June 2015 - Boost - lists.boost.org

[Hana] Formal review
by Manu343726 28 Jun '15

28 Jun '15

Here's my formal review of Hana - Whether you believe the library should be accepted into Boost Yes - Your name Manuel Sánchez - Your knowledge of the problem domain. I have been doing TMP side projects as a hobby, including my own tmp library in the same sense of Hana but metafunction based (Like Boost.MPL). - What is your evaluation of the library's: * Design Hana design and wording makes it look more like a Hakell library than a C++ one (All the functional concepts, algorithms etc). I think it's fine since Hana algorithms are about declarative data transformation. C++ needs that change in the way of thinking, but I expect some others (more conservative C++ programmers) to not accept Hana for not being too much "C++ish". About metaprogramming, wrapping types into template variables is a game changer. Some others noticed that doing type and value manipulation with the same code may be confusing since with templates there is a clear line between type manipulation code (templates) and value manipulation code (normal C++). I'm partially agree, but I prefer not to write/maintain two different libraries for exactly the same algorithms. That's the core value of Hana. * Implementation Tmp is usually ugly, but Louis does a great work at making code as clear as possible. Code is well divided and documented. * Documentation The library is documented in depth. I have mainly two issues: More references about basic concepts and navigation. Both are already covered by issues at github, so I will not dive into them here. * Tests Not looked. * Usefulness There are only a few libraries out there that provide this kind of STL-quality set of algorithms. Having those work with types and values worths it. As others said, there's a problem on current compiler support (Only recent versions of Clang). I like the idea of pushing towards compiler vendors, but it's true that since the beginning Boost libraries were designed to work on any C++ platform available. In my opinion, we should give Louis an opportunity, while giving vendors time to update their implementations. - Did you attempt to use the library? If so: * Which compiler(s) clang 3.6.1 * What was the experience? Any problems? I tried some experiments regarding type manipulation. No special issues raised out. It worked as expected. - How much effort did you put into your evaluation of the review? A few hours playing with the lib, plus a couple of hours to write the review. -- View this message in context: http://boost.2283326.n4.nabble.com/Hana-Formal-review-tp4677606.html Sent from the Boost - Dev mailing list archive at Nabble.com.

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[hana] Review
by John Bytheway 28 Jun '15

28 Jun '15

This is a somewhat perfunctory review of Hana, because I wanted to get something in before the end of the review period. I have submitted a few issues on GitHub, for minor things that need not be repeated here. Below are the things I found that might warrant more discussion. - Whether you believe the library should be accepted into Boost * Conditions for acceptance Yes it should. No specific conditions. - Your name John Bytheway - Your knowledge of the problem domain. User of TMP for years. Once wrote a source-to-source translator to help me write MPL programs because it was prohibitively difficult to write them correctly by hand. - What is your evaluation of the library's: * Design The design seems reasonable, and I like the adherence to mathematical concepts. The most difficult thing is getting the names right, and I know there's been plenty of debate on that. The name that most concerns me is Range, given that that term is already commonly used in Boost as a concept with a completely different meaning (in the Boost.Range sense). * Implementation Did not look. * Documentation Mostly very good, but of course there is always room for improvement. One particular thing I wanted to raise here is that I struggled to find enough information about Hana-convertibility (i.e. using the 'to' function). For example, I wondered if I could create a Tuple from a Range, and it seems I can. Then I wondered whether I could create a std::Array from a homogeneous Tuple, but it seems I cannot. How should I know these things? (This latter case of converting to an array is something I feel ought to be supported for easing the boundary between runtime and compile-time sequences) * Tests Did not look. * Usefulness Very, although not useful for me personally until I decide to bite the ABI-breaking bullet and recompile all my code in gcc 5.x with the new libstdc++. The biggest risk I see is MSVC support. Microsoft seem to be much more standards-gung-ho than they once were, so I hope it won't take too much longer before we see support. But I do encourage Louis to be wary of taking advantage of any new language features (e.g. a potential change in C++17 lambdas-in-unevaluated-contexts rules, or the compiler extension for compile-time string literals) lest it delay MSVC support. - Did you attempt to use the library? If so: * Which compiler(s) clang 3.6.1 * What was the experience? Any problems? I played around a bit, mostly with a view to finding out how bad the compiler errors are when things go wrong. The results were promising. I went looking for some code of mine to try porting to Hana, and got sidetracked by one difficulty. The first project I came across using Boost.Fusion was passing a lot of fusion::vectors across function interfaces, but the vector types were specific and the functions not defined in headers. Hana's tuple cannot easily be used in this way since the type is unspecified. I don't think this is a problem, because (a) that code was just poorly written and ought instead to be using adapted structs, which Hana does support, and (b) I can use Hana algorithms with Fusion's tuples anyway. - How much effort did you put into your evaluation of the review? A few hours reading and playing. Thanks very much to Louis for his effort. I look forward to being able to use Hana in the not-too-distant future, and I'll make GitHub issues for any more things I discover in my testing. John

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Hana Views and References
by Joel de Guzman 27 Jun '15

27 Jun '15

Hello Louis, Mario Lang, a Spirit developer, played around with Hana and investigated on it's suitability for Spirit. His conclusion is that "Hana is really quite nice!". Then, he adds that: "However, Hana lacks a way to retrieve the members of a struct as references currently, which will pretty much kill a Hana based Spirit effort." So the question is: will Hana support references without resorting to using reference wrappers? I do appreciate the FP nature of Hana, but please be reminded that we're in C++. I also recall some discussion that Hana also does not support Fusion-like lightweight views. Is there a plan to support them? I haven't fully investigated yet what else Hana does not support that Fusion does, but at least these two important aspects of fusion come to mind. At the very least, I don't think Hana should advertize itself as a superset of Boost.Fusion. Faster runtime performance is also questionable, when lightweight views and reference members come into play. Regards, -- Joel de Guzman http://www.ciere.com http://boost-spirit.com http://www.cycfi.com/

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Re: [boost] [hana] Lorenzo's Formal review for Hana
by Brian Wood 27 Jun '15

27 Jun '15

Louis Dionne writes: > I'm coding against a standard, not a specific compiler. If I introduce > workarounds in Hana, the whole purpose of the library is lost. Performance, > ease of use, and most importantly hackability will be lost. > Hmm. > Quite honestly, I'd rather have my library never get into Boost than > bastardize it so it works on MSVC. If it can be made to work on MSVC > without bastardizing it, however, I'm all for it. I face similar issues and agree with your remarks here. It seems like it's easier to use MSVC and Windows than it used to be, but it's still not easy. I've recently reduced my Windows support and feel a burden lifted. -- Brian Ebenezer Enterprises - "Free at last; free at last. Thank G-d Almighty we are free at last." Martin Luther King Jr. http://webEbenezer.net

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[Boost] [Hana] David Stone's formal review
by David Stone 27 Jun '15

27 Jun '15

- Whether you believe the library should be accepted into Boost Yes - Your name > David Stone > - Your knowledge of the problem domain. > Advanced > - What is your evaluation of the library's: > * Design Good. It seems like most of the library follows the naming conventions of boost and the standard library (identifiers_like_this), but there are a few exceptions. The most notable is boost::hana::IntegralConstant. Why not integral_constant? Aside from minor issues like this, I am a huge fan of the overall idea of making compile-time and run-time code the same. Ideally we would have just a single language in C++ (as opposed to plain C++, template C++, constexpr C++, macro C++, and concept C++) and a single style of programming. The design of this library follows and extends this general trend in C++ that started with constexpr. > * Implementation > Looking through the source, it seems to flow naturally. Most of the code looks essentially the same as I would have written it. It has small, self-contained functions and appropriate use of macros, comments, and static_asserts. It would be nice if your IntegralConstant provided a specialization of std::numeric_limits. This would allow it to work properly with a few libraries (two examples are my bounded::integer library and this fixed point library: https://github.com/mizvekov/fp) You could then detect type-level compile-time constants as being any integer type for which std::numeric_limits<T>::min() == std::numeric_limits<T>::max(), which would allow the interoperability to flow the other way, but I do not know if the library ever requires this information or if it just relies on the compiler to complain about things that are not constexpr. > * Documentation > Very good from some perspectives. I started using the library by trying out checking expression validity, and it followed a logical progression, covering all types of members. This naturally led to me wondering if it is possible to use the library to test for the existence of a member named `blah`, but without knowing what category of member it is (variable, function, type, or template). I am assuming that this is as simple as saying `is_valid(variable) or is_valid(function) or ...` However, I feel that the documentation is trying to serve two incompatible purposes. On the one hand, it is trying to explain the theory of type computation using terms from functional programming. On the other hand, it also trying to be a practical guide to using the library. I feel that the second goal is compromised by the first. It seems that most of the content needed for the "cut to the chase" user is present, but by having this presentation in the form of a single document dilutes it. In other words, I don't know that the documentation passes the coworker test. If I were to show it to my coworkers, I can already hear them saying "All this stuff about computational quadrants and heterogeneous algorithms is all well and good, but how do I actually use this thing?". >From the perspective of someone who has never used MPL or Fusion (I started metaprogramming in C++11 and C++14 and never found a need for them), I do not have a problem with the comparisons to the other libraries in the documentation. I know another reviewer had mentioned that as a concern, but it just reads as evaluating prior art rather than reading as assuming prior knowledge. * Tests > I have not looked at the library's tests, I just tried to use it. > * Usefulness > The lack of constexpr lambdas really hurts the library's usefulness. It is because of this hole in the language that it can be difficult to slowly move to hana. I would like to just replace the implementation of a few functions with hana implementations at first, but then my functions are no longer constexpr if I do the obvious implementation. I have to make sure to change all of my types to IntegralConstant, for instance, to get a non-constexpr value from which I can extract a constexpr value from its type. This has a larger ripple throughout than I would like for just testing out a library before committing to it. That being said, once updating your code to fit into this paradigm, it does seem to simplify things a bit. I expect that as I update my library to be more hana friendly throughout, this simplification will increase. It was a bit disheartening at first when my code size grew slightly as I wrote various shims to translate to the correct types (I had more constexpr functions returning bool, and not so much classes that derive from integral_constant), but that ended up being a temporary state until I worked through more code. I wonder if I passed a constexpr function object rather than a non-constexpr lambda if these limitations would be removed? In practice this would probably lead to more code in the intermediate step even if it did work due to the boilerplate of defining a non-lambda function object. > - Did you attempt to use the library? If so: > * Which compiler(s)? > * What was the experience? Any problems? > clang 3.6.0 The first thing I tried was to use is_valid to determine the existence of a member type. This immediately crashed clang in the parser (I haven't had time to extract the bug report yet, but I will). It didn't seem to be the library directly, especially since others have used this feature, but the combination of my library (bounded::integer) with this feature of hana seemed to interact to cause a crash. clang seemed to perform a bit better with my second test, which was to replace some enable_if with if_. > - How much effort did you put into your evaluation of the review? > > In addition to talking with Louis at C++Now, I spent a few days trying out the library.

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comparing test results between master and develop
by Stefan Seefeld 26 Jun '15

26 Jun '15

Hello, I'm trying to compare the state of the develop and master branch for the Boost.Python project, to figure out whether I can merge the develop branch to master. I find that a bit difficult, though, and was wondering whether people here have any advice. Are there any tools to generate an easy-to-analyze diff ? Right now I'm visually inspecting http://www.boost.org/development/tests/master/developer/python.html and http://www.boost.org/development/tests/develop/developer/python.html, which in itself is non-trivial given the size of the table. In addition, some testers only run on develop, some only on master, creating incommensurable results. Is there a better way to do this ? Thanks, Stefan -- ...ich hab' noch einen Koffer in Berlin...

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[build] msvc-14.0 toolset can't find mt.exe?
by Peter Dimov 26 Jun '15

26 Jun '15

I've installed Visual Studio 2015 RC Community, and the msvc-14.0 toolset can't find mt.exe. I have mt.exe (twice), once in the 7.1A SDK, once in the 8.1 SDK. Does anyone have an idea what's wrong?

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[hana]recursive data type?
by Larry Evans 25 Jun '15

25 Jun '15

How would one define a recursive data type in hana something described by the type equation: hana_list<T> = hana::nothing | std::pair<T,hana_list<T> > where hana_list<T> is a list of T's terminated by nothing?

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future/packaged_task Sean Parent design
by Vicente J. Botet Escriba 25 Jun '15

25 Jun '15

Hi, Sean Parent suggests (See [1] Better Code: Concurrency) to remove the promise and left the packaged_task serve as single provider of a future. Both are created at once using the package factory. His future library doesn't include a shared_future as the future contains a value that can be observed several times. The continuation takes the value and not the future. So a future can have several continuations. If the store type is movable only, then the future can have only one continuation. Not really strange coming from Sean, future and packaged_task are copyables :) One more thing, there is not get no wait, but a get_try that return an optional<T>. Scales better. IIUC the implementation allows to implement when_all on top of future/packaged_task. The trick is that that the packaged_task can store some context. async has always an Scheduler as parameter. Scheculers are just Copyable Callables having this signature void(void()). There is no need for function add/spawn. when_all has also a callable as argument. I find the Sean's design clean and simple (See the code [2]). What do you think of it? Do you see any issues on it? * I don't understand why when_all continuation has the futures as parameters (I suspect that this is a type on the documentation). * I would rename get_try to try_get. This function could return optional<expected<T>>. What are you missing ? * catch_error/recover that is already planed. * when_any Best, Vicente [1] https://github.com/sean-parent/sean-parent.github.io/wiki/Papers-and-Presen… [2] https://github.com/stlab/libraries/tree/develop

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Using Clang compiler in place of GCC
by Paul A. Bristow 25 Jun '15

25 Jun '15

I have installed Clang 3.6.1 (along with previously used versions of GCC) downloaded from LLVM and using the clang for LLVM Windows installer on Windows 8.1 I:\modular-boost\libs\fixed_point\example>clang++ --version clang version 3.6.1 (tags/RELEASE_361/final) Target: i686-pc-windows-gnu Thread model: posix suggests that I have the compiler in place OK and it should be in my PATH (becos I asked for it to be). --debug-configuration notice: will use 'C:/LLVM/bin/clang++.exe' for clang-linux, condition <toolset>clang-linux-3.6.1 For a project, I have a jamfile starting project : requirements <include>../include # quickdox/include <include>../../.. # modular-boost root #toolset requirements. # GCC requirements. #<toolset>gcc:<cxxflags>-std=gnu++11 # If requires C++11 library. <toolset>gcc:<cxxflags>-Wno-unused-local-typedefs <toolset>gcc:<cxxflags>-Wno-missing-braces # Clang requirements. #<toolset>clang:<cxxflags>-std=c++11 # If requires C++11 library. (I also have environment BOOST_ROOT = I:\modular-boost) when I run b2 toolset=gcc all compiles and run as expected. when I run b2 toolset=clang I get messages like common.mkdir ..\..\..\bin.v2\libs\quickdox\example\quick_auto_dox_index.test\clang-linux-3.6.1 common.mkdir ..\..\..\bin.v2\libs\quickdox\example\quick_auto_dox_index.test\clang-linux-3.6.1\debug clang-linux.compile.c++.without-pth ..\..\..\bin.v2\libs\quickdox\example\quick_auto_dox_index.test\ clang-linux-3.6.1\debug\quick_auto_dox_index.obj quick_auto_dox_index.cpp:53:10: fatal error: 'iostream' file not found (or other files like cstddef, iomanip on other projects) #include <iostream> ^ 1 error generated. "C:/LLVM/bin/clang++.exe" -c -x c++ -O0 -g -fno-inline -Wall -g -march=i686 -m32 -DBOOST_ALL_NO_L IB=1 -I"..\..\.." -I"..\include" -o "..\..\..\bin.v2\libs\quickdox\example\quick_auto_dox_index.test \clang-linux-3.6.1\debug\quick_auto_dox_index.obj" "quick_auto_dox_index.cpp" (Full log attached). This suggests that it is not finding the system file <iostream> ... but I'm puzzled at what is missing (and why). Suggestions most welcome. Paul --- Paul A. Bristow Prizet Farmhouse Kendal UK LA8 8AB +44 (0) 1539 561830

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Stupid Constexpr Lambda Trick
by Giovanni Piero Deretta 24 Jun '15

24 Jun '15

Hi All, In the last few months constexpr lambdas and their absence in the standard came up multiple times in boost-devel, expecially when discussing the Hana library. I just wanted to share a C++14 emulation of the feature. The emulation uses both the already known conditional operator trick to allow constepr function objects to be initialized from lambda expressions, plus what I think is a novel trick to allow the actual function object operator() to be constexpr. Implementation + example is here: https://github.com/gpderetta/libtask/blob/master/lambda.cpp Sorry about the macro obfuscation, I was experimenting with a 'cute' lambda interface, but the underlying idea is very simple and pretty obvious in retrospect. I haven't tested that forwarding is always correc and I probably got some cases wrong. Lambda captures and multiple statemens are doable, but are left as an exercise for the reader :) I came up with the trick when trying to implement an emulation of N3617 (Lifting overload sets into function objects). Turns out that implementing the 'quote' syntax is almost trivial in C++14 with generic lambdas, but making it constexpr reliably has so far eluded me as all implementations I have tried ICE both gcc and clang. Still the constexpr lambda emulation itself seems to work. HTH, -- gpd

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Re: [boost] future/packaged_task Sean Parent designn
by Giovanni Piero Deretta 24 Jun '15

24 Jun '15

On 24 Jun 2015 10:11 am, "Niall Douglas" <s_sourceforge(a)nedprod.com> wrote: > > On 24 Jun 2015 at 1:09, Vicente J. Botet Escriba wrote: > > > Sean Parent suggests (See [1] Better Code: Concurrency) to remove the > > promise and left the packaged_task serve as single provider of a future. > > Both are created at once using the package factory. > > I was at his talk at C++ Now. > > The first thing which put me off his proposal was that he appears to > be unaware of the highly optimised and very flexible de facto task > concurrency system in C++ which has been around for years, and has > just recently been standardised. It's called ASIO. > > I also think packaged_task is overkill for creating futures. There > are some times you really do just want a promise and nothing more. There is no reason for a packaged task implementation to be more heavy weight than a promise. If the packaged task is [](T x) { return x; } then it is also semantically equivalent to promise<T>, just in a nicer interface. Bonus points it works beautifully with ASIO without any explicit support from ASIO itself. > There are even times you just want to create a future standalone, and > for that we now have make_ready_future(). > > > His future library doesn't include a shared_future as the future > > contains a value that can be observed several times. > > If I remember rightly, internally his future has a shared_ptr, which > really means he's proposing that future becomes a shared_future. I > had doubts before until that part, but that killed his proposal for > me. It's a non-starter as a practical design for my needs, but is > still useful for ideas. > His implementation uses a shared ptr, but I think you could do without by deep copying the futures and internally chaining via then. This way you only pay the cost if you actually copy. I strongly believe that 'then' and other accessors should be non const so that concurrent calls *on the same future* need not be supported. -- gpd

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[hana] Formal review
by Christophe Henry 24 Jun '15

24 Jun '15

Dear all, Following is my review of Hana. - Whether you believe the library should be accepted into Boost Yes, unconditionally. Having only one compiler compiling it is not the library's fault and it should not be held against it. If possible, I'd like to have some gcc support (and a clear note of what can be used with gcc). - Your name Christophe Henry - Your knowledge of the problem domain. Good knowledge of TMP, MPL and Fusion through my authoring of MSM. No expert of C++14 - What is your evaluation of the library's: * Design Very nice and interesting. What really slapped me in the face is writing this: template <typename ...T> auto smallest = minimum(make_tuple(type<T>...), [](auto t, auto u) { return sizeof_(t) < sizeof_(u); }); Instead of with MPL: template <typename ...T> struct smallest : deref< typename min_element< vector<T...>, less<sizeof_<_1>, sizeof_<_2>> >::type > { }; Ouch! I had forgotten how hard MPL can be... However, being value-based instead of type-based turns out to be a strength but also a weakness. To test the library, I replaced some simple MPL-based implementation parts of MSM with Hana. It works, but the code is not as simple and clean as I had hoped. For example: typedef typename ::boost::mpl::fold< stt_simulated,mpl::vector0<>, ::boost::mpl::push_back< ::boost::mpl::placeholders::_1, make_row_tag< ::boost::mpl::placeholders::_2 , BaseType > > >::type type; Became: static auto fold() { return boost::hana::fold.left(stt_simulated{}, boost::mpl::vector0<>{}, [](auto vec, auto t) { return typename ::boost::mpl::push_back< decltype(vec), typename make_row_tag <typename decltype(t)::type, BaseType>::type>::type{}; }); } typedef decltype(fold()) type; I had to create object where I actually just wanted types and also a static function so I can decltype. This is because this code was written within a struct (serving as metafunction). Honestly, my win in readability is limited ;-) But my problems started earlier. The heart of MSM is the transition table: struct transition_table : mpl::vector< Row < Stopped , stop , Stopped , none , none >, ... >{} All states and events being types, using Hana would lead me to write: Row < Stopped{} , stop{} , Stopped{} , none{} , none{} > which would be a regression. I'd love to get rid of my mpl::vector but Hana won't help me there. Maybe MSM was the wrong test object. The lack of support for mpl::set reduces to a very small part the algorithms I could port to Hana. Louis seems to want to change this, which I can only welcome. In the end, I feel that using Hana with MSM would be a take all or nothing choice. With the current compiler support, it is not something I will do in the next few months. Still, the library has a nice design and potential and I will probably use it either later in other use cases (or with MSM with better support of MPL). * Implementation I had a short glance and found it very clean. I found only one thing which bugged me, the use of non fully qualified names in some places. True, many other boost libraries do the same and it brings a lot of problems (anyone who tried to include Geometry and TypeErasure in one TU will love the duplicate definition of use_default). Still, a "return true_;" is begging for conflicts. * Documentation Great! Way above Boost level. As others said, please use fully qualified names where possible. It makes it much easier to follow. * Tests Did not look. * Usefulness Very useful if you have objects in the first place, maybe less to do TMP. - Did you attempt to use the library? If so: * Which compiler(s)? Clang 3.5. * What was the experience? Any problems? I got a few compiler errors. - A static_assert "hana::fold.left(xs, state, f) requires xs to be Foldable" when forgetting to #include <boost/hana/ext/boost/mpl/vector.hpp> I had included boost/hana.hpp but it did not include all, which is annoying. - a name conflict with std::size_t, though I deserved punishment by adding a using namespace boost::hana before including other headers. - How much effort did you put into your evaluation of the review? 8 hours reading the doc and rewriting some MSM algorithms with Hana. Thank you Louis for writing this excellent library and thank you Glen for managing the review! Christophe

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[hana] Lorenzo's Formal review for Hana
by Lorenzo Caminiti 24 Jun '15

24 Jun '15

Hello Glen, Louis, and all, Please find below my review of the proposed Boost.Hana library. > - Whether you believe the library should be accepted into Boost Yes, Boost.Hana should be accepted into Boost. I decided to make my acceptance vote unconditional. However, I do have some concerns and I hope these can be addressed if Hana is in fact accepted into Boost. I marked these concerns as "[CONCERN]" below. > - Your name Lorenzo Caminiti. > - Your knowledge of the problem domain. I have been using C++ Template Meta-Programming (TMP) for 10+ years now. I routinely maintain ~23,000 lines of production code that extensively uses Boost.MPL, Boost.Fusion, and a TMP-based serialization mechanism (among a number of other Boost libraries) -- compilation times are a *huge* issue with this code! > You are strongly encouraged to also provide additional information: > - What is your evaluation of the library's: > * Design The library API seems reasonable, consistent, and powerful. * [CONCERN] Assertions should be renamed from ..._CHECK to ..._ASSERT (to be consistent with assert, static_assert, BOOST_STATIC_ASSERT, BOOST_MPL_ASSERT, etc.). * Is there a ..._MSG version for the assertion macros? (These should probably just variadic macros where a second optional parameter represents the error message to display in case the asserted condition if false.) * The following is very nice! auto has_toString = is_valid([](auto&& obj) -> decltype(obj.toString()) { }); I've been wanting to do the above at function scope for a long time (so I can program it within the function where I actually need it). Now with C++14 generic lambdas we finally can :) Also this is very nice! template <typename T> std::string optionalToString(T const& obj) { return if_(has_toString(obj), [](auto& x) { return x.toString(); }, [](auto& x) { return "toString not defined"; } )(obj); } Somewhat similar to my static_if (renamed call_if, after Vicente's suggestion) proposal using C++14 generic lambdas: http://boost.2283326.n4.nabble.com/static-if-Is-there-interest-in-a-static-… BTW, how would you program the following possible implementation of std::advance in Hana? template<typename Iter> struct is_random_access_iterator : std::is_same< typename std::iterator_traits<Iter>::iterator_category, std::random_access_iterator_tag > {}; template<typename Iter> struct is_bidirectional_iterator : std::is_same< typename std::iterator_traits<Iter>::iterator_category, std::bidirectional_iterator_tag > {}; template<typename Iter> struct is_input_iterator : std::is_same< typename std::iterator_traits<Iter>::iterator_category, std::input_iterator_tag > {}; template<typename Iter, typename Dist> void myadvance(Iter& i, Dist n) { Iter *p = &i; // So captures change actual pointed iterator value. call_if<is_random_access_iterator<Iter> >( std::bind([] (auto p, auto n) { *p += n; }, p, n) ).template else_if<is_bidirectional_iterator<Iter> >( std::bind([] (auto p, auto n) { if(n >= 0) while(n--) ++*p; else while(n++) --*p; }, p, n) ).template else_if<is_input_iterator<Iter> >( std::bind([] (auto p, auto n) { while(n--) ++*p; }, p, n) ).else_( std::bind([] (auto false_) { static_assert(false_, "requires at least input iterator"); }, std::false_type()) // Use constexpr value. ); } * This macro: struct Person { BOOST_HANA_DEFINE_STRUCT(Person, (std::string, name), (int, age) ); }; Will it work even if the data member types contain commas? For example, the following is supported, correct? (It should be because these can use variadic macros...) struct Person { BOOST_HANA_DEFINE_STRUCT(Person, (std::map<int, char>, name), (int, age) ); }; P.S. These sort of macros /could/ be implemented as follows if users found this syntax to be more readable (but maybe not...): struct Person { BOOST_HANA_DEFINE_STRUCT(Person, (std::map<int, char>) name, (int) age, ); }; * [CONCERN] The docs say: "Hana's design assumes that most of the time, we want to access all or almost all the elements in a sequence anyway, and hence performance is not a big argument in favor of laziness." Especially given that other well-established libraries like Fusion addressing the same problem domain have gone in favor of laziness instead... Is this a good assumption? If so, why? * [CONCERN] The docs say: "By default, Hana assumes functions to be pure. A pure function is a function that has no side-effects at all." Will this assumption limit what users will be able to do with Hana? Do MPL and Fusion relay on a similar assumption? Yes/no, why... * [CONCERN] I would prefer a descriptive name for the library instead of Hana. I am well aware that Phoenix, Spirit, Wave, etc. are examples of non-descriptive names in Boost. I consider those bad naming choices and I would not follow them. Changing the library name should only take a few days (maybe 2-5 days... especially with tools like grep and sed) so that should not be a problem. Others pointed out that there might be copyright/trademark issues with the name "Hana". The possibility to have to change such name at some point /after/ the library has been released in Boost would be a disaster for the users... such risk should be avoided. Possible names? typeval (given the library is about "TYPEs as VALuses", plus the similar, already familiar, name std::declval) meta metaval metaexpr generic (assuming Matt Calabrese is no longer planning to use this) ... * [CONCERN] Rename Map, Range, etc. to map, range, etc. (all lower case). In Boost and STL capital letters are only used for template parameters, and maybe concepts. (If it is important to distinguish that those are tags (I don't think so) then name them map_tag, range_tag, etc. but still no capital letters.) * [CONCERN] is_empty, length, and few other names should be changed to empty, size, etc. to match STL naming conventions (so I don't have to remember different names for the same thing). > * Implementation Some code can be optimized, but the author already mentioned he will look into that this summer. I did not see any specific issue otherwise. > * Documentation * [CONCERN] The documentation will be much (much!) more readable is the "hana" namespace was not stripped away. Please write hana::..., mpl::... (if not the full boost::hana::..., boost::mpl::...) in the docs. * The docs say: "Notice how we cast the result of x.member to void? This is to make sure that our detection also works for types that can't be returned from functions, like array types." auto has_member = is_valid([](auto&& x) -> decltype((void)x.member) { }); But obviously, the following (without the cast) would work too, correct? auto has_member = is_valid([](auto&& x) -> decltype(x.member, void()) { }); * I would expect the following example to use operator|| instead of or_: auto ts = filter(types, [](auto t) { return or_(is_pointer(t), is_reference(t)); }); * Performance graphs would be more readable if they always used the same color for the same entity. For example, sometimes mpl::vector is blue, other times it is orange... * Why the "Runtime performance of reverse on normal container" for fusion::vector stops at "Number of elements" = 50? > * Tests > > * Usefulness * If not for anything else, I will use this library for its SFINAE facilities. Second, I will use this library in production code for its improved compilation times (assuming these can be confirmed on MSVC). Finally, I am curious to use this library in general because it seems it will improve my meta-programming, also making easier to read. * [CONCERN] The author should be committed to support the library on GCC and MSVC once that becomes feasible, even if that requires a good deal of workarounds. For example, Boost.Preprocessor is full of MSVC workaround (because MSVC preprocessor is still not standard compliant... after 30+ years of existence of the C preprocessor). Maybe MSVC will never be 100% C++14 standard compliant... I don't know. But I do know that if this library is not ported to MSVC at some future point, I won't be able to use it in my production code. I do hope that adoption into Boost will push vendors to support C++14 constructs used by this library TMP techniques. I also hope the author is committed to do whatever it takes to make the library work on MSVC. * [CONCERN] What compiler was used to measure performance? CLang? I hope the promised performance gains (especially compile-time reductions) will be there for GCC, and especially later also for MSVC. If not, that will significantly limit my motivation on using this library in production code. TMP compilation times are largely dependant on specific compiler implementations of C++ template machinery which might vary significantly from vendor to vendor. Therefore, at the moment I only know that the library is expected to compile faster on Clang, but unfortunately that does not tell me anything about expected compilation time improvements on GCC, and even less on MSVC... > - Did you attempt to use the library? If so: > * Which compiler(s)? Clang. > * What was the experience? Any problems? Overall, pretty good experience. No specific issue to report a part from what already noted. > - How much effort did you put into your evaluation of the review? A total of about 2 days between reading docs, playing with some examples, and looking at the code a bit. My thanks to Luis for his outstanding work with this library! --Lorenzo On Wed, Jun 10, 2015 at 2:19 AM, Glen Fernandes <glen.fernandes(a)gmail.com> wrote: > Dear Boost community, > > The formal review of Louis Dionne's Hana library begins today,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. > > 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 > * Conditions for acceptance > - 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? > > We await your feedback! > > Best, > Glen > > _______________________________________________ > Unsubscribe & other changes: http://lists.boost.org/mailman/listinfo.cgi/boost

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[graph] depth_first_visit_impl
by Michael Marcin 24 Jun '15

24 Jun '15

I was doing some work with depth_first_search and came across some issues that seem surprising with the implementation. First vis.finish_edge doesn't seem to ever get called on msvc. Second changing the code to call finish_edge directly instead of through the call_finish_edge machinery seems to result in incorrect edges being finished. Third the implementation of depth_first_visit_impl pushes into a std::vector stack even for vertices with no out_edges. If I have a graph with a large number of vertices but few or no edges this seems bad. This seems to force a dependency on optional as well. Finally the loop as written should probably be a do..while since the stack will never be empty on the first test. I attached a patch that addresses the second and third issues. The tests continue to pass for me with this change.

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[Hana] Formal review
by Bruno Dutra 23 Jun '15

23 Jun '15

Dear all, Following is my review of Hana. - 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. Yes, absolutely, but please read on. - Are you knowledgeable about the problem domain? I've been playing with metaprogramming as a hobby since 2011 when I first came across Boost.MPL. I experimented with a library that implements the unification algorithm at compile time using Boost.MPL for a long time, on and off, and recently I've decided giving a shot at my own implementation of a C++11 version of Boost.MPL. - What is your evaluation of the design? The design seems to be very general and abstract, based on formal mathematical concepts. I've had my dose of FP through SML and lisp, however I've never dug deep into category theory, so I won't venture into judging the way these abstract concepts were translated to C++, but all looks sound to me. I'm very fond of the way type computations are carried out by value through the use of type<> and decltype(). Such an ingenious simplicity. Once one gets it, one realizes how beautifully it merges value and type computations into one. I also like very much the design of compile time constants, their custom _c suffix and operators. To me, that is material for standardization. I would like to point out however, that from the point of view of someone who has basically solely done C++ his entire life, just like myself, Hana can look *very* unfamiliar. I understand it is mostly my fault for not properly having learnt FP before, however I believe I'm not alone among average C++ programmers, so I fear this could prevent many potential users from adopting Hana, simply because one tends to stick to things that look familiar to one. Now I'm not sure that is any easy way around this unfamiliarity. I've seen others pointing out that names could better reproduce the C++ standard library (to what I agree) and perhaps that's indeed all one could do to tighten the gap that separates Hana from mainstream C++ libraries. At any rate, I just felt I should stress this point, to make sure it is not underestimated. - What is your evaluation of the implementation? I've just briefly peeked at the code base out of curiosity and it looks pretty clean and organized. The use of global function objects however intrigues me, why not free functions? I've also found myself stumbling on variable templates. Perhaps that's just me, but really I find they make everything so cryptic. Anyways, I guess it's not Hana's fault to make arguably good use of something that is part of the language. - What is your evaluation of the documentation? I find myself blindly using the search button in hope to find whatever I'm looking for more often than I'd rather do, but perhaps it's just a matter of getting used to how the documentation is organized. One thing I'd like to see improved is the alphabetical index. I'd expect it to be thorough, but at least "is_a" is missing, so I assume a rationale exists to decide what goes there? I think it would be better to list everything exhaustively, so users may rely on the browser's find tool to explore the library. - What is your evaluation of the potential usefulness of the library? At first I was afraid Hana were too academical and abstract to be a good tool for getting down to business, but after playing with it a little bit I can see that, once one gets its design, it does make metaprogramming quite straightforward. I believe however that most users will attain to a very limited subset of functionalities in order to just get their tasks accomplished. So much so, that I'd strongly advise Hana to be split into one highly specialized tool for straightforward metaprogramming and another more abstract halve providing the more generic concepts. This could ease user experience considerably, reducing the novelty presented by Hana and thus tightening the gap I've mentioned before. - Did you try to use the library? With what compiler? Did you have any problems? Yes on Clang 3.6.1. I tried to implement the unification algorithm [1] at compile time using Hana and, though I haven't actually finished, I could see it would be straightforward. In fact I gave up on it when I found a bug which prevented the construction of optional maps, but not too long after I contacted Louis and opened an issue [2] it seems to have already been fixed on develop branch. I didn't test the fix myself though. - How much effort did you put into your evaluation? A glance? A quick reading? In-depth study? About 4 hours reading the documentation, another 4 hours trying the library and about 2 hours to write this review. *Bruno C. O. Dutra* [1]: https://en.wikipedia.org/wiki/Unification_(computer_science) [2]: https://github.com/ldionne/hana/issues/149

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[test] Re: [Boost-testing] Develop branch test runners crashing
by Rene Rivera 23 Jun '15

23 Jun '15

Please fix ASAP. On Tue, Jun 23, 2015 at 8:32 AM, Tom Kent <lists(a)teeks99.com> wrote: > Sometime between 22:30 and 03:30 last night (pacific time) all the develop > tests started crashing on windows and linux. > > The tail of results/bjam.log is: > > notice: iostreams: not using bzip2 compression > notice: iostreams: not using bzip2 compression > ..\libs\test\test\Jamfile.v2:59: in docs-example-as-test > *** argument error > * rule boost.test-self-test ( test-rule : test-suite : test-name : > usage-variant ? : pattern_file * : source_files * : extra-libs ? : > extra-options ? ) > * called with: ( : ../doc/examples : : included : : > /D:/t08/run/boost_root/libs/test/doc/examples/boost_test_bitwise.run-fail.cpp > ) > * missing argument test-rule > ..\libs\test\test\Jamfile.v2:18:see definition of rule > 'boost.test-self-test' being called > (builtin): in sequence.transform > ..\libs\test\test\Jamfile.v2:162: in modules.load > D:/t08/run/boost_bb/src/build\project.jam:325: in load-jamfile > D:/t08/run/boost_bb/src/build\project.jam:64: in load > D:/t08/run/boost_bb/src/build\project.jam:145: in project.find > D:/t08/run/boost_bb/src/build\targets.jam:452: in find-really > D:/t08/run/boost_bb/src/build\targets.jam:474: in find > D:/t08/run/boost_bb/src/build\targets.jam:305: in targets-to-build > D:/t08/run/boost_bb/src/build\targets.jam:270: in > class(a)project-target.generate > D:/t08/run/boost_bb/src\build-system.jam:707: in load > D:\t08\run\boost_bb\src/kernel\modules.jam:295: in import > D:\t08\run\boost_bb\src/kernel/bootstrap.jam:139: in boost-build > D:\t08\run\boost_root\boost-build.jam:17: in module scope > > Any thoughts? > > _______________________________________________ > Boost-Testing mailing list > Boost-Testing(a)lists.boost.org > http://lists.boost.org/mailman/listinfo.cgi/boost-testing > -- -- Rene Rivera -- Grafik - Don't Assume Anything -- Robot Dreams - http://robot-dreams.net -- rrivera/acm.org (msn) - grafikrobot/aim,yahoo,skype,efnet,gmail

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Re: [boost] [test] Develop branch test runners crashing
by Andrey Semashev 23 Jun '15

23 Jun '15

On Tue, Jun 23, 2015 at 4:32 PM, Tom Kent <lists(a)teeks99.com> wrote: > Sometime between 22:30 and 03:30 last night (pacific time) all the develop > tests started crashing on windows and linux. > > The tail of results/bjam.log is: > > notice: iostreams: not using bzip2 compression > notice: iostreams: not using bzip2 compression > ..\libs\test\test\Jamfile.v2:59: in docs-example-as-test > *** argument error > * rule boost.test-self-test ( test-rule : test-suite : test-name : > usage-variant ? : pattern_file * : source_files * : extra-libs ? : > extra-options ? ) > * called with: ( : ../doc/examples : : included : : > /D:/t08/run/boost_root/libs/test/doc/examples/boost_test_bitwise.run-fail.cpp > ) > * missing argument test-rule > ..\libs\test\test\Jamfile.v2:18:see definition of rule > 'boost.test-self-test' being called > (builtin): in sequence.transform > ..\libs\test\test\Jamfile.v2:162: in modules.load > D:/t08/run/boost_bb/src/build\project.jam:325: in load-jamfile > D:/t08/run/boost_bb/src/build\project.jam:64: in load > D:/t08/run/boost_bb/src/build\project.jam:145: in project.find > D:/t08/run/boost_bb/src/build\targets.jam:452: in find-really > D:/t08/run/boost_bb/src/build\targets.jam:474: in find > D:/t08/run/boost_bb/src/build\targets.jam:305: in targets-to-build > D:/t08/run/boost_bb/src/build\targets.jam:270: in > class(a)project-target.generate > D:/t08/run/boost_bb/src\build-system.jam:707: in load > D:\t08\run\boost_bb\src/kernel\modules.jam:295: in import > D:\t08\run\boost_bb\src/kernel/bootstrap.jam:139: in boost-build > D:\t08\run\boost_root\boost-build.jam:17: in module scope > > Any thoughts? Looks like a Boost.Test issue.

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Develop branch test runners crashing
by Tom Kent 23 Jun '15

23 Jun '15

Sometime between 22:30 and 03:30 last night (pacific time) all the develop tests started crashing on windows and linux. The tail of results/bjam.log is: notice: iostreams: not using bzip2 compression notice: iostreams: not using bzip2 compression ..\libs\test\test\Jamfile.v2:59: in docs-example-as-test *** argument error * rule boost.test-self-test ( test-rule : test-suite : test-name : usage-variant ? : pattern_file * : source_files * : extra-libs ? : extra-options ? ) * called with: ( : ../doc/examples : : included : : /D:/t08/run/boost_root/libs/test/doc/examples/boost_test_bitwise.run-fail.cpp ) * missing argument test-rule ..\libs\test\test\Jamfile.v2:18:see definition of rule 'boost.test-self-test' being called (builtin): in sequence.transform ..\libs\test\test\Jamfile.v2:162: in modules.load D:/t08/run/boost_bb/src/build\project.jam:325: in load-jamfile D:/t08/run/boost_bb/src/build\project.jam:64: in load D:/t08/run/boost_bb/src/build\project.jam:145: in project.find D:/t08/run/boost_bb/src/build\targets.jam:452: in find-really D:/t08/run/boost_bb/src/build\targets.jam:474: in find D:/t08/run/boost_bb/src/build\targets.jam:305: in targets-to-build D:/t08/run/boost_bb/src/build\targets.jam:270: in class(a)project-target.generate D:/t08/run/boost_bb/src\build-system.jam:707: in load D:\t08\run\boost_bb\src/kernel\modules.jam:295: in import D:\t08\run\boost_bb\src/kernel/bootstrap.jam:139: in boost-build D:\t08\run\boost_root\boost-build.jam:17: in module scope Any thoughts?

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[coroutine2] Difference between coroutine and coroutine2
by Aaron Levy 23 Jun '15

23 Jun '15

Are boost::coroutines::symmetric_coroutine<> and boost::coroutines::asymmetric_coroutine<> part of the coroutine library or coroutine2 library. Besides being C++14-only, in what ways does coroutine2 differ from coroutine? -- Aaron Levy aaron.levy(a)yandex.com

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[Optional] Monadic bind
by Tobias Loew 23 Jun '15

23 Jun '15

While playing around with boost::optionals I had code like the following struct A { ... int i; ... }; boost::optional a; // do something with 'a' // optional-projection to a::i boost::optional<int> a_i; if(a) a_i = a->i; which seemed quite verbose for something that's rather natural in functional languages: boost::optional is a monadic structure, which lifts a type T by extending it with a new bottom-element (represented by the empty optional<T>), thus it should also have a "bind" and a "map"-equivalent, which could be implemented for instance as as member functions of optional template<class B> auto bind(B&& binder) const -> boost::optional<typename std::decay<decltype(std::bind(binder, get())())>::type> { if(this->is_initialized()) { return std::bind(binder, get())(); } else { return boost::none; } } and template<class B> auto map(B&& f) const -> boost::optional<typename std::decay<decltype(std::bind(f, get())())>::type> { if(this->is_initialized()) { return std::bind(f, get())(); } else { return boost::none; } } where map lifts f from A->B to optional -> optional< B > and applies 'this' to it. This would allow things like boost::optional a; auto a_i = a.map(&A::i); // "optional-projection"; type of a_i is boost::optional<int> Tobias -- View this message in context: http://boost.2283326.n4.nabble.com/Optional-Monadic-bind-tp4677431.html Sent from the Boost - Dev mailing list archive at Nabble.com.

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[test] Where we are with the new version?
by Vicente J. Botet Escriba 23 Jun '15

23 Jun '15

Hi, I'm wondering if the new Boost.Test will be merged one day to the master branch. Best, Vicente

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[config] 'requres' doesn't take differing -std into account
by Peter Dimov 22 Jun '15

22 Jun '15

I have, in my user-config.jam, using gcc ; feature.subfeature toolset gcc : std : cxx0x cxx11 cxx1y cxx14 : optional composite propagated ; feature.compose <toolset-gcc:std>cxx0x : <cxxflags>-std=c++0x ; feature.compose <toolset-gcc:std>cxx11 : <cxxflags>-std=c++11 ; feature.compose <toolset-gcc:std>cxx1y : <cxxflags>-std=c++1y ; feature.compose <toolset-gcc:std>cxx14 : <cxxflags>-std=c++14 ; using clang : : : <cxxflags>-Wno-variadic-macros <cxxflags>-Wno-c99-extensions ; feature.subfeature toolset clang : std : cxx0x cxx11 cxx1y cxx14 : optional composite propagated ; feature.compose <toolset-clang:std>cxx0x : <cxxflags>-std=c++0x ; feature.compose <toolset-clang:std>cxx11 : <cxxflags>-std=c++11 ; feature.compose <toolset-clang:std>cxx1y : <cxxflags>-std=c++1y ; feature.compose <toolset-clang:std>cxx14 : <cxxflags>-std=c++14 ; This allows me to use toolset=clang (without -std) and toolset=clang-cxx11 (with -std=c++11). The 'requires' rule however caches the results of the configuration check when I run with toolset=clang, and then when I rerun with toolset=clang-cxx11, it uses the cached values, which is wrong. I use something like run test.cpp : : : [ requires cxx11_variadic_templates cxx11_template_aliases cxx11_hdr_type_traits cxx11_hdr_tuple ] ;

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[hana] question
by Christophe Henry 22 Jun '15

22 Jun '15

Hi Louis, I'm experimenting with hana for the review and have one question. I can fold with boost::hana::fold.left(boost::mpl::vector<...>{}...) Do you have a way to iterate on elements of a mpl::set? Thanks, Christophe

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[Boost] [Hana] Formal review for Hana
by Glen Fernandes 22 Jun '15

22 Jun '15

Dear Boost community, The formal review of Louis Dionne's Hana library begins today,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. 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 * Conditions for acceptance - 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? We await your feedback! Best, Glen

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