March 2012 - Boost - lists.boost.org

Boost Fusion suggestion
by Pavel Bažant 28 Mar '12

28 Mar '12

I am not actually a Boost developer, but have the following suggestion regarding boost.fusion: I find the macro BOOST_FUSION_DEFINE_STRUCT potentially very useful, but it does not provide means to influence the initialization list of the default constructor. Alternatively, means to emulate c++11 default initialization (the struct Foo {int x=10;} syntax) could be emulated. Such feature would be very useful, as it would minimize repetition and make it easier to ensure that uninitialized variables are nowhere used. I already generate my structs from BOOST_PP sequences in a similar way to BOOST_FUSION_DEFINE_STRUCT to avoid having to write json serialization boilerplate, but a variant of BOOST_FUSION_DEFINE_STRUCT i am suggesting would make this task even simpler. Pavel Bazant

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[functional] [overloaded_function] polymorphic functions?
by Lorenzo Caminiti 27 Mar '12

27 Mar '12

Hello all, I spent some time trying to make overloaded_function support polymorphic functions but I had little success :( 1) I was able to do this (see code below): overloaded_function< void (int) , functor<poly, void (generic)> > o(f, p); o(321); o(3.21); o("cba"); But I don't like it because I explicitly have to pass the functor type poly. I wanted instead to only use generic to tag the template parameters in the signature: overloaded_function< void (int) , void (generic) > o(f, p); o(321); o(3.21); o("cba"); I'd consider this acceptable but I wasn't able to program this because I loose p's type (poly) in base so base cannot hold a reference to the functor p... Is there a way around this? (Some type-erasure magic maybe??) 2) I don't think this can work with function templates because in order to get a pointer to a function template you have to instantiate it: g<char*> Now I can get the function pointer but it's not polymorphic anymore... 3) I don't think there is any way to implement make_overloaded_function with polymorphic types because I can't re-construct the function signature from the functor given that its operator contains template parameters... I have no idea on how to work around this... If you have suggestions for 1, 2, or 3), they are welcome. Otherwise, it seems that supporting polymorphic functions in overloaded_function is not really feasible... The little I got so far: #include <boost/function.hpp> #include <boost/type_traits/function_traits.hpp> #include <iostream> void f(int x) { std::cout << x << std::endl; } template<typename T> void g(T x) { std::cout << x << std::endl; } struct poly { template<typename T> void operator()(T x) { std::cout << x << std::endl; } }; template<typename F> struct base { template<typename G> base(G g) : f_(g) {} typename boost::function_traits<F>::result_type operator()( typename boost::function_traits<F>::arg1_type arg1 ) { return f_(arg1); } private: boost::function<F> f_; }; struct generic; template<typename Ftor, typename F> struct functor; template<typename Ftor, typename R> struct base< functor<Ftor, R (generic)> > { base(Ftor& ftor) : ftor_(ftor) {} template<typename Arg1> R operator()(Arg1 arg1) { return ftor_(arg1); } private: Ftor& ftor_; }; template<typename F1, typename F2> struct overloaded_function : base<F1>, base<F2> { template<typename G1, typename G2> overloaded_function(G1 g1, G2 g2) : base<F1>(g1), base<F2>(g2) {} using base<F1>::operator(); using base<F2>::operator(); }; int main() { f(123); g("xyz"); boost::function<void (char*)> gg = g<char*>; poly p; p(1.23); p("abc"); overloaded_function< void (int) , functor<poly, void (generic)> > o(f, p); o(321); o(3.21); o("cba"); return 0; } Thanks a lot. --Lorenzo

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[git] What's the IDE picture like?
by Rene Rivera 27 Mar '12

27 Mar '12

All this talk about switching to git brings up one important question for me, and I suspect others.. Given all the various git-flow, git-this, git-that, git-whatever, tools that are getting mentioned.. What is the process for a user that wants to do their development, including version control, like? Specifically what does an: * Eclipse user do? * Xcode user do? * VIsualStudio user do? I ask because I'm really tired of learning yet more command lines tools at this stage in my life. And even though all GUI tools have drawbacks they do have the advantage that they condense the workflow usages to something understandable. And I would be really hard pressed to use any new version control system that I can't use a GUI. And preferably an integrated GUI. -- -- -- Grafik - Don't Assume Anything -- Redshift Software, Inc. - http://redshift-software.com -- rrivera/acm.org - grafik/redshift-software.com -- 102708583/icq - grafikrobot/aim - grafikrobot/yahoo

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[move] explicit moving from a rvalue
by Vicente J. Botet Escriba 27 Mar '12

27 Mar '12

Hi Ion, With the current emulation of move semantics of Boost.Thread using Boost.move, I have a case that I would like to make working in a portable way boost::thread t = boost::thread( MoveOnly()); The library declares the template move constructor from a movable callable as as follows template <class F> explicit thread(boost::rv<F>& f); and MoveOnly is declared as defined below. The problem is a know limitation as the compiler is unable to deduce F as been MoveOnly even if MoveOnly is convertible to boost::rv<MoveOnly>& Jeffrey Lee Hellrung, Jr. made a proposal to try to solve the issue, but his proposal has a performance penality. Here it is a less elegant but efficient enough alternative. The addition of a explicit move conversion as ::boost::rv<MoveOnly>& move() { return *static_cast< ::boost::rv<MoveOnly>* >(this); } allows to the following to work as expected boost::thread t = boost::thread( MoveOnly().move()); While this workaround works when we are using the emulation it doesn't works when rvalue references are supported. I have defined a macro BOOST_EXPLICIT_MOVE that allows to write portable code #if ! defined BOOST_NO_RVALUE_REFERENCES #define BOOST_MOVE(RVALUE) RVALUE #else #define BOOST_MOVE(RVALUE) RVALUE.move() #endif that can be used as boost::thread t = boost::thread( BOOST_MOVE(MoveOnly())); The move() function is not really needed as the macro can hide the needed conversion, but could be preferred by users that don't need to make portable programs. The evident liability is of course the use of the macro. Is there something wrong on this design, something to to improve? The same design can be used on compilers, such as as SunStudio (see https://svn.boost.org/trac/boost/ticket/6222) that prefer the overload of a private copy constructor to an public move constructor. On these kind of compilers the following overload private: MoveOnly(MoveOnly&); public MoveOnly(boost::rv<MoveOnly>&) makes the following to fail at compile time MoveOnly MakeMoveOnly() { return MoveOnly(); } but MoveOnly( MakeMoveOnly(() { return BOOST_MOVE(MoveOnly()); } will work. Do you think that member functions as the explicit move() and a macro as BOOST_MOVE can be added to Boost.Move emulation? Best, Vicente ///////////////////////////// class MoveOnly { #ifndef BOOST_NO_DELETED_FUNCTIONS public: MoveOnly(const MoveOnly&)=delete; MoveOnly& operator=(MoveOnly const&); #else private: MoveOnly(MoveOnly&); MoveOnly& operator=(MoveOnly&); public: #endif MoveOnly() { } #ifndef BOOST_NO_RVALUE_REFERENCES MoveOnly(MoveOnly&&) {} #else #if defined BOOST_THREAD_USES_MOVE MoveOnly(boost::rv<MoveOnly>&) {} MoveOnly& operator=(boost::rv<MoveOnly>&) { return *this; } operator ::boost::rv<MoveOnly>&() { return *static_cast< ::boost::rv<MoveOnly>* >(this); } operator const ::boost::rv<MoveOnly>&() const { return *static_cast<const ::boost::rv<MoveOnly>* >(this); } ::boost::rv<MoveOnly>& move() { return *static_cast< ::boost::rv<MoveOnly>* >(this); } const ::boost::rv<MoveOnly>& move() const { return *static_cast<const ::boost::rv<MoveOnly>* >(this); } #else #error #endif #endif void operator()() { } };

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[quickbook] Controling the layout of table columns in docbook/fo output
by Andreas Pokorny 27 Mar '12

27 Mar '12

Hi, In an earlier thread I mentioned that I am using quickbook to write software design specification/documentation. The whole document grows nicely now. Since more people are contributing, I added howto chapters to the end of the document, including some kind of guided quickbook skeleton for new chapters and the quickbook documentation itself. The quickbook documentation creates warnings with fop: Mar 12, 2012 8:11:46 PM org.apache.fop.events.LoggingEventListener processEvent WARNING: table-layout="fixed" and column-width unspecified => falling back to proportional-column-width(1) (See position 1686:869) Mar 12, 2012 8:11:46 PM org.apache.fop.events.LoggingEventListener processEvent WARNING: table-layout="fixed" and column-width unspecified => falling back to proportional-column-width(1) (See position 1686:905) Mar 12, 2012 8:11:46 PM org.apache.fop.events.LoggingEventListener processEvent WARNING: table-layout="fixed" and column-width unspecified => falling back to proportional-column-width(1) (See position 1896:796) and more. That happens for every table. Inside the documentation about tables there one containing hello world source. There the proportional column width makes the source code leave the table and text area of the page. Is there a yet undocumented way to control column sizes? regards Andreas

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Re: [boost] [utility] Adding noexcept to boost::declval
by Michel Morin 27 Mar '12

27 Mar '12

Vicente J. Botet Escriba wrote >> Summary: >> Defining declval<T>() as add_lvalue_reference<T>::type is wrong; >> add_lvalue_reference should be removed! >> >> > There is something that disturb me by returning just T, doesn't this forces > the type T to CopyConstructible? Nope. T needs not to be CopyConstructible (Note that declval can be used only in unevaluated contexts.) > The idea to use T& instead was to avoid > this. You shouldn't do this, because this transforms rvalues to lvalues. > I have rolled back at revision 77562. Thanks, Vicente! Minor issue: `#include <boost/type_traits/add_lvalue_reference.hpp>` is not removed yet. Regards, Michel

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[filesystem] Heads up; filesystem in trunk unstable while V2 removed
by Beman Dawes 27 Mar '12

27 Mar '12

To ensure that history is preserved, the removal of version 2 will be done as three commits. Filesystem in trunk will be unstable during until all three commits are completed. Hopefully this will take less than an hour. I'll post a notice when complete. --Beman

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[gsoc]
by Andrew Sutton 26 Mar '12

26 Mar '12

It looks like there will be no summer of Code for Boost this year. For whatever reason, Google has decided not to accept Boost as a mentoring organization. Andrew

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Re: [boost] [utility] Adding noexcept to boost::declval
by Michel Morin 26 Mar '12

26 Mar '12

(Forgot to send to the list; now back to the list again.) Vicente J. Botet Escriba wrote: > OK, I will rollback it and analyze the breaking change. The important thing is that declval<T>() should preserve the constness/non-constness and the rvalueness/lvalueness of T. Essentially, it's OK to define declval<T>() as simply T. Then, why declval<T>() is defined as add_rvalue_reference<T>::type? This is because * When declval<T>() is defined as T, we cannot use abstract types as T. * When declval<T>() is defined as T&&, we cannot use void as T. The definition with add_rvalue_reference<T>::type also allows to use incomplete types as T. In C++03, it is not possible to construct rvalues of abstract types or incomplete types. So, the correct way to define declval<T>() in C++03 is to just use T. And this is the definition of declval<T>() in the previous version of boost::declval when BOOST_NO_RVALUE_REFERENCES is defined. Summary: Defining declval<T>() as add_lvalue_reference<T>::type is wrong; add_lvalue_reference should be removed! Regards, Michel

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Re: [boost] [gsoc]
by Andrzej Krzemienski 26 Mar '12

26 Mar '12

> From an outside point of view, i do agree. I don't see a lot of Boost GSOC > projects completed. And that's really disapointing. > In my fileds of interests, i would love to see some libraries integrated > that deals with : > - large integer / large fixed point computation > - json parser/ writer > - xml parser/ writer like pugiwml > - crossplatform async file io for boost asio (not only for windows) > - xmpp/sip stack Boost does provide parsers and writers for JSON and XML files. See http://www.boost.org/doc/libs/1_49_0/doc/html/property_tree.html. Regards, &rzej

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