep '18

I'm retiring, so Boost.Endian needs a maintainer. This is a low/medium complexity library that requires only minor effort to maintain. --Beman

2 1

[timer] Library maintainer needed
by Beman Dawes 22 Sep '18

22 Sep '18

I'm retiring, so Boost.Timer needs a maintainer. This is a simple low complexity library, and requires little effort to effort to maintain. --Beman

1 0

[build][testing] Tests naming in Jamfile
by Mateusz Loskot 21 Sep '18

21 Sep '18

Hi, I'm updating Jamfile-s of Boost.GIL and it made me wondering: For example: test-suite "boost-gil-test" : [ run promote_integral.cpp ] ; Apart from replacing the deprecated test-suite with alias, I wonder what is the recommended policy of naming the test suites, are there any rules? For example, should it be more or less hierarchical boost-{lib}-{testname} {lib}-{testname} {testname} or the name is completely local to/internal in a library and library maintainers are free to name as they desire? I could not find anything in the development guidelines and the testing policy docs. Best regards, -- Mateusz Loskot, http://mateusz.loskot.net p.s. Originally posted to boost-testing incorrectly https://lists.boost.org/boost-testing/2018/09/8446.php

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[system] A non-allocating message() overload
by Peter Dimov 20 Sep '18

20 Sep '18

One of the objections against <system_error> is that message() needs to allocate memory, because it returns an std::string. This is true even for user-defined categories that can implement it without allocating, with a static message table. To address this, I'm thinking of adding the following overload to boost::system::error_category (with the intent of proposing it for std::error_category): virtual char const* message( int ev, char* buffer, size_t len ) noexcept; This is modeled after the glibc-specific version of strerror_r (and in fact has the exact same signature and behavior). If the implementation has a static character literal corresponding to `ev`, it returns it directly. If not, it composes an error message into the provided buffer, then returns `buffer`. Comments?

3 7

HoF Problems with Boost 1.68 / LLVM-Clang / Windows
by Adam Hartshorne 20 Sep '18

20 Sep '18

The following two bits of code compile ok with MSVC, but using LLVM/Clang produces the following errors. Using the code in print.cpp BOOST_HOF_STATIC_FUNCTION(simple_print) = fix(first_of( BOOST_HOF_LIFT(print_with_cout), BOOST_HOF_LIFT(print_with_range), BOOST_HOF_LIFT(print_with_tuple) )); produces the following error 1>./boost_hof_functions.h(45): error : templates cannot be declared inside of a local class 1>C:\boost_1_68_0\boost/hof/lift.hpp(90): note: expanded from macro 'BOOST_HOF_LIFT' 1>C:\boost_1_68_0\boost/hof/lift.hpp(105): note: expanded from macro 'BOOST_HOF_LIFT_CLASS' And BOOST_HOF_STATIC_LAMBDA_FUNCTION(print) = boost::hof::proj(simple_print); produces >./boost_hof_functions.h(51): error : non-const lvalue reference to type 'reveal_adaptor<...>' cannot bind to a temporary of type 'reveal_adaptor<...>' 1>C:\boost_1_68_0\boost/hof/lambda.hpp(241): note: expanded from macro 'BOOST_HOF_STATIC_LAMBDA_FUNCTION'] There are nearly identical errors with functions from in.cpp.

2 1

"is-assignable" compile error using Boost 1.68 / LLVM-Clang / Windows
by Adam Hartshorne 20 Sep '18

20 Sep '18

I receive the following build error when switching to LLVM toolset in VS2017 to build code using Boost 1.68. The code builds fine with MSVC compiler. 1>C:\boost_1_68_0\boost/type_traits/has_trivial_move_assign.hpp(49): error : no template named 'is_assignable'; did you mean 'std::is_assignable'? 1>C:\boost_1_68_0\boost/type_traits/intrinsics.hpp(233): note: expanded from macro 'BOOST_HAS_TRIVIAL_MOVE_ASSIGN'

4 6

Unexpected behavior in reverse lookup (asio resolver)
by LC 19 Sep '18

19 Sep '18

When performing a reverse lookup of an address: *r->async_resolve( boost::asio::ip::tcp::resolver::endpoint_type( adr, 80 ) ...* the address itself is returned (as string), when the name of the host cannot be found. I would expect an error/exception, telling me this instead. Consider the following (custom class which does both): *Resolver::resolve< ResolverClass >( &rc, "www.yahoo.com", 1 ); Resolver::resolve< ResolverClass >( &rc, "8.8.8.8", 2 ); Resolver::resolve< ResolverClass >( &rc, "none.exist.end", 3 ); Resolver::resolve< ResolverClass >( &rc, "2.18.77.109", 4 ); Resolver::resolve< ResolverClass >( &rc, "198.252.206.16", 5 ); Resolver::resolve< ResolverClass >( &rc, "234.255.173.123", 6 );* And the result: *1: hostname: www.yahoo.com, address: 87.248.98.7, error: 1: hostname: www.yahoo.com, address: 87.248.98.8, error: 2: hostname: google-public-dns-a.google.com, address: 8.8.8.8, error: 3: hostname: , address: 0.0.0.0, error: Host not found (authoritative) 4: hostname: a2-18-77-109.deploy.static.akamaitechnologies.com, address: 2.18.77.109, error: 5: hostname: stackoverflow.com, address: 198.252.206.16, error: 6: hostname: 234.255.173.123, address: 234.255.173.123, error:* 2 is looking up of "8.8.8.8", which of course can be found and returns the google.com entry. Likewise, 4 and 5 can be found and return the correct result. *Nr. 6, however, is a non-existent ip-address. As you can see, instead of an error, the address itself is returned when calling "endpoint_iterator->host_name();".* This is unexpected and (I think) undocumented. It can be easily detected by testing if host_name returns an address, but this would require another (test) conversion; as a result you'd end up with forth&back conversions. Wouldn't it be better, if the reverse lookup returned an error/exception, if the name of the host cannot be found? This would be more consistent with the "Host not found (authoritative)" error in example 3. -- Sent from: http://boost.2283326.n4.nabble.com/Boost-Dev-f2600599.html

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[cmake] Pull request announcement
by Mike Dev 18 Sep '18

18 Sep '18

Dear all, unless I'm encountering an overwhelming resistance to this idea here on the ml, I intend to create a batch of PRs that introduce minimal cmake support to a large subset of boost libraries (maybe even all). It appears that cmake efforts have yet again stalled. Last I heard was that everyone is waiting for BCM and the author of that library still tries to find a review manager. As we probably can't expect a full-fledged, boost-wide solution in the near future I'm trying it with a low-effort approach that will establish the minimal framework needed such that each library can be (where necessary) build with cmake and specify it's dependencies on other libraries (the latter being the really important part). >From that starting point a more holistic solution can then be developed step by step and (in most cases) library by library. The only fundamental thing that needs to be decided by the community is a canonical naming scheme for the cmake targets that should be used by other libraries in their `target_link_libraries` call. For that I suggest that each library should provide an alias target called Boost::<library_name> (e.g. Boost::program_options) This also follows the naming scheme provided by cmake itself when using boost libraries that are installed on the system. Now about what I'm specifically going to put into the PRs: - I'll propose a trivial, top-level cmake file be added to the boost super project that doesn't do anything but look for CMakeLists.txt files in the root folder of each library and calls that file if present - Individual libraries get a simple CMakeLists.txt file that will - create an appropriate build target - INTERFACE library for header-only - STATIC for regular libraries - create an alias named Boost::<library_name> - build the library if necessary - specifying the minimum required c++ version - specify the local include directory (iirc that will always be "include") - specify all required dependencies This will not address - Testing - Installation - Creation of shared libraries - Creation of documentation - Special provisions for IDE integration In short: all the difficult stuff is left out ;) The goal is not to present a solution that can replace b2 but to have a minimal starting point upon which individual library authors or the community as a whole can make iterative improvements. If and when BCM (or an alternative) is accepted into boost, individual libraries can then easily switch to this full-fledged solution and of course any author can create a more complete CMake solution for his library at any time (as some already have). Finally, please don't nick-pick this to death. I'd like to have a more complete solution too, but it isn't coming, so let's do the minimum we can and go on from there. Note that the advantage of such a minimal solution is also that there are very few design decisions to make that may later turn out to be wrong and then create a maintenance burden. The only things that are visible on an interface level (and thus should remain reasonable stable) are: - The alias name Boost::<library_name> - How the public dependencies are specified: target_link_libraries( boost_ foo PUBLIC Boost::config Boost::core Boost::bar ) - The position of the CMakeLists.txt file in the library root folder All of this is long established best practice. Anything else can gradually be built on top of that. Best Michael

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[config] does BOOST_ATTRIBUTE_UNUSED defined implies __attribute__((used)) exists ?
by Raffi Enficiaud 17 Sep '18

17 Sep '18

Hi, I have a problem with symbol visibility in boost.test: https://github.com/boostorg/boost/pull/190 I am wondering if __attribute__((used)) is a portable way to flag a static const ref as being used, or there are variations (__attribute__((used)) vs __attribute__((__used__))). I am also wondering if __attribute__((used)) can be considered as available if BOOST_ATTRIBUTE_UNUSED is defined. Would it make sense to have an BOOST_ATTRIBUTE_USED in boost.config? Thanks, Raffi

2 1

[system] Do you use the deprecated features or cygwin/linux/windows_error.hpp?
by Peter Dimov 17 Sep '18

17 Sep '18

I'd like to query the Boost community as to whether certain legacy features of Boost.System are in use; namely, (1) everything guarded by BOOST_SYSTEM_ENABLE_DEPRECATED and (2) the cygwin_error.hpp, linux_error.hpp, or windows_error.hpp headers. Does anyone use these, and for what purpose? I'm thinking of dropping the deprecated features. In addition, does anyone use boost::throws()? I'm thinking of at least discouraging its use in the documentation, if not deprecating it outright.

2 1

CMake and the Boost Steering Committee
by Edward Diener 16 Sep '18

16 Sep '18

I think it is a huge waste of time for anyone to discuss or implement a CMake solution for Boost until the Boost Steering Committee actually gets involves and defines what "Boost using CMake" actually means and gives the specifics as to what this actually entails. Otherwise nearly everything said about Boost and CMake, although well-intentioned, is just a lot of hot air and we are going absolutely nowhere trying to make any progress in this so-called direction. The Boost Steering Committee is largely at fault for saying that Boost would be using CMake, without defining what this actually means. Once again, as in our discussion about Boost dropping support for C++03, we are all wasting our time because the meaning of some language having been used is not clear and way too general to reach any meaningful conclusions. But in this case the only people who can really define what Boost using CMake actually means is the Boost Steering Committee, or someone representing the Boost Steering Committee on this mailing list, who can clarify what Boost using CMake is actually about, since it was the Boost Steering Committee who made the decision in the first place. If it is not the case that the Boost Steering Committee defines what Boost using CMake actually is supposed to mean but rather it is up to those on this mailing list to decide the issue, I would argue that Boost should focus on the simplest solution first, making Boost libraries, whether header-only or not, available for use in end-user CMake scripts in such a way that it will be easy to add this functionality for the 130 or so individual Boost libraries with the least amount of effort or work involved for each library, without arguing unduly about more complicated or more purist solutions. In other words lets start with the easiest, most practical solution, because I assure you when the smoke has cleared, 99% of those people involved in the discussion will not want to do the practical work of actual adding necessary CMake scripts to any of the 130 or so libraries involved, and even the maintainers of those libraries will not want to spend much time implementing some complicated CMake solution for their library. But I still think that without a specific definition of what Boost using CMake actually entails from the steering committee we are just wasting time and breath and to no good purpose.

1 0

How do I test more configurations locally
by Joshua Marshall 14 Sep '18

14 Sep '18

Hello all, How do I test more configurations on my local systems rather than relying on TravisCI and AppVeyor? I've been working on fixing up BGL to pass basic TravisCI and AppVeyor tests, but it seems I have to be particularly reliant on those online tests. I'd like to have more of that done on my local system. There is probably a way to do that, but I don't know what it is.

3 3

REMINDER: Formal Review of Histogram by Hans Dembinski
by Mateusz Loskot 14 Sep '18

14 Sep '18

Dear All, (NOTE: This is not start the review announcement yet) I'd just like to *remind* you all that the review of the Histogram library developed by Hans Dembinski is going to happen according to the schedule [1], from September 17, 2018 to Septenber 26, 2018. I will be sending the official START announcement this weekend. [1] https://www.boost.org/community/review_schedule.html Best regards, -- Mateusz Loskot, http://mateusz.loskot.net

1 0

[outcome] Change semantics on UB from peer review agreed semantics?
by Niall Douglas 14 Sep '18

14 Sep '18

Dear Boost, At https://github.com/ned14/outcome/issues/150, Andrzej has raised his desire to change Outcome's semantics on UB from what the two peer reviews here agreed to previously. As this would be a major change to interface different to what the consensus here agreed to, I am asking boost-dev to weigh in with its opinion. Status: ------- Outcome has been finished, apart from docs, since April (http://boost.2283326.n4.nabble.com/outcome-v2-1-progress-report-td4702900.h…) for the Boost and standalone variants, and since July for the experimental P1028 edition. The documentation has not been touched since the February review, but will be tackled when my current work contract ends this November, and I regain free time. Preamble: --------- Outcome has the notion of programmable "default actions" which occur when the user does something like call `.value()` on a `result<T, E>` which has an error. Let's call this "value-on-valueless". Outcome, as was approved here, has the following selector on `result<T, E>` in the Boost edition: ``` template <class T, class EC, class E> using default_policy = std::conditional_t< std::is_void<EC>::value && std::is_void<E>::value, terminate, std::conditional_t< trait::has_error_code_v<EC>, error_code_throw_as_system_error<T, EC, E>, std::conditional_t< trait::has_exception_ptr_v<EC> || trait::has_exception_ptr_v<E>, exception_ptr_rethrow<T, EC, E>, all_narrow >>>; template <class R, class S = boost::system::error_code, class NoValuePolicy = policy::default_policy<R, S, void>> using boost_result = basic_result<R, S, NoValuePolicy>; template <class R, class S = boost::system::error_code, class NoValuePolicy = policy::default_policy<R, S, void>> using result = boost_result<R, S, NoValuePolicy>; ``` So, if result's `E` is: - `void`, value-on-valueless calls `std::terminate()`. - contains an error code, value-on-valueless throws `system_error()`. - otherwise is hard undefined behaviour i.e. we tell the compiler that value-on-valueless will never happen, and the compiler doesn't even compile code for it to happen. The documentation, as was approved here, made it very clear that hard UB is the default for custom defined `E` types. See https://ned14.github.io/outcome/tutorial/default-actions/happens1/. A nice segfault usually emerges. For the standalone edition, judging from user feedback and bug reports, this hard UB behaviour is the most common intentional configuration for Outcome users. I have not received any complaints about this choice, if anything a majority has been choosing Outcome precisely *because* of this choice. Andrzej's request ----------------- Andrzej points out in https://github.com/ned14/outcome/issues/150 that it's too easy to get surprised by a small source change which causes the error code trait to no longer match the `E` type, thus flipping the code base from throwing `system_error` into hard UB unexpectedly and without warning. He wishes to change the default to failure to compile i.e. if result's `E` is: - `void`, value-on-valueless calls `std::terminate()`. - contains an error code, value-on-valueless throws `system_error()`. - otherwise a failure to compile with useful diagnostic. Users can, of course, manually specify a `NoValuePolicy` of `all_narrow` if they wish hard UB on value-on-valueless. It would be a non-trivial change from what peer review (twice) agreed, as the default would have substantially changed. What is boost-dev's opinion on this proposed change in semantics? Thanks, Niall

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list.boost.org
by David Bellot 09 Sep '18

09 Sep '18

Hi, I'm looking for the person in charge of lists.boost.org, the mailing list server. We're having an issue on one of the mailing list (ublas). Cheers, David

3 2

[ublas] How to merge a PR?
by Frédéric 09 Sep '18

09 Sep '18

Hi, I submitted a PR 1 month ago. Something rather trivial. How can it be merge? https://github.com/boostorg/ublas/pull/56 Thanks, F

2 1

Re: [boost] list.boost.org
by Bjorn Reese 09 Sep '18

09 Sep '18

On 09/09/18 00:13, David Bellot via Boost wrote: > I'm looking for the person in charge of lists.boost.org, the mailing list > server. We're having an issue on one of the mailing list (ublas). https://lists.boost.org/Archives/boost/2017/02/232710.php

1 0

[all] Request for out of the box visibility support
by Antony Polukhin 09 Sep '18

09 Sep '18

I'd like to draw attention to a problem with Boost binaries for Linux. There's an awesome -fvisibility=hidden flag for Linux compilers that improves load times, performance, size of binaries and reduces the chance of symbol collisions. More info at https://gcc.gnu.org/wiki/Visibility . Unfortunately, most of the Boost libraries do not set it by default: - atomic - chrono - container - context - contract - coroutine - date_time - exception - fiber - filesystem - graph - graph_parallel - iostreams - locale - mpi - program_options - python - random - regex - signals - system - test - thread - timer - type_erasure - wave Moreover minority of the above libraries just do not work with the flag. Users just can not run ./b2 cxxflags="-fvisibility=hidden" because there's a chance that some library could stop linking. Actually things are even more ugly. Linux distributions usually do not tune the build flags for each package so at least Debian based distributions build Boost with default flags. Users get suboptimal builds. If you're a maintainer of one of the above libraries *please do* the following steps: * Make sure that all the public symbols are accordingly marked with appropriate BOOST_SYMBOL_* macro. Instruction is available here: https://www.boost.org/doc/libs/1_68_0/libs/config/doc/html/boost_config/boo… * Turn on the visibility=hidden by default: * by adding <target-os>linux:<cxxflags>"-fvisibility=hidden" to the Jamfile if you do not care much for antique compilers (Example https://github.com/boostorg/stacktrace/blob/819f2b1c861dec7530372a990ecabab… ) * by using a more advanced technique for detecting the flag availability (For example see https://github.com/boostorg/math/blob/develop/build/Jamfile.v2#L20 or https://github.com/boostorg/log/blob/develop/build/Jamfile.v2#L24 ) P.S.: I would appreciate any comments or updates on the feature request. P.P.S.: Log, Math, Serialization (and Stacktrace) libraries already use that flag by default. Many thanks! -- Best regards, Antony Polukhin

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[range] #11202: boost.sort header conflicts with boost.range header
by Steven Ross 07 Sep '18

07 Sep '18

https://svn.boost.org/trac10/ticket/11202 has been sitting for years. The "using range::sort" causing the namespace pollution needs to be deleted, and then everything depending on that inside boost needs to be fixed. This will break people dependent on the namespace pollution, but that's the only way to clean it up. Is anyone willing to take on this cleanup? Is there a good way to identify cross-library dependency breakages in situations like this so they can be fixed?

10 20