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[preprocessor metaprogramming] tools
by Nathan Ridge 31 Jul '12

31 Jul '12

Hello, I've noticed preprocessor metaprogramming has become more popular of late, both as a means to provide a cleaner alternative interface to a library (e.g. the DEFINE and ADAPT macros in Boost.Fusion or the proposed macro wrappers for Boost.TypeErasure) and as a means to emulate new language features (e.g. Boost.LocalFunction, Boost.Generic, and Boost.Contract). Sadly, IDE support for writing macro metaprograms is fairly poor in comparison to IDE support for writing regular C++ code. I wanted to share with you something I've found very useful for tracing/debugging macro metaprograms: the Eclipse CDT IDE has a "macro stepper" that allows you to step through the expansion of a macro step-by-step from the initial invocation to the final expansion. (This feature can be accessed by using the "Explore Macro Expansion" context menu item on a macro invocation.) I would be curious to hear what tools you have found useful for writing or debugging macro metaprograms. Regards, Nate

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Re: [boost] BlueGo Beta 0.0.1
by Julian Amann 30 Jul '12

30 Jul '12

> How can I get the sources? the sources can be found at https://bitbucket.org/Vertexwahn/bluego Julian

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[date_time] Who is in charge?
by Philippe Vaucher 30 Jul '12

30 Jul '12

According to the tracker, it looks like the last ticket with activity is https://svn.boost.org/trac/boost/ticket/5257 which is 16 months ago. Also, according to the mailing list I see a lot of discussion/patches dieing out of inactivity ("[boost] [date_time] warning removal", "[boost] [Date Time] bug in documentation example (Localization Demonstration)"). I'm not here to point fingers, we all have busy times where we just cannot handle open-source responsabilities anymore, but maybe this lib should be switched to "no active maintainers" to avoid any confusion? Also, and probably I should have begin with this, is there a page that lists who is the maintainer of what lib beside the Trac? I couldn't find any, but I didn't look very hard either. Philippe

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[type_erasure]any(U,static_binding) stores wrong type
by Larry Evans 30 Jul '12

30 Jul '12

When the attached is run, it produces output: ./static_binding.exe std::is_copy_constructible<ph_erasee_type>=0 53:ph_ctor_arg<boost::type_erasure::_a>::CTOR.default:my_instance=0 creating a_fst from a_ctor_arg 64:ph_ctor_arg<boost::type_erasure::_a>::CTOR.copy:my_instance=1:(void*)this=0x66ab50 :*fst_cast=ph_erasee<boost::type_erasure::_a>.my_instance=0:(void*)fst_cast=0x66ab50 dynamic_cast<ph_ctor_arg_type*>(value_base_ptr)=0x66ab50 dynamic_cast<ph_erasee_type*>(value_base_ptr)=0 Indicating that a ph_ctor_arg_type is being stored in a_fst instead of the expected ph_erasee_type. -regards, Larry

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[1.51][thread] Compile errors when chrono is disabled
by Andrey Semashev 29 Jul '12

29 Jul '12

Hi, There is a problem with Boost.Thread on windows, when BOOST_THREAD_USES_CHRONO macro is defined. In win32/basic_timed_mutex.hpp there are references to Boost.Chrono not guarded with this macro, which results in compile errors. Could this be fixed before the 1.51 release? I can apply the change, if permission is granted.

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[offtopic] C++11 useful trick
by Eric Niebler 29 Jul '12

29 Jul '12

I recently ran into a limitation in recursive functions that make use of decltype in trailing return types. I've come up with a work-around that I think is a little non-obvious, so I thought I'd share. The problem came up while trying to implementing something like a variadic back() function. The "obvious" implementation doesn't work: template<typename T> T back(T && t) { return t; } template<typename T, typename ...U> auto back(T && t, U &&... u) -> decltype(::back(static_cast<U &&>(u)...)) // ERROR { return ::back(static_cast<U &&>(u)...); } int main() { int i = ::back(1,2,3); } The problem occurs on the line marked "HERE". Trouble is, the variadic "back" function is not yet in scope until after the return type. However, we'd like to use it when specifying the return type. The solution uses a default function template parameter to make the ::back symbol dependent, thereby deferring it's lookup until phase 2, when the symbol is visible. Check it: struct S { template<typename T> static T back(T && t) { return t; } template<typename T, typename ...U, typename Impl = S> static auto back(T && t, U &&... u) -> decltype(Impl::back(static_cast<U &&>(u)...)) { return Impl::back(static_cast<U &&>(u)...); } }; int main() { int i = S::back(1,2,3); } The trick is the "typename Impl = S" followed by a (now dependent) invocation of Impl::back. Voila. Apologies if this is a known technique, and I'm spamming the list with old news. It's news to me. -- Eric Niebler BoostPro Computing http://www.boostpro.com

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[type_erasure]broken link in any.html#any(const U&, const static_binding&)
by Larry Evans 29 Jul '12

29 Jul '12

The html page fragment: http://steven_watanabe.users.sourceforge.net/type_erasure/libs/type_erasure… contains a link, CopyConstructible, which sends my browser to: http://steven_watanabe.users.sourceforge.net/trunk/doc/html/CopyConstructib… which is not there. Maybe it should go to: http://www.boost.org/doc/libs/1_50_0/libs/utility/CopyConstructible.html or something similar? Also, why couldn't there be any number of arguments, something like: template<typename Map, class... U> explicit any(const static_binding< Map > & binding, U &&... arg); I think this would then allow any constructor to be used for the contained type. Of course then the requirement would have to be modified to be something like: The underlying type has a constructor accepting arguments, U&... arg. -regards, Larry

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[fusion] typo in documentation
by Steve Lorimer 28 Jul '12

28 Jul '12

In the fusion documents for algorithm pop-back, the example shows usage of pop_back as: assert(___pop_back__(make_vector <http://www.boost.org/doc/libs/1_50_0/libs/fusion/doc/html/fusion/container/…>(1,2,3)) == make_vector <http://www.boost.org/doc/libs/1_50_0/libs/fusion/doc/html/fusion/container/…>(1,2)); this should read: assert(pop_back(make_vector <http://www.boost.org/doc/libs/1_50_0/libs/fusion/doc/html/fusion/container/…>(1,2,3)) == make_vector <http://www.boost.org/doc/libs/1_50_0/libs/fusion/doc/html/fusion/container/…>(1,2)); link: http://www.boost.org/doc/libs/1_50_0/libs/fusion/doc/html/fusion/algorithm/…

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[type_erasure]any(const binding<Concept>&, ...) compile error
by Larry Evans 28 Jul '12

28 Jul '12

The attached, when compiled with with gcc4.8-20120624, produces compile error: ../../../boost/type_erasure/detail/construct.hpp: In instantiation of 'boost::type_erasure::any<Concept, T>::any(const boost::type_erasure::binding<Concept>&, U0&) [with U0 = value<boost::type_erasure::_a>; Concept = boost::mpl::vector<boost::type_erasure::copy_constructible<boost::type_erasure::_a>, boost::type_erasure::copy_constructible<boost::type_erasure::_b> >; T = boost::type_erasure::_a]': binding_of.cpp:71:32: required from here ../../../boost/type_erasure/detail/construct.hpp:99:9: error: invalid use of void expression ) ^ Am I doing something wrong? TIA. -Larry

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[1.51][ICL] Last minute commit
by Joachim Faulhaber 28 Jul '12

28 Jul '12

Hi, unaware of the fact that commits to the release branch need permission this week I did a commit today (Revision 79767). Sorry for that. So I'd like to ask for permission now. In other words, is it possible to not reverse this commit? Thanks, Joachim -- Interval Container Library [Boost.Icl] http://www.joachim-faulhaber.de

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