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Suggested policy for dropping C++03 support in Boost libraries
by Peter Dimov 26 Nov '19

26 Nov '19

We need a policy on phasing out C++03 support in Boost. C++03 support is holding us back. It impedes development, increases maintenance costs, increases dependencies, and increases compilation times. Library authors and maintainers need to have an approved mechanism for dropping C++03 support in their libraries. The suggested way forward is to allow library authors to declare C++03 support deprecated via a notice in the documentation and a message issued at compile time, then be allowed to drop C++03 support no earlier than three Boost releases later. For instance, a library may declare C++03 support deprecated in Boost 1.73, and drop it no earlier than in Boost 1.76. More at https://pdimov.github.io/articles/phasing_out_cxx03.html.

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Beginner's guide
by Siddhartha Sen 26 Nov '19

26 Nov '19

Could anyone help me get started? This is my first time contributing to open source. I am proficient with C++11 and C++14(Not so much with 17 though). Also, I am not sure whether this is useful or not but I have a very keen interest in algorithms and problem solving techniques in general. Any help would be appreciated.

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Re: [boost] [Boost-users] Interest in a C++20 Unit Testing Framework?
by Krzysztof Jusiak 25 Nov '19

25 Nov '19

Thanks for your valuable feedback. I added initial versions of tutorial and user-guide to README. It's not ideal yet but it's a start. * https://github.com/boost-experimental/ut#tutorial * https://github.com/boost-experimental/ut#user-guide I also updated benchmarks with Boost.Test-1.71.0 (static library). I didn't add Boost.LightweightTest though as it's just assertions (no tests/suites/etc...) so it makes it difficult to compare due to missing features. * https://github.com/boost-experimental/ut#benchmarks I hope that helps a bit. Thanks again, Kris On Fri, Nov 22, 2019 at 1:17 AM Richard Hodges via Boost-users < boost-users(a)lists.boost.org> wrote: > It looks very interesting. The idea of not using macros is very appealing > to me. > > From looking at the examples, I get the feeling of "I could probably use > this". > > However, as the other commenters have mentioned, without a tutorial and > full reference it's difficult to judge whether it's ready for use in > production. > > Are there plans to develop this? > > > > > On Thu, 21 Nov 2019 at 16:24, Krzysztof Jusiak via Boost-users < > boost-users(a)lists.boost.org> wrote: > >> Hi, >> >> I was wondering whether there is any interest in exploring a C++20 single >> header/single module, macro-free Unit Testing Framework with no >> dependencies? >> >> Github: https://github.com/boost-experimental/ut >> >> Additional links: >> - Try it online: https://godbolt.org/z/uVDxkW >> - Benchmarks: https://github.com/boost-experimental/ut#benchmarks >> - How it works?: https://github.com/boost-experimental/ut#how-it-works >> >> Thanks, Kris >> _______________________________________________ >> Boost-users mailing list >> Boost-users(a)lists.boost.org >> https://lists.boost.org/mailman/listinfo.cgi/boost-users >> > > > -- > Richard Hodges > hodges.r(a)gmail.com > office: +442032898513 > home: +376841522 > mobile: +376380212 > > _______________________________________________ > Boost-users mailing list > Boost-users(a)lists.boost.org > https://lists.boost.org/mailman/listinfo.cgi/boost-users >

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[review] [STLInterfaces] STLInterfaces review starts December 10
by Barrett Adair 23 Nov '19

23 Nov '19

The Boost formal review of Zach Laine's STLInterfaces library will take place December 10 - 19, 2019. Please consider participating in this review. The success of Boost depends on our robust library review process. STLInterfaces is a C++14 library targeting ISO standardization. The following templates are provided, all C++20-friendly: 1. iterator_interface - a modern version of the iterator_facade and iterator_adaptor parts of Boost.Iterator 2. view_interface - a pre-C++20 implementation of C++20's eponymous feature 3. container_interface - a tool to eliminate boilerplate when writing new containers. Code: https://github.com/tzlaine/stl_interfaces Docs: https://tzlaine.github.io/stl_interfaces/doc/html/index.html Thanks, Barrett Adair

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icl
by Andreas Fislage 22 Nov '19

22 Nov '19

Hello all, I am new here... I recently used icl and ran into a rather surprising behavior: Assertion failed: (numeric_minimum<domain_type, domain_compare, is_numeric<domain_type>::value> ::is_less_than_or(upper(object), is_right_closed(object.bounds())) ), file ...\boost\icl\concept\interval.hpp, line 438 This is the code to produce the problem: #include <boost/icl/discrete_interval.hpp> int main() { boost::icl::discrete_interval<size_t> x{0, 0}; boost::icl::discrete_interval<size_t> y{0, 1}; boost::icl::contains(x, y); } Note that the assertion fails only with size_t not with int. What could be reason for this?

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Boost serialization (bug?) issue with MSVC, with vector<shared_ptr> in several libraries
by Nicolas Guillot 22 Nov '19

22 Nov '19

We use boost serialization in ours projects, both on linux (gcc) and Windows. We encounter a problem only on Windows (for "every" versions of Windows (7 and 10) and of MSVC: Visual 2010 and 2015, ie. MSVC++ 10.0 _MSC_VER == 1600 or MSVC++ 14.0 _MSC_VER == 1900). *Here is the problem summarized*, but I need to give more details after: When I serialize a class - which have base class - and have 2 vector of shared_ptr of ClassB, with the same contents, and B inherits from the same base class the serialization works, but the deserialization doesn't ("input stream error"). The following image is here : https://i.stack.imgur.com/osoiF.png (if it's not displayed) [image: enter image description here] <https://i.stack.imgur.com/osoiF.png> Yes, it's very strange: - if I remove the base class, it works. - if I inline the serialization code (empty function) of the base class, it works. - if the 2 vectors don't have the same content, it works !! - if I register the ClassBase in the serialize method of ClassTest, it works. I.e.: // in ClassTest:template <class Archive>void serialize(Archive & ar, const unsigned int version) { ar.template register_type<ClassBase>(); ...} *Some details* *When it works* on linux, and when it works on Windows with ClassBase type registration in the archive, we have the same xml output. It's worth noting that: - boost_serialization is version 17 on Windows and 9 on linux (I didn't tried to update boost on linux yet). - On BaseClass xml tag, the tracking_level="1", so we have object_id. *And when it doesn't work* (once again: the serialization of ClassTest is OK, but cannot deserialized "input stream error"): - The main difference is in the serialization of ClassTest: the ClassBase part has no tracking_level. - However it's not the only cause, because if the vectors are differents (same 2 first items, and a third item in one vector), tracking_level of ClassBase in ClassTest part is "0". Last thing, if it can give you some clues: while we debugged our application, we noticed that the deserialization framework tries to deserialize a class into another. It makes me think the serialization framework is confused about the classe types identifications. Could it be a matter of dll linking? Of global static shared storage ? I've posted a visual studio solution here <https://1drv.ms/u/s!Aoy4ax0S3ZS5gkxv1UIvRUd32oVO?e=ACVi4c>. Thanks a lot for your help. And if any clarification is needed, I'm available of course !

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[xpressive] Accept one line pull that's been outstanding for a couple years?
by Brian Kuhl 21 Nov '19

21 Nov '19

Hi Boost, We've been running nightly regression on this for years now at Wind River over a couple Boost releases. Any reason it can't be merged? https://github.com/boostorg/xpressive/pull/5 Thanks Brian

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Re: [boost] Jason is getting MARRIED!
by julien.blanc＠tgcm.eu 21 Nov '19

21 Nov '19

"Vinnie Falco" vinnie.falco(a)gmail.com – 21 novembre 2019 15:29 > Yep, the bench program and input files are here: thanks. I'll try to compile it for raspberry pi and report the results here. > > A 200MB file would be a good start to see how the library deals with large files. > > I don't have a 200MB JSON file, and I have doubts that it would > provide much more information than what we have already. I'd also > prefer not to put a 200MB file into the repository. The goal of this > library is to be in the same ballpark as rapidjson, it doesn't try to > be the top performer (in fact, rapidjson achieves its performance by > making usability tradeoffs which are unsuited for vocabulary types). > > However if someone wants to run the bench program on a 200MB file or > any other custom inputs and report the results, that would be great! Just made the test, and the validator performs well (memory consumption is about the size of the file, which i is expected since the whole file is read in memory), while the printer memory usage was huge (i had to stop it, but it was at that time already eating more than 1Gbyte memory, which is not expected). Regards, Julien

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istream_iterator_limited
by Frederick Gotham 21 Nov '19

21 Nov '19

[MODERATOR: I tried to post this a week ago, but for some reason the word SPAM was prefixed to the subject line and so it didn't show up on the GMane server. I don't think many people actually saw it.] - - - - WHY I NEEDED THIS: I wanted to open a file using "ifstream", and then I wanted to read 32 bytes from the file and feed them directly into boost::algorithm::hex. Unfortunately I couldn't do this because 'hex' takes two iterators [begin,end), and there's no alternative function "hex_n". So I had to read the file into a string first, and then pass the string to 'hex'. - - - - THE IDEA I CAME UP WITH: Open the file using "ifstream", and then use a special iterator that will stop reading from the file after 32 bytes, with syntax like this: ifstream logfile("log.txt"); hex( istream_iterator_limited<char>(logfile,32), istream_iterator_limited<char>(), g_some_global_container.begin() ); - - - - SAMPLE CODE: #include <cstddef> /* size_t */ #include <iterator> /* istream_iterator */ template <typename T> class istream_iterator_limited : public std::istream_iterator<T> { protected: std::size_t const m_limit; std::size_t m_current_count; public: /* Shorter names */ typedef std::istream_iterator<T> Base; typedef istream_iterator_limited<T> This; istream_iterator_limited(typename Base::istream_type &obj_stream, size_t const arg_limit) : Base(obj_stream), m_limit(arg_limit), m_current_count (1) { /* The initialiser list above does all the construction work */ } istream_iterator_limited(void) /* This gives the End-Of-Stream iterator */ : Base() , m_limit(0), m_current_count(1) { /* The initialiser list above does all the construction work */ } This &operator++(void) { if ( m_limit <= m_current_count ) { Base::operator=( Base() ); /* Becomes End-Of- Stream iterator */ } else { ++m_current_count; Base::operator++(); } return *this; } }; #include <algorithm> /* copy */ #include <string> /* string */ #include <sstream> /* istringstream */ #include <iostream> /* cout, endl */ #include <iterator> /* back_inserter */ auto main(void) -> int { std::istringstream iss("123456789"); std::string str; /* Let's use copy to read 5 char's into our string */ std::copy( istream_iterator_limited<char>(iss,5), istream_iterator_limited<char>(), std::back_inserter(str) ); std::cout << str << std::endl; str.clear(); /* Get another 3 */ std::copy( istream_iterator_limited<char>(iss,3), istream_iterator_limited<char>(), std::back_inserter(str) ); std::cout << str << std::endl; }

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[release] Boost 1.72.0 Beta 1
by Michael Caisse 21 Nov '19

21 Nov '19

Boost release 1.72.0 beta 1 is now available at: <https://dl.bintray.com/boostorg/beta/1.72.0.beta.1/source/> The SHA256 checksums are as follows: 5a6b5cbd27b8ca0c7741b715e022a3bf05aecbb1e73dc72dd82eef9622374bd5 boost_1_72_0_b1.7z 6c85a7aed198757f5e4be66a971ae90a25c4ce32703fecfb5bb19019bd80947c boost_1_72_0_b1.tar.bz2 be4a3fdaa84d5a8b25863651043308e02645f3fbf772b7623ee6462fb1dbad09 boost_1_72_0_b1.tar.gz 95181a5f3de0078b8fc031f63a4dc8be4d70b7d3d5cde3b266d2cd98bd4b61b0 boost_1_72_0_b1.zip For details of what's in the release, see <https://www.boost.org/users/history/version_1_72_0.html>. Please download the beta, give it a try, and report any problems you encounter. Thanks, -- The Boost Release Team

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[release] Boost 1.72.0 Beta 1 Release Candidate 2
by Marshall Clow 21 Nov '19

21 Nov '19

Boost release 1.72.0 beta 1 rc2 is now available at: <https://dl.bintray.com/boostorg/beta/1.72.0.beta.1.rc2/source/> The release notes are not yet available. The updated documentation is not yet available. [ They will be available in a day or two. ] The SHA256 checksums are as follows: 5a6b5cbd27b8ca0c7741b715e022a3bf05aecbb1e73dc72dd82eef9622374bd5 ./boost_1_72_0_b1_rc2.7z 6c85a7aed198757f5e4be66a971ae90a25c4ce32703fecfb5bb19019bd80947c ./boost_1_72_0_b1_rc2.tar.bz2 be4a3fdaa84d5a8b25863651043308e02645f3fbf772b7623ee6462fb1dbad09 ./boost_1_72_0_b1_rc2.tar.gz 95181a5f3de0078b8fc031f63a4dc8be4d70b7d3d5cde3b266d2cd98bd4b61b0 ./boost_1_72_0_b1_rc2.zip Changes since RC1: * Fix Boost.IOStreams to allow compilation on Mac OS w/LZMA support. Please download the beta release candidate, give it a try, and report any problems you encounter. Thanks, -- The Boost Release Team

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[release] Boost 1.72.0 Beta 1 Release Candidate 1
by Michael Caisse 18 Nov '19

18 Nov '19

Boost release 1.72.0 beta 1 rc1 is now available at: <https://dl.bintray.com/boostorg/beta/1.72.0.beta.1.rc1/source/> The release notes are not yet available. The updated documentation is not yet available. [ They will be available in a day or two. ] The SHA256 checksums are as follows: 3dd80fc3979c312bf892398c35778d821f6744a7fbf76c8248c85b4f3702e4d4 boost_1_72_0_b1_rc1.7z 676e476a2a1246c7c5e8f40230fa70469f29dfe8aaa5bce0a85f94692e605c68 boost_1_72_0_b1_rc1.tar.bz2 e62e5fdffe0772309c77fc9463a95350ebcabb2ce03f2c6ee177123016756044 boost_1_72_0_b1_rc1.tar.gz e3199f3f5046541570fffacd804d736e1999cfac05df6cc054ec97c8098d000d boost_1_72_0_b1_rc1.zip Please download the beta release candidate, give it a try, and report any problems you encounter. Thanks, -- The Boost Release Team

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回复：Re: [release] Boost 1.72.0 Beta 1 Release Candidate 1
by ckgppl_yan＠sina.cn 18 Nov '19

18 Nov '19

I can compile this release in my macOS catalina, 10.15.1. I don't have lama installed in my OS, so I didn't have the issue below.only some warnings out. Thanks Liang----- 原始邮件 ----- 发件人：Marshall Clow via Boost <boost(a)lists.boost.org> 收件人：turkanis(a)coderage.com, Michael Caisse <mcaisse-lists(a)ciere.com> 抄送人：Marshall Clow <mclow.lists(a)gmail.com>, "boost(a)lists.boost.org List" <boost(a)lists.boost.org> 主题：Re: [boost] [release] Boost 1.72.0 Beta 1 Release Candidate 1 日期：2019年11月19日 04点38分 This appears to be https://github.com/boostorg/iostreams/issues/102, and https://github.com/boostorg/iostreams/pull/103 is a suggested fix. -- Marshall On Mon, Nov 18, 2019 at 11:56 AM Marshall Clow <mclow.lists(a)gmail.com> wrote: > On my Mac, I the version of LZMA that I have installed (via homebrew) does > not have the multi-tasking calls (_lzma_cputhreads and > _lzma_stream_encoder_mt). > It identifies itself: > > $ cat junk.cpp > #include <iostream> > #include "lzma.h" > > int main() { > std::cout << LZMA_VERSION << std::endl; > } > > $ clang++ junk.cpp && ./a.out > 50020042 > $ > > Changing libs/iostreams/src/lzma.cpp thus solves enables things to build: > > #ifndef BOOST_IOSTREAMS_LZMA_NO_MULTITHREADED > - #if LZMA_VERSION < 50020002 > + #if LZMA_VERSION <= 50020042 > #define BOOST_IOSTREAMS_LZMA_NO_MULTITHREADED > #endif > #endif > > -- Marshall > _______________________________________________ Unsubscribe & other changes: http://lists.boost.org/mailman/listinfo.cgi/boost

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Required C++ version in meta/libraries.json
by Mateusz Loskot 18 Nov '19

18 Nov '19

Hi, How can I specify required version of the standard in the library meta info? Where is documentation of libraries.json schema? I've learned that "std":"C++17", for example, in Boost.Any states which standard adopted the library. That is not what I'm after. -- Mateusz Loskot, mateusz(a)loskot.net (Sent from mobile, may suffer from top-posting)

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Jason is getting MARRIED!
by Vinnie Falco 18 Nov '19

18 Nov '19

My JSON library is going to propose to Boost soon, is there anyone who might be willing and able to function in the role of review manager? Thanks!

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pulling the plug on Boost Library Incubator
by Robert Ramey 17 Nov '19

17 Nov '19

I've been maintaining the Boost Library Incubator (www.blincubator.com) for some years now. Maintaining is sort of mis-nomer since it not required any change for years now. I never, ever touch it. I was painful to get to that point though. My motivation is the continuing evolution of github which I believe has come to embody almost of the goals I've had for the inclubator. I would like a couple of tweaks to git hub - or maybe just some changes in our usage of it. For example I'd like to see us proliferate the tags #Boost and #ProposedForBoost to help us search stuff but basically I believe that it has made boost library incubator obsolete. So I'm inclined to terminate it when the domain comes up for renewal the next time. Currently it has about 200 page views / day. I don't really know how much of that a bots/rss feeds and the like. I do you a service which detects and filters out almost all the obvious bogus hits, but still one never knows. BTW - the tipping point for me is the addition of "sponsership" to github. This looks to be the realization of an idea which I've promoted for many years in one for or another. I would like to successful open source project developers and maintainers get rewarded financially rewarded for their efforts and I see that git hub promoters seem to share this view - and they're in a position to move it toward reality. When I can't sleep at night, I imagine that microsoft looked at the incubator and copied features from it into the git hub. Feels like I'm dreaming so I don't feel like I'm awake anymore. Robert Ramey

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Re: [boost] Jason is getting MARRIED!
by Peter Dimov 17 Nov '19

17 Nov '19

> or even `{ "size": 3, "data": [ 1, 2 ] }`. Er, "size": 2 obviously. :-)

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Fwd: Markdown to Quickbook
by Mateusz Loskot 15 Nov '19

15 Nov '19

As boost-docs may not be as popular among subscribers as the development list, I'm bumping my chances for solution... ---------- Forwarded message --------- From: Mateusz Loskot <mateusz(a)loskot.net> Date: Mon, 11 Nov 2019 at 21:25 Subject: Markdown to Quickbook To: <boost-docs(a)lists.boost.org> Hi, Is there an established known method for converting a Markdown document to Quickbook dokument? Best regards, Mateusz Loskot, mateusz(a)loskot.net (Sent from mobile, may suffer from top-posting) -- Mateusz Loskot, http://mateusz.loskot.net

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Removing old branches
by Edward Diener 15 Nov '19

15 Nov '19

I received an issue about Boost PP having lots of old branches which the issuer would like removed. I notice most other Boost libraries also have lots of old branches. Is there any policy about removing these old branches from a Boost library repository ? Many of these old branches are svn-branches, but most of them do not have any value any more and, of course, do not affect the current 'develop' or 'master' branch.

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[preprocessor] Testing C++ standard macro examples
by Edward Diener 14 Nov '19

14 Nov '19

I have added to the 'develop' branch of Boost PP an 'explicit' test with the alias of 'test_iso' in the 'test' subdirectory. This test, depending on the compiler toolset and C++ standard setting used, will test a compiler's ability to expand correctly the macros listed in a C++ standard document's "Macro Replacement" section for C++ standards 2003, 2001, 2014, 2017, and 2020 ( N4835 ). The test uses the __cplusplus setting and the Boost PP BOOST_PP_VARIADICS setting to determine which C++ standard's set of macros to test. This is because the __cplusplus setting alone is misleading for a number of compilers, most notably vc++ and compilers who mimic vc++, who do not set the correct __cplusplus setting for the C++ standard level being used. There are really only three sets of macros from the C++ standard documents which can potentially be tested, despite five different standards being considered. This is because the set of macros to be tested for C++11, C++14, and C++17 are exactly the same. Some compilers do allow C++20 support but do not implement the full __VA_OPT__ support yet, so these compilers will fail the C++20 macro tests with compiler errors. Among these are gcc and vc++, who both document that they do not yet support the stringizing operator with the __VA_OPT__ parameter. Clang also supports C++20 and will run the test and succeed in that mode. You can of course test any compiler at any C++ level and view the results. These tests, unlike Boost PP, do not have any workarounds for any compilers. So the tests form a really good basis for reporting macro expansion preprocessor bugs to various compiler implementations. In the 'test' subdirectory of Boost PP you should be able to run: b2 toolset=atoolset cxxstd=astandard( optional ) test_iso to get the results for any compiler. Any failed results will show the test output, where the original expression, the expanded expression, and for individual failed tests the expected expanded expression will be shown. The actual macros being used are in the appropriate C++ Standard documents or can be seen in the test program which is called cpp_standard.cpp in the same 'test' subdirectory. After the upcoming release I will push this to the 'master' branch. Please note that the test is an 'explicit' test so it is not normally run when you just run the tests for Boost PP.

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fixed_string: Request for review
by Krystian Stasiowski 13 Nov '19

13 Nov '19

Hi all, My name Is Krystian Stasiowski. I'm currently attending college as a Computer Science major, am active on the C++ Language Slack, and starting to contribute to ISO C++. Vinnie offered for me to take the lead on submitting Boost.FixedString for a formal review, so here I am! Applicable links: Github: https://github.com/18 Repo: https://github.com/18/fixed_string Docs: https://18.github.io/doc/fixed_string

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Late fix for Boost PP
by Edward Diener 12 Nov '19

12 Nov '19

I had added support in the Boost PP library in C20 mode ( __cplusplus > 201703L ) for the __VA_OPT__ construct and enhanced an internal function used fairly extensively in the library to use this functionality in c20 mode when __VA_OPT__ was supported. I had tested this against the compilers which I knew could operate in c20 mode, gcc and clang, and all was well. I just discovered that the vc++ compiler can also work in c20 mode in Boost PP as defined above if you pass the '/std:c++latest' and the '/Zc:__cplusplus' command line switches and that vc++, in its usual non-standard way, blows up badly when doing so using the preprocessor library because it can not handle the rather simple code that checks for __VA_OPT__ support in c20 mode. I have a simple fix for this which is to turn off the __VA_OPT__ support and __VA_OPT__ support checking in c20 mode specifically for vc++ and removes which I have pushed to 'develop'. Can I push this fix to the 'master' branch now ? The fix needs to get in the coming release or else vc++ programmers specifying both the '/std:c++latest' and the '/Zc:__cplusplus' command line switched will not be able to use Boost PP and the many libraries which use Boost PP in the upcoming release. I apologize for the seeming aggressiveness of this change, which incorporated the c20 __VA_OPT__ support internally in some much-used Boost PP functionality when c20 mode is being used, but I did not anticipate that it would blow up on me, although maybe I should have. I can also remove that internal dependency with a very simple one-line change. I realize that Boost PP stability has to be maintained, even in c20 mode for the few compilers which support that mode and apologize again that I have endangered it there.

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Re: [boost] [Boost][Proposal] library for enhanced switch syntax.
by рустам абдумаликов 12 Nov '19

12 Nov '19

Phil Endecott wrote: > Specifically thinking about strings, there are numerous ways > that it could be done. Starting with > (1): the obvious sequence of if-else-if: > ... > (2): binary search using nested switches: > ... > (3) character-by-character comparison using nested switches: > ... > (4) converting to a 64-bit integer, for strings of up to 8 characters: > ... Firstly my implementation was never particularly about string in "switch" it is just one of the applications. Secondly, example 3-4 assume additional implementation( can take quite a time to do it right ), it isn't like you have it out of the box, this is exactly what my statement was about( example 1-2 don't count, they are non-scalable ). Lets rather consider something that is more complex: -- Example_1 "Parse file by extension": switch( hash_it( get_file_extention( file_name ) ) ) { case "cpp"HASH: case "cc"HASH: case "c++"HASH: case "cxx"HASH: case "C"HASH: { ... } break; case "hpp"HASH: case "hh"HASH: case "h++"HASH: case "hxx"HASH: case "H"HASH: { ... } break; } // OR // I think this way it is much readable eswitch( get_file_extention( file_name ) ) >> case_( any_from( "cpp", "cc", "c++", "cxx", "C" ) ) >> [&]{...} >> case_( any_from( "h", "hpp", "hh", "h++", "hxx", "H" ) ) >> [&]{...}; // OR // even this could be possible( but not yet implemented ) eswitch( get_file_extention( file_name ) ) >> case_( "cpp", "cc", "c++", "cxx", "C" ) >> [&]{...} >> case_( "h", "hpp", "hh", "h++", "hxx", "H" ) >> [&]{...}; -- Example_2 "Parse HTTP header with Regex": // O_o too much boilerplate if( std::regex_match( line, "^.+ 200 .+$"_r ) ){...} else if( std::regex_match( line, "^.+ 404 .+$"_r ) ){...} else if( std::regex_match( line, "^.+: .+$"_r ) ){...} else { terminate(); } // OR // I think this way your intention is clearer eswitch( line ) >> case_( "^.+ 200 .+$"_r ) >> []{...} // match for "HTTP/1.1 200 OK" case_( "^.+ 404 .+$"_r ) >> []{...} // match for "HTTP/1.1 404 Not Found" case_( "^.+: .+$"_r ) >> [&]{...} >> // match for "key: value" default_ >> []{ terminate(); }; -- Example_2 "match in range of values": // Error prone approach if( value >= 1 && value <= 10 ){ Print("Value in a range[1,10]"); } if( value >= 11 && value <= 20 ){ Print("Value in a range[11,20]"); } else { Print('?'); }; /// OR eswitch( value ) >> case_( _1.in( 1, 10 ) ) >> []{ Print("Value in a range[1,10]"); } >> case_( _1.in( 11, 20 ) ) >> []{ Print("Value in a range[11,20]"); } >> default_ >> []{ Print('?'); }; // _1 it is lazy index mapping for the params in eswitch I my opinion "eswitch" looks more readable, more intuitive, less error prone and furthermore it is extensible. P.S. Here https://github.com/rabdumalikov/proposals/blob/master/eswitch_boost_proposa… I had described why I think it is important( just in case you've missed it ).

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[release] 1.72.0 closed for Beta
by Michael Caisse 11 Nov '19

11 Nov '19

The master branch is now closed for all changes except by permission for the Beta release. Also, remember to add your libraries' changes to the release notes at: <https://github.com/boostorg/website/blob/master/feed/history/boost_1_72_1.q…> Thanks, -- The Boost Release Team

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[Boost][Proposal] library for enhanced switch syntax. Request for Comments
by рустам абдумаликов 11 Nov '19

11 Nov '19

Hi All, I wrote a library *eswitch* which provides enhanced functionality for* C++ switch*. Please take a look and leave your comments. *=====================* *Motivation:* *=====================* To overcome "*native switch*" limitations: - one parameter per "*native switch*" - the parameter restricted to only *integral *types( int, char, enum ... ). "*eswitch*" supports any number of parameters and almost without restriction on their *type*, as long as the *type *is comparable( i.e. has* operator==* ). *=====================Why it is important?=====================* Here is the most viewed questions on the *stackoverflow*: FEATURE VIEWS Multiple conditions in switch case <https://stackoverflow.com/questions/68578/multiple-cases-in-switch-statement> 850k Switch for string <https://stackoverflow.com/questions/650162/why-the-switch-statement-cannot-…> 693k Case match in range <https://stackoverflow.com/questions/9432226/how-do-i-select-a-range-of-valu…> 133k Over a million views indicate how many people out there are disappointed with limited functionality of "*native switch*". Building parallels with such operators as "*if*"/"*while*"... it is expected by default that "*native switch*" should have the same possibilities: - be able to work with *non-integral* types as well - be able to compose complex conditions like we do in other operators " *if*"/"*while*"... Unfortunately it is not the case up till now. There was a proposal in 2013 *Relax switch statement <http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2013/n3627.html>*, and committee agreed about importance of this topic. There also was *StringSwitch <http://llvm.org/doxygen/classllvm_1_1StringSwitch.html>* implementation by *LLVM *and *Case ranges <https://gcc.gnu.org/onlinedocs/gcc/Case-Ranges.html>* non-standard extension which is supported by *gcc*, *intel C/C++* and *clang*. Nevertheless, we still don't have common and universal solution. People want to overcome current "*native switch*" limitation either by implementing their own solution, non-standard extension or even trying to standardize it. Making proposed *eswitch <https://github.com/rabdumalikov/eswitch_v4>* functionality part of the *Boost-Library *will provide millions of developers useful, universal and agile functionality in order to finally fulfill their needs. *=====================repository:=====================* https://github.com/rabdumalikov/eswitch_v4 *=====================References:=====================/// "switch for non-integral" on stackoverflow* 1. https://stackoverflow.com/questions/650162/why-the-switch-statement-cannot-… 2. https://stackoverflow.com/questions/16388510/evaluate-a-string-with-a-switc… 3. https://stackoverflow.com/questions/5452188/switch-case-statement-in-c-with… 4. https://stackoverflow.com/questions/19273092/character-in-switch-statement-c 5. https://stackoverflow.com/questions/4165131/c-c-switch-for-non-integers 6. https://stackoverflow.com/questions/27536575/switch-case-on-char */// "Multiple conditions" on stackoverflow* 7. https://stackoverflow.com/questions/8644096/multiple-conditions-in-switch-c… 8. https://stackoverflow.com/questions/68578/multiple-cases-in-switch-statement */// "Ranges in case" on stackoverflow* 9. https://stackoverflow.com/questions/9432226/how-do-i-select-a-range-of-valu… */// "Case ranges" - non-standard extension* 10. https://gcc.gnu.org/onlinedocs/gcc/Case-Ranges.html */// LLVM "StringSwitch"* 11. http://llvm.org/doxygen/classllvm_1_1StringSwitch.html */// "Relax switch statement" proposal* 12. http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2013/n3627.html */// "N3627 Relaxed switch statement" c++ committee status* 13. https://cplusplus.github.io/EWG/ewg-active.html *Best Regards.*

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