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Whatever happened to singleton class?
by Kurt Kohler 15 Sep '08

15 Sep '08

Back in January, the review of Tobias Schwinger's singleton package resulted in it being rejected. At the time it was stated that a new version would be out for review in three months or so. Has anything happened since then? I've been using the class without problems for some time, but I'd feel more comfortable if it was an official part of boost.

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boost.extensions and boost.reflection.
by Germán Diago 15 Sep '08

15 Sep '08

Hello. I'm implementing a property class which uses my own library (still in early stages) and I want to extend it to general reflection (not for now) and shared library loading. I found boost.extensions, which is not a boost library for now. I don't know if this is the place to ask for this, if it is not, point me where I could go. It's great to see I won't have to taje any more pain to load plugins :-). I would like to make a feature request. In boost.extensions, factories are used to construct types of a derived class with pointers. So, in order to register a new class, you have to tell which is the base class to the extensions system. I think there is a better way, with which you wouldn't need to do this. It is inspired in this type style of value-based type system: http://stlab.adobe.com/wiki/index.php/Image:2008_06_26_classes_that_work.pdf An object which can contain any other object (like boost::any) could be created. This way (this is how I do in my own solution) you just have to register a type without worrying about its base class: REGISTER_CLASS(myns, myclass) Now I can do like this: object_t myobject = introspection::create_object("myns", "myclass"); when I want my object to become "myclass" I do: myns::myclass & refclass = get_reference<myns::myclass>(myobject); This works fairly well, and factories go away, freeing the user from learning more interfaces. Just register your type and use it. Everything else is transparent. The interface is simple, no factories or anything else to handle. This can be also used from shared libraries without problems. At least, I think that it should be provided a way to register a factory of non-pointer types. In the documentation it says a pointer is created for the animal class, disabling this type of value-based registration.

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fusion::result_of::transform<Seq1,Seq2,F>
by e r 15 Sep '08

15 Sep '08

hello, here's what I'm trying to do: *.cpp //result_type() not valid typedef fusion::vector<A,B,C> result_type; //arg2s_type() is valid typedef fusion::vector<Arg2A,Arg2B,Arg2C> arg2s_type; //transforms // (fusion::vector<identity<A>,identity<B>,identity<C> >(),arg2s_type()) // into {A(arg1,Arg2A()),B(arg1,Arg2B()),C(arg1,Arg2C()))} result_type result( range<result_type,args2_type>::create( arg1 //arbitrary type Arg1 ) ); here's my attempt. problems/questions are shown in comments. *.hpp: template<template<typename> class metafun = mpl::identity> struct apply_wrapper{ template<typename T> struct apply{ typedef metafun<T> type; }; }; template<typename Seq,template<typename> class metafun = mpl::identity> struct apply_wrapper_to_seq{ typedef typename mpl::transform< Seq, // e.g. fusion::vector<A,B,C> apply_wrapper<metafun> >::type type; //e.g. fusion::vector<identity<A>,identity<B>,identity<C> > }; template<typename Arg1> struct fun{ fun(const Arg1& args):args_(args_){} //copy, assign... // probably not what result_of::transform expects, based on compile // errors (below) template<typename Metafun,typename Arg2> struct result{ typedef typename Metafun::type type; }; template<typename Metafun,typename Arg2> typename Metafun::type //e.g Metafun = identity<A> operator()(const Metafun& meta,const Arg2& arg2)const{ typedef typename Metafun::type result_type; //e.g. A return result_type(args,arg2); } const Arg1& args_; }; template<typename Result,typename Arg2s> struct range{ //e.g. fusion<identity<A>,identity<B>,identity<C> > typedef typename apply_wrapper_to_seq<Result>::type wrappers_type; //e.g. fusion::vector<Arg2A,Arg2B,Arg2C> typedef Arg2s arg2s_type; template<typename Arg1> struct result{ typedef typename fusion::result_of::transform< wrappers_type, arg2s_type, fun<Arg1> >::type type; }; template<typename Arg1> static typename result<Arg1>::type create(const Arg1& args){ typedef fun<Arg1> f_type; wrappers_type wrappers; arg2s_type arg2s; f_type f(args); BOOST_MPL_ASSERT( ( mpl::equal< Result, typename result<Arg1>::type > ) );//result_of::fun causes compile error /usr/local/boost_1_35_0/boost/utility/result_of.hpp|34|instantiated from ‘boost::detail::result_of_impl< factory::fun<Arg1>, factory::fun<Arg1> > ()(boost::mpl::identity<A>, Arg2A), false>’| ... //usr/local/boost_1_35_0/boost/utility/result_of.hpp|68|error: wrong number of template arguments (1, should be 2)| //factory/range.hpp|32|error: provided for ‘template<class Arg1> template<class Metafun, class Arg2> struct factory::fun<Arg1>::result’| //usr/local/boost_1_35_0/boost/fusion/view/transform_view/detail/value_of_impl.hpp|55|error: no type named ‘type’ in ‘struct //boost::mpl::apply<boost::fusion::detail::apply_transform_result<factory::fun<Arg1>, boost::mpl::identity<A>, Arg2A, mpl_::na, mpl_::na, mpl_::na>’| return fusion::transform( wrappers, arg2s, f ); } }; any help would appreciated. thanks!

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boost.extensions bugs?
by Germán Diago 15 Sep '08

15 Sep '08

Hello. I downloaded boost.extensions from http://boost-extension.blogspot.com/?gclid=CNjp5dfJ2JUCFQsZQgod0mHbWg When I tried the first example (the shared_library one) in the tutorial, I realized that the macro BOOST_EXTENSION_EXPORT_DECL didn't prevent c++ name mangling for the example function. I had to add extern "C" before void manually. And in the second tutorial (the animals tutorial) BOOST_EXTENSION_TYPE_MAP_FUNCTION seems to be called, but when I get the map from main, it is empty. The library is found (LD_LIBRARY_PATH is set so that it finds the library) but it does not work. Thank you. Tested in gcc 4.2.3 under ubuntu 8.04.

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Memory/CPU usage
by Jean-Sebastien Stoezel 15 Sep '08

15 Sep '08

Hi, Is there a library in Boost that provides memory/CPU usage estimates? Thanks, Jean

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question about boost::thread
by PingShan Li 15 Sep '08

15 Sep '08

Here is my test program using boost::thread. I would expect this program to crash inside FunctionA because m_ClassA is no longer available. Can anybody help me to understand why it does not crash? thank you. [root@localhost]# uname -a Linux localhost.localdomain 2.6.9-22.EL #1 Mon Sep 19 18:20:28 EDT 2005 i686 i686 i386 GNU/Linux [root@localhost]# g++ --version g++ (GCC) 3.4.4 20050721 (Red Hat 3.4.4-2) Copyright (C) 2004 Free Software Foundation, Inc. This is free software; see the source for copying conditions. There is NO warranty; not even for MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. g++ -I/opt/third_party_libraries/boost_1_33_1 -L/opt/third_party_libraries/boost_1_33_1/stage/lib -lboost_thread-gcc-mt main.cpp -o test #include <boost/bind.hpp> #include <boost/thread.hpp> #include <iostream> void SleepTime( int a ) { boost::xtime xt; boost::xtime_get( &xt, boost::TIME_UTC ); xt.sec += a; boost::thread::sleep( xt ); } class ClassA { public: ClassA( int member ) : m_member( member ) { std::cout << "ClassA constructor: " << m_member << std::endl; } virtual ~ClassA( ) { std::cout << "ClassA destructor: " << m_member << std::endl; } void SetMember( int a ) { m_member = a; } int GetMember() const { return m_member; } private: int m_member; }; class TestClass { public: TestClass( ) : m_ClassA( 0 ) { std::cout << "TestClass constructor: " << m_ClassA.GetMember() << std::endl; } virtual ~TestClass( ) { std::cout << "TestClass destructor: " << m_ClassA.GetMember() << std::endl; } void RunThreadFunction() { std::cout << "RunThreadFunction start" << std::endl; boost::thread thr( boost::bind( &TestClass::ThreadFunction, this ) ); std::cout << "RunThreadFunction end" << std::endl; } void ThreadFunction( ) { std::cout << "ThreadFunction start" << std::endl; m_ClassA.SetMember( 5 ); SleepTime( 5 ); FunctionA( ); return; } void FunctionA( ) { std::cout << "Inside FunctionA: " << m_ClassA.GetMember() << std::endl; } private: ClassA m_ClassA; }; int main() { { TestClass a; a.RunThreadFunction(); } std::cout << "main wait" << std::endl; SleepTime( 10 ); return 0; }

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[review] FSM Library review result
by Martin Vuille 15 Sep '08

15 Sep '08

This is a summary of the comments received during the review of Andrey Semashev's Finite State Machines (FSM) library. Apologies for the delay in getting these out. DOCUMENTATION * Relocate ToC to make it stand out. * Several people used the Wikipedia article http://en.wikipedia.org/wiki/Finite_state_machine as a reference for FSM terminology and operation, and found discrepancies between Boost.FSM and that description. Perhaps Boost.FSM should explicitly describe its FSM metamodel, or refer to an existing metamodel (Wikipedia FSM or Harel or UML Statechart, for example). The latter was mentioned several times as being preferred since it is a standard. * If possible, use standard terminology. For example, "transition map" vs. "state transition table". Or define the non-standard terms. * Include a comprehensive rationale mapping the design choices to the design objectives. * Compare/contrast Boost.FSM with the FSM implementation as described in "C++ Template Metaprogramming". * Add an example of event deferral using boost::function. * Clarify support for multithreading vs. asynchronous FSM, as some were confused by existing text. * Clarify lifetime of objects. * Add implementation of example using transition map/STT. * Add more complex example(s). SCOPE/FEATURES These were features that were suggested or asked about. Some or all may not be suited for addition to the library. In that event, it may be useful to explicitly mention in the documentation that they are not supported, and why. * Support nested states. Return-to-history was cited as an example of a benefit of nested states over nested FSM. * In STT, support matching "any" from state. * Add syntactic sugar to support "synthetic" states (cf. http://lists.boost.org/Archives/boost/2008/08/140714.php) * Support event deferral. * Support data-dependent transitions (perhaps this is the same as the synthetic state suggestion above). * Improve modeling of the "transition" concept. Specifically, there was an issue with the fact that the action was associated with a state rather than a transition. INTERFACE * There was a lot of discussion comparing the amount of code required to implement an "ad hoc" FSM, vs. the amount of code required to implement the same FSM using Boost.FSM. * The "transition map" representation was deemed to contain too much syntactic noise and not sufficiently similar to a traditional STT, and it was suggested that it should include the transition action. * Some felt that the interface was too procedural rather than being declarative. IMPLEMENTATION * There was quite a bit of discussion of the Boost.FSM implementation vs. the C++TM implementation, but I don't believe there were any specific conclusions reached. * Handling of event is different depending on whether or not transition map is used (handled by "to" state vs. current state, respectively). This is also the case when an event is not found in the transition map. This could lead to errors. Thanks again to Andrey for his submission and to all the reviewers and other who made comments for their input. MV

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[serialization] broken in 1.36
by gast128 15 Sep '08

15 Sep '08

Dear all, yesterday we upgraded to vstudio 2008 and Boost 1.36. However it seems that the serialization library gives a STATIC_WARNING now. the code uses a shared_ptr of a data structure which has no virtual function. This was ok in Boost 1.34 and I don't see why this should be wrong: #include "stdafx.h" #include <sstream> #include <boost\shared_ptr.hpp> #include <boost\serialization\shared_ptr.hpp> #include <boost\serialization\nvp.hpp> #include <boost\archive\xml_iarchive.hpp> struct Data { std::string m_str; }; template <class Archive> void serialize(Archive& ar, Data& r, const unsigned int /*version*/) { ar & BOOST_SERIALIZATION_NVP(r.m_str); } struct DataStorage { template <class Archive> void serialize(Archive& ar, const unsigned int /*version*/) { ar & BOOST_SERIALIZATION_NVP(m_ptrBla); } private: //data typedef boost::shared_ptr<Data> DataPtr; DataPtr m_ptrBla; }; int _tmain() { DataStorage data; std::stringstream sstr; //boost::archive::xml_oarchive oa(sstr); //oa << boost::serialization::make_nvp("bla", data); boost::archive::xml_iarchive ia(sstr); ia >> boost::serialization::make_nvp("bla", data); return 0; } It gives warning c4099 where '<---': const extended_type_info * get_derived_extended_type_info(const T & t) const { // note: this implementation - based on usage of typeid (rtti) // only does something if the class has at least one virtual function. BOOST_STATIC_WARNING(boost::is_polymorphic<T>::value); //<--- return detail::extended_type_info_typeid_0::get_extended_type_info( typeid(t) );

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[shared_ptr] why isn't null_deleter included into smart_ptr lib
by Ovanes Markarian 15 Sep '08

15 Sep '08

Hi all! I am wondering, why null_deleter which is sugested in the programming techniques web site of shared_ptr library not a part of utility lib or smart_ptr lib. In the past I worked in at least 3 projects where people defined there own null_deleter. Best Regards, Ovanes

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Problems with boost::asio::local::stream_protocol::iostream under Boost 1.36.0
by Jason Bertschi 15 Sep '08

15 Sep '08

I'm trying to use asio::local::stream_protocol::iostream to connect to a server (using Boost library version 1.36.0). The code looks something like this: boost::asio::local::stream_protocol::iostream mgmtStream("/tmp/pipes/mgmtsock"); if (!mgmtStream) throw std::exception(); // Send cmd to mgmt mgmtStream << cmd << std::flush; I get a compilation error on the line creating mgmtStream. The interesting part is this: no type named 'resolver_query' in 'class boost::asio::local::stream_protocol' I tried breaking the creation into two steps (create local::stream_protocol::endpoint with the name of the socket then passing the endpoint into the iostream constructor), but the result was about the same (the failure occurred on the line creating the iostream, not the line creating the endpoint). The problem seems to be that basic_socket_streambuf<stream_protocol> requires the definition of type resolver_query (within stream_protocol in this case). It seems that ip::tcp::iostream declares it to be of type ip::basic_resolver_query<tcp>; I saw no obvious equivalent in the local namespace, and my attempt to add 'typedef ip::basic_resolver_query<stream_protocol> resolver_query;' to stream_protocol of course did nothing helpful (just added a lot more compilation errors). Frankly, I'm not sure how stream_protocol::iostream could possibly compile without this definition somewhere... Any ideas? Below is the full output from g++ (in case there's something helpful): export_Darwin_i386/include/boost/asio/basic_socket_streambuf.hpp: In instantiation of 'boost::asio::basic_socket_streambuf<boost::asio::local::stream_protocol, boost::asio::stream_socket_service<boost::asio::local::stream_protocol> >': export_Darwin_i386/include/boost/utility/base_from_member.hpp:69: instantiated from 'boost::base_from_member<boost::asio::basic_socket_streambuf<boost::asio::local::stream_protocol, boost::asio::stream_socket_service<boost::asio::local::stream_protocol> >, 0>' export_Darwin_i386/include/boost/asio/basic_socket_iostream.hpp:86: instantiated from 'boost::asio::basic_socket_iostream<boost::asio::local::stream_protocol, boost::asio::stream_socket_service<boost::asio::local::stream_protocol> >' build_Darwin_i386/confdb/ObjectManager.cc:461: instantiated from here export_Darwin_i386/include/boost/asio/basic_socket_streambuf.hpp:252: error: no type named 'resolver_query' in 'class boost::asio::local::stream_protocol' export_Darwin_i386/include/boost/asio/basic_socket_streambuf.hpp: In member function 'boost::asio::basic_socket_streambuf<Protocol, StreamSocketService>* boost::asio::basic_socket_streambuf<Protocol, StreamSocketService>::connect(T0) [with T0 = const char*, Protocol = boost::asio::local::stream_protocol, StreamSocketService = boost::asio::stream_socket_service<boost::asio::local::stream_protocol>]': export_Darwin_i386/include/boost/asio/basic_socket_iostream.hpp:106: instantiated from 'boost::asio::basic_socket_iostream<Protocol, StreamSocketService>::basic_socket_iostream(T0) [with T0 = const char*, Protocol = boost::asio::local::stream_protocol, StreamSocketService = boost::asio::stream_socket_service<boost::asio::local::stream_protocol>]' build_Darwin_i386/confdb/ObjectManager.cc:461: instantiated from here export_Darwin_i386/include/boost/asio/basic_socket_streambuf.hpp:131: error: no type named 'resolver_query' in 'class boost::asio::local::stream_protocol' export_Darwin_i386/include/boost/asio/basic_socket_streambuf.hpp:131: error: no type named 'resolver_query' in 'class boost::asio::local::stream_protocol' export_Darwin_i386/include/boost/asio/basic_socket_streambuf.hpp:131: error: no type named 'resolver_query' in 'class boost::asio::local::stream_protocol' export_Darwin_i386/include/boost/asio/basic_socket_streambuf.hpp:131: error: 'resolve_and_connect' was not declared in this scope Thanks, Jason Bertschi jbertschi(a)mac.com

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