June 2015 - Boost - lists.preview.boost.org

[Better Enums] Non-integral underlying types
by Anton Bachin 18 Jun '15

18 Jun '15

About a week ago, I generalized Better Enums somewhat to accept non-integral underlying types, with some conditions and restrictions. I’d like to ask for comments/opinions/ideas on this feature. I made a little write-up on it [1], but I will summarize here as well. The write-up is a superset of the content of this message, so don’t read the message if you click the link :) If you have a literal type “foo”, you can do: ENUM(SomeEnum, foo, A, B = 2, C = foo(…)) SomeEnum value = SomeEnum::A; switch(value) { case SomeEnum::A: // … case SomeEnum::B: // … case SomeEnum::C: // ... } The switch above can have its cases checked for exhaustiveness by the compiler. Also, “value” above behaves like a “container” for one value of type foo, whose members can be accessed using operator ->. So, basically, you can have enumerated, reasonably type-safe sets of arbitrary literal types. The catch is that you have to provide an invertible mapping from foo into some underlying integral type, which mapping is declared either by equipping foo with the right constructor and conversion operator, or specializing a traits template. I would love to make a default implementation for this mapping, but it seems like I need to achieve the effect of a reinterpret_cast at compile time, and I haven’t been able to do so. [1]: http://aantron.github.io/better-enums/GeneralUnderlyingTypes.html

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Making lots of compile FAIL tests
by Paul A. Bristow 18 Jun '15

18 Jun '15

I've started to devise some tests to ensure that things that really should not compile, do in fact compile-fail. So far I've produced a few files with a single statement that should fail inside a int main(){}. But it's looking at though it will get pretty tedious pretty soon :-( (I see for example that Boost.Multiprecision has some 50-ish compile_fail items) Is there some slicker way of doing this? Paul --- Paul A. Bristow Prizet Farmhouse Kendal UK LA8 8AB +44 (0) 1539 561830

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Re: [boost] [Boost-announce] [Boost] [Hana] Formal review for Hana next week (June 10th)
by Glen Fernandes 17 Jun '15

17 Jun '15

[Correction: 10th June is a Wednesdsay, not Monday.] Dear Boost community, The formal review of Louis Dionne's Hana library starts Wednesday, 10th June and ends on 24th June. Hana is a header-only library for C++ metaprogramming that provides facilities for computations on both types and values. It provides a superset of the functionality provided by Boost.MPL and Boost.Fusion but with more expressiveness, faster compilation times, and faster (or equal) run times. To dive right in to examples, please see the Quick start section of the library's documentation: http://ldionne.com/hana/index.html#tutorial-quickstart Hana makes use of C++14 language features and thus requires a C++14 conforming compiler. It is recommended you evaluate it with clang 3.5 or higher.[1] Hana's source code is available on Github: https://github.com/ldionne/hana Full documentation is also viewable on Github: http://ldionne.github.io/hana To read the documentation offline: git clone http://github.com/ldionne/hana --branch=gh-pages doc/gh-pages For a gentle introduction to Hana, please see: 1. C++Now 2015: http://ldionne.github.io/hana-cppnow-2015 (slides) 2. C++Con 2014: https://youtu.be/L2SktfaJPuU (video) http://ldionne.github.io/hana-cppcon-2014 (slides) We encourage your participation in this review. At a minimum, kindly state: - Whether you believe the library should be accepted into Boost - Your name - Your knowledge of the problem domain. You are strongly encouraged to also provide additional information: - What is your evaluation of the library's: * Design * Implementation * Documentation * Tests * Usefulness - Did you attempt to use the library? If so: * Which compiler(s)? * What was the experience? Any problems? - How much effort did you put into your evaluation of the review? [1] A note for Windows users: As mentioned, Hana requires a C++14 conforming compiler. If you would like to try it, a VM with Linux and clang 3.5 is a fairly painless option. Some users have also reported success with using Clang 3.5 on Windows. If you would like assistance configuring the former option, feel free to reach out to us for this. Best, Glen

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[Hana] Migrating sqlpp11 to Hana (hypothetically)
by Roland Bock 17 Jun '15

17 Jun '15

Hi Louis, First of all: Hats off to you, your library and the documentation! I wanted to play with Hana for quite some time now. The review certainly offers a good reason to do so :-) Here's my test project: In sqlpp11 [1], lets assume I wanted to replace my own implementations of * compile time strings * type sets * functions like any/all/none with something from Hana. _Compile__time strings:_ This one seems easy. There probably won't be a C++14 version of sqlpp11, but there will be a C++17 version, hopefully allowing me to use the string literal without relying on a non-standard compiler extension. This is what I currently have [2]: struct _alias_t { static constexpr const char _literal[] = "delta"; using _name_t = sqlpp::make_char_sequence<sizeof(_literal), _literal>; }; This is what I would like to do: struct _alias_t { using _name_t = decltype("delta"_s); }; But the whole thing is in a header. * I do not want to "using namespace ::boost::hana::literals" at top-level or in one of the namespaces in the header. * Neither one of the following lines is valid: o using _name_t = decltype(::boost::hana::operator"_s"("delta")); o using _name_t = decltype("delta"::boost::hana::literals::operator"_s"); o using _name_t = decltype("delta"::boost::hana::literals::operator""_s); Is there a valid version? Obviously, I would also be happy with something like using _name_t = decltype(ct_string("delta")); * I also cannot use the BOOST_HANA_STRING macro, btw, because that would be a lambda in a decltype... I want to gradually migrate to Hana, so I'd really like to use a type here, not a variable. But I could not even use a variable, because the following does not compile (clang-3.5.1) struct A { static constexpr auto hana_name = BOOST_HANA_STRING("cheesecake"); }; Any hints? _ _ _type sets:_ Currently I store a bunch of types in type sets to do all kinds of tests at compile time. My type set code will need some cleanup or replacement one fine day. Hana to the rescue... Er, wait a second. There is no type set, or is there? There is a set for objects (which might represent types). Replacing all those types with objects would take some time, but I could live with that, I guess. But then I would have to replace all my type_sets (which are types themselves) with static constexpr objects, which use tons of constexpr template variables. And there are other constructs which use the types I now have replaced with objects. So I would have to adjust them, too, probably turning even more types into objects. Can I be sure (given today's compilers) that all these objects stay away from the generated binary? Also, I did not find some of the methods I would expect for sets: * Create a joined set * Create an intersect set * Create a difference set * Test if two sets are disjunct * Test if A is a subset of B, no, strike that, just found it in Searchable I probably could create the methods above with just a few lines of code using the available functions. But it would be convenient to have them available, of course (or did I just miss them?). By the way, I guess it would be easy for you to compile a list of available methods for each type, e.g. Set. Such a mini-index would be quite helpful IMO. _any/all/none: _Quite a bit of code is tuned to stuff like std::is_same: a type that contains a value (true or false). My current versions of any/all/none work like that, too. If I wanted to get rid of my own versions, could I use a drop-in from hana? Or would I have to write something like template<bool... B> struct my_all { static constexpr bool value = ::boost::hana::all(::boost::hana::make_tuple(B...)); }; ? _Intermediate summary:_ * I am not sure if I could replace my current compile-time string yet * I would like to have a few more convenience methods for Set. * It seems to me like if I wanted to use Hana, I should switch to Hana-style completely. Otherwise it will just be a weird mixture. Best, Roland [1]: https://github.com/rbock/sqlpp11 [2]: https://github.com/rbock/sqlpp11/blob/master/tests/Sample.h#L14-L17

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[Boost] [Hana] Announcing Hana's formal review next week (June 10th)
by Fletcher, John P 17 Jun '15

17 Jun '15

Here is my review and some comments. > We encourage your participation in this review. At a minimum, kindly > state: > - Whether you believe the library should be accepted into Boost Yes please > - Your name John Fletcher > - Your knowledge of the problem domain. I have been working for some years on functional programming in C++. This is mainly run time work, but it inevitably has involved a lot of work on compile time issues as well. I am also involved in the maintenance of Boost Phoenix. Currently I mainly work to be C++03 compatible, but have done work on C++11 variadics. I am learning from this review how some of the features of C++14 can be deployed to advantage. > You are strongly encouraged to also provide additional information: > - What is your evaluation of the library's: > * Design I have not dug into the Hana code. Instead I have been attempting to adapt its code to work with some of my current examples. It seems to me to be consistent in its approach. > * Implementation I have not found any problems at all with the implementation. > * Documentation It is not always clear exactly which headers are needed for any given example from the manual. It is necessary to look at the example codes. I would like more information about some topics, e.g. monads and comonads. * Tests I have been adapting some of the tests to run with other codes. In particular I have been working with Boost Phoenix and Boost Bimap without any problems once the namespaces are adjusted. * Usefulness I think it is a very useful code for someone attempting to implement a higher level library. There are several things which can be done very easily with it and I am only scratching the surface at the moment. One example is to be able to detect a member function name() in a struct: auto has_name = hana::is_valid([](auto&& obj) -> decltype(obj.name()) { }); and then to be able to print the name if it is present, or do something sensible. // I want to output the name from name() if it is present. template <typename F> std::string print_name(F const& f) { if (has_name(f)) std::cout << "has_name(f) true : "; else std::cout << "has_name(f) false : "; return hana::if_(has_name(f), [](auto& x) { return x.name(); }, [](auto& x) { return std::string("no_name"); } )(f); } > - Did you attempt to use the library? YES > If so: > * Which compiler(s)? Clang 3.5 and 3.6 with libc++ running on Ubuntu 12.04 > * What was the experience? Any problems? No > - How much effort did you put into your evaluation of the review? I have spent some hours implementing examples and running them. John Fletcher _______________________________________________ Unsubscribe & other changes: http://lists.boost.org/mailman/listinfo.cgi/boost

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boost [fusion]: tests failing in develop branch
by Aparna Kumta 17 Jun '15

17 Jun '15

Several regression tests for develop branch fail today. http://www.boost.org/development/tests/develop/developer/output/oracle-spar… "../libs/fusion/test/algorithm/copy.cpp", line 8: Error: Could not open include file<boost/fusion/container/vector/vector.hpp>. "../libs/fusion/test/algorithm/copy.cpp", line 9: Error: Could not open include file<boost/fusion/container/list/list.hpp>. Is this known? Thanks, Aparna

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Boost::Filesystem
by Amit Kumar 16 Jun '15

16 Jun '15

Hi All Is there any functionality in boost::filesystem to identify local drives on Linux box. I want something similar to windows API *GetDriveType*(). Regards Amit

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Preliminary submission of Boost Synapse
by Emil Dotchevski 16 Jun '15

16 Jun '15

I've made changes to Boost Synapse (a signal programming library) in part based on feedback I received on the Boost mailing list, and I've uploaded the updated source code and documentation to github: http://zajo.github.io/boost-synapse/. There is also a new tutorial: http://zajo.github.io/boost-synapse/Tutorial.html. I welcome more feedback. Thanks, Emil Dotchevski <http://www.revergestudios.com/reblog/index.php?n=ReCode>

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[config] Using SD-6 macros
by Edward Diener 16 Jun '15

16 Jun '15

I realize I may be late to the discussion, but what is the reason why Boost.config does not use the SD-6 macro functionality as the first check for all C11 and C14 related configuration options ? Is it because Boost.config feels that the few current SD-6 implementations are buggy ? As I understand SD-6 the implementation of SD-6 itself can always be checked effortlessly by an #if defined(__SOME_SD6_MACRO) before attempting to use the functionality defined by SD-6, so for the majority of compilers which do not implement SD-6 functionality yet Boost.config can always and easily fall back on its current checks. But for those compilers which do implement SD-6 ( latest clang and gcc 5.1.0 ) surely using SD-6 is easier than the many clever ways which Boost.config currently finds out how compilers and standard libraries are configured.

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Re: [boost] boost [fusion]: tests failing in develop branch
by Lee Clagett 16 Jun '15

16 Jun '15

On Tue, Jun 16, 2015 at 3:57 PM, Aparna Kumta <aparna.kumta(a)oracle.com> wrote: > Several regression tests for develop branch fail today. > > > http://www.boost.org/development/tests/develop/developer/output/oracle-spar… > > "../libs/fusion/test/algorithm/copy.cpp", line 8: Error: Could not open > include file<boost/fusion/container/vector/vector.hpp>. > "../libs/fusion/test/algorithm/copy.cpp", line 9: Error: Could not open > include file<boost/fusion/container/list/list.hpp>. > > Is this known? > > > Thanks, > > Aparna > > Yes, a pull request [1] was merged that was marked as a WIP. Another pull request [2] has already been made. The new pull request re-introduces those files - they were moved in [1], and [2] adds them back with new a new header that includes the original (now moved) files. Kohei Takahashi is eventually trying to replace the pre-processor based variadics with true variadics when compilers support it [3]. Joel or Kohei would have to provide more specifics on that effort, but it will be interesting if any compilation time improvements result (hopefully!). Lee [1] https://github.com/boostorg/fusion/pull/80 [2] https://github.com/boostorg/fusion/pull/81 [3] https://github.com/boostorg/fusion/pull/57

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