September 2015 - Boost-users - lists.preview.boost.org

testing boost version
by Mathieu Champlon 05 Sep '15

05 Sep '15

Hello, I have a library supposed to work with several versions of Boost. It uses features from Boost.Test which API has changed between 1.58 and 1.59 I naively tried to use Snippet BOOST_PP_LESS to test BOOST_VERSION (e.g. Snippet 105900) but it only accepts values up to BOOST_PP_LIMIT_MAG (e.g. 256). What would be the best way to solve my problem ? Thanks a lot ! MAT.

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Boost.Signals2 - if slot (functor of lambda) destructs the signal, calling the slot itself -> safe for functor?
by nice sw123 04 Sep '15

04 Sep '15

Hi there, If I connect a signal to a slot (functor or lambda), and the signal is then run, it calls the slot. What if the slot now has code that causes the signal to destruct? Will this "self-destruct" the slot (functor or lambda), by calling it's destructor BEFORE the slot-call has finished executing??? This would be a disaster! But it seems like is is safe. It seems: Even if the signal is destructed (from it's own slot-call), the slot destructor does not yet get called, until the slot-call has finished. Which would be safe. (Code example below) But is this really the case? Is this always safe? (If so: how does this roughly work?) Thanks. ///////////////////////////////////////////////////////////////////// #include <iostream> #include <string> #include <boost/signals2.hpp> #include <functional> #include <map> using namespace std; using FuncSig = void(); class BaseWrapper { public: BaseWrapper() { cout << "BaseWrapper() " << ++mm[""] << endl; } BaseWrapper(const string &n) : name{n} { cout << "BaseWrapper() " << name << ' ' << ++mm[name] << endl; } BaseWrapper(const BaseWrapper &other) : name{other.name} { cout << "BaseWrapper(const BaseWrapper &other) " << name << ' ' << ++mm[name] << endl; } virtual ~BaseWrapper() { cout << "~BaseWrapper() " << name << ' ' << mm[name]-- << endl; } private: static map<const string, int> mm; // static counter const string name; }; map<const string, int> BaseWrapper::mm; class MySig : BaseWrapper, public boost::signals2::signal<FuncSig> { }; using Sig = MySig; //boost::signals2::signal<FuncSig>; class A { public: A() {} boost::signals2::connection add_listener(const string &str, const Sig::slot_type &slot) { //my_map.emplace(str, Sig{}); auto x = my_map.emplace(std::piecewise_construct, std::forward_as_tuple(str), std::forward_as_tuple()); return x.first->second.connect(slot); } void remove_listener(const string &str) { auto it = my_map.find(str); if (it != my_map.cend()) { my_map.erase(it); } } void call(const string &str) { auto it = my_map.find(str); if (it != my_map.cend()) { it->second(); } } private: map<const string, Sig> my_map; }; class Functor : BaseWrapper { public: Functor(A *a_, int x_) : BaseWrapper{"Functor"}, a{a_}, x{x_} {} void operator()() const { cout << " this == " << this << endl; cout << " x == " << x << endl; a->remove_listener("hello"); cout << " this == " << this << endl; cout << " x == " << x << endl; } private: A *a; int x; }; int main() { A a; { Functor fun{&a, 4}; a.add_listener("hello", fun); } a.call("hello"); std::cout << "end" << endl; return 0; } /////////////////////////////////////////////////////////////////////

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[Chrono] IO formatting doc minimal/ missing/ appears not to match the actual code base
by Hickman, Steve (AdvTech) 04 Sep '15

04 Sep '15

As of at least Boost 1.58 / 1.59 (possibly earlier), the documentation for Boost.Chrono V2 IO appears to be out of synch with the actual libraries in the following ways: 1) Header file names to include as described in the doc don't match the file names actually available to include. I was unable to find <boost/chrono/io/ios_state.hpp>. I did find <boost/chrono/io/ios_base_state.hpp> but it appears to include things not described in the doc for <boost/chrono/io/ios_state.hpp>. 2) Some format tags are listed as 'unsupported', but there is no description of what that means. Does it mean they are ignored? Does a string still match (which means the input reader will move past those bytes)? 3) I was able to find some examples in chrono\test\io . It would be nice if the tutorial made reference to these as a source of additional info. 4) There appear to be a number of interfaces whose doc appears to consist only of what is embedded in the header files (or I just didn't find the doc for them): time_point_get, etc. Not being familiar with how facets work, I'm not certain if I should be using these directly or not. It would be *really nice* if this were updated. More doc is always better. :) Steve Hickman System Architect, Flight Deck of the Future 480-236-8367

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Re: [Boost-users] [boost] Boost.Fiber mini-review September 4-13
by Nat Goodspeed 04 Sep '15

04 Sep '15

On Fri, Sep 4, 2015 at 2:10 PM, Giovanni Piero Deretta <gpderetta(a)gmail.com> wrote: > - Boost.Fiber is yet another library that comes with its own future > type. For the sake of interoperability, the author should really > contribute changes to boost.thread so that its futures can be re-used. > > - In theory Boost.Thread any_condition should be usable out of the box. > > This probably should lead to a boost wide discussion. There are a few > boost (or proposed) libraries abstract hardware and OS capabilities, > for example boost.thread, boost.asio, boost.filesystem, > boost.iostream, boost.interproces (which also comes with its own > mutexes and condition variables) and of course the proposed afio and > fiber. At the moment they mostly live in separated, isolated worlds. > It would be nice if the authors were to sit down and work out a shared > design. Or more practically at least added some cross library > interoperability facilities. This is C++, generalization should be > possible, easy and cheap. The problem is this: what does it mean to "suspend"? There is no existing facility that can suspend exactly the calling fiber -- which means passing control to the fiber manager, leaving the current thread running to resume another fiber. You're right: if we had a pluggable notion of a suspend operation, we could reuse all Boost.Thread synchronization primitives -- as well as normal "blocking" I/O functions. I would like to see that happen. But it requires that all such libraries be reimplemented in terms of the pluggable suspend. I have a vague notion that this concept is tied to the use of executors, which are themselves a work in progress. Meanwhile -- Fiber requires its own set of synchronization primitives because only those primitives can permit other fibers to continue running on the same thread.

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Re: [Boost-users] [TypeErasure] Reference of forward declared type requires complete type
by Yuan Yao 04 Sep '15

04 Sep '15

On 2015-09-03 23:36:03, Steven Watanabe wrote: > > <snip> > > > > struct Type; > > > > BOOST_TYPE_ERASURE_MEMBER((HasTest), Test, 1) > > > > <snip> > > HasTest<void(Type&)>, > > <snip> > > ================================================ > > > > However, the compiler (e.g. clang) complains about incomplete type: > > > > ================================================ > > /usr/local/include/boost/type_traits/is_base_and_derived.hpp:228:42: > > error: incomplete type 'Type' used in type trait expression > > BOOST_STATIC_CONSTANT(bool, value = (BOOST_IS_BASE_OF(B,D) && ! > > ::boost::is_same<ncvB,ncvD>::value)); > > ================================================ > > > > Replacing Type& with Type* can fix the problem. Is this a bug? > > > > Probably. Is boost::type_erasure::is_placeholder in > the instantiation backtrace? Yes. And the following is the full error message: ================================================ In file included from main.cpp:1: In file included from /usr/local/include/boost/type_erasure/any.hpp:36: In file included from /usr/local/include/boost/type_erasure/detail/normalize.hpp:30: In file included from /usr/local/include/boost/type_erasure/detail/get_placeholders.hpp:25: In file included from /usr/local/include/boost/type_erasure/is_placeholder.hpp:15: /usr/local/include/boost/type_traits/is_base_and_derived.hpp:228:42: error: incomplete type 'Type' used in type trait expression BOOST_STATIC_CONSTANT(bool, value = (BOOST_IS_BASE_OF(B,D) && ! ::boost::is_same<ncvB,ncvD>::value)); ^ /usr/local/include/boost/type_traits/intrinsics.hpp:189:53: note: expanded from macro 'BOOST_IS_BASE_OF' # define BOOST_IS_BASE_OF(T,U) (__is_base_of(T,U) && !is_same<T,U>::value) ^ /usr/local/include/boost/config/suffix.hpp:394:72: note: expanded from macro 'BOOST_STATIC_CONSTANT' # define BOOST_STATIC_CONSTANT(type, assignment) static const type assignment ^ /usr/local/include/boost/type_traits/is_base_and_derived.hpp:237:25: note: in instantiation of template class 'boost::detail::is_base_and_derived_impl<boost::type_erasure::placeholder, Type>' requested here , (::boost::detail::is_base_and_derived_impl<Base,Derived>::value) ^ /usr/local/include/boost/type_traits/detail/bool_trait_def.hpp:74:30: note: expanded from macro 'BOOST_TT_AUX_BOOL_TRAIT_DEF2' BOOST_TT_AUX_BOOL_C_BASE(C) \ ^ /usr/local/include/boost/type_traits/detail/bool_trait_def.hpp:55:81: note: expanded from macro 'BOOST_TT_AUX_BOOL_C_BASE' # define BOOST_TT_AUX_BOOL_C_BASE(C) : public ::boost::integral_constant<bool,C> ^ /usr/local/include/boost/type_erasure/is_placeholder.hpp:27:25: note: in instantiation of template class 'boost::is_base_and_derived<boost::type_erasure::placeholder, Type>' requested here struct is_placeholder : ::boost::is_base_and_derived<placeholder, T> {}; ^ /usr/local/include/boost/mpl/aux_/nested_type_wknd.hpp:27:7: note: in instantiation of template class 'boost::type_erasure::is_placeholder<Type>' requested here : T::type ^ /usr/local/include/boost/mpl/not.hpp:41:11: note: in instantiation of template class 'boost::mpl::aux::nested_type_wknd<boost::type_erasure::is_placeholder<Type> >' requested here BOOST_MPL_AUX_NESTED_TYPE_WKND(T)::value ^ /usr/local/include/boost/mpl/aux_/nested_type_wknd.hpp:38:24: note: expanded from macro 'BOOST_MPL_AUX_NESTED_TYPE_WKND' ::boost::mpl::aux::nested_type_wknd<T> \ ^ /usr/local/include/boost/mpl/aux_/nested_type_wknd.hpp:27:7: note: in instantiation of template class 'boost::mpl::not_<boost::type_erasure::is_placeholder<Type> >' requested here : T::type ^ /usr/local/include/boost/mpl/aux_/preprocessed/gcc/or.hpp:51:11: note: (skipping 17 contexts in backtrace; use -ftemplate-backtrace-limit=0 to see all) BOOST_MPL_AUX_NESTED_TYPE_WKND(T1)::value ^ /usr/local/include/boost/mpl/aux_/nested_type_wknd.hpp:38:24: note: expanded from macro 'BOOST_MPL_AUX_NESTED_TYPE_WKND' ::boost::mpl::aux::nested_type_wknd<T> \ ^ /usr/local/include/boost/mpl/eval_if.hpp:38:22: note: in instantiation of template class 'boost::mpl::fold<boost::mpl::vector<HasTest<void (Type &), boost::type_erasure::_self>, boost::type_erasure::destructible<boost::type_erasure::_self>, boost::type_erasure::relaxed, mpl_::na, mpl_::na, mpl_::na, mpl_::na, mpl_::na, mpl_::na, mpl_::na, mpl_::na, mpl_::na, mpl_::na, mpl_::na, mpl_::na, mpl_::na, mpl_::na, mpl_::na, mpl_::na, mpl_::na>, boost::mpl::s_item<boost::mpl::vector<HasTest<void (Type &), boost::type_erasure::_self>, boost::type_erasure::destructible<boost::type_erasure::_self>, boost::type_erasure::relaxed, mpl_::na, mpl_::na, mpl_::na, mpl_::na, mpl_::na, mpl_::na, mpl_::na, mpl_::na, mpl_::na, mpl_::na, mpl_::na, mpl_::na, mpl_::na, mpl_::na, mpl_::na, mpl_::na, mpl_::na>, boost::mpl::set0<mpl_::na> >, boost::type_erasure::detail::collect_concepts<mpl_::arg<2>, boost::mpl::map0<mpl_::na>, mpl_::arg<1> > >' requested here typedef typename f_::type type; ^ /usr/local/include/boost/type_erasure/detail/normalize.hpp:388:36: note: in instantiation of template class 'boost::mpl::eval_if<boost::mpl::is_sequence<boost::mpl::vector<HasTest<void (Type &), boost::type_erasure::_self>, boost::type_erasure::destructible<boost::type_erasure::_self>, boost::type_erasure::relaxed, mpl_::na, mpl_::na, mpl_::na, mpl_::na, mpl_::na, mpl_::na, mpl_::na, mpl_::na, mpl_::na, mpl_::na, mpl_::na, mpl_::na, mpl_::na, mpl_::na, mpl_::na, mpl_::na, mpl_::na> >, boost::mpl::fold<boost::mpl::vector<HasTest<void (Type &), boost::type_erasure::_self>, boost::type_erasure::destructible<boost::type_erasure::_self>, boost::type_erasure::relaxed, mpl_::na, mpl_::na, mpl_::na, mpl_::na, mpl_::na, mpl_::na, mpl_::na, mpl_::na, mpl_::na, mpl_::na, mpl_::na, mpl_::na, mpl_::na, mpl_::na, mpl_::na, mpl_::na, mpl_::na>, boost::mpl::s_item<boost::mpl::vector<HasTest<void (Type &), boost::type_erasure::_self>, boost::type_erasure::destructible<boost::type_erasure::_self>, boost::type_erasure::relaxed, mpl_::na, mpl_::na, mpl_::na, mpl_::na, mpl_::na, mpl_::na, mpl_::na, mpl_::na, mpl_::na, mpl_::na, mpl_::na, mpl_::na, mpl_::na, mpl_::na, mpl_::na, mpl_::na, mpl_::na>, boost::mpl::set0<mpl_::na> >, boost::type_erasure::detail::collect_concepts<mpl_::arg<2>, boost::mpl::map0<mpl_::na>, mpl_::arg<1> > >, boost::mpl::identity<boost::mpl::s_item<boost::mpl::vector<HasTest<void (Type &), boost::type_erasure::_self>, boost::type_erasure::destructible<boost::type_erasure::_self>, boost::type_erasure::relaxed, mpl_::na, mpl_::na, mpl_::na, mpl_::na, mpl_::na, mpl_::na, mpl_::na, mpl_::na, mpl_::na, mpl_::na, mpl_::na, mpl_::na, mpl_::na, mpl_::na, mpl_::na, mpl_::na, mpl_::na>, boost::mpl::set0<mpl_::na> > > >' requested here typedef typename ::boost::mpl::eval_if< ::boost::mpl::is_sequence<Concept>, ^ /usr/local/include/boost/type_erasure/any.hpp:65:49: note: in instantiation of template class 'boost::type_erasure::detail::collect_concepts<boost::mpl::vector<HasTest<void (Type &), boost::type_erasure::_self>, boost::type_erasure::destructible<boost::type_erasure::_self>, boost::type_erasure::relaxed, mpl_::na, mpl_::na, mpl_::na, mpl_::na, mpl_::na, mpl_::na, mpl_::na, mpl_::na, mpl_::na, mpl_::na, mpl_::na, mpl_::na, mpl_::na, mpl_::na, mpl_::na, mpl_::na, mpl_::na>, boost::mpl::map0<mpl_::na>, boost::mpl::set0<mpl_::na> >' requested here typename ::boost::type_erasure::detail::collect_concepts< ^ /usr/local/include/boost/type_erasure/any.hpp:132:43: note: in instantiation of template class 'boost::type_erasure::detail::compute_bases<boost::type_erasure::any<boost::mpl::vector<HasTest<void (Type &), boost::type_erasure::_self>, boost::type_erasure::destructible<boost::type_erasure::_self>, boost::type_erasure::relaxed, mpl_::na, mpl_::na, mpl_::na, mpl_::na, mpl_::na, mpl_::na, mpl_::na, mpl_::na, mpl_::na, mpl_::na, mpl_::na, mpl_::na, mpl_::na, mpl_::na, mpl_::na, mpl_::na, mpl_::na>, boost::type_erasure::_self>, boost::mpl::vector<HasTest<void (Type &), boost::type_erasure::_self>, boost::type_erasure::destructible<boost::type_erasure::_self>, boost::type_erasure::relaxed, mpl_::na, mpl_::na, mpl_::na, mpl_::na, mpl_::na, mpl_::na, mpl_::na, mpl_::na, mpl_::na, mpl_::na, mpl_::na, mpl_::na, mpl_::na, mpl_::na, mpl_::na, mpl_::na, mpl_::na>, boost::type_erasure::_self>' requested here public ::boost::type_erasure::detail::compute_bases< ^ main.cpp:17:10: note: in instantiation of template class 'boost::type_erasure::any<boost::mpl::vector<HasTest<void (Type &), boost::type_erasure::_self>, boost::type_erasure::destructible<boost::type_erasure::_self>, boost::type_erasure::relaxed, mpl_::na, mpl_::na, mpl_::na, mpl_::na, mpl_::na, mpl_::na, mpl_::na, mpl_::na, mpl_::na, mpl_::na, mpl_::na, mpl_::na, mpl_::na, mpl_::na, mpl_::na, mpl_::na, mpl_::na>, boost::type_erasure::_self>' requested here Any obj; ^ main.cpp:4:8: note: forward declaration of 'Type' struct Type; ^ 1 error generated. ================================================

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[TypeErasure] Reference of forward declared type requires complete type
by Yuan Yao 04 Sep '15

04 Sep '15

Hi all, I try to use boost.type_erasure (boost 1.59) with forward declared type as shown below: ================================================ #include <boost/type_erasure/any.hpp> #include <boost/type_erasure/member.hpp> struct Type; BOOST_TYPE_ERASURE_MEMBER((HasTest), Test, 1) using Any = boost::type_erasure::any < boost::mpl::vector < HasTest<void(Type&)>, boost::type_erasure::destructible<>, boost::type_erasure::relaxed > >; int main() { Any obj; } ================================================ However, the compiler (e.g. clang) complains about incomplete type: ================================================ /usr/local/include/boost/type_traits/is_base_and_derived.hpp:228:42: error: incomplete type 'Type' used in type trait expression BOOST_STATIC_CONSTANT(bool, value = (BOOST_IS_BASE_OF(B,D) && ! ::boost::is_same<ncvB,ncvD>::value)); ================================================ Replacing Type& with Type* can fix the problem. Is this a bug?

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[msvc-14] Status of _HAS_AUTO_PTR_ETC=0 support
by Mateusz Loskot 03 Sep '15

03 Sep '15

Hi, VS2015 allows to disable the C++ library features deprecated in C++11: [1] "By default, we provide auto_ptr/etc. If you define _HAS_AUTO_PTR_ETC to 0 project-wide (which you should do via the command line or project file, not via #define), then we won't provide auto_ptr/etc." Attempt to compile the following test.cpp based on up-to-date Boost (master) fails: #include <boost/algorithm/string.hpp> int main() { return 0; } cl /EHsc /ID:\dev\boost.git /D_HAS_AUTO_PTR_ETC=0 test.cpp Below are two problems that can be solved with additional define of BOOST_NO_AUTO_PTR=1 D:\dev\boost.git\boost/get_pointer.hpp(48): error C2065: 'auto_ptr': undeclared identifier D:\dev\boost.git\boost/get_pointer.hpp(62): error C2923: 'std::unique_ptr': 'T' is not a valid template type argument for parameter '_Ty' I also expected _HAS_AUTO_PTR_ETC=0 should imply BOOST_NO_AUTO_PTR=1. Then, I hoped this would work: cl /EHsc /ID:\dev\boost.git /D_HAS_AUTO_PTR_ETC=0 /DBOOST_NO_AUTO_PTR=1 test.cpp Unfortunately, it fails due to uses of std::unary_function and std::binary_function in boost/algorithm/string/detail/case_conv.hpp. Those functions have been deprecated since C++11 and are disable by _HAS_AUTO_PTR_ETC=0. This basic evaluation made me wonder, does Boost support compilation with _HAS_AUTO_PTR_ETC=0 defined at all? [1] http://blogs.msdn.com/b/vcblog/archive/2015/04/29/c-11-14-17-features-in-vs… Best regards, -- Mateusz Loskot, http://mateusz.loskot.net

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Include line number in boost logs
by Florian Lindner 03 Sep '15

03 Sep '15

Hello, I try to implement that a log entry also logs its line number with boost::log. If any developer of it reads here, please also consider this a wishlist item... I think the best way to add an additional attribute for it core::get()->add_global_attribute( "Line", attributes::mutable_constant<size_t>(0) ); in my logger config that is called once at startup. #define logInfo(methodname, message) \ boost::log::core::get()->get_global_attributes()["Line"].set(__LINE__); \ BOOST_LOG_SEV(_log, boost::log::trivial::severity_level::trace) << message \ Is my idea, but boostlog.cpp:126:5: error: no member named 'set' in 'boost::log::v2_mt_posix::aux::attribute_set_reference_proxy' getting the attribute somehow seems to work, but how can I set the value of the attribute? Thanks! Florian

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[Type Erasure] Ambiguous call with vs 2015 community
by Yuan Yao 02 Sep '15

02 Sep '15

Dear all, I try to use type erasure on the free function foo. However, VS 2015 failed to compile the following code, which is OK with GCC and CLang. ========================================================= #include <boost/type_erasure/any.hpp> #include <boost/type_erasure/free.hpp> #include <typeindex> std::type_index foo(int); BOOST_TYPE_ERASURE_FREE((HasGetField), foo, 1) using Type = boost::type_erasure::any< HasGetField<std::type_index(boost::type_erasure::_self const&)>, boost::type_erasure::_self const& >; std::type_index foo(int) { return typeid(int); } int main() { Type x{ 1 }; foo(x); return 0; } ========================================================= Source.cpp C:\Program Files\Microsoft Visual Studio 14.0\VC\INCLUDE\xlocale(341): warning C4530: C++ exception handler used, but unwind semantics are not enabled. Specify /EHsc Source.cpp(20): error C2668: 'boost::type_erasure::injectHasGetField<R (const boost::type_erasure::_self &),Base,boost::type_erasure::index_list<0>>::foo': ambiguous call to overloaded function with [ R=std::type_index, Base=boost::type_erasure::any_base<boost::type_erasure::any<HasGetField<std::type_index (const boost::type_erasure::_self &)>,boost::type_erasure::_self &&>> ] Source.cpp(7): note: could be 'std::type_index boost::type_erasure::injectHasGetField<R (const boost::type_erasure::_self &),Base,boost::type_erasure::index_list<0>>::foo(eval_if_c<0,boost::type_erasure::detail::maybe_const_this_param<const boost::type_erasure::_self &,Base>,boost::type_erasure::as_param<Base,const boost::type_erasure::_self &>>::type)' [found using argument-dependent lookup] with [ R=std::type_index, Base=boost::type_erasure::any_base<boost::type_erasure::any<HasGetField<std::type_index (const boost::type_erasure::_self &)>,boost::type_erasure::_self &&>> ] Source.cpp(7): note: or 'std::type_index boost::type_erasure::injectHasGetField<R (const boost::type_erasure::_self &),Base,boost::type_erasure::index_list<0>>::foo(eval_if_c<0,boost::type_erasure::detail::maybe_const_this_param<const boost::type_erasure::_self &,Base>,boost::type_erasure::as_param<Base,const boost::type_erasure::_self &>>::type)' [found using argument-dependent lookup] with [ R=std::type_index, Base=boost::type_erasure::any_base<boost::type_erasure::any<HasGetField<std::type_index (const boost::type_erasure::_self &)>,boost::type_erasure::_self &>> ] Source.cpp(7): note: or 'std::type_index boost::type_erasure::injectHasGetField<R (const boost::type_erasure::_self &),Base,boost::type_erasure::index_list<0>>::foo(eval_if_c<0,boost::type_erasure::detail::maybe_const_this_param<const boost::type_erasure::_self &,Base>,boost::type_erasure::as_param<Base,const boost::type_erasure::_self &>>::type)' [found using argument-dependent lookup] with [ R=std::type_index, Base=boost::type_erasure::any_base<boost::type_erasure::any<HasGetField<std::type_index (const boost::type_erasure::_self &)>,boost::type_erasure::_self>> ] Source.cpp(7): note: or 'std::type_index boost::type_erasure::injectHasGetField<R (const boost::type_erasure::_self &),Base,boost::type_erasure::index_list<0>>::foo(eval_if_c<0,boost::type_erasure::detail::maybe_const_this_param<const boost::type_erasure::_self &,Base>,boost::type_erasure::as_param<Base,const boost::type_erasure::_self &>>::type)' [found using argument-dependent lookup] with [ R=std::type_index, Base=boost::type_erasure::any_base<boost::type_erasure::any<HasGetField<std::type_index (const boost::type_erasure::_self &)>,const boost::type_erasure::_self &>> ] Source.cpp(14): note: or 'std::type_index foo(int)' Source.cpp(20): note: while trying to match the argument list '(Type)' ========================================================= Moreover, I wonder whether the declaration is a must? Thank you!

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Re: [Boost-users] is it possible to group values with Boost's rtree?
by Andy Edwards 01 Sep '15

01 Sep '15

Noel wrote: > I had to do something similar packing 100k 3d objects into the smallest > number of groups, where each group contains only non-overlapping 3d > objects. I used the Boost Graph library with a smallest least ordering > graph coloring algorithm. Since this is a quasi-np hard problem, I know > the packing density is sub-optimal but still quite good for our > application. Perhaps that approach would work for you? Unfortunately > I?m not familiar with Boost rtree. > > ? Noel Belcourt Thanks for the tip Noel, but it sounds like I'll be able to accomplish it using Adam's suggestions (I don't need completely optimal packing density). Since I'll be using the rtree for spatial queries as well it's the best approach for me. Adam wrote: > It is possible though it isn't officially supported. Have a look at the > utilities in this directory: > > https://github.com/boostorg/geometry/tree/master/include/boost/geometry/ind… > > To traverse the rtree you must write a visitor similar to the > Boost.Variant visitor, defining operator() overloads taking nodes. There > is a boost::geometry::index::detail::rtree::utilities::view<> providing > read-only access to the rtree's internals, in particular to the > apply_visitor() method applying the visitor to the root node of the > rtree and depth() function returning the number of tree levels. To > access the node's elements container you may use > boost::geometry::index::detail::rtree::elements() function and to apply > the visitor to the child node you may call > boost::geometry::index::detail::rtree::apply_visitor() function. The > elements of an internal node are of type similar to std::pair<> where > the first member is a Box and the second member is a pointer to the > child node. The elements of a leaf node are of type value_type. This way > you may recursively traverse the rtree in depth-first order counting the > current level, create containers of values when some level is met and > then gather the values from leafs. See e.g. how the utilities in the > directory mentioned above are implemented. > > Regards, > Adam Thanks Adam! That sounds ideal. Glad I'll be able to use this! I wonder if a per-node predicate is planned for the public API in the future (rather than the value-only satisfies predicate)?

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