June 2010 - Boost - lists.boost.org

iterator_category> algorithm selection with cast operator
by gzp 26 Jun '10

26 Jun '10

Hello, I've read the article of ranges vs. iterators from Andrei Alexandrescu and I've start to implement something similar and wanted to extend the idea to 2D grids (popFront, front, popLine). OK, I now s/g similar can be achieved using iterators(ranges) returning iterators(ranges) as the current item, I was just simple experimenting. Using the iterator_category concept empty structs are used to check, select functions at compile time. struct A {}; struct B : A {} void foo( A ) { alg1... } void foo( B ) { alg2... specialized for B } template<typename T> void foofoo( T ){ foo( getCategory<T>() ); } My first idea was to use multiple inheritance, but it result error (ambiguous call) struct A {}; struct B : A {}; struct A2 : A {}; struct B2 : A2, B {}; void foo( A ) { alg1... } void foo( B ) { alg2... specialized for B } void foo( A2 ) { alg3... specialized for A2 } void g() { B2 b; f(b); } // error: is it f(B) or f(A2) Than I've used cast operators and inheritance stating that, a B2 is mainly an A2 and secondly a B: struct A {}; struct B : A {}; struct A2 : A {}; struct B2 : A2 { operator B() { return B(); } }; void foo( A ) { alg1... } void foo( B ) { alg2... specialized for B } void foo( A2 ) { alg3... specialized for A2 } void g() { B2 b; f(b); } // shall call f(A2) So my question is that, is it a working method, or the whole concept is wrong ? Has anyone used something similar ? If so, is there some sample codes/results? Thank you, Gzp -- View this message in context: http://old.nabble.com/iterator_category%3E-algorithm-selection-with-cast-op… Sent from the Boost - Dev mailing list archive at Nabble.com.

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Assertion `slot->m_to_python == 0' failed in when trying to expose custom iterator
by Yongning Zhu 26 Jun '10

26 Jun '10

Hi, I am following a tutorial to expose a custom iterator to python, The iterator was used in C++ by for(T_ITERATOR it();it.Valid();it.Next()){ T_VALUE v=it.Value(); } And I wrote the following wrapper: template<class Klass, class KlassIter> struct iterator_wrappers { static Klass next(KlassIter& o) { o.Next(); Klass result = o.Value(); if (!o.Valid()) { PyErr_SetString(PyExc_StopIteration, "No more data."); boost::python::throw_error_already_set(); } return result; } static void wrap(const char* python_name) { //using namespace boost::python; class_<KlassIter>(python_name, init<>())//no_init .def("next", next) .def("__iter__", pass_through) ; } }; and expose it by iterator_wrappers<T_VALUE,T_ITERATOR>().wrap("t_iterator"); It compiles but when I am importing the module in python, there is an error saying: python: ../../../../libs/python/src/converter/registry.cpp:212: void boost::python::converter::registry::insert(PyObject* (*)(const void*), boost::python::type_info, const PyTypeObject* (*)()): Assertion `slot->m_to_python == 0' failed. Aborted Could some one please help me? Thanks a lot! Yong

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[graph] ambiguity for 'tie' VC10
by Andreas Fabri 25 Jun '10

25 Jun '10

Hello, For Windows7 VC10 64 bit, boost_1_43_0 the following code produces an error message #include <tuple> #include <boost/graph/adjacency_list.hpp> typedef boost::adjacency_list< boost::vecS, boost::vecS, boost::undirectedS > G; int main() { G g1; G g2(g1); return 0; } C:\boost\boost_1_43_0\boost/graph/detail/adjacency_list.hpp(2157) : error C2668: 'boost::tuples::tie' : ambiguous call to overloaded function C:\boost\boost_1_43_0\boost/tuple/detail/tuple_basic.hpp(889): could be 'boost::tuples::tuple<T0,T1,T2,T3,T4,T5,T6,T7,T8,T9> boost::tuples::tie<boost::detail::undirected_edge_iter<EdgeIter,EdgeDescriptor,Difference>,boost::detail::undirected_edge_iter<EdgeIter,EdgeDescriptor,Difference>>(boost::detail::undirected_edge_iter<EdgeIter,EdgeDescriptor,Difference> &,boost::detail::undirected_edge_iter<EdgeIter,EdgeDescriptor,Difference> &)' .... OR C:\Program Files (x86)\Microsoft Visual Studio 10.0\VC\INCLUDE\xxtuple1(34): or 'std::tr1::tuple<_Arg0,_Arg1,_Arg2,_Arg3,_Arg4,_Arg5,_Arg6,_Arg7,_Arg8,_Arg9> std::tr1::tie<boost::detail::undirected_edge_iter<EdgeIter,EdgeDescriptor,Difference>,boost::detail::undirected_edge_iter<EdgeIter,EdgeDescriptor,Difference>>(boost::detail::undirected_edge_iter<EdgeIter,EdgeDescriptor,Difference> &,boost::detail::undirected_edge_iter<EdgeIter,EdgeDescriptor,Difference> &)' [found using argument-dependent lookup] Best regards, andreas fabri

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Re: [boost] boost [msm] deferring event by base type
by Christophe Henry 25 Jun '10

25 Jun '10

> I'm now using Row and Defer functor I have now an other problem whit the : > > void defer_event(Event const& e) > { > // to call this function, you need either a state with a > deferred_events typedef > // or that the fsm provides the activate_deferred_events typedef > BOOST_MPL_ASSERT(( has_fsm_deferred_events<library_sm> )); > execute_return (library_sm::*pf) (Event const& evt)= > &library_sm::process_event; > Event temp (e); > ::boost::function<execute_return ()> f= ::boost::bind(pf, this,temp); > post_deferred_event(f); > } > > actually it tries to instantiate the base class ( Event temp (e); ) > but in my case the base class is an abstract class -> compiler error; > and after deferring I want to dispatch the original derived event not > the copy constructed base class instance of the event. What you get is a slicing. The Defer functor works like any action, meaning that the type of the event is encoded in the transition. If you consider a transition: a_row < Stopped , play , Playing , &p::start_playback > and an action: void start_playback(play const&) The type of the event in the action is the one defined in the transition. So what defer_event gets (from Defer) is the type defined in the transition, in your case the base event. It's harder to spot than a vector<base> but about the same. A solution would be to have msm's process_event reinterpret_cast action signature. I will take it into my feature list but probably not at the top as I consider the feature as only nice to have. In the meantime, I, like Juraj, would also suggest you to pimpl your data (with or without a shared_ptr) or define one entry inside deferred_events for every derived event. Regards, Christophe

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boost [msm] deferring event by base type.
by Richard Szabo 25 Jun '10

25 Jun '10

I try to use the following code struct base {}; struct event1 : public base {}; struct MyState1 : public msm::front::state<> { typedef mpl::vector<base> deferred_events; }; than MySm.process_event(event1()); when state machine in MyState1 causes that event gets dispatched and not deferred the same code works if I replace typedef mpl::vector<base> deferred_events; with typedef mpl::vector<event1> deferred_events; than it works fine and event1 is deferred in MyState1; It would be nice to able to defer event by it's base types it would make code maintenance easier not have to declare all events one by one for deferring. Br. Richie

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[filesystem][v3] Class path codecvt argument now available for appropriate functions
by Beman Dawes 25 Jun '10

25 Jun '10

The initial V3 implementation, like V2, could alter the codecvt facet used for conversion via a static imbue() function. This has a number of problems, including: * It is, in effect, a global variable, and thus "considered harmful" as being prone to abuse. * It is subject to data races in multi-threaded environments. * It can be hard to use. * It can be hard to explain. As of revision 63283 this morning, V3 class path in trunk now has an additional "const codecvt&" for all functions where conversion may be required. So you can now write: utf8_codecvt_facet utf8; // UTF-8 facet from boost or other sources path p(some_string, utf8); // some_string will be treated as UTF-8 encoded ... operations on p That's great, but where does that leave path::imbue? I think it should be deprecated. What do others think? --Beman

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[asio] Re: Pass some parameter to io_service::run
by Dmytro Ovdiienko 24 Jun '10

24 Jun '10

James, it is not academic reason. I need latency 1-2us. Right now I have 15us. I cannot waste time on locks and I cannot create bottlenecks. And how about just let user pass "void *"? I know it is not type safe... maybe boost has something like type-safe variable argument list? On 11 January 2010 17:13, James Mansion <james(a)mansionfamily.plus.com>wrote: > Dmytro Ovdiienko wrote: > >> >> I don't understand why you would have an objection to a permanent >> binding with TLS >> >> TLS looks like global variables. Global variables violate encapsulation. I >> suppose to support my program at least 2 years. I don't want to hate myself >> two years :) >> > I think that's quite a silly reason. So are singletons, but they are both > useful. ... > > >> or >> a temporary binding using a pool of parsers, since it seems that >> each datagram must be >> parsed entirely and then the parser reset for the next? >> >> Exactly. But I don't want to create pool of the parsers. Access to the >> pool should be synchronized. Synchronization eats CPU times. >> > ... but not nearly as silly as this one. Getting an item from a pool is a > great candidate for a spinlock and if you're concerned you can easily > segment the pool. Its a non-issue. I defy you to measure it in the context > of all teh context switching and system calls you're doing. > > Of course, the pool is a singleton. And that's like a global. > > The right tools to get you what you want are right there - you're just > choosing not to use them for academic reasons. > > James > > -- Dmytro Ovdiienko e-mail: dmitriy.ovdienko(a)gmail.com skype: dmitriy.ovdienko(a)gmail.com mobile: +38050-1909731 -- Dmytro Ovdiienko e-mail: dmitriy.ovdienko(a)gmail.com skype: dmitriy.ovdienko(a)gmail.com mobile: +38050-1909731

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[thread] once_flag causes dynamic initialization?
by Andrey Semashev 24 Jun '10

24 Jun '10

Hi, I've noticed that on Windows using call_once is not thread-safe as the once_flag structure has a destructor which makes it dynamically initialized. I can see the ticket [1] for this problem is hanging for quite a while, whereas the bug is quite critical, IMHO. Are there any plans on fixing it, perhaps by reverting the change that introduced it? [1] <https://svn.boost.org/trac/boost/ticket/4225> PS: Curiously, the change was made on April, 1st. A long-term joke? :)

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[standard] mutable references
by Gennady Proskurin 24 Jun '10

24 Jun '10

According to 7.1.1-10, reference members cannot be mutable. I think its worth to apply attached patch. ---

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[chrono] Documentation suggestions
by Roland Bock 24 Jun '10

24 Jun '10

Hi, I have a few remarks/suggestions for the documentation of Boost.Chrono: *General: *http://svn.boost.org/svn/boost/sandbox/chrono/libs/chrono/doc/html/index.html There are several sections which attract my attention when trying to get a grip on the library: * Getting Started * Tutorial * Examples Each of those looks a bit like a random collection of valuable hints to me (sorry, if I missed the pattern). My personal troubles in understanding the basics are documented in the mail referenced in the tutorial section. I think it would be worth it to reorganize all three into one section (e.g. tutorial) which shows how to utilize the different parts of the library. For instance with the following subsections: * Clocks (including stopwatch and thread_clock) * Formatters * Reporters * Conversions (see also Tutorial section below) * ...? Each section would contain usage patterns and complete sample programs. *Users Guide: *http://svn.boost.org/svn/boost/sandbox/chrono/libs/chrono/doc/html/boost_chrono/users_guide.html * Personally, I would move the references section to the appendices (I clicked there several times when I really wanted to see the Reference section) *Reference: *http://svn.boost.org/svn/boost/sandbox/chrono/libs/chrono/doc/html/boost_chrono/reference.html * thread_clock is missing in the reference section * typo "chorno.hpp>" on several pages *Examples:* http://svn.boost.org/svn/boost/sandbox/chrono/libs/chrono/doc/html/boost_ch… * There are several hints like "See the file i_dont_like_the_default_duration_behavior.cpp". It would be nice to have a working link to the file instead * Some examples are not linked to a file. I think it would be good to have a working sample file for each example *Tutorial:* http://svn.boost.org/svn/boost/sandbox/chrono/libs/chrono/doc/html/boost_ch… * The section "How to define a thread clock" is now obsolete, isn't it? thread_clock is now integral part of chrono. * An example on how to use the thread_clock would be very helpful. * An example on how to obtain a duration in some unit would be helpful See here (http://lists.boost.org/boost-users/2010/04/58204.php) for what I meant with the last item. The answers by Howard Hinnant in this mail were extremely helpful and could probably be re-used in the tutorial. Regards, Roland

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