- Boost - lists.boost.org

[smart_ptr] Is there any interest in unique_ptr with type erased deleter?
by Andrey Davydov 21 Mar '17

21 Mar '17

It is widely known that deleter type is part of std::unique_ptr type. It is the most effective decision, but sometimes not very convenient. The most important use cases (for me) when std::unique_ptr<T, std::default_delete<T>> doesn't work are following: 1. unique_ptr to incomplete class struct MyClass; unique_ptr<MyClass> create(); auto ptr = create(); // compilation error 2. upcast to base without polymorphic destructor struct Base { // ... // no virtual ~Base() here }; struct Derived : Base { // ... }; unique_ptr<Base> ptr = make_unique<Derived>(); // compiles by leaks! 3. unique_ptr with non-default deleter unique_ptr<FILE, int (FILE *)> open_file(std::string const & path) // works but looks ugly, why should the fact that fclose returns `int` be visible from the signature of the function `open_path`? { return { std::fopen(path, "r"), &std::fclose }; } Of course, all this examples could be fixed if unique_ptr would be replaced by shared_ptr, but the semantic of the shared ownership is not desirable often. I have implemented smart pointer with semantics of unique ownership and type erased deleter (https://github.com/AndreyG/unnamed) It has size of 3 pointers and it doesn't require additional memory allocations for the case when deleter is empty class (for example, std::default_delete or non-capturing lambda) and for the case when deleter is known at compile time function (for instance, fclose). The are some simple examples of usage and tests in the repo. Why don't just use unique_ptr<T, function<void (void *>>? The main reason is that due to the small object optimization std::function has rather big size. For instance, sizeof(unique_ptr<T, function<void (void *>>) == 72 for MSVC x64! Results for the other platforms can be found in the repo README. Does it seem useful? -- Andrey Davydov

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[GSOC17] Regarding project Boost.uBLAS
by SHIVAM MITTAL 21 Mar '17

21 Mar '17

Hi, I am *Shivam Mittal*, a sophomore student of *Computer Science & Engineering *discipline of *Indian Institute of Technology, Ropar, India.* I wish to contribute to *Boost.uBLAS*, and develop cool and useful things with the community in GSOC 17. While going through the ideas list, I found the project *Data.Frames in boost.uBlas *very interesting and suitable for me. I think I am well prepared for the task as described in the requirement section. I am very comfortable in C/C++ and fairly comfortable in MATLAB, Python, HTML, CSS, PHP, SQL. I have more than 6 years of experience coding in C++. I have been developing data structures, algorithms, hardware simulators, artificial intelligence programs, and miscellaneous things in C++. The coursework (relevant to this project) which I have completed is : 1. Introduction to computing (in C++) 2. Data structures (in C++) 3. Linear Algebra Some of my selected projects are uploaded on github: https://github.com/shivam5 Please have a look at them. Some projects which I have implemented in C++ are: 1. Simple_RISC plagiarism checker 2. Simple_RISC functional and pipeline simulator 3. Pattern matching system by implementing hash tables. 4. Implementing graphs 5. Implementing AVL and Red black trees 6. Solcvng combinatorial auctions 7. Room booking system 8. Sudoku Solver I have implemented the programming competency test and sent the mentor on personal mail. Can you guide me further on how should I proceed and increase my chances of getting selected. Thank You, Shivam Mittal B.Tech Computer Science & Engineering, IInd Year Indian Institute of Technology Ropar Phone: +91-9888927245, +91-9899461223

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Boost MSM parallel behavior with delayed self-transitions?
by Danylo Malyuta 21 Mar '17

21 Mar '17

Hi community, This is my first post, so I'm sorry for any mistakes in style. I have also posted this question on StackOverflow: http://stackoverflow.com/questions/42920777/boost-msm-parallel-behavior-wit…. I am using Boost MSM (basic and functor front-ends) and am trying to implement the following state machine (https://i.stack.imgur.com/K79qk.png) enter image description here I am using Boost MSM (basic and functor front-ends) and am trying to implement the following state machine: enter image description here In words: 1. Enter state State1 2. Enter state A and execute action_A. After 2 seconds, print "Trying again..." and re-execute state A (i.e. call its entry action). This loops forever... 3. At the same time as 2 (i.e. "in parallel"), enter state B and execute action_B. After 5 seconds, print "Trying again..." and re-execute state B (i.e. call its entry action). This loops forever... I would like to know the way to create this state machine in Boost MSM. There are two tricks here which I cannot figure out how to do: - Execution in parallel (i.e. running action_A does not stop running action_B at the same time) - Delayed transition (i.e. the transitions which happen after 2 seconds for state A and after 5 seconds for state B). Neither delay should be blocking! The transitions should just "fire" after this time. Thank you very much for helping, Danylo.

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Fwd: [gsoc17] Regarding Boost.Geometry
by Aditya Gupta 21 Mar '17

21 Mar '17

Hi I am Aditya Gupta, IInd Yr. B. Tech. Computer Science at IIT Ropar and I wish to work on Project 3 of Boost.Geometry (Nearly antipodal points distance accuracy improvement.) I have completed the competency test <https://github.com/adityagupta1089/earth-geometry>, but I think maybe it was too small or have I misinterpreted, anyways. I have an initial draft of my [GSoC proposal](https://gist.github. com/adityagupta1089/39863577e1716c55d86c98ff57623893) I have also attached my CV.

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Re: [boost] [smart_ptr] Is there any interest in unique_ptr with type erased deleter?
by Andrey Semashev 21 Mar '17

21 Mar '17

For some reason my email went directly to Andrey instead of the mailing list. I'm re-sending the message below. PS: This has happened to me multiple times now after we moved the ML infrastructure. Is there a way to protect oneself from such mistakes? Am I the only one so inattentive to have this problem? On 03/21/17 16:11, Andrey Semashev wrote: > On 03/21/17 14:54, Andrey Davydov wrote: >> On Tue, Mar 21, 2017 at 2:15 PM, Andrey Semashev via Boost >> <boost(a)lists.boost.org <mailto:boost@lists.boost.org>> wrote: >> >> On 03/21/17 12:54, Andrey Davydov via Boost wrote: >> >> On Tue, Mar 21, 2017 at 12:00 PM, Richard Hodges >> <hodges.r(a)gmail.com <mailto:hodges.r@gmail.com>> wrote: >> >> What is required, more than simply creating a type-erased >> deleter? >> >> >> Also deleter must capture pointer, because pointer which was >> passed to >> constructor can differ from the pointer which will be deleted. >> For example, >> >> struct Base { /* ... */ }; >> struct Derived : Base { /* ... */ }; >> >> ptr<Derived> p1(new Derived); >> void * raw_p1 = p1.get(); >> ptr<Base> p2 = std::move(p1); >> void * raw_p2 = p2.get(); >> assert(raw_p1 != raw_p2); >> >> >> The above piece of code strikes me as very unsafe and better be >> avoided in the first place. Designing new tools to handle this case >> is IMHO misguided. >> >> Why this code is very unsafe? If change `ptr` to `shared_ptr` this will >> become perfectly valid and widely used pattern. > > Because comparing the void pointers is not safe in general. The above > code in particular will probably work (although not sure if even that's > guaranteed, depending on whether Base and Derived qualify as standard > layout classes), but if the class hierarchy is different, that code will > silently break. > >> Now, I can understand the need to perform casts on smart-pointers, >> but they should still provide some level of safety, at least the >> same level that is provided by pointer casts in the core language. >> But supporting casts should not require a new smart-pointer. And >> indeed it doesn't: >> >> template< typename U, typename T, typename D > >> std::unique_ptr< U, D > static_pointer_cast( >> std::unique_ptr< T, D >&& p) >> { >> D d = p.get_deleter(); >> return std::unique_ptr< U, D >( >> static_cast< U* >(p.release()), >> std::move(d)); >> } >> >> What is `D`? If it is std::default_delete<T> then function result type >> will be std::unique_ptr<U, std::default_delete<T>> and unlikely this >> type is very useful (even if it compiles). > > Ok, that won't work with std::default_delete<T>. But it will work with > this deleter: > > struct static_polymorphic_deleter > { > template< typename T > > void operator() (T* p) const noexcept > { > std::default_delete<T>()(p); > } > }; > > And it should work with a runtime polymorphic deleter that can be > written to implement your proposal (see below). > >> The other part of your proposal, which is polymorphic behavior with >> a deleter knowing the type to call the destructor on, can be solved >> by a custom deleter. I'm not sure a generalized version of such >> deleter would have a large demand, given that there is the >> alternative TONGARI J suggested, but I'm not opposed to a proposal. >> >> May be I doesn't understand what TONGARI J suggested, but >> how can `unique_ptr<T, void(*)(T*)>` hold stateful deleter? > > It doesn't, unless the required state is contained within the object > itself. But just to implement runtime polymorphism, no additional state > is required. > > struct base > { > protected: > ~base() = default; > }; > > struct derived : base > { > }; > > template< typename T > > void poly_deleter(base* p) noexcept > { > delete static_cast< T* >(p); > } > > template< typename T > > using poly_unique_ptr = std::unique_ptr< T, void(*)(base*) >; > > template< typename T > > poly_unique_ptr< T > make_poly_unique() > { > T* p = new T(); > return poly_unique_ptr< T >{ p, &poly_deleter< T > }; > } > > poly_unique_ptr< derived > pd1 = make_poly_unique< derived >(); > poly_unique_ptr< base > pb1 = std::move(pd1); > poly_unique_ptr< derived > pd2 = > static_pointer_cast< derived >(std::move(pb1)); > > But, of course, nothing stops you from saving the state in the deleter. > > struct poly_deleter > { > template< typename T > > poly_deleter(T* p) : m_p(p), m_delete(&poly_deleter::do_delete< T >) > { > } > > void operator() (void*) const noexcept > { > m_delete(m_p); > } > > private: > template< typename T > > static void do_delete(void* p) noexcept > { > delete static_cast< T* >(p); > } > > void* m_p; > void (*m_delete)(void*); > }; > > This will work even if you form std::unique_ptr<void, poly_deleter> > (i.e. don't have a universal base class). >

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Problem with using matrix library with unit test library
by SHIVAM MITTAL 21 Mar '17

21 Mar '17

Hi everyone, I have been developing something, and basically it requires the two boost libraries - the matrix library and unit test library. I have a file test.cpp : #include <boost/numeric/ublas/matrix.hpp> #include <boost/numeric/ublas/io.hpp> #include <boost/test/included/unit_test.hpp> #define BOOST_TEST_DYN_LINK #define BOOST_TEST_MODULE test BOOST_AUTO_TEST_SUITE(Integer_matrices) BOOST_AUTO_TEST_CASE(Constructors) { BOOST_CHECK(2 == 2); } BOOST_AUTO_TEST_SUITE_END() I am compiling this with: g++ -I <path to boost_1_63_0> test.cpp I'm getting the following error: /tmp/ccnxRzsf.o: In function `main': test.cpp:(.text+0x18aa1): undefined reference to `init_unit_test_suite(int, char**)' collect2: error: ld returned 1 exit status Any help will be greatly appreciated. Thanks.

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[Convert] std::isspace requires unsigned #28
by Olaf van der Spek 21 Mar '17

21 Mar '17

Hi, > boost\convert\base.hpp(112): warning C6330: 'const char' passed as _Param_(1) when 'unsigned char' is required in call to 'isspace'. > boost\convert\base.hpp(115): warning C6330: 'const char' passed as _Param_(1) when 'unsigned char' is required in call to 'isspace'. https://github.com/boostorg/convert/issues/28 IMO the code should be fixed and it's not a documentation issue. What do you think? -- Olaf

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Re: [boost] [release] 1.64.0 Delayed because of Microsoft (version numbers)
by Tom Kent 20 Mar '17

20 Mar '17

Sorry all, I meant to send this to the list but only replied to Daniel. This adds an option 4 and 5. On Sun, Mar 19, 2017 at 3:58 PM, Tom Kent <lists(a)teeks99.com> wrote: > > > On Sun, Mar 19, 2017 at 10:17 AM, Daniel James <dnljms(a)gmail.com> wrote: > >> On 19 March 2017 at 13:10, Tom Kent via Boost <boost(a)lists.boost.org> >> wrote: >> > >> > Option 1 - 14.10 Use microsoft toolset version based on cl.exe version >> -5. >> > This is the official version of the c++ toolset that microsoft has been >> > pushing (somewhere). The new $(VCToolsVersion) macro is "14.10.25017", >> this >> > macro is not available in previous versions of visual studio. >> > >> > build bootstrap would use bootstrap.bat vc1410 >> >> [snip] >> >> > Option 2 - 14.1 Use the abbreviated toolset version that microsoft uses >> for >> > their toolset version. The $(PlatformToolsetVersion) macro is "141". In >> > VS2015 this was "140". >> >> [snip] >> >> > I *think* that is all the reasonable options. Let the consensus form! >> >> I disagree, I think we should limit ourselves to values that Microsoft >> actually uses. As far as I'm aware, they don't use 1410, and they >> don't use 14.1. There are already too many ways of writing the version >> number, adding more will just add to the confusion. >> > > So 2-a would meet these requirements. However, I did overlook the mixed > options: > > Option 4 (141 and 14.10) - > build bootstrap would use bootstrap.bat vc141 > build of source would use b2 toolset=msvc-14.10 > build would generat libraries of the format libboost_NAME_vc141-OPTIONS-1_ > 64.lib > config would auto-link libraries of the same format > (4-a is the same as 2-a) > > Option 5 (1410 and 14.1) - > build bootstrap would use bootstrap.bat vc1410 > build of source would use b2 toolset=msvc-14.1 > build would generat libraries of the format libboost_NAME_vc1410-OPTIONS- > 1_64.lib > config would auto-link libraries of the same format > (5-a is the same as 1-a) > > Tom > >

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About all these metaprogramming libraries
by Louis Dionne 20 Mar '17

20 Mar '17

Dear Boost, We've seen two metaprogramming libraries ask for a formal review on the list recently. I expect a third (Brigand) might join the party soon, and maybe even a fourth (Eric Niebler's meta). I think it would be wise to have a plan for how we're going to deal with this. Before going further, I'd also like to clear something out. Some people have asked whether "classic" metaprogramming libraries still had their place given that we now have Hana. As the author of Hana, I think the answer is yes. While Hana is (IMHO) easier to use and more powerful, it also has an important shortcoming. Hana is too slow when dealing with very large inputs. This is due to the fact that it can also handle values, which is much heavier than dealing with types only. This can be alleviated to some extent, but the truth is that our execution model (the compiler) simply has to do more work when handling values. Hence, I think Boost does need a modern classic TMP library to handle these cases where a library writer needs to handle gigantic type lists. I think marketing such a library as an advanced tool for library writers would be a service to the overall C++ community, but that's an orthogonal concern. However, Boost needs one such library, not four. I think we can't just do 4 reviews and include all the libraries that pass in Boost; that would be a huge disservice to our users, who will be left with the burden of choosing. Heck, if we can't even make our mind, how can they? So, how do we pick? Have we ever been in a similar situation where we have multiple competing libraries solving _exactly_ the same problem? Louis -- View this message in context: http://boost.2283326.n4.nabble.com/About-all-these-metaprogramming-librarie… Sent from the Boost - Dev mailing list archive at Nabble.com.

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Newcomer Contributor to Boost C++ Libraries
by Aman Gupta 20 Mar '17

20 Mar '17

Hello everyone, I am Aman Kumar Gupta, an undergraduate 1st year student from International Institute of Information Technology, Bhubaneswar, India. I'm a newcomer to Boost C++ community. I have ,what i think, medium to good C++ coding background as i've been coding in C++ since past 5-6 years and have won some coding competitions as well. I have a good C++ STL knowledge and am very keen and interested in contributing to Boost's STL libraries. But as i'm a newbie to this community, i'm little confused where and how to start. I would be very glad and thankful if anyone would please help me and guide me through.

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