June 2016 - Boost - lists.preview.boost.org

Start to contribute to Boost.
by Зайцев Александр 11 Jun '16

11 Jun '16

Hello. I very want to start contribute to Boost library. I want to help this project. And... maybe for start i can try to fix some bugs. Can you give me some pieces of advice, what i can do at start? Thanks. -- С уважением, Зайцев Александр.

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Pimpl Again?
by Vladimir Batov 10 Jun '16

10 Jun '16

Don't laugh but it is only fairly recently at work that I managed to move all our supported platforms to C++11. So, then, I started moving our code to C++11 (what a delight!) and stumbled upon my old pimpl which is used quite a bit around my workplace for all its good properties... :-) Now C++11-ed piml turned out to be very small and very basic. So basic it felt it did not have the right to exist. Still, it encapsulates and enforces the "proper" pimpl properties and behavior, reduces implementation minutia and offers a recognizable deployment pattern (helps other people reading the code). Over the years IMO the technique has been proven as legitimate and useful, a basic but important building block... rather than a curiosity item. Unfortunately, despite many articles and a few Sutter's GotWs about it there is nothing ready-to-go like std::unique_ptr. I feel that pimpl and its deployment pattern need to be codified, described, "standardized" and in our toolboxes to stop/avoid everyone re-inventing the pimpl and making the same mistakes. IMO Boost is best positioned for that. Do you think we might review what I've got and/or maybe collectively come up with something better... It's no MPL or Hana but as std::unique_ptr it's one of the first "little things" I personally reach out for in my everyday work. IMO having pimpl in Boost would save quite a few hours of frustration for many. Thoughts? No pressure. I am easy either way. :-) https://github.com/yet-another-user/pimpl Docs are freshened up but still somewhat out of date. Apologies.

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[config] Changes needed for VC++ 2015 Update 3?
by Beman Dawes 09 Jun '16

09 Jun '16

The VS 2015 Update 3 release candidate has been announced. See https://blogs.msdn.microsoft.com/vcblog/2016/06/07/compiler-improvements-in… (The following is partially for Boost developers who care about msvc, and partially to remind myself of what may need to be done to support update 3. It will be several weeks before I can work on this, so if any of the other config maintainers want to step in, please do so.) Update 3 supports standards versioning switches similarly to gcc, clang, and other compilers. We probably want to update Boost.Config accordingly. See https://blogs.msdn.microsoft.com/vcblog/2016/06/07/standards-version-switch… Update 3 fixes lots of constexpr bugs, so we need to review whether or not BOOST_NO_CXX11_CONSTEXPR is still required. Note that in develop there is an undocumented config macro BOOST_MSVC_CXX11_CONSTEXPR that turns off BOOST_NO_CXX11_CONSTEXPR to facilitate testing. Update 3 fixes the expression SFINAE issues that were causing most of the Boost develop test failures. https://blogs.msdn.microsoft.com/vcblog/2016/06/07/expression-sfinae-improv… Quoting from that: There are still three failing tests in the Boost [develop] test suite when compiling with MSVC. Two test failures relate to using the noexcept operator in a template type argument. We currently parse it immediately, even in a dependent context. One test failure is a Boost library issue that we’ve reported to the [library's] maintainers. There are still known update 3 expression SFINAE issues (see "What remains to be done?" in the blog article) so do we continue to define BOOST_NO_SFINAE_EXPR? There is an undocumented BOOST_MSVC_SFINAE_EXPR macro in develop that turns off BOOST_NO_SFINAE_EXPR, so it is easy for developers to use msvc expression SFINAE if the want to. But our usual criteria for a _NO_ macro is not full compliance, but whether or not Boost code works with a feature. So using that criteria for update 3 we would remove BOOST_NO_SFINAE_EXPR. Opinions? --Beman <aside> We always urged Microsoft to test their releases against Boost. For update 3 expression SFINAE, they did exactly that. Thanks to Microsoft's Andrew Pardoe for coordinated the effort and to Xiang Fan for running the tests and tracking down the reason for each test failure. An undocumented Boost.Config macro BOOST_MSVC_SFINAE_EXPR to support their testing. The approach was to run tests for all libraries with the normal test setup, and then run again with BOOST_MSVC_SFINAE_EXPR defined. If the problem was with the Boost library, Xiang then reported it to me. I need to review a long series of email exchanges with him to make sure I alerted library maintainers to any Boost problems. </aside>

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Boost Best Practice text download option fails.
by Fletcher, John P 08 Jun '16

08 Jun '16

This is a very interesting item to me. https://svn.boost.org/trac/boost/wiki/BestPracticeHandbook This has an option at the end to download as plain text. This fails on my browser (Firefox) with "Corrupted Content Error" which I have never seen before. Please sort this out someone. John

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[variant] spirit broken
by Jürgen Hunold 08 Jun '16

08 Jun '16

Hi Antony, according to git bisect, your commit ----------- commit b3650685f941a0c35cadfd878a185f274e132788 Author: Antony Polukhin <antoshkka(a)gmail.com> Date: Sat May 28 01:29:52 2016 +0300 Variant constructors and assignment operators now do not participate in overload resolutions if variant can not hold the input type (trac 5871, trac 11602) ------------ broke Boost.Spirit. The test failures can be seen in the regression matrix. For example: http://www.boost.org/development/tests/develop/developer/output/Flast-FreeB… fails with ../boost/variant/variant.hpp:1152:7: note: while substituting deduced template arguments into function template 'operator=' [with T = boost::variant<boost::spirit::info::nil_, std::__1::basic_string<char>, boost::recursive_wrapper<boost::spirit::info>, boost::recursive_wrapper<std::__1::pair<boost::spirit::info, boost::spirit::info> >, boost::recursive_wrapper<std::__1::list<boost::spirit::info, std::__1::allocator<boost::spirit::info> > > >] class variant ^ ../boost/spirit/home/support/info.hpp:29:12: note: definition of 'boost::spirit::info' is not complete until the closing '}' struct info It seems that the commit somehow disabled support for recursive variant usage. To reproduce this, just run the Spirit regression test. Yours, Jürgen -- * Dipl.-Math. Jürgen Hunold ! * voice: ++49 4257 300 ! Fährstraße 1 * fax : ++49 4257 300 ! 31609 Balge/Sebbenhausen * jhunold(a)gmx.eu ! Germany

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[Spirit] real_policies<> and 1.0#NAN
by Pete Bartlett 08 Jun '16

08 Jun '16

Hi, Boost.Spirit is not sure of itself when it comes to parsing representations of infs and nans such as “1.0#NAN”. The docs [1] for the default real_policies<T> for parsing numbers say: “[…] with the additional detection of NaN and Inf as mandated by the C99 Standard and proposed for inclusion into the C++0x Standard: nan, nan(...), inf and infinity (the matching is case-insensitive). This corresponds to the following grammar:” The first sentence suggests that 1.0#NAN etc will not be parsed. But the grammar itself then says: <quote> nan = -lit("1.0#") >> no_case["nan"] >> -('(' >> *(char_ - ')') >> ')') ; inf = no_case[lit("inf") >> -lit("inity")] ; </quote> suggesting that "#1.0NAN" is intended to parsed, but "#1.0INF" is not! Then the in-code docs [2] however suggest that both "1.0#NAN" and "1.0#INF" are intended to be parsed: <quote> // The second call allows to recognize representation formats starting // with a 1.0 (such as 1.0#NAN or 1.0#INF etc.). </quote> However, the actual code fails to parse either of these these. This is because in [3] the presence of the "0" causes frac_digits to be non-zero and so the "traits::is_equal_to_one(..)" condition is never tested. In the case "1.#NAN" (without a zero) frac_digits is zero so the condition is tested and we enter the traits::parse_nan code, but now the text parsed to this sub-parser is "#NAN" and the parser does not cater for the initial "#". Could the maintainers state which behaviour is intended...hopefully I may be able to supply a patch to docs/code/tests knowing that. Regards, Pete [1] http://www.boost.org/doc/libs/1_61_0/libs/spirit/doc/html/spirit/qi/referen… [2] <boost/spirit/home/qi/numeric/real_policies.hpp> [3]<boost/spirit/home/qi/numeric/detail/real_impl.hpp>

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RFC : About forking a C++11 standard library and adapt it to C++98 compilers
by Vicente J. Botet Escriba 07 Jun '16

07 Jun '16

Hi, Some of us have to work yet with C++98 compiler at work (due to well know reasons) and this for a long time. This is a reality. I was wondering about forking a public domain C++11/14/17 standard library and adapt it to C++98 compilers. This library could be seen as another TR1, an extension of the C++03 standard library. Does this make any sens? Would this project be of interest for the Boost/C++ community? I have not a clear idea of the cost of doing this work, how it should be done, what would be the limitations, ... but I'm sure that this would be quite useful on the projects that are forced to use C++98 and an excellent bridge to those that will move from C++98 to C++11 compilers. There are some Boost libraries that could be used to reduce the limitations, as Boost.Config/Predef, Boost.Move, ...and others that could be used as inspiration on how to implement them using C++98. Anyway, if you find that this will be useful to you at your work we will need your participation. Would you be interested in working on it? as a Boost community project? outside Boost, as an independent project? Comments and suggestion welcome. Best, Vicente P.S. The same can be done for C++14 standard libraries and the future standard C++17 libraries P.S.S. The same can be done for C++14 libraries and the future C++17 libraries but this time adapting to C++11 compilers (this will be much easier but the concerned community will be quite different ).

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Make libs/maintainers.txt a template file
by Daniel James 07 Jun '16

07 Jun '16

Hi, If you haven't noticed, on develop libs/libraries.htm is now a template which gets filled in as part of the documentation build. You can see the template and generated files at: https://github.com/boostorg/boost/blob/develop/libs/libraries.htm http://www.boost.org/doc/libs/develop/libs/libraries.htm This will be merged to master pretty soon. The only obstacle is updating the website automatically from the latest build, which should be happening very soon. The file libs/maintainers.txt is also automatically updated, but that's done in the repo itself, so that you have the full copy in you normal checkout. But I'm finding that people don't realise this, and we've had a few pull requests to update it manually. So instead, I think it might be a good idea to convert it to a template as well. This means you won't have a local copy, but will still be able to see a reasonably up to date copy online at: http://www.boost.org/doc/libs/develop/libs/maintainers.txt Any objections? I'm think of using similar templates for some other files, such as the root index.html (for the version number and new libraries). thanks, Daniel

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Cxx dual library
by Edward Diener 06 Jun '16

06 Jun '16

I have finished all the main work on the Cxx dual library at https://github.com/eldiener/cxx_dual. The library is also in the Boost Library Incubator at http://rrsd.com/blincubator.com/bi_library/cxx_dual-2/?gform_post_id=1597. The Cxx dual library, or CXXD for short, is a C++ macro header-only library which chooses between using a Boost library or its C++ standard equivalent library for a number of different C++ implementations, while using the same code to program either choice. An 'implementation' is a Boost library which has a C++ standard library equivalent whose public interfaces are nearly the same in both cases. An 'implementation' is called a 'dual library' in this documentation, or 'CXXD-mod' for short. The library does this by defining object-like macros for including the appropriate header file and namespace or using either the Boost library version or the C++ standard library version of a particular dual library. CXXD currently supports twenty eight different dual libraries, where the Boost version and the C++ standard version is nearly interchangeable in some respects. CXXD also provides a macro-based solution for distinguishing between the Boost version and the C++ standard version of a dual library so that specific code for a particular dual library choice may be written in those cases where the public interfaces diverge. The library came out of my initial PR to add such a feature to Boost.Config, and then I decided to create a separate library and expand on the functionality. The gist of the library is to write a single set of code for a particular implementation and have it work whether or not that code targets a Boost implementation or its C++ standard equivalent. The default algorithm will choose the C++ standard implementation if it is available, otherwise it chooses the Boost implementation. The default can be overriden for any of the 28 different implementations which CXXD supports. With all the talk about supporting C++11 or C++14 in new code, the library offers a way of supporting C++11 or C++14 standard libraries if available whether one writes in C++03 dialect or uses the new language features of C++11 on up. The Cxx dual library itself, being macro based, should work with any C++ code at that code's language level. The library itself is NOT, repeat NOT, an attempt to enforce a C++ language level for anybody who wants to use it. I have a little more work I am doing on increasing the support for Boost Build in the library, but all the central implementation of the library is complete in my mind. Questions, comments, or bug reports are always welcome, either here in this mailing list, in the Boost Library Incubator, or as Github issues, by those who are interested in trying the library out or reading the documentation. I will be using CXXD in another library on which I am working but hopefully others will find a use for it in their own code.

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[exception] Broken in master?
by John Maddock 06 Jun '16

06 Jun '16

Anything that includes Boost.Exception is currently broken on master for all compilers, for example: http://www.boost.org/development/tests/master/developer/output/teeks99-09j-… http://www.boost.org/development/tests/master/developer/output/Flast-FreeBS… The cause is the use of a partial-template specialization in info.hpp with no previous definition of class set_info_rv. Thanks, John.

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