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crc.hpp:569 msvc warning C4800
by Kenneth Porter 13 Apr '19

13 Apr '19

<https://github.com/boostorg/crc/pull/2> Visual Studio 2010-2019 issue this warning for crc.hpp line 569: warning C4800: "'int' : forcing value to bool 'true' or 'false' (performance warning) bool const quotient = remainder & high_bit_mask; Replace with: bool const quotient = (remainder & high_bit_mask) != 0;

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[build] Bootstrap failures in Appveyor CI
by Andrey Semashev 12 Apr '19

12 Apr '19

Hi, I'm seeing multiple Appveyor job failures at bootstrap stage, here's an example: https://ci.appveyor.com/project/Lastique/winapi/build/job/qnu5dhfcpjx3vh1y The code did not change for quite a while and it was passing before. It first failed after the jobs were triggered by the 1.70 tag. Only some of the jobs have failed, and after I re-ran the jobs, a different set of jobs failed the second time. Is this something related to Boost.Build or superproject?

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[release] Boost 1.70.0
by Marshall Clow 12 Apr '19

12 Apr '19

Release 1.70.0 of the Boost C++ Libraries is now available. These open-source libraries work well with the C++ Standard Library, and are usable across a broad spectrum of applications. The Boost license encourages both commercial and non-commercial use. This release contains numerous enhancements and bug fixes for existing libraries. For details, including download links, see < http://www.boost.org/users/news/version_1.70.0> You can also download directly from: < https://dl.bintray.com/boostorg/release/1.70.0/source> SHA-256 sums: ae2bb1b35d1f238e72e3f819b42336f4bd27c9ed2092aab5d87818ccb0c9161a boost_1_70_0.7z 430ae8354789de4fd19ee52f3b1f739e1fba576f0aded0897c3c2bc00fb38778 boost_1_70_0.tar.bz2 882b48708d211a5f48e60b0124cf5863c1534cd544ecd0664bb534a4b5d506e9 boost_1_70_0.tar.gz 48f379b2e90dd1084429aae87d6bdbde9670139fa7569ee856c8c86dd366039d boost_1_70_0.zip To install this release on your system, see < http://www.boost.org/doc/libs/release/more/getting_started/index.html> Thanks to everyone who participated in this release. Thanks, -- The Boost Release Team Vladimir Prus, Marshall Clow, Daniel James, Micheal Caisse

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[release] 1.71.0 open for merging
by Marshall Clow 12 Apr '19

12 Apr '19

The master branch is open for merging all stable changes from develop, including bug fixes and major upgrades to existing libraries. Breaking changes should be coordinated via the mailing list with the developers of the other libraries affected. New libraries may be added, but require permission of a release manager. In other words, merging does not require permission from a release manager, except for new libraries. Boost Calendar with the release schedule: http://www.boost.org/development/index.html Release schedule explanation: https://github.com/boostorg/boost/wiki/Release-Schedule Release practices for developers: http://svn.boost.org/trac/boost/wiki/ImprovingPractices -- The Boost Release Team

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[variant2] Gavin's review
by Gavin Lambert 12 Apr '19

12 Apr '19

This is my review of Variant2. I vote to ACCEPT this library. However I find the ambiguous state of "expected" a bit too ambiguous (and the "expected" concept in general has caused quite a bit of discussion and contention in the past) so I would prefer that it not be considered part of the library as is, and go through at least a mini-review before entering Boost. I'm not suggesting that this be a formal acceptance condition, however. (I did not look at this type for my review.) I also question whether a more descriptive name than "Variant2" can be used for it, although I recognise that at least starting the library name with "variant" is a good idea to aid discoverability in alphabetic sorting order. - What is your evaluation of the design? As I've stated elsewhere, I feel that if you're willing to pay the cost of double-buffering then you might as well go all-in and implement the strong guarantee as well (or at least a partially strong guarantee, where any attempt to change the stored type provides the full strong guarantee but attempts to assign the same type merely delegates to the underlying type's assignment operation and so provides the same guarantee as that -- this seems sufficiently reasonable and useful to me without sacrificing too much performance, and still lets you single-buffer as an optimisation when all types are noexcept assignable). Having said that, I recognise that others have different lines in the sand, and this is a reasonable design choice within those lines. - What is your evaluation of the implementation? Overall, good. I do have a few minor nitpicks: 1. bad_variant_access's constructor should be "constexpr = default" to preserve constexpr and/or triviality (if std::exception is also constexpr and/or trivially constructible, although this is not the case in VS2017, but could be in other implementations). 2. When std::monostate exists, it should treat both equivalently, for compatibility. (It should not alias its own to std::monostate, as that poses ABI problems if not all code is compiled in C++17 mode.) 3. The duplicated include guard around <boost/mp11.hpp> seems both ugly and unnecessary. Also it should probably be included after <boost/config.hpp>. 4. It's not clear why some of the internal methods (such as _get_impl) have leading underscores while others (such as emplace_impl) do not. It seems inconsistent. 5. It's not clear what purpose the "none" storage type serves (other than apparently requiring the indexing to be offset by one). It seems rather like an empty state... (and the continual offsetting seems inefficient; most of it happens at compile time, but not all). 6. variant_base_impl::_replace has a "requires" comment; why doesn't it have a matching assert? Also, why are these not BOOST_ASSERTs? 7. As discussed elsewhere, a public trait should be provided which lets you static_assert which implementation was actually instantiated. - What is your evaluation of the documentation? It is minimal but sufficient for readers already familiar with std::variant. (And who can read standardese.) It is not sufficient for readers not familiar with std::variant. I think this is mostly fine, but I would prefer the addition of a Motivation and/or Design Rationale section which explains why this is better than std::variant and boost::variant. In future it would also be nice to have a Porting section which explains what code changes are required to move from those to this. - What is your evaluation of the potential usefulness of the library? It seems potentially useful for others, although I would personally have preferred different design choices. - Did you try to use the library? With which compiler(s)? Did you have any problems? I did not try it. - How much effort did you put into your evaluation? A glance? A quick reading? In-depth study? I read through the documentation and code in moderate detail, but not in-depth. - Are you knowledgeable about the problem domain? I am familiar with variants, but have not as yet used them much in production code.

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Variant2 review
by Phil Endecott 11 Apr '19

11 Apr '19

Dear All, Here is my brief review of Peter Dimov's proposed Boost.Variant2. Sorry that this is not a particularly thorough review. I have read the docs, scanned the code, and followed the discussion on the mailing list; I have not tried to compile or use it. I have recently been using the original Boost.Variant for the first time. I actually started writing code based on std::variant, but then realised that I don't have support for it on one C++14-only platform, so changed to Boost.Variant. It's unfortunate that Boost.Variant has a somewhat different interface from std::variant, so it would be useful to have a Boost variant that is (more) compatible with std::variant. It would also be useful if it were somewhat backward compatible with the old Boost.Variant. The proposed Boost.Variant2 is compatible with std::variant; could some thin layer of compatibility be added to make it possible to port from Boost.Variant code? Specifically, the differences I have noticed are apply_visitor vs. visit and get(V*) vs. get_if. In my case, my stored types are typically raw pointers or small POD structs; none of these can throw during construction/assignment so the complicated arguments about exception guarantees are not applicable. Personally for my current application I'd be happy with a simpler variant that requires noexcept types, or disables assignment for types that might throw, or just doesn't offer an exception safety guarantee. Ideally, perhaps a Boost.Variants *library* should provide a selection of different variants with different features? That leads to the question of naming; we have boost::variant, boost::variant2 and std::variant and those names tell us nothing about how they differ. I'm unsure how or if this can be improved; I'm not suggesting that variant2 should be renamed variant_never_empty_maybe_double_size! But maybe the long-name of the library, i.e. what people will see when they look at the list of Boost libraries, could say "Never empty variant" rather than "Variant 2"? Prior to the review I was familiar with the issue of dynamic allocation, the fact that is is needed in some cases by some variant implementations, and the desire to avoid it. However I was not aware of the alternative of storing two copies of the union, doubling the size of the variant. Much of my work is with memory-constrained systems and unknowingly using twice as much memory as expected would be very undesirable. (I noticed Niall Douglas' comment earlier today "There is nothing wrong, *whatsoever*, with a variant which is sized the largest of its possible states multiplied by two" - I strongly disagree with that.) I'd like to at least get a warning if that were going to happen. A specific concern is that I might accidentally get this fallback due to forgetting to write "noexcept" somewhere (e.g. when using types from older code). On the subject of size, I note that the index is stored in an int, while virtually all uses would surely need fewer than 256 (or certainly 2^16) alternatives. Of course changing the index to uint16_t would not actually help on many platforms due to structure alignment requirements. This makes me wonder about a specialised variant for pointers that uses the spare bits in (most/some) 64-bit pointers to store the variant index. This could usefully be part of a variants *library*. I read Andrzej Krzemienski's comments about the documentation and largely agree with them - though I would say that this library is close enough to std::variant that perhaps the right thing to do is simply to say "go and read about std::variant and then come back here to see the differences". Peter posted a link to some benchmark results last week; those numbers are encouraging and it is also good to know that Peter actually made the effort to measure them! I do wonder how a "trivial" variant supporting only noexcept types would compare, though. Boost.Variant has something called polymorphic_get. I am unclear whether Boost.Variant2 (and/or std::variant) somehow support this functionality. The situation re. expected is unfortunate. I believe really the review should have waited for it to be completed. Peter's comment that if it is decided that it needs to be reviewed then he would remove it and never resubmit it was ... surprisingly undiplomatic? I have always found it a bit odd that Boost requires a thorough review of an initial library submission but nothing at all for later additions. In summary: - I believe the library should be accepted. - It would be great if some compatibility features with Boost.Variant could be added, to make it possible for users of that older library to transition more easily. That is not a condition for acceptance. - I would love to have some way to get a warning or error if the double storage mode had been triggered, or to disable that mode (with an error). - It would be great to see some alternative variants, with different features / trade-offs, included in the library. Ideally, naming of types and headers should allow for that. I'm not suggesting that Peter should be personally expected to supply these alternatives, but perhaps he would accept offerings from others. - I think we should allow Peter to "slip in" his expected when it is ready; I say this largely because Peter has a long history with Boost. Future review managers should try to avoid situations like this arising. Regards, Phil.

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[release] Boost 1.70.0 Release Candidate 2 available
by Marshall Clow 11 Apr '19

11 Apr '19

The second release candidate for the 1.70.0 release are now available at: <https://dl.bintray.com/boostorg/release/1.70.0/source/> Changes since rc1: * Boost.Config changes to work better with msvc-14.2 * Boost.Beast bug fixes * Boost.Move bug fix * Boost.Math non-ascii characters removed from header file The SHA256 checksums are as follows: 882b48708d211a5f48e60b0124cf5863c1534cd544ecd0664bb534a4b5d506e9 ./boost_1_70_0_rc2.tar.gz 430ae8354789de4fd19ee52f3b1f739e1fba576f0aded0897c3c2bc00fb38778 ./boost_1_70_0_rc2.tar.bz2 48f379b2e90dd1084429aae87d6bdbde9670139fa7569ee856c8c86dd366039d ./boost_1_70_0_rc2.zip ae2bb1b35d1f238e72e3f819b42336f4bd27c9ed2092aab5d87818ccb0c9161a ./boost_1_70_0_rc2.7z As always, the release managers would appreciate it if you download the candidate of your choice and give building it a try. Please report both success and failure, and anything else that is noteworthy. -- The Boost Release Managers

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Problem with generating file_descriptor suing existing pipe file descriptor
by Russell West 10 Apr '19

10 Apr '19

Our program just installed version 69 of Boost and I am running into a compile issue that I am not sure how to resolve. Following is the associated section of C++ code that I am unable to figure out the changes to get it to compile. int filedes[2]; if ( pipe(filedes) == 0) { using namespace boost::iostreams; stream<file_descriptor> results(filedes[0], close_handle); .... .... } The last provided line of code does not compile with a no matching function for call to 'boost::iostreams::file_descriptor::file_descriptor(int&, file_descriptor_flags&)' error. I noticed in the version of the boost file_descriptor.hpp loaded and being used the following exists: #ifdef BOOST_IOSTREAMS_WINDOWS file_descriptor(int fd, file_descriptor_flags); #endif The associated application attempting to be built and deployed is only for servers running the Linux operation system so BOOST_IOSTREAMS_WINDOWS is not enabled, causing the above constructor not to be available. The other constructor available is file_descriptor(handle_type fd, file_descriptor_flags); but I can not figure out how to generate a detail::file_handle from the available int file descriptor generated from above pipe command. Will it cause any issues enabling BOOST_IOSTREAMS_WINDOWS so the required constructor will be available? Thanks ahead of time for your time and feedback. Russell West

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Re: [boost] [Boost-GIL] Image Processing Algorithms
by Mateusz Loskot 10 Apr '19

10 Apr '19

On Wed, 10 Apr 2019 at 18:54, Amir Ali <amirqadir(a)live.com> wrote: > > I really want to do this project even if I am not considered for GSOC. > I am still willing to do it on my own with guidance and supervision from any mentor. There are two mentors who will mentor three students in total. So, we can not offer any supervision to more projects. You are welcome to post your questions to the boost or boost-gil lists, or ask on Gitter room or the Slack channels as any user of / contributor to Boost libraries can do. Best regards, -- Mateusz Loskot, http://mateusz.loskot.net

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[Boost-GIL] Image Processing Algorithms
by Amir Ali 10 Apr '19

10 Apr '19

Hi, I am looking for someone to mentor me for my project that is to implement image processing algorithms in Boost-GIL. Here’re some of the algorithms I am aiming to make. Mathematical Morphology (Dilation, Erosion, Opening, Closing) Filters (High pass Filters, Low Pass Filter which includes Gaussian etc) And Other Image enhancement basic algorithms. Regards Amir

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