August 2011 - Boost - lists.boost.org

Conversion review
by Jeroen Habraken 23 Aug '11

23 Aug '11

My review of the Conversion library: Please note that I'll be referring to the pre-review thread which can be found here: http://lists.boost.org/Archives/boost/2011/07/183525.php. * What is your evaluation of the design? Please refer to the section discussing the potential usefulness of this library. * What is your evaluation of the implementation? The code looks clean but I'm worried about the abundant use of boost::enable_if. While it is a useful tool SFINAE does make code fragile, possibly using something akin the following is an option: template <typename Target, typename Source, bool CA, bool EEC, bool A> struct assigner_impl { // No cookies BOOST_STATIC_ASSERT(sizeof(Target) == 0); }; template <typename Target, typename Source> struct assigner_impl<Target, Source, true, true, false> { // Copy-assignable, extrinsically explicitly convertible and not assignable ... }; template <typename Target, typename Source, bool CA, bool EEC> struct assigner_impl<Target, Source, CA, EEC, true> { // Assignable ... }; template <typename Target, typename Source> struct assigner : assigner_impl< Target, Source, is_copy_assignable<Target>::value, is_extrinsically_explicitly_convertible<Source, Target>::value is_assignable<Target, Source>::value > { }; (Note, this was written on the fly in this email, it may not actually compile.) * What is your evaluation of the documentation? Everything seems to be covered well, small comment though: template <> struct is_assignable<X&, X const&> : true_type { }; I initially missed that true_type is boost::true_type, this should be made more obvious. * What is your evaluation of the potential usefulness of the library? Let me tackle this in several parts: - type-to-string and string-to-type conversions In the pre-review we came to the following conclusions: "Coming back to the string to int conversion, if we can not have a default string-to-type or type-to-string, Boost.Conversion must remove these specializations." "I don't think that Boost.Conversion can provide a string-to-type conversion that is configurable. It could provide one if there is a consensus of a default. We should see Boost.Conversion customization as if we were adding some methods to one of the classes. For the string to float conversions, it is as if we were adding explicit operator float() const; to the std::string class. " I still maintain that this is the case, there is no sane way to let the user select between Convert or LexicalCast at the moment and possibly Coerce in the future and it's not something this library should be tackling. - STL conversions I believe these functions are of little use as when I would have to convert a list of integers to a list of doubles I'd simply write a loop (possibly aided by BOOST_FOREACH) instead of looking up a library (and reading the necessary documentation) to do it for me. With the offered customization points the cure seems to be worse than the disease, if I had to convert a std::pair<int, int> to a std::pair<double, double> I'd write a quick function to do so. The Conversion documentation however shows the following: template <typename Target1, typename Target2, typename Source1, typename Source2> struct implicit_converter_cp< std::pair<Target1,Target2>, std::pair<Source1, Source2> , typename enable_if_c< is_extrinsically_convertible<Source1, Target1>::value && is_extrinsically_convertible<Source2, Target2>::value >::type > : true_type { std::pair<Target1, Target2> operator()(std::pair<Source1, Source2>& v) { return std::pair<T1, T2>(implicit_convert_to<T1>(from.first), implicit_convert_to<T2>(from.second)); } }; This is a more generic solution but it seems like an awful lot of trouble for something this simple. - The Boost conversions These do seem very useful, but as discussed in the pre-review: "You are right and the same applies to any type-to-type conversion. And maybe this is the MAJOR flaw of Boost.Conversion: to think that we can define extrinsically THE conversion between two types. Every body admit that if a class T defines a constructor from a std::string THE conversion from std::string to T is the one defined by this constructor." I do believe that this library isn't the place for the conversions, they should be added to the specific libraries themselves in the form of constructors. * Did you try to use the library? With what compiler? Did you have any problems? I've tried several examples with GCC 4.2.1 (the default shipped with OS X), 4.5.3 and clang 2.9 on OS X. Both versions of GCC worked fine, clang however was unable to compile the examples with the following error: In file included from no_throw.cpp:13: In file included from ../../../boost/conversion/include.hpp:20: In file included from ../../../boost/conversion/convert_to.hpp:22: In file included from ../../../boost/conversion/explicit_convert_to.hpp:38: In file included from ../../../boost/conversion/implicit_convert_to.hpp:40: In file included from ../../../boost/conversion/type_traits/is_convertible.hpp:25: In file included from ../../../../library/boost-trunk/boost/fusion/tuple.hpp:10: In file included from ../../../../library/boost-trunk/boost/fusion/tuple/tuple.hpp:11: In file included from ../../../../library/boost-trunk/boost/fusion/container/vector/vector.hpp:11: In file included from ../../../../library/boost-trunk/boost/fusion/container/vector/detail/vector_n_chooser.hpp:14: In file included from ../../../../library/boost-trunk/boost/fusion/container/vector/vector10.hpp:14: In file included from ../../../../library/boost-trunk/boost/fusion/sequence/intrinsic/begin.hpp:17: In file included from ../../../../library/boost-trunk/boost/fusion/sequence/intrinsic/detail/segmented_begin.hpp:11: In file included from ../../../../library/boost-trunk/boost/fusion/iterator/segmented_iterator.hpp:13: In file included from ../../../../library/boost-trunk/boost/fusion/container/list/cons.hpp:14: In file included from ../../../../library/boost-trunk/boost/fusion/sequence/intrinsic/end.hpp:17: ../../../../library/boost-trunk/boost/fusion/sequence/intrinsic/detail/segmented_end.hpp:33:70: error: invalid use of incomplete type 'fusion::nil' segmented_end_impl<Sequence, fusion::nil>::call(seq, fusion::nil())); ^~~~~~~~~~~~~ Not sure what's going on here exactly. * How much effort did you put into your evaluation? A glance? A quick reading? In-depth study? Something between a quick reading and an in-depth study. * Are you knowledgeable about the problem domain? As the author of Coerce I'm knowledgeable about the string-to-type and type-to-string domain, less so about the generic type-to-type domain though. * 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. NO, the library should not be accepted as a Boost library in the current form. However the following should be done: - There are several type traits which can possibly be added to Boost.TypeTraits. This is not something I can judge, it is up to the auteurs of Conversion and TypeTraits to judge which are useful. - The conversions regarding Boost classes should be added to the respective libraries in the form of constructors if the respective auteurs believe this adds value to their library. Kind regards, Jeroen Habraken

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[GSoC] Coerce summary and request for feedback
by Jeroen Habraken 23 Aug '11

23 Aug '11

Hi, As the Google Summer of Code has ended yesterday I'd like to thank Google and my mentor Hartmut Kaiser for the opportunity and guidance. Whilst Coerce is an on-going project (it's more than a year old already, time does fly when you're having fun) the GSoC sped up development significantly. To summarize Coerce for those not familiar with it, it's a type-to-string and string-to-type conversion library aiming at speed and extensibility. During the GSoC the following major things have happend: * Added tests, catching bugs and allowing me to prevent bugs in the future (hopefully). * Rewritten the tag system to be more flexible. * Added documentation, the latest version of which can be found over at http://vexocide.org/coerce/. In general the library matured, and while it's not done yet (the documentation in particular) I believe it's approaching production stability with the number of impacting changes dropping significantly over time. The current code can be found at http://svn.boost.org/svn/boost/sandbox/coerce/ and as usual I'd be grateful for any comments or critique. If you have questions do not hesitate to contact me. Kind regards, Jeroen Habraken P.S. If you're still using construe_cast (a previous incarnation of this project) please consider migrating to Coerce as I plan on removing https://github.com/VeXocide/construe_cast soon.

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[Units] test_trig fails on Sandia-darwin-4.4 (caused by compile-time evaluation of math functions)
by Michel MORIN 23 Aug '11

23 Aug '11

The Units' test (libs/units/test/test_trig.cpp) fails on Sandia-darwin-4.4: http://tinyurl.com/3wherck The failure is caused by the fact that the results of `std::acos(0.2)` and `std::acos(d)` (double d = 0.2) are NOT equal on Sandia-darwin-4.4. On gcc-4.3 and newer versions, built-in math functions having constant arguments are evaluated at compile time using the MPFR (Multiple Precision Floating-Point Reliable) library. This happens even if optimization is disabled. So, the results of std::acos(0.2); // evaluated by the MPFR library at compile time and double d = 0.2; std::acos(d); // evaluated by the built-in function at run time are different. (If we compile with optimization enabled, the latter code is also evaluated by the MPFR library at compile time.) The solution to this problem is * Change BOOST_CHECK_EQUAL to BOOST_CHECK_CLOSE_FRACTION. or * Change `std::acos(0.2)` to `std::acos(d)` (with `double d = 0.2`) An interesting thing is that the test fails only on Sandia-darwin (x86-64) platform. On other platforms using gcc 4.3-4.6, the test runs successfully. I suspect that they have 80-bit registers and so the result of `std::acos(d)` is as accurate as the result of the MPFR library. Do you have any thoughts about this? Regards, Michel

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[odeint] GSoC Summary and Feedback request
by Mario Mulansky 23 Aug '11

23 Aug '11

Hi, this is a summary of the progress of the odeint-library during this years GSoC. First of all I would like to thank Andrew for mentoring this project and also for the many fruitful comments and hints he gave during the past months. The aim of the project was to finalize odeint and prepare it for a boost review. This goal has been, more or less, achieved, I think. Although some work on docs and maybe some minor usability improvements are to be done we think we have reached a state of development ready for a review and we might try take this step in the near future. The puropose of odeint is to provide algorithms to numerically solve ordinary differential equations (ODEs) given as initial value problems: x'(t) = f(x,t) , x(0) = x0. It is written by Karsten Ahnert and myself. Please visit the docs to find out more about the features and abilities of odeint: http://headmyshoulder.github.com/odeint-v2/doc/index.html During the GSoC project, we switched from a svn branch in the boost sandbox to a new git project called odeint-v2: https://github.com/headmyshoulder/odeint-v2 In terms of code, I have made the following improvements to odeint: * Implementation and performance tests of a generic Runge-Kutta algorithm. * Implementation of several algorithms using the generic Runge-Kutta scheme (rk4, rk54ck, rk78) * Redesign of the construction/destruction of temporary states by use of a state_wrapper * Redesign of the resizing functionality by usage of boost::bind * Redesing of the algebra implementation to now use instances instead of static functions. * Creating mkl_operations to make use of Intel's MKL for optimal performance * major refactorings (e.g. renaming stepper classes) * Implementation of a Bulirsch-Stoer stepper with dense output * Improvement of integrate functions so they have consistent behavior * Adding integrate_times function to allow for observation at user defined time points * Adding unit tests for integrate functions Additionally, I worked on the documentation: * Created an overview over all implemented algorithms * Adding a resizing example to the tutorials section * Adding a description of the integrate functions * Adding a brief concept description of steppers, system and observer * Adding a brief overview on the Algebra/Operations and how they interact Besides his fruitful input and discussions related to my work presented above, Karsten also put quite some effort into odeint during the GSoC period, e.g. providing examples and tutorials in the docs section or adding multistep and implicit algorithms (adams-bashforth, rosenbrock4). We are very happy about any feedback on the work done within this GSoC or on odeint in general. If you have any further question please feel also invited to contact us. Finally, I want to thank the boost communtity for giving me the possibility to take part in this years GSoC as part of the boost organization. I have learned a lot during this time and I think odeint took a major step forward in terms of design and extent. Regards, Mario

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Boost.Conversion review
by Gordon Woodhull 22 Aug '11

22 Aug '11

Hi all, The review of Vicente Botet Escriba's Conversion library starts this Saturday August 20 and continues through August 29. This library provides a general system for type-to-type conversion. As such, it can be thought of either as a substitute for overloading static_cast, or as an alternative to lexical_cast when the intermediate conversion to text is not wanted. The code is in the sandbox: http://svn.boost.org/svn/boost/sandbox/conversion/ And the docs are here: http://svn.boost.org/svn/boost/sandbox/conversion/libs/conversion_ext/doc/h… I'll send out a formal announcement when the review begins, but I wanted to send out this reminder because participation in summer months tends to be somewhat low. Your review and/or discussion would be greatly appreciated. As always, please post to the main Boost list if possible, or the boost-users list, or you can send your review directly to the Review Managers. Thanks, Gordon Woodhull, Review Manager Espen Harlinn, Review Manager Assistant

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[containers] Templated map::find?
by Lars Viklund 22 Aug '11

22 Aug '11

Hi list. I was asked today why the std::map container didn't have templated versions of functions like find, lower_bound, and so on. I could not give a good answer on why there could not exist such a thing, assuming that the comparator had sufficient symmetric overloads for the real Key type and the FauxKey that the query would be performed with. Would something like this be possible to add to Boost.Containers, considering that going through the typical standard routes would have a latency of a couple years at best? I'm told that the Boost.Intrusive containers already supports this. Some use cases would be querying with a type that's convertible (in an expensive way) to the held key type, or querying with a key type that has only the fields that affect ordering in the case of a rich key type. -- Lars Viklund | zao(a)acc.umu.se

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[Locale] Request to merge to release branch
by Artyom Beilis 22 Aug '11

22 Aug '11

Hello, I want to request a permission to merge Boost.Locale to the release branch. Testing Status: =============== Link:http://beta.boost.org/development/tests/trunk/developer/locale.html Fully tested and pass 100% compilers/platforms: ----------------------------------------------- Compilers: - MSVC-8,9,10 with native libraries - GCC all versions - Intel - on Linux - Visual Age on Linux Current major faults: --------------------- - Sun Studio - reported bug in Boost.Thread - Intel on Darwin - seems to be general compiler regression for all libraries (not related to Boost.Locale) - MSVC for Windows Mobile - not supported, will not be supported due to lack of standard library functionality - Visual Age/AIX - iconv has poor implementation on AIX and ICU not provided on the testing machine so, there is no way to test. Minor faults: ------------- - GCC prior to 4.5 on Windows - will not work with dynamic build (dll) due to lack of linking with dynamic runtime (libstdc++6.dll) - Pathscale-4 and MSVC-9 with STL-Port: minor fults in wide file I/O where invalid UTF-8 prevents reading valid part. Can't debug it due to lack of access to platform and compiler. Thank you very much, Artyom Beilis -------------- CppCMS - C++ Web Framework: http://cppcms.sf.net/ CppDB - C++ SQL Connectivity: http://cppcms.sf.net/sql/cppdb/

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[fusion] segmented fusion 2.0
by Eric Niebler 22 Aug '11

22 Aug '11

I took the liberty of rewriting all my old broken segmented fusion code and checked in something (hopefully) a bit more maintainable and friendly. Along with the changes, I added an algorithm called segmented_fold_until. Many of the existing algorithms have segmented versions that can be implemented trivially in terms of this one. (Recall that the biggest problem with the old implementation was the need to write a separate implementation of every algorithm for segmented data structures, which was very complicated. Now that's almost trivial.) I hope in the coming weeks and months to produce segmented versions of most of the existing fusion algorithms. Once that's done, I hope to "bake it in" by making the existing algorithms select the segmented flavors automatically. Also, some containers and views are naturally segmented, like joint_view. Practically all of joint_view's implementation, including its iterator, would vanish if it just advertised itself as segmented. Thoughts? Objections? -- Eric Niebler BoostPro Computing http://www.boostpro.com

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[intrusive] Move constructors
by Rei Thiessen 21 Aug '11

21 Aug '11

Could we add move constructors to all intrusive containers? Rei

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[enums] Request for comments on an enum-oriented library
by Beren Minor 21 Aug '11

21 Aug '11

Hi all, I'm currently writing a C++ library to add some functionalities to enums, and am looking for comments and feedbacks. Boost is a reference, and I would be glad if some C++ expert here could take a moment to look at what I've written and tell me his thoughts. I know that there was already some discussions about enums here, and some early implementations of enum libraries at Boost, but I couldn't find any that fitted my requirements, or any that was in an stable enough stage. My goal wasn't to submit another one to Boost (although I would be really proud of it, I'm not thinking about it yet, just looking for comments), but to implement something usable for some of my specific needs. Initially I was only looking for enum (de)serialization, however I think that these needs can be quite common, and that the library could be used by others as well. That's why I'm trying to find some comments and to share my work. My goal was to implement a library following these requirements : - Extend the enum concept with different flavors. - Scope the enum constants out of namespace scope. - Do not get rid of implicit integer cast, or at least, try to provide enum/integer interoperability so we don't have to cast all the time. - No overhead, keep the enum constants as light as they are natively. For the first requirement, I wanted to add three new flavors to enums, that I've called "static enums", "dynamic enums" and "bit fields". The main difference between them is the way these enums are (de)serialized and the available enum / enum and enum / integer operators when this is meaningful (only when using C++0x, with scoped enums). - Static enums only allow explicitly defined constants (with specified or implicit integer values), any other value will result in a (de)serialization to special value "unknown". - Dynamic enums allow explicitly defined constants and offsets from these constants, within a given global range (from the first constant to the specified upper integer limit). Every value within the range will be serializable, any other will result in "unknown". An integer value between two enum constants will be (de)serialized as the nearest lower enum constant plus an offset. For example, if the enum is defined as { value1 = 1, value2 = 5..., unknown = 10 }, the available range would be from 1 to 9, and the integer 4 will be serialized as "value1#3" which means (value1 + 3). - Bit fields enums only allow combination of explicitely defined constants. These will be (de)serialized as a combination of every defined enum constants, any other value will be (de)serialized as "unknown". This flavor restricts constants values to bitwise distinct integers, and to values different from 0 in order to be able to decompose the enum into the specified enum constants. 0 being the special "unknown" value for this flavor. For example, for an enum defined as { bit1 = 0b001, bit2 = 0b010, bit3 = 0b100... }, an instance of this enum with an integer value of 3 will be serialized as "bit1+bit2", and "bit1+bit3" will be deserialized as an enum instance of integer value 5. As I said, the library obviously uses Boost, and in an extensive way Boost Preprocessor macros, and tries to integrate nicely with Boost libraries. Serialization, for example, is done through stream template operators, and should be usable with the Boost Lexical Cast library. These isn't any real documentation yet, except from doxygen (although not yet complete, I've tried to be verbose), but I think that the library is simple enough to be understood by reading the source code, and I've got some unit tests to help getting the genereal idea. Lastly, I still have some issues about some points, mostly because of the use of macros and boilerplate code, but I hope to be able to fix them. - No namespace support. - Enum declaration comes with the serialization code. I would like to be able to separate definition and declaration of this code, but I'm not sure how to do that properly without overhead for the developer. I'll have to think about it. - The writing overhead of the enum declaration (compared to plain old enum) is still a little bit too much for my taste, but I don't know if I'll be able to do much better without introducing some obscure and meaningless helper macros. This is mainly because of the need of declaring the enum constants in a Boost Preprocessor sequence, in order to be able to use it at various places to generate the enum declaration as well as the serialization code. - Also, the declaration could be cleaner if I could find a way to implement optional parameters in macros, but that seems like difficult to do (or I haven't found out yet how to do). - I don't have any other environment available except from my Debian Linux box, so I couldn't test on anything else than gcc. I don't really expect it to work with anything else. Actually, my main build scripts themselves are probably broken on anything else than my computer. [1] That said, if anyone wants to take a look at it and share his thoughts, the library can be found here : https://github.com/berenm/libtenum Best regards, Beren Minor Notes: [1] I've added a "portable-build" branch to my git repo if anyone want to try running the tests cases somewhere else. Build is done with bjam.

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