August 2014 - Boost - lists.preview.boost.org

[Python] Improved exception handling for Python embedding
by Michael Koenig 04 Aug '14

04 Aug '14

Hey guys! Boost.Python throws boost::python::error_already_set exceptions whenever calls to embedding functions such as boost::python::import() or boost::python::exec() fail. This exception is just an empty class. It does not provide any information on the error which occurred on the Python side. It is not even a standard exception in the C++ sense. As a result, debugging problems with embedded Python code or even the Python environment (available packages etc.) with the current exception handling mechanism is difficult. So far, in our company we wrap most Boost.Python functions with custom exception handling code. In our exception handling code, we basically work the CPython API to extract details of Python exceptions such as * Exception types, * Error messages, and * Stack traces. We want to put this part of our embedding library back into the Boost.Python project. At the EuroPython 2014 conference in Berlin, I had a few discussions with Reinhard Wobst, Austin Bingham, and others, and the current exception handling mechanism was perceived an impediment on the usability of Boost.Python. I am most grateful for feedback of seasoned Boost contributors (and users) whether my proposal is of sufficient interest and how best to pursue it. Cheers Michael -- Dr. Michael König Software Engineer Blue Yonder GmbH Ohiostraße 8 76149 Karlsruhe Tel +49 (0) 721 383 117 38 Fax +49 (0) 721 383 117 69 michael.koenig(a)blue-yonder.com www.blue-yonder.com Registergericht Mannheim, HRB 704547 USt-IdNr. DE 277 091 535 Geschäftsführer: Jochen Bossert, Uwe Weiss (CEO)

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Re: [boost] [GSoC] [Boost.Hana] Formal review request
by Dave Gomboc 04 Aug '14

04 Aug '14

> > [pfultz2] > > Yet it uses a lot of foreign functional concepts. Despite what google says, > > boost libraries are built around mostly C++-like 'interfaces'. I don't think > > its bad to introduce some functional-interfaces, but I know in the past > > libraies that libraries that were very functional were rejected from boost, > > because many people didn't grasp the purpose of them. So introducing a lot > > of functional interfaces on the surface of a library can hinder its adoption. This is a solid caution. Louis, it would be worth your while to review the comments made regarding the Boost review of FC++ some years back, in order to prepare you for the kinds of questions and concerns that primarily imperative-style developers raise. > [Louis Dionne] > That is sad, because the functional concepts are exactly what makes Hana so > powerful. Some problems are well suited for functional programming, and some > are not. Metaprogramming is __inherently__ functional, and it's about time > people embrace it. +1. On a related note (not quoting that other discussion here, but there's been some other postings on the subject), inventing new terminology for well-established programming concepts is not merely pointless, it's actually harmful. If C++ already has an established name for the programming concept, that would be a justifiable reason to use that other name instead of the standard functional programming name. So, it would not at all disturb me if "maybe" ends up being called something like "optional" (C++ is not even alone: Scala calls it "Option"). However, http://www.disi.unige.it/person/MoggiE/ftp/ic91.pdf serves as an existence proof that "monad" has been in use within the programming community since at least 1991. C++ doesn't directly model this concept elsewhere in its most generic form (notwithstanding http://bartoszmilewski.com/2014/02/26/c17-i-see-a-monad-in-your-future/) In this case, I am aware of no justification for using any other name. Dave

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Hana Searchable
by Robert Ramey 04 Aug '14

04 Aug '14

I can't review the whole library. So I'm confining my observations to just a couple of aspects. My method is to review some section of the documentation. it looks like a critique of the documentation, but it's really observations on the underlying design of the library. In this post I'm addressing Searchable in the reference section of the documentation. Searchable >From the explanation of Type class - given a type T, I'm expecting to see some sort of list of operations such that Searchable<T> will compile. What I see is: boost::hana::Searchable Struct Reference Type classes Description Data structures that can be searched. Searchables have a concept of keys and values. Searching is always done on the keys and the result is always the associated value. There is no requirement that the keys and values be different. Synopsis of methods constexpr auto any Return whether any key of the structure satisfies the predicate. More... … Instances and minimal complete definitions struct instance< Map > A map can be searched by its keys with a predicate yielding a boolean Integral. More... struct instance< Maybe > Instance of Searchable for Maybes. More... struct instance< Set > The keys and the values of a Set are its elements; the Searchable instance follows naturally from that. More... My first thought is: Searchable is (sort of) a C++ Concept (type constraints) "Synopsis of methods" is what we customarily refer to as "valid expressions" "Instances and minimal complete definitions" is what we customarily refer to as "models" But right away I have a problem - since "any" doesn't show a valid C++ expression at this level of the documentation I click "auto" and get: Initial value: = [](auto predicate, auto searchable) { return Searchable::instance< datatype_t<decltype(searchable)> >::any_impl(predicate, searchable); } which is totally mystifying to me. I realize that it's a C++ lambda expression. But the only reference I see to "any" is (maybe) Searchable::any_impl. I'm guessing that any_impl has some sort of code which uses predicate and searchable to to return some static_assert - or not. The usage of any_impl seems designed to hide the vary thing I'm interested it - what kind of type can I use as an argument to Searchable. This seems not at helpful to the user. Now "predicate" and "searchable" parameters are define (in text). All "searchable" says is that it's a structure to be searched - nothing about what constitutes such a structure. can std::vector<int> be used as this "searchable" parameter? don't know - and the document doesn't tell me. "predict is a little better in that it says that it's something that is called and that it returns a type fulfilling the constraints of "Logical" which itself linked (thank you). Now I have a few examples which are a little more helpful. BOOST_HANA_CONSTEXPR_LAMBDA auto odd = [](auto x) { return x % 2_c != 0_c; }; So now I see what a predicate is supposed to look like - in this case it's a function which returns a bool. The usage of auto certainly isn't helpful here. The syntax x % 2_c != 0_c is suggestive. It seems that 2_c and 0_c refer to integer constants 2 and 0 respectively. I'm sort of wondering why we can't just use 2 and 0 themselves since it seems we're using constexpr here. BOOST_HANA_STATIC_ASSERT(any(odd, list(1, 2))); The above is interesting. From the explanation of type class I expect this to trap at compile time - or not depending upon the type of list. First of all, I don't know whether this refers to std::list or some type of compile time list of types. Again the documentation leaves me mystified. Documentation BOOST_HANA_STATIC_ASSERT leaves me even more befuddled. It says that it resolves to either static_assert or assert depending on whether the argument is a constexpr or not. An interesting idea. But here we're inside the Searchable type class definition - so wouldn't it make more sense to invoke static_assert directly? The most confusing thing about the example is that Searchable is never mentioned. Isn't the point of defining a Typeclass (C++ concept)?. How it envisioned that this be used. Here is what I would expect to see using our customary way of looking at things in the customary way. I realize that it's not an exact match but it's the best I can do from looking at the documentation. #include "boost/concept/assert.hpp" // define concept Searchable template struct<class S, class P, class T> struct Searchable { BOOST_CONCEPT_ASSERT((std::UnaryPredicate<P>)); BOOST_CONCEPT_ASSERT((std::Sequence<T>)); }; // define any for searchable types template<class S, class P, class T> constexpr bool any(const S &s, const P & p){ BOOST_CONCEPT_ASSERT((Searchable<S, P>)); } // example auto constexpr odd = [](auto x) { return x % 2 != 0; }; ?::list<1, 2, 3> l; static_assert( any(list, odd) ); // should not trap ?::list<2, 4, 6> l2; static_assert( any(list, odd) ); // should trap with error at compile time There are lots of "holes" in my example above, I think this more or less captures what you have in mind. But it's much simpler to understand and use. I confess I've failed to understand the runtime aspects of your library. This is true even though I have worked with fusion more than most and a lot with MPL. I think this should be easy for me - but it's not. BTW - I only used "Searchable" as it happened to be the first one I looked at. Personally I don't believe that thinks like "Searchable", and "Sortable" don't belong as models of type constraints. Using "Sortable as a quick example, my complaint is that it's tautological. Something is defined here as "Sortable" if you can sort it. Actually something like "Sortable should be defined as: template<class Iterator> void quicksort(Iterator begin, Iterator end){ BOOST_CONCEPT_ASSERT((RandomAccessIterator<Iterator>)); BOOST_CONCEPT_ASSERT((LessThanComparable<Iterator::value_type)); … } while a different sorting algorithm void mergesort(C & c){ BOOST_CONCEPT_ASSERT((ForwardIterator<Iterator>)); BOOST_CONCEPT_ASSERT((LessThanComparable<Iterator::value_type)); } So the the idea of "Sortable" doesn't make any sense when not coupled with the data structure which holds the data. Although my example above is based on "Sortable" - it really applies to any type constraints with names like "Searchable", "Foldable", etc. Robert Ramey -- View this message in context: http://boost.2283326.n4.nabble.com/Hana-Searchable-tp4665987.html Sent from the Boost - Dev mailing list archive at Nabble.com.

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What are the things that we HAVE TO fix before shipping 1.56.0?
by Marshall Clow 03 Aug '14

03 Aug '14

We’re coming down to the end of the release process, so I’m taking a poll. * What bugs do you think MUST be fixed before shipping 1.56? In other words, if bug XXX is not fixed, then (in your opinion) we should not bother making a release. Thanks in advance. — Marshall

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Algorithm Packages
by Varun Raj 03 Aug '14

03 Aug '14

Hello everyone, I would like to develop packages for Boost Library specifically in the Algorithms section. So i would like to know the feedback on what Algorithms are most needed by the members of the community right now.Thank you for sparing your time for giving me a feedback.

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[utility] string_ref construction from rvalue reference to string
by Андрей Давыдов 03 Aug '14

03 Aug '14

Hello, boost. Are the any reasonable cases when construction boost::string_ref from std::string && is desirable? I mean that usage string_ref in the following examples is totally wrong, but not for compiler: using std::string; using boost::string_ref; // 1 { auto ref = string_ref(string("abacaba") + string("upyachka")); std::cout << ref << std::endl; } // 2 { string very_long(1000000, 'a'); auto ref = string_ref(very_long + "b"); std::cout << ref << std::endl; } In practice it gets worse, because the first example example works (gcc 4.9.1) thanks to optimizations with short literals, I suspect, and the second example leads to segmentation fault, as expected. Those errors can be caught at compile time if class "basic_string_ref" defintion would contain lines like following: template<typename Allocator> basic_string_ref(std::basic_string<charT, traits, Allocator> &&) = delete; I cannot understant does it prevent any correct usage of string_ref? -- Andrey Davydov

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Hangs with Boost 1.56 on clang armhf
by Niall Douglas 03 Aug '14

03 Aug '14

I'm seeing consistent hangs of AFIO on Boost 1.56 on Ubuntu 14.04 LTS for clang armhf. GCC armhf works fine, so this is a clang armhf related issue. https://ci.nedprod.com/view/Boost.AFIO/job/Boost.AFIO%20Test%20POSIX_A RM_clang%203.4/10/console I talked to Ubuntu upstream about this, and I had the idea of trying the LLVM armhf binaries provided at http://llvm.org/releases/3.4.2/clang+llvm-3.4.2-armv7a-linux-gnueabihf .tar.xz as surely LLVM provide good binaries. Same problem - tests hang. I tried running a test manually and I get this: terminate called after throwing an instance of 'boost::thread_interrupted' terminate called recursively terminate called recursively terminate called recursively terminate called recursively terminate called recursively terminate called recursively terminate called recursively terminate called recursively terminate called recursively terminate called recursively terminate called recursively terminate called recursively terminate called recursively terminate called recursively terminate called recursively terminate called recursively terminate called recursively terminate called recursively terminate called recursively terminate called recursively Remember, this is identical code to any other Linux target, plus this works a-ok for GCC armhf. A quick backtrace with gdb reveals this: terminate called after throwing an instance of 'boost::thread_interrupted' [Thread 0xb5b76450 (LWP 12610) exited] Program received signal SIGABRT, Aborted. [Switching to Thread 0xb6376450 (LWP 12609)] __libc_do_syscall () at ../ports/sysdeps/unix/sysv/linux/arm/libc-do-syscall.S:44 44 ../ports/sysdeps/unix/sysv/linux/arm/libc-do-syscall.S: No such file or directory. (gdb) bt #0 __libc_do_syscall () at ../ports/sysdeps/unix/sysv/linux/arm/libc-do-syscall.S:44 #1 0xb639f0fe in __GI_raise (sig=sig@entry=6) at ../nptl/sysdeps/unix/sysv/linux/raise.c:56 #2 0xb63a1956 in __GI_abort () at abort.c:89 #3 0xb65377a8 in __gnu_cxx::__verbose_terminate_handler() () from /usr/lib/arm-linux-gnueabihf/libstdc++.so.6 #4 0xb65361c8 in ?? () from /usr/lib/arm-linux-gnueabihf/libstdc++.so.6 Backtrace stopped: previous frame identical to this frame (corrupt stack?) What looks to be happening here is that thread cancellation, which works by having an exception thrown, appears to not be caught by the thread being cancelled for some odd reason. I don't have time to investigate this until maybe Saturday. I guess we'll just have to ship 1.56 and look into this for 1.57. Niall -- ned Productions Limited Consulting http://www.nedproductions.biz/ http://ie.linkedin.com/in/nialldouglas/

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Re: [boost] [1.56.0] Release candidates available
by Eric Niebler 03 Aug '14

03 Aug '14

On 07/29/2014 02:44 PM, Boris Schäling wrote: > On Tue, 29 Jul 2014 19:06:43 +0200, Marshall Clow > <mclow.lists(a)gmail.com> wrote: > >> Release candidate files for 1.56.0 are available at >> http://boost.cowic.de/rc/ > > I get a compiler error with g++ 4.8.3 on Cygwin (64-bit): > > In file included from libs\system\src\error_code.cpp:19:0: > ./boost/system/detail/error_code.ipp: In member function ‘virtual > std::string > boost::system::{anonymous}::system_error_category::message(int) const’: > ./boost/system/detail/error_code.ipp:413:5: error: > ‘local_free_on_destruction’ is not a member of ‘boost::detail’ > detail::local_free_on_destruction lfod(lpMsgBuf); > ^ > > This looks like the bug Eric had reported at > <https://svn.boost.org/trac/boost/ticket/10137>. Crud. Beman, did a merge get missed? Eric

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Re: [boost] b2 headers is unreliable on 1.56 on Windows
by Matthew Musto 01 Aug '14

01 Aug '14

Nial, I found you need to run your cmd prompt as administrator before running b2 in order for the sym links to work correctly, otherwise you end up with hard links and the process fails 9 times out of 10. At least that is what I found on Win 8.1, -Matt From: Niall Douglas <s_sourceforge <at> nedprod.com> Subject: b2 headers is unreliable on 1.56 on Windows <http://news.gmane.org/find-root.php?message_id=53D91411.15683.55F433CE%40s%…> Newsgroups: gmane.comp.lib.boost.devel <http://news.gmane.org/gmane.comp.lib.boost.devel> Date: 2014-07-30 15:49:37 GMT (8 hours and 40 minutes ago) Anyone else found that b2 headers in 1.56 randomly misses things to hard link on Windows? If you run it four or five times it eventually hard links everything through monte-carlo, but it is a bit annoying. Niall -- ned Productions Limited Consultinghttp://www.nedproductions.biz/ http://ie.linkedin.com/in/nialldouglas/

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Boost logos on mailing list archives linking to non-boost pages instead of boost.org
by Curdeius Curdeius 01 Aug '14

01 Aug '14

Hi all, I have just spotted a curious detail on 3 Boost mailing lists. The logos (C++ Boost / Boost C++ libraries) point to web pages that are not affiliated in any way to boost. The concerned lists are: - http://lists.boost.org/boost-docs/ points to www [dot] boost [dot] com - http://lists.boost.org/boost-testing/ points to www [dot] boost [dot] com - http://lists.boost.org/geometry/ points to www [dot] osl [dot] iu [dot] edu I am not sure if this is the correct list to write to. If anyone knows what to do about it, please answer to the list or inform the correct person. Regards, Marek Kurdej

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Understanding Jam Files
by Axel Ismirlian 01 Aug '14

01 Aug '14

I have been working on boost for about a month now, but I still don't fully understand boost's build configuration very well. More specifically, I do not understand where the properties array gets filled in and where that data comes from. I saw the property.jam file which seems to refine the list of properties and take away unmet conditions, and bind dependencies. I also saw the property-set.jam file which creates property lists from raw properties, but where do the raw properties come from exactly? Does every property-set created come through this file? It would be very helpful if someone could point me in the right direction. Sincerely, -Axel

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synchorize or strand
by dd 01 Aug '14

01 Aug '14

Hi all, There is multi-threaded application which will access data containers at the same time. Which is the best choice between synchronization and strands. Thanks, dd

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