July 2010 - Boost - lists.boost.org

accurate sum accumulator (kahan)
by Gaetano Mendola 27 Apr '11

27 Apr '11

Hi all, I had to implement in terms of boost accumulators the Kahan summation algorithm. I will paste at the end of this message the accumulator, the feature and the extractor source code. This accumulator reduces the numerical error obtained with standard sequential sum, as example the sum of 1e6f elements equal to 1e-6f should give 1.0f, this is the results obtained with sum and sum_kahan: tag::sum: 1.009038925 tag::sum_kahan: 1.000000000 I'm not sure if that sum_kahan is worth to be inserted in the accumulators provided with boost, I'm not an expert of boost:accumulators (I just followed the guide to make this new accumulator) so not sure if you prefer to have a fast_sum and an accurate_sum instead of sum and sum_kahan. Regards Gaetano Mendola // File kahan_sum.hpp #ifndef KAHAN_SUM #define KAHAN_SUM #include <boost/accumulators/framework/accumulator_base.hpp> #include <boost/accumulators/framework/parameters/sample.hpp> #include <boost/numeric/conversion/cast.hpp> namespace boost { namespace accumulators { namespace impl { template<typename Sample> struct sum_kahan_accumulator : accumulator_base { typedef Sample result_type; template<typename Args> sum_kahan_accumulator(Args const & args) : sum(args[sample | Sample()]), compensation(boost::numeric_cast<Sample>(0.0)) { } template<typename Args> void operator ()(Args const & args) { const Sample myTemp1 = args[sample] - this->compensation; const Sample myTemp2 = this->sum + myTemp1; this->compensation = (myTemp2 - this->sum) - myTemp1; this->sum = myTemp2; } result_type result(dont_care) const { return this->sum; } private: Sample sum; Sample compensation; }; }}} namespace boost { namespace accumulators { namespace tag { struct sum_kahan : depends_on< > { typedef impl::sum_kahan_accumulator< mpl::_1 > impl; }; }}} namespace boost { namespace accumulators { namespace extract { extractor< tag::sum_kahan > const sum_kahan = {}; } using extract::sum_kahan; }} #endif

21 68

[serialization] boost/serialization/path.hpp
by Johan Råde 21 Feb '11

21 Feb '11

There is no boost/serialization/path.hpp. I suggest the following: ---------------------------------------------------------------------------------------------------------------- #ifndef BOOST_SERIALIZATION_PATH_HPP #define BOOST_SERIALIZATION_PATH_HPP // MS compatible compilers support #pragma once #if defined(_MSC_VER) && (_MSC_VER >= 1020) #pragma once #endif #include <boost/config.hpp> #include <boost/filesystem/path.hpp> #include <boost/serialization/level.hpp> BOOST_CLASS_IMPLEMENTATION(boost::filesystem::path, boost::serialization::primitive_type) #ifndef BOOST_NO_STD_WSTRING BOOST_CLASS_IMPLEMENTATION(boost::filesystem::wpath, boost::serialization::primitive_type) #endif namespace boost { namespace serialization { template<class Archive, class String, class Traits> void serialize(Archive& ar, boost::filesystem::basic_path<String, Traits>& p, const unsigned int version) { String s; if(Archive::is_saving::value) s = p.string(); ar & boost::serialization::make_nvp("string", s); if(Archive::is_loading::value) p = s; } }} #endif //-------------------------------------------------------------------------------------------------------------- Comments? Any suggested improvements? --Johan Råde

5 11

[C++0x] Emulation of scoped enums
by Beman Dawes 16 Feb '11

16 Feb '11

The improved type safety of the C++0x scoped enum feature is attractive, so I'd like to start using it as it becomes available in compilers. See http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2007/n2347.pdf for a description. Note that the committee changed the name from strongly typed enums to scoped enums. See the attached for a boost/detail header that provides macro wrappers that use scoped enums if available, otherwise fall back on C++03 namespaces and unscoped enums. It lets a library write: BOOST_SCOPED_ENUM_START(algae) { green, red, cyan }; BOOST_SCOPED_ENUM_END ... BOOST_SCOPED_ENUM(algae) sample( algae::red ); void func(BOOST_SCOPED_ENUM(algae)); and then a user can write: sample = algae::green; func( algae::cyan ); Comments or suggestions appreciated, --Beman // scoped_enum_emulation.hpp ---------------------------------------------------------// // Copyright Beman Dawes, 2009 // Distributed under the Boost Software License, Version 1.0. // See http://www.boost.org/LICENSE_1_0.txt // Generates C++0x scoped enums if the feature is present, otherwise emulates C++0x // scoped enums with C++03 namespaces and enums. The Boost.Config BOOST_NO_SCOPED_ENUMS // macro is used to detect feature support. // // Caution: only the syntax is emulated; the semantics are not emulated and // the syntax emulation doesn't include being able to specify the underlying type. // // See http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2007/n2347.pdf for a // description of the feature. Note that the committee changed the name from // strongly typed enums to scoped enums. // // Sample usage: // // BOOST_SCOPED_ENUM_START(algae) { green, red, cyan }; BOOST_SCOPED_ENUM_END // ... // BOOST_SCOPED_ENUM(algae) sample( algae::red ); // void foo( BOOST_SCOPED_ENUM(algae) color ); // ... // sample = algae::green; // foo( algae::cyan ); #ifndef BOOST_SCOPED_ENUM_EMULATION_HPP #define BOOST_SCOPED_ENUM_EMULATION_HPP #include <boost/config.hpp> #ifndef BOOST_NO_SCOPED_ENUMS # define BOOST_SCOPED_ENUM_START(name) enum class name # define BOOST_SCOPED_ENUM_END # define BOOST_SCOPED_ENUM(name) name #else # define BOOST_SCOPED_ENUM_START(name) namespace name { enum enum_t # define BOOST_SCOPED_ENUM_END } # define BOOST_SCOPED_ENUM(name) name::enum_t #endif #endif // BOOST_SCOPED_ENUM_EMULATION_HPP

14 27

[process] How to run test cases
by Boris 23 Jan '11

23 Jan '11

As Boost.Process 0.3 has been released it would be great if the test cases are run on various platforms. So far I've tested Boost.Process on WinXP with MSVC 9.0, Cygwin with g++ 3.4.4 and Solaris with g++ 3.4.6 and Sun C++ 5.9. To make it as easy as possible for others to run the test cases here's a short description of how to proceed. Nearly all test cases depend on a program called "helpers". This program is built first and is started by many test cases as a child process. In order to find the program "helpers" the test cases must know its location. As there is no way to get the location at runtime it is hardcoded in the file libs/process/test/misc.hpp. As the location differs depending on what compiler is used YOU MUST CHECK FIRST THE PATH IN libs/process/test/misc.hpp! Otherwise most of the test cases will fail as they look for a program "helpers" in the wrong directory. As of today only those paths are correct and have been tested which are set for Windows, Cygwin and Solaris. Only after you have checked and maybe updated the path in libs/process/test/misc.hpp you should try to build and run the test cases: WinXP/MSVC 9.0 ************** With MSVC 9.0 you only need to open the Visual Studio 2008 Command Prompt, change to the directory with the test cases and run bjam: C:\boost_1_36_0\libs\process\test> ..\..\..\bjam.exe -q Cygwin/GCC 3.4.4 **************** On Cygwin it's important to know if the Boost libraries have been built for the POSIX or Windows API. By default Boost libraries on Cygwin use the Windows API. With the Windows API the Boost.Process test cases are not passed successfully though (there are compiler errors where I'm not sure currently if they are a Boost.Process problem and how they could be fixed). If you want to run the test cases on Cygwin you must (re-)build the Boost libraries to use the POSIX API: $ cd ~/boost_1_36_0 $ ./bjam cxxflags=-DBOOST_POSIX_API Afterwards you can run the test cases: $ cd ~/boost_1_36_0/libs/process/test $ ../../../bjam cxxflags=-DBOOST_POSIX_API -q Solaris/GCC 3.4.6 ***************** At first you have to put the following line in ~/user-config.jam: using gcc : : : <linker-type>sun ; Then start building the Boost libraries: $ cd ~/boost_1_36_0 $ ./bjam --toolset=gcc cxxflags=-mcpu=ultrasparc For the test cases to be passed successfully you must update Boost.Test. Change line 624 in ~/boost_1_36_0/boost/test/impl/execution_monitor.ipp temporarily to: - , m_CHLD_action( SIGCHLD, catch_system_errors, attach_dbg, alt_stack ) + , m_CHLD_action( SIGCHLD, false, attach_dbg, alt_stack ) It is important that the second parameter is false as the signal SIGCHLD should not be handled by the execution monitor and should not be reported as an error. Afterwards the test cases can be run: $ cd ~/boost_1_36_0/libs/process/test $ ../../../bjam --toolset=gcc cxxflags=-mcpu=ultrasparc -q Solaris/Sun C++ 5.9 ******************* Build the Boost libraries with the sun toolset: $ cd ~/boost_1_36_0 $ ./bjam --toolset=sun stdlib=sun-stlport For the test cases to be passed successfully you must update Boost.Test. Change line 624 in ~/boost_1_36_0/boost/test/impl/execution_monitor.ipp temporarily to: - , m_CHLD_action( SIGCHLD, catch_system_errors, attach_dbg, alt_stack ) + , m_CHLD_action( SIGCHLD, false, attach_dbg, alt_stack ) It is important that the second parameter is false as the signal SIGCHLD should not be handled by the execution monitor and should not be reported as an error. If you run the test cases now you'll get this compiler error for one test case: "../../../boost/asio/detail/socket_ops.hpp", line 218: Error: Cannot assign void* to char*. "../../../boost/asio/detail/socket_ops.hpp", line 229: Error: Cannot assign void* to char*. "../../../boost/asio/detail/descriptor_ops.hpp", line 66: Error: Cannot assign void* to char*. "../../../boost/asio/detail/descriptor_ops.hpp", line 72: Error: Cannot assign void* to char*. The bug has been reported to the Boost.Asio mailing list. If you want to build that one test case, too, you need to fix the two files in Boost.Asio 1.36.0 yourself. All the test cases can be built and run with: $ cd ~/boost_1_36_0/libs/process/test $ ../../../bjam --toolset=sun stdlib=sun-stlport -q

4 9

[SoC] BGL project idea
by Gautam Sewani 03 Jan '11

03 Jan '11

Hi, I am a Computer Science student hoping to contribute to Boost for this year's summer of code. I had a few questions regarding the BGL project idea (https://svn.boost.org/trac/boost/wiki/SoC2010#Boost.Graph) for SOC 2010. 1. I can think of only a few places where the suggested algorithms will be used. Does the community think that these algorithms are used frequently enough to put them in a library? How important does the community consider this project? 2. Will the project proposal be expected to include the API design? Thanks and Regards Gautam

5 29

[GIL] [patch] read multipage TIFF files
by Robert Pollak 29 Nov '10

29 Nov '10

Hello, the following patch (against the current trunk) allows to read any page of a multipage TIFF file, by optionally specifying the zero-based directory number. (The correct term for a TIFF page is "directory".) It adds a "dirnum" to the relevant functions, and uses the corresponding libtiff functionality. The "dirnum" default value is 0 for compatibility with present callers. Additionally, it defines the function tiff_get_directory_count to get the number of directories in the TIFF file. Please give me some feedback or consider applying the patch. This patch would close the corresponding feature request https://svn.boost.org/trac/boost/ticket/2373 . Credits go to Roland Richter, whose code the patch is based on. Best Regards, Robert Pollak Index: boost/gil/extension/io/tiff_io.hpp =================================================================== --- boost/gil/extension/io/tiff_io.hpp (revision 64065) +++ boost/gil/extension/io/tiff_io.hpp (working copy) @@ -122,9 +122,13 @@ protected: TIFF *_tp; public: - tiff_reader(const char* filename) { + tiff_reader(const char* filename,tdir_t dirnum=0) { io_error_if((_tp=TIFFOpen(filename,"r"))==NULL, "tiff_reader: fail to open file"); + if(dirnum>0) { + io_error_if(TIFFSetDirectory(_tp,dirnum)!=1, + "tiff_reader: fail to set directory"); + } } ~tiff_reader() { TIFFClose(_tp); } template <typename View> @@ -171,10 +175,10 @@ private: CC _cc; public: - tiff_reader_color_convert(const char* filename) : - tiff_reader(filename) {} - tiff_reader_color_convert(const char* filename,CC cc_in) : - tiff_reader(filename),_cc(cc_in) {} + tiff_reader_color_convert(const char* filename,tdir_t dirnum=0) : + tiff_reader(filename,dirnum) {} + tiff_reader_color_convert(const char* filename,CC cc_in,tdir_t dirnum=0) : + tiff_reader(filename,dirnum),_cc(cc_in) {} template <typename View> void apply(const View& view) { point2<std::ptrdiff_t> dims=get_dimensions(); @@ -336,18 +340,34 @@ }; /// \ingroup TIFF_IO +/// \brief Returns the number of directories in the TIFF file +inline int tiff_get_directory_count(const char* filename) { + TIFF *tif; + io_error_if((tif=TIFFOpen(filename,"r"))==NULL, + "tiff_get_count: fail to open file"); + + int dircount = 0; + do { + dircount++; + } while (TIFFReadDirectory(tif)); + + TIFFClose(tif); + return dircount; +} + +/// \ingroup TIFF_IO /// \brief Returns the width and height of the TIFF file at the specified location. /// Throws std::ios_base::failure if the location does not correspond to a valid TIFF file -inline point2<std::ptrdiff_t> tiff_read_dimensions(const char* filename) { - detail::tiff_reader m(filename); +inline point2<std::ptrdiff_t> tiff_read_dimensions(const char* filename,tdir_t dirnum=0) { + detail::tiff_reader m(filename,dirnum); return m.get_dimensions(); } /// \ingroup TIFF_IO /// \brief Returns the width and height of the TIFF file at the specified location. /// Throws std::ios_base::failure if the location does not correspond to a valid TIFF file -inline point2<std::ptrdiff_t> tiff_read_dimensions(const std::string& filename) { - return tiff_read_dimensions(filename.c_str()); +inline point2<std::ptrdiff_t> tiff_read_dimensions(const std::string& filename,tdir_t dirnum=0) { + return tiff_read_dimensions(filename.c_str(),dirnum); } /// \ingroup TIFF_IO @@ -356,17 +376,17 @@ /// Throws std::ios_base::failure if the file is not a valid TIFF file, or if its color space or channel depth are not /// compatible with the ones specified by View, or if its dimensions don't match the ones of the view. template <typename View> -inline void tiff_read_view(const char* filename,const View& view) { +inline void tiff_read_view(const char* filename,const View& view,tdir_t dirnum=0) { BOOST_STATIC_ASSERT(tiff_read_support<View>::is_supported); - detail::tiff_reader m(filename); + detail::tiff_reader m(filename,dirnum); m.apply(view); } /// \ingroup TIFF_IO /// \brief Loads the image specified by the given tiff image file name into the given view. template <typename View> -inline void tiff_read_view(const std::string& filename,const View& view) { - tiff_read_view(filename.c_str(),view); +inline void tiff_read_view(const std::string& filename,const View& view,tdir_t dirnum=0) { + tiff_read_view(filename.c_str(),view,dirnum); } /// \ingroup TIFF_IO @@ -375,25 +395,25 @@ /// Throws std::ios_base::failure if the file is not a valid TIFF file, or if its color space or channel depth are not /// compatible with the ones specified by Image template <typename Image> -void tiff_read_image(const char* filename,Image& im) { +void tiff_read_image(const char* filename,Image& im,tdir_t dirnum=0) { BOOST_STATIC_ASSERT(tiff_read_support<typename Image::view_t>::is_supported); - detail::tiff_reader m(filename); + detail::tiff_reader m(filename,dirnum); m.read_image(im); } /// \ingroup TIFF_IO /// \brief Allocates a new image whose dimensions are determined by the given tiff image file, and loads the pixels into it. template <typename Image> -inline void tiff_read_image(const std::string& filename,Image& im) { - tiff_read_image(filename.c_str(),im); +inline void tiff_read_image(const std::string& filename,Image& im,tdir_t dirnum=0) { + tiff_read_image(filename.c_str(),im,dirnum); } /// \ingroup TIFF_IO /// \brief Loads and color-converts the image specified by the given tiff image file name into the given view. /// Throws std::ios_base::failure if the file is not a valid TIFF file, or if its dimensions don't match the ones of the view. template <typename View,typename CC> -inline void tiff_read_and_convert_view(const char* filename,const View& view,CC cc) { - detail::tiff_reader_color_convert<CC> m(filename,cc); +inline void tiff_read_and_convert_view(const char* filename,const View& view,CC cc,tdir_t dirnum=0) { + detail::tiff_reader_color_convert<CC> m(filename,cc,dirnum); m.apply(view); } @@ -401,31 +421,31 @@ /// \brief Loads and color-converts the image specified by the given tiff image file name into the given view. /// Throws std::ios_base::failure if the file is not a valid TIFF file, or if its dimensions don't match the ones of the view. template <typename View> -inline void tiff_read_and_convert_view(const char* filename,const View& view) { - detail::tiff_reader_color_convert<default_color_converter> m(filename,default_color_converter()); +inline void tiff_read_and_convert_view(const char* filename,const View& view,tdir_t dirnum=0) { + detail::tiff_reader_color_convert<default_color_converter> m(filename,default_color_converter(),dirnum); m.apply(view); } /// \ingroup TIFF_IO /// \brief Loads and color-converts the image specified by the given tiff image file name into the given view. template <typename View,typename CC> -inline void tiff_read_and_convert_view(const std::string& filename,const View& view,CC cc) { - tiff_read_and_convert_view(filename.c_str(),view,cc); +inline void tiff_read_and_convert_view(const std::string& filename,const View& view,CC cc,tdir_t dirnum=0) { + tiff_read_and_convert_view(filename.c_str(),view,cc,dirnum); } /// \ingroup TIFF_IO /// \brief Loads and color-converts the image specified by the given tiff image file name into the given view. template <typename View> -inline void tiff_read_and_convert_view(const std::string& filename,const View& view) { - tiff_read_and_convert_view(filename.c_str(),view); +inline void tiff_read_and_convert_view(const std::string& filename,const View& view,tdir_t dirnum=0) { + tiff_read_and_convert_view(filename.c_str(),view,dirnum); } /// \ingroup TIFF_IO /// \brief Allocates a new image whose dimensions are determined by the given tiff image file, loads and color-converts the pixels into it. /// Throws std::ios_base::failure if the file is not a valid TIFF file template <typename Image,typename CC> -void tiff_read_and_convert_image(const char* filename,Image& im,CC cc) { - detail::tiff_reader_color_convert<CC> m(filename,cc); +void tiff_read_and_convert_image(const char* filename,Image& im,CC cc,tdir_t dirnum=0) { + detail::tiff_reader_color_convert<CC> m(filename,cc,dirnum); m.read_image(im); } @@ -433,23 +453,23 @@ /// \brief Allocates a new image whose dimensions are determined by the given tiff image file, loads and color-converts the pixels into it. /// Throws std::ios_base::failure if the file is not a valid TIFF file template <typename Image> -void tiff_read_and_convert_image(const char* filename,Image& im) { - detail::tiff_reader_color_convert<default_color_converter> m(filename,default_color_converter()); +void tiff_read_and_convert_image(const char* filename,Image& im,tdir_t dirnum=0) { + detail::tiff_reader_color_convert<default_color_converter> m(filename,default_color_converter(),dirnum); m.read_image(im); } /// \ingroup TIFF_IO /// \brief Allocates a new image whose dimensions are determined by the given tiff image file, loads and color-converts the pixels into it. template <typename Image,typename CC> -inline void tiff_read_and_convert_image(const std::string& filename,Image& im,CC cc) { - tiff_read_and_convert_image(filename.c_str(),im,cc); +inline void tiff_read_and_convert_image(const std::string& filename,Image& im,CC cc,tdir_t dirnum=0) { + tiff_read_and_convert_image(filename.c_str(),im,cc,dirnum); } /// \ingroup TIFF_IO /// \brief Allocates a new image whose dimensions are determined by the given tiff image file, loads and color-converts the pixels into it. template <typename Image> -inline void tiff_read_and_convert_image(const std::string& filename,Image& im) { - tiff_read_and_convert_image(filename.c_str(),im); +inline void tiff_read_and_convert_image(const std::string& filename,Image& im,tdir_t dirnum=0) { + tiff_read_and_convert_image(filename.c_str(),im,dirnum); } /// \ingroup TIFF_IO

2 7

[fusion] [intro] ADAPT_STRUCT extensions
by Stefan Strasser 04 Oct '10

04 Oct '10

Hi, in the discussion about the library I called "Intro" at the time it has been suggested to use BOOST_FUSION_ADAPT_STRUCT of Boost.Fusion for data member access. based on that I'd like to propose two extensions to ADAPT_STRUCT, which I think are useful beyond my use case: 1) ADAPT_STRUCT can adapt public data members only. with the modifications I uploaded here: http://svn.boost.org/svn/boost/sandbox/intro/boost/fusion/adapted/struct/ all data members can be adapted. for example: class A{ private: friend class fusion::access; int a; }; BOOST_FUSION_ADAPT_STRUCT(A,(int,a) ) 2) adaption of a class including its base class members. for example: struct A{ int a; }; struct B{ int b; }; struct C : A,B{ int c; } BOOST_FUSION_ADAPT_STRUCT(A,(int,a) ) BOOST_FUSION_ADAPT_STRUCT(B,(int,b) ) BOOST_FUSION_ADAPT_DERIVED( C, (A)(B), (int,c) ) an instance of C is now a fusion sequence of size 3. http://svn.boost.org/svn/boost/sandbox/intro/boost/fusion/adapted/struct/ad… private inheritance is supported as above, virtual inheritance is not. I'm not sure if virtual inheritance can be supported.

8 30

[Boost-users] [BGL] Stoer–Wagner min-cut algorithm
by Daniel Trebbien 26 Sep '10

26 Sep '10

> The usual idiom for that in BGL algorithms is to use an > iterator_property_map on the graph's vertices, built using a vector and > indexed by the vertex_index property map of the graph. You can also use a > shared_array_property_map, which manages its storage internally. If you > are doing a generic algorithm, the logic to manage these maps correctly is > somewhat difficult. One place to look for a template of what to do is the > distance map handling at the bottom of > <boost/graph/dijkstra_shortest_paths.hpp>, particularly > dijkstra_shortest_paths() and detail::dijkstra_dispatch1(). The basic > logic is to look at the named parameter structure that the user passes is > and see if there is an assignment map there. If so, use it; otherwise, > look for a vertex_index map in the named parameter structure, defaulting > to get(vertex_index, g), then use the found vertex_index map to create an > iterator_property_map or shared_array_property_map. Now that compilers > are more compliant, there are probably simpler ways to implement the logic > than to use multiple dispatch functions, but the approach in > dijkstra_shortest_paths.hpp is known to work. > > When you get this algorithm done, you may want to contribute it to BGL to > be added to Boost. We are always interested in new algorithms. > > -- Jeremiah Willcock Hello Jeremiah, I would very much like to contribute my implementation of the Stoer–Wagner min-cut algorithm to BGL. In preparation for this, I have attached a "pre-release" version to this e-mail which has everything needed to build the test case with g++ and GNU Make. Before I add in all of the template code to support "default" template parameters and other niceties, I figured that it would be good to have a review of the code to make sure that I am headed in the right direction. Also, I have tested my code against the example from Stoer & Wagner (1997). It appears to be working correctly, but there might be bugs. I think that it would be good to have more testing. Would someone please review my code? Also, is anyone aware of good examples for testing min-cut implementations? Daniel

4 57

[Review] Formal Review: Boost.Move
by OvermindDL1 19 Sep '10

19 Sep '10

Greetings Boost Developers and Users, It's my pleasure to announce that the review of Ion Gaztañagas' Move library starts May 10th and lasts until May 24th, 2010, unless an extension occurs. What is it? =========== The Boost.Move library would supply an emulated C++1x Move semantics interface, aka RValue References, allowing for a wide variety of easy to use and easy to add in optimization abilities. The most used function it would add would be: val_b = boost::move( val_a ); Which would move val_a to val_b; val_a should not be used after this line. This semantic allows for a vast amount of optimizations, especially in regards to temporaries, see the documentation for further examples and use. Other patterns emulated are && rvalue references for functions/members and constructors. There are also a number of STL containers in the sandbox that support move semantics using this library for higher efficiency. Getting the library =================== The latest version of this library may be downloaded from SVN: http://svn.boost.org/svn/boost/sandbox/move/ and the docs may be viewed here Docs: http://igaztanaga.drivehq.com/libs/move/doc/html/index.html and do note, this library is header-only and is designed to be absolutely generic to be useful in all areas of C++ programming. Writing a review ================ If you feel this is an interesting library, then please submit your review to the developer list (preferably), or to the review manager. Here are some questions you might want to answer in your review: - What is your evaluation of the design? - What is your evaluation of the implementation? - What is your evaluation of the documentation? - What is your evaluation of the potential usefulness of the library? - Did you try to use the library? With what compiler? Did you have any problems? - How much effort did you put into your evaluation? A glance? A quick - reading? In-depth study? - Are you knowledgeable about the problem domain? And finally, every review should answer this question: - 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. Special considerations ====================== If you want or need a primer on the subject, please look at the working draft for C++1x. This linked site has also been shown to be quite useful in describing move usefulness: Want Speed? Pass by Value.: http://cpp-next.com/archive/2009/08/want-speed-pass-by-value/ Move It With Rvalue References: http://cpp-next.com/archive/2009/09/move-it-with-rvalue-references/ And there are further links in that series, but those two will get you started in the domain. Best regards, OvermindDL1, Review Manager (Boost.Move)

15 78

Any interest in dynamic dispatching mechanism from "interface" to template functions ?
by Raffi Enficiaud 16 Sep '10

16 Sep '10

Hello all, The idea behind is not new and consists in dispatching a call of an interface function to the correct template instance, depending on the runtime or compile time parameters. The field of application is (to me) the release of static/dynamic libraries including functions with a predefined set of types combination. This way, the library (compiled once) can easily be plugged to another framework or a script program (I personally use it with boost.python). An example of use could be (general idea, not a real code of course): // -------------- template <class real_type> int template_function(real_type const& r_class1, double param_d, int& param_out) { // ... return 0; } int interface_function(MyInterface const* i_class1, variant const& param, variant& out) { // return value int return_value; // constructs the dispatcher object with a reference to the values passed to interface_function dispatcher<int, MyInterface const*, variant const&, variant&> dispatch_object(return_value, i_class1, param, out); bool res = dispatch_object.calls_first( fusion::vector_tie( template_function < class_t1 >, template_function < class_t2 > //... ) ); if(res) return return_value; return -1; } // -------------- The dispatch_object tests for the convertibility of each instance ui of the arguments Ui of the interface function, with the corresponding argument Ti of the template function. The type of matching is defined by external objects, with a simple interface providing two methods: a convertibility test and a conversion. The types are "cleaned" in order to have a limited number of conversion structures. Currently this mechanism is used in a generic image processing library. The images have all the same virtual interface and the dispatch calls the correct template function based on the concrete type of the image. It also includes a "back conversion" for Ui's that are non-const reference or pointers. The dispatch mainly makes use of boost.fusion, boost.mpl and boost.function_types. I have checked a little bit the Boost.Vault but, correct me if I am wrong, the current dispatching mechanisms do not address exactly this issue. The code is already open-source released under the boost license. I can put some samples in the Vault if there is any interest. Your comments are very welcome ! Kind regards, Raffi Enficiaud

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