January 2010 - Boost - lists.preview.boost.org

[contract] Contract Programming Library
by Lorenzo Caminiti 09 Feb '10

09 Feb '10

Hi all, I am thinking to submit a library for Contract Programming (a.k.a. Design By Contract (TM) ) for C++. I have drafted some of the library documentation in Boost-like format: http://dbcpp.sourceforge.net/boost/libs/contract/doc/html/ Comments? Regards, Lorenzo

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[lexical_cast] efficiency
by Domagoj Saric 08 Feb '10

08 Feb '10

'A while back', in the "error_code debate" I used a lexical_cast<> example for demonstrating certain concerns/aspects but the whole post was so long (as usual :) that it was probably read by less than 0.1% of people :) Anyways I'm extracting and reposting this bit now as I think it warrants attention. The first problem is the ('standard') "std::streams vs efficency" issue: - on msvc 9.0 sp1 the single line boost::lexical_cast<int>( "321" ); caused 14 calls to new and 26 calls to EnterCriticalSection() (not to mention vtable initializations, virtual function calls, usage of locales...) the first time it is called, and 3 calls to new and 15 calls to EnterCriticalSection() on subsequent calls...It also caused the binary (which does not otherwise use streams) to increase by 50 kB! ...which is IMNHO abhorrent... (with my usual 'put things in perspective' examples http://www.theprodukkt.com/kkrieger http://www.youtube.com/watch?v=3vzcMdkvPPg :) As a start maybe this problem could be sufficiently "lessened" by providing lexical_cast specializations/overloads that use C library functions (strtol, itoa and the likes) as they suffer less from bloat/performance issues than std::streams. Ideally, IMHO, lexical_cast<> should provide the power/configurability of boost::numeric_cast (so that one can, for example, say I do not need/want to use locales/assume ASCII strings and things like that). The second problem is the use of exceptions (or better of only using exceptions): if, for example, one uses lexical_cast<> deep in the bowels of some parser it is probably "natural" to use a bad_cast exception to report an error to the outside world but if one uses lexical_cast<> to convert a string entered into a widget by a user into an int it would mostly be simpler to have a simple error code if the user entered an invalid string and issue a warning and retry "at the face of the place" (without the need for try-catch blocks)... In other words maybe a dual/hybrid approach of using both exceptions and error codes (through different overloads would be justified). -- "That men do not learn very much from the lessons of history is the most important of all the lessons of history." Aldous Huxley

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boost::mpl::for_each and value_initialized
by Peter Foelsche 08 Feb '10

08 Feb '10

Dear All, what is the use of value_initialized in boost::mpl::for_each? It should be sufficient if the value is initialized by the constructor. value_initialized() calls memset() in before calling the constructor. This memset() is not being optimized away with gnu-c++ 4.4.1. What class does require zeroed memory to work correctly? Peter *** boost_1_40_0/boost/mpl/for_each.hpp Mon Aug 17 22:16:53 2009 --- boost_1_40_0.saved/boost/mpl/for_each.hpp Tue Sep 1 12:54:55 2009 *************** *** 71,78 **** // dwa 2002/9/10 -- make sure not to invoke undefined behavior // when we pass arg. ! value_initialized<arg> x; ! aux::unwrap(f, 0)(boost::get(x)); typedef typename mpl::next<Iterator>::type iter; for_each_impl<boost::is_same<iter,LastIterator>::value> --- 71,78 ---- // dwa 2002/9/10 -- make sure not to invoke undefined behavior // when we pass arg. ! //value_initialized<arg> x; ! aux::unwrap(f, 0)(arg()); typedef typename mpl::next<Iterator>::type iter; for_each_impl<boost::is_same<iter,LastIterator>::value>

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Re: [boost] boost::mpl::for_each and value_initialized
by Niels Dekker - address until 2010-10-10 07 Feb '10

07 Feb '10

Peter Foelsche wrote: > in boost_1_41_0 there is still an unconditional call to memset in > value_initialized() Fernando Cacciola and I originally added the memset call within value_initialized() for MSVC only, because MSVC's implementation of value-initialization was known to incorrectly leave some bytes uninitialized, in some very relevant use cases. https://svn.boost.org/trac/boost/changeset/39157/trunk/boost/utility/value_… Thereby we also added extra unit tests, which were passed by MSVC by then, because of the memset. But unfortunately they failed on other compilers (GCC, Borland/Codegear and Sun), because of similar value-initialization issues. That's when we thought it was wise to just have the memset call there for all compilers: https://svn.boost.org/trac/boost/changeset/41942/trunk/boost/utility/value_… Do I understand correctly that you want the memset call to be skipped for those compiler versions that have implemented value-initialization entirely correctly? Do you know exactly which compiler versions do implement value-initialization correctly? Personally I do appreciate that the behavior of value_initialized is now exactly the same for all compilers. But I do understand you're concerned about the performance penalty of the memset call, for those compilers that have implemented value-initialization correctly. If so, can you please create a ticket, preferably including a patch? Kind regards, Niels -- Niels Dekker http://www.xs4all.nl/~nd/dekkerware Scientific programmer at LKEB, Leiden University Medical Center

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[chrono] v0.3.1 Support for wide characters
by vicente.botet 07 Feb '10

07 Feb '10

Hi, this new version includes: * Added support for wide characters on formatters. * Added chrono.hpp and stopwatches.hpp header files at the boost level. * Update of the doc taking care of preceding comments. Comments are welcome :) Best, Vicente ----- Original Message ----- From: "vicente.botet" <vicente.botet(a)wanadoo.fr> To: <boost(a)lists.boost.org>; <boost-users(a)lists.boost.org> Sent: Sunday, January 17, 2010 9:14 PM Subject: [chrono] v0.3 New Stopwatch Feature Hi, I'm pleased to announce the new version of the Boost.Chrono library. The implementaton is quite stable; the new interface could suffer of some modifications, renaming, ... as far as you submit some proposals. I would request a formal review soon and I will need a review manager. I know that review managers are hard to find, so if you are interested in the library, please the Review Wizards. The library can be downloaded from http://www.boostpro.com/vault/index.php?action=downloadfile&filename=chrono… and the documentation is online on the sandbox http://svn.boost.org/svn/boost/sandbox/chrono/libs/chrono/doc/html/index.ht…. I've tested it with gcc and MSVC. Previoous version of the library have been testted on Mac, but I'm not able to test this platform. Could someone check if there are some regressions on Mac? New Features: * Process cpu clocks * Independent process cpu clocks for real, user, system process CPU time * Global process cpu clock for real, user, system process CPU time * Stopwatch concept measuring elapsed time between different points in time associated to the operations start, stop, suspend and resume. * stopwatch is a model Stopwatch measuring the elapsed time between the start and the stop operations. * stopwatch_accumulator is a model Stopwatch allowing to accumulate several time samples and give the average, ... * Scoped helper classes allowing to pairwise start/stop operations, suspend/resume and resume/suspend a Stopwatch. * Stopwatch Formatter concept * stopwatch formatter "%ds\n" * stopwatch accumulator formatter "%c times, sum%ss, min%ms, max%Ms, mean%as\n" * time formatter "real %rs, cpu %cs (%p%), user %us, system %ss\n" * digital_time decomposition class separating days, hours,minutes,seconds, nanoseconds from any duration class (looking for a better name) * digital_time formatter "%d days(s) %h:%m:%s.%n\n" * stopwatch_reporter is a convenient generic class reporting elapsed time for the Stopwatch concept. * stopclock<Clock> shortcut stopwatch_reporter<stopwatch<Clcok>> * typeof registration for classes duration and time_point Depreceated Features: * The classes process_times, process_clock, process_timer, timer and run_timer are now deprecated as the preceding additions are more generic. However for backward compatibility they are preserved until inclusion of the library in Boost. Next follows the equivalences: timer<> ~ stopwatch<> process_timer ~ stopwatch<process_cpu_clock> run_timer ~ stopclock<> Bug Fixes * Try to correct warning C4251: 'boost::chrono::run_timer::m_format' : class 'std::basic_string<_Elem,_Traits,_Ax>' needs to have dll-interface to be used by clients of class 'boost::chrono::run_timer', by don't including inlines functions using the std::string m_format. For people that doesn't know it yet, Boost.Chrono library provides: * The C++0x Standard Library's common_type. * The C++0x Standard Library's compile-time rational arithmetic. * The C++0x Standard Library's time utilities, including: * Class template duration * Class template time_point * Clocks: * system_clock * monotonic_clock * high_resolution_clock * typeof registration for classes duration and time_point * Process clocks: * process_real_CPU_clocks, capturing real-CPU times. * process_user_CPU_clocks, capturing user-CPU times. * process_system_CPU_clocks, capturing system-CPU times. * process_cpu_clock, tuple-like class capturing at once real, user-CPU, and system-CPU times. * Stopwatches: * stopwatch, capturing elapsed Clock times. * stopwatch_accumulator, capturing cummulated elapsed Clock times. * scoped helper classes allowing to pairwise start/stop operations, suspend/resume and resume/suspend a Stopwatch. * Stopclocks or Stopwatch reporters: * stopwatch_reporter, convenient reporting of models of Stopwatch results. * stopclock<Clock> shortcut of stopwatch_reporter<stopwatch<Clock>> Best regards, _____________________ Vicente Juan Botet Escribá

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[1.42] The PDF build of the docs for the 1.42 BETA available
by John Maddock 04 Feb '10

04 Feb '10

The PDF build of the docs for 1.42 BETA are now available for download from the sourceforge download page https://sourceforge.net/projects/boost/files/boost-docs/1.42.0/boost_pdf_1_…. Please let me know if you spot any issues, Thanks, John Maddock.

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[gil] trac #3619
by Christian Henning 03 Feb '10

03 Feb '10

Hi there, could someone please tell whether or not this bug still exists. I don't have access to gcc 4.4. This is marked as a showstopper and I would like to get rid of it. Is it a compiler bug maybe? Thanks, Christian

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[multi_index][serialization] save_construct_data not called for multi_index collection
by Felipe Magno de Almeida 03 Feb '10

03 Feb '10

Hi, Boost.Serialization has support for non-default classes using save_construct_data and load_construct_data overloads. These are called before serialization to save and load information that's important for the construction of the object. Unfortunately, multi_index doesn't call these functions when serializing, so serialization of non-default-constructible classes is impossible with multi_index. I wanted to patch it so that it becomes possible, but to be honest I'm a bit lost in the serialization code for multi_index. collections_save_impl calls boost::serialization::save_construct_data_adl before serializing each item in the collection. I'm using boost 1.38.0, is there anyway to do the same for multi_index? Thanks in advance, -- Felipe Magno de Almeida

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crash in boost serialization 1.41
by Est 02 Feb '10

02 Feb '10

Hi All I'm developing an image processing app. In my app, I serialize a boost::ptr_vector of an abstract base class to a polymorphic xml archive. I checked all my polymorphic classes are exported with BOOST_SERIALIZATION_EXPORT and BOOST_SERIALIZATION_ASSUME_ABSTRACT for abstract classes, and it's working correctly with boost 1.38. If I update to boost 1.41, I can save archives without problems. When I try to load the resulting archive, I get a crash: Program received signal EXC_BAD_ACCESS, Could not access memory. Reason: KERN_PROTECTION_FAILURE at address: 0x00000000 boost::archive::detail::basic_iarchive_impl::load_pointer (this=0x1b955a00, ar=@0xbfffe598, t=@0xbfffd8d0, bpis_ptr=0x0) at libs/serialization/src/basic_iarchive.cpp:429 429 class_id_type new_cid = register_type(bpis_ptr->get_basic_serializer()); I can read the archive with my app compiled with boost 1.38. I'm using gcc 4.0.1 on OSX and gcc 4.3 on linux, all 32 bits. I'm not using DLLs. I ran the unit tests of the serialization library. All passed. I'm in the process of extracting a small example that reproduces the crash. Do you have any idea how can I fix it? Thank you. Est. Here is the backtrace: node_t is my abstract base class. #0 boost::archive::detail::basic_iarchive_impl::load_pointer (this=0x1b955a00, ar=@0xbfffe598, t=@0xbfffd8d0, bpis_ptr=0x0) at libs/serialization/src/basic_iarchive.cpp:429 #1 0x005a5506 in boost::archive::detail::basic_iarchive::load_pointer (this=0x0, t=@0x0, bpis_ptr=0x0) at libs/serialization/src/basic_iarchive.cpp:538 #2 0x00043f2e in boost::archive::detail::polymorphic_iarchive_route<boost::archive::naked_xml_iarchive>::load_pointer (this=0xbfffe58c, t=@0xbfffd8d0, bpis_ptr=0x0) at polymorphic_iarchive_route.hpp:65 #3 0x0003d0f9 in boost::archive::detail::load_pointer_type<boost::archive::polymorphic_iarchive>::invoke<ramen::node_t*> (ar=@0xbfffe58c, t=@0xbfffd8d0) at iserializer.hpp:486 #4 0x0003d157 in boost::archive::load<boost::archive::polymorphic_iarchive, ramen::node_t*> (ar=@0xbfffe58c, t=@0xbfffd8d0) at iserializer.hpp:554 #5 0x0003d1a6 in boost::archive::polymorphic_iarchive_impl::load_override<ramen::node_t*> (this=0xbfffe58c, t=@0xbfffd8d4) at polymorphic_iarchive.hpp:137 #6 0x0003d1f8 in boost::archive::detail::interface_iarchive<boost::archive::polymorphic_iarchive>::operator>><boost::serialization::nvp<ramen::node_t*> const> (this=0xbfffe58c, t=@0xbfffd8d4) at interface_iarchive.hpp:61 #7 0x0003d253 in boost::ptr_container_detail::load_helper<boost::archive::polymorphic_iarchive, boost::ptr_container_detail::sequence_config<ramen::node_t, std::vector<void*, std::allocator<void*> > >, boost::heap_clone_allocator> (ar=@0xbfffe58c, c=@0x193b1bd8, n=1) at detail/serialize_reversible_cont.hpp:52 #8 0x0003d2e9 in boost::serialization::load<boost::archive::polymorphic_iarchive, ramen::node_t, boost::heap_clone_allocator, std::allocator<void*> > (ar=@0xbfffe58c, c=@0x193b1bd8) at serialize_ptr_vector.hpp:28 #9 0x0003d327 in boost::serialization::free_loader<boost::archive::polymorphic_iarchive, boost::ptr_vector<ramen::node_t, boost::heap_clone_allocator, std::allocator<void*> > >::invoke (ar=@0xbfffe58c, t=@0x193b1bd8, file_version=0) at split_free.hpp:58 #10 0x0003d349 in boost::serialization::split_free<boost::archive::polymorphic_iarchive, boost::ptr_vector<ramen::node_t, boost::heap_clone_allocator, std::allocator<void*> > > (ar=@0xbfffe58c, t=@0x193b1bd8, file_version=0) at split_free.hpp:74 #11 0x0003d36b in boost::serialization::serialize<boost::archive::polymorphic_iarchive, ramen::node_t, boost::heap_clone_allocator, std::allocator<void*> > (ar=@0xbfffe58c, c=@0x193b1bd8, version=0) at serialize_ptr_vector.hpp:34 #12 0x0003d3a9 in boost::serialization::serialize_adl<boost::archive::polymorphic_iarchive, boost::ptr_vector<ramen::node_t, boost::heap_clone_allocator, std::allocator<void*> > > (ar=@0xbfffe58c, t=@0x193b1bd8, file_version=0) at serialization.hpp:133 #13 0x0003d456 in boost::archive::detail::iserializer<boost::archive::polymorphic_iarchive, boost::ptr_vector<ramen::node_t, boost::heap_clone_allocator, std::allocator<void*> > >::load_object_data (this=0xbcc2f0, ar=@0xbfffe598, x=0x193b1bd8, file_version=0) at iserializer.hpp:173 #14 0x005a5423 in boost::archive::object_id_type::operator= () at basic_archive.hpp:390 #15 0x005a5423 in boost::archive::detail::basic_iarchive_impl::load_object () at libs/serialization/src/basic_iarchive.cpp:391 #16 0x005a5423 in boost::archive::detail::basic_iarchive::load_object (this=0xbfffe598, t=0x193b1bd8, bis=@0xbcc2f0) at libs/serialization/src/basic_iarchive.cpp:529 #17 0x00043f0a in boost::archive::detail::polymorphic_iarchive_route<boost::archive::naked_xml_iarchive>::load_object (this=0xbfffe58c, t=0x193b1bd8, bis=@0xbcc2f0) at polymorphic_iarchive_route.hpp:59 #18 0x00039f93 in boost::archive::detail::load_non_pointer_type<boost::archive::polymorphic_iarchive>::load_standard::invoke<boost::ptr_vector<ramen::node_t, boost::heap_clone_allocator, std::allocator<void*> > > (ar=@0xbfffe58c, t=@0x193b1bd8) at iserializer.hpp:363 #19 0x00039fbc in boost::archive::detail::load_non_pointer_type<boost::archive::polymorphic_iarchive>::invoke<boost::ptr_vector<ramen::node_t, boost::heap_clone_allocator, std::allocator<void*> > > (ar=@0xbfffe58c, t=@0x193b1bd8) at iserializer.hpp:415 #20 0x00039fdb in boost::archive::load<boost::archive::polymorphic_iarchive, boost::ptr_vector<ramen::node_t, boost::heap_clone_allocator, std::allocator<void*> > > (ar=@0xbfffe58c, t=@0x193b1bd8) at iserializer.hpp:554 #21 0x0003a02a in boost::archive::polymorphic_iarchive_impl::load_override<boost::ptr_vector<ramen::node_t, boost::heap_clone_allocator, std::allocator<void*> > > (this=0xbfffe58c, t=@0xbfffdbc4) at polymorphic_iarchive.hpp:137 #22 0x0003a07c in boost::archive::detail::interface_iarchive<boost::archive::polymorphic_iarchive>::operator>><boost::serialization::nvp<boost::ptr_vector<ramen::node_t, boost::heap_clone_allocator, std::allocator<void*> > > const> (this=0xbfffe58c, t=@0xbfffdbc4) at interface_iarchive.hpp:61 #23 0x0003a0ac in boost::archive::detail::interface_iarchive<boost::archive::polymorphic_iarchive>::operator&<boost::serialization::nvp<boost::ptr_vector<ramen::node_t, boost::heap_clone_allocator, std::allocator<void*> > > const> (this=0xbfffe58c, t=@0xbfffdbc4) at interface_iarchive.hpp:68 #24 0x0003aa49 in ramen::dataflow::graph<ramen::node_t>::load<boost::archive::polymorphic_iarchive> (this=0x193b1bd8, ar=@0xbfffe58c, version=0) at graph.hpp:168 #25 0x0003ab9b in boost::serialization::access::member_load<boost::archive::polymorphic_iarchive, ramen::dataflow::graph<ramen::node_t> > (ar=@0xbfffe58c, t=@0x193b1bd8, file_version=0) at access.hpp:101 #26 0x0003abbd in boost::serialization::detail::member_loader<boost::archive::polymorphic_iarchive, ramen::dataflow::graph<ramen::node_t> >::invoke (ar=@0xbfffe58c, t=@0x193b1bd8, file_version=0) at split_member.hpp:54 #27 0x0003abdf in boost::serialization::split_member<boost::archive::polymorphic_iarchive, ramen::dataflow::graph<ramen::node_t> > (ar=@0xbfffe58c, t=@0x193b1bd8, file_version=0) at split_member.hpp:69 #28 0x0003ac01 in ramen::dataflow::graph<ramen::node_t>::serialize<boost::archive::polymorphic_iarchive> (this=0x193b1bd8, ar=@0xbfffe58c, file_version=0) at graph.hpp:175 #29 0x0003ac23 in boost::serialization::access::serialize<boost::archive::polymorphic_iarchive, ramen::dataflow::graph<ramen::node_t> > (ar=@0xbfffe58c, t=@0x193b1bd8, file_version=0) at access.hpp:109 #30 0x0003ac45 in boost::serialization::serialize<boost::archive::polymorphic_iarchive, ramen::dataflow::graph<ramen::node_t> > (ar=@0xbfffe58c, t=@0x193b1bd8, file_version=0) at serialization.hpp:74 #31 0x0003ac83 in boost::serialization::serialize_adl<boost::archive::polymorphic_iarchive, ramen::dataflow::graph<ramen::node_t> > (ar=@0xbfffe58c, t=@0x193b1bd8, file_version=0) at serialization.hpp:133 #32 0x0003ad30 in boost::archive::detail::iserializer<boost::archive::polymorphic_iarchive, ramen::dataflow::graph<ramen::node_t> >::load_object_data (this=0xbcc260, ar=@0xbfffe598, x=0x193b1bd8, file_version=0) at iserializer.hpp:173 #33 0x005a5423 in boost::archive::object_id_type::operator= () at basic_archive.hpp:390 #34 0x005a5423 in boost::archive::detail::basic_iarchive_impl::load_object () at libs/serialization/src/basic_iarchive.cpp:391 #35 0x005a5423 in boost::archive::detail::basic_iarchive::load_object (this=0xbfffe598, t=0x193b1bd8, bis=@0xbcc260) at libs/serialization/src/basic_iarchive.cpp:529 #36 0x00043f0a in boost::archive::detail::polymorphic_iarchive_route<boost::archive::naked_xml_iarchive>::load_object (this=0xbfffe58c, t=0x193b1bd8, bis=@0xbcc260) at polymorphic_iarchive_route.hpp:59 #37 0x000365fb in boost::archive::detail::load_non_pointer_type<boost::archive::polymorphic_iarchive>::load_standard::invoke<ramen::dataflow::graph<ramen::node_t> > (ar=@0xbfffe58c, t=@0x193b1bd8) at iserializer.hpp:363 #38 0x00036624 in boost::archive::detail::load_non_pointer_type<boost::archive::polymorphic_iarchive>::invoke<ramen::dataflow::graph<ramen::node_t> > (ar=@0xbfffe58c, t=@0x193b1bd8) at iserializer.hpp:415 #39 0x00036643 in boost::archive::load<boost::archive::polymorphic_iarchive, ramen::dataflow::graph<ramen::node_t> > (ar=@0xbfffe58c, t=@0x193b1bd8) at iserializer.hpp:554 #40 0x00036692 in boost::archive::polymorphic_iarchive_impl::load_override<ramen::dataflow::graph<ramen::node_t> > (this=0xbfffe58c, t=@0xbfffdf8c) at polymorphic_iarchive.hpp:137 #41 0x000366e4 in boost::archive::detail::interface_iarchive<boost::archive::polymorphic_iarchive>::operator>><boost::serialization::nvp<ramen::dataflow::graph<ramen::node_t> > const> (this=0xbfffe58c, t=@0xbfffdf8c) at interface_iarchive.hpp:61 #42 0x00036714 in boost::archive::detail::interface_iarchive<boost::archive::polymorphic_iarchive>::operator&<boost::serialization::nvp<ramen::dataflow::graph<ramen::node_t> > const> (this=0xbfffe58c, t=@0xbfffdf8c) at interface_iarchive.hpp:68 #43 0x0002c3fb in ramen::composition_t::serialize (this=0x193b1bd8, ar=@0xbfffe58c, version=0) at /Users/est/Devel/ramen/trunk/ramen/app/composition.cpp:193 #44 0x0004570f in boost::serialization::access::serialize<boost::archive::polymorphic_iarchive, ramen::composition_t> (ar=@0xbfffe58c, t=@0x193b1bd8, file_version=0) at access.hpp:109 #45 0x00048387 in boost::serialization::serialize<boost::archive::polymorphic_iarchive, ramen::composition_t> (ar=@0xbfffe58c, t=@0x193b1bd8, file_version=0) at serialization.hpp:74 #46 0x0004574f in boost::serialization::serialize_adl<boost::archive::polymorphic_iarchive, ramen::composition_t> (ar=@0xbfffe58c, t=@0x193b1bd8, file_version=0) at serialization.hpp:133 #47 0x00048436 in boost::archive::detail::iserializer<boost::archive::polymorphic_iarchive, ramen::composition_t>::load_object_data (this=0xbcc410, ar=@0xbfffe598, x=0x193b1bd8, file_version=0) at iserializer.hpp:173 #48 0x005a5423 in boost::archive::object_id_type::operator= () at basic_archive.hpp:390 #49 0x005a5423 in boost::archive::detail::basic_iarchive_impl::load_object () at libs/serialization/src/basic_iarchive.cpp:391 #50 0x005a5423 in boost::archive::detail::basic_iarchive::load_object (this=0xbfffe598, t=0x193b1bd8, bis=@0xbcc410) at libs/serialization/src/basic_iarchive.cpp:529 #51 0x00043f0a in boost::archive::detail::polymorphic_iarchive_route<boost::archive::naked_xml_iarchive>::load_object (this=0xbfffe58c, t=0x193b1bd8, bis=@0xbcc410) at polymorphic_iarchive_route.hpp:59 #52 0x0004835f in boost::archive::detail::load_non_pointer_type<boost::archive::polymorphic_iarchive>::load_standard::invoke<ramen::composition_t> (ar=@0xbfffe58c, t=@0x193b1bd8) at iserializer.hpp:363 #53 0x00043692 in boost::archive::detail::load_non_pointer_type<boost::archive::polymorphic_iarchive>::invoke<ramen::composition_t> (ar=@0xbfffe58c, t=@0x193b1bd8) at iserializer.hpp:415 #54 0x000436b1 in boost::archive::load<boost::archive::polymorphic_iarchive, ramen::composition_t> (ar=@0xbfffe58c, t=@0x193b1bd8) at iserializer.hpp:554 #55 0x00043700 in boost::archive::polymorphic_iarchive_impl::load_override<ramen::composition_t> (this=0xbfffe58c, t=@0xbfffe5c8) at polymorphic_iarchive.hpp:137 #56 0x00043752 in boost::archive::detail::interface_iarchive<boost::archive::polymorphic_iarchive>::operator>><boost::serialization::nvp<ramen::composition_t> const> (this=0xbfffe58c, t=@0xbfffe5c8) at interface_iarchive.hpp:61 #57 0x00043782 in boost::archive::detail::interface_iarchive<boost::archive::polymorphic_iarchive>::operator&<boost::serialization::nvp<ramen::composition_t> const> (this=0xbfffe58c, t=@0xbfffe5c8) at interface_iarchive.hpp:68 #58 0x0004379c in boost::archive::detail::polymorphic_iarchive_route<boost::archive::naked_xml_iarchive>::operator&<boost::serialization::nvp<ramen::composition_t> const> (this=0xbfffe58c, t=@0xbfffe5c8) at polymorphic_iarchive_route.hpp:173

1 1

metaprogramming: associating a type with another type
by DE 02 Feb '10

02 Feb '10

hi boosters while solving my own design problems i accidentally discovered an interesting technique let's assume we want to associate some value (a type) to a newly created type so we can easily access the associated type during metaprogramming let's call the associated type a property then we have the following property types: struct property0 {}; struct property1 {}; struct property2 {}; now we want to access the associated property for an arbitrary type in a natural traits manner: property<arbitrary_type>::type it appears we can implement it almost trivially (if know how) (let's assume we have portable typeof() facility) consider the code //the return type of this function appears to be the default property template<typename type> property0 get_prop(type*); //do not implement! template<typename t> struct property { typedef typeof(get_prop((type*)42) type; }; template<typename type, typename p = typename property<type>::type> struct base { friend p get_prop(type*) { return p(); } }; template<typename type> void foo(const base<type>&) //handles ALL types derived from base { typedef typename property<type>::type associated_property; } template<typename type> void bar(const base<type, property2>&) //handles ONLY types with property2 {} struct s : public expression<s> //default property used here {}; struct s1 : public expression<s1, property1> {}; struct s2 : public expression<s2, property2> {}; int main() { foo(s()); foo(s1()); foo(s2()); //bar(s()); //should not compile //bar(s1()); //should not compile bar(s2()); return 0; } even with the lack of typeof(), given a fixed set of properties it is very easy to implement this technique see working example at http://codepad.org/qXkESprl personally i see it as extremely useful for generic lib writers for some designes (of course if appropriately applied) as well as for users of such libs i would appreciate any thoughts on improvement of this technique within C++98 standard also any thoughts on portability are welcome if you have questions about how and/or why does it work feel free to ask -- Pavel

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