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Re: [boost] [optional] generates unnessesary code for trivial types
by Hite, Christopher 09 Feb '12

09 Feb '12

On Tuesday, February 07, 2012 17:00:04 Andrey Semashev wrote: > Do I understand it correctly that optional_with_traits is an advanced > replacement for optional? If so, will the good old optional be optimized? No, optional will be ("isA") optional_with_traits. It's just a work around. I'd prefer to redefine optional: template<typename T, typename Traits=optional_traits<T> > class optional; That might in rare cases it could break user code like: mpl::quote1<optional> Personaly I doubt that this is such an issue, but have the best of both worlds I can define a temporary "optional_with_traits" which when boost goes to 2.0 we could deprecate and add the parameter to optional. template<typename T, typename Traits=optional_traits<T> > class optional_with_traits; template<typename T> class optional : public optional_with_traits<T> {...}; Do we gurantee boost users that templates will never add default parameters? > BTW, I would really like to see optional< T& > optimized to store T* > internally. I'm going to say something provacative here. I agree with Lucanus. I see no reason for optional<T&>. As far I can tell you could use a T*. The only justification I can think of is on system without memory protection you can build checks into operator*(). Maybe if you're mixing code with old libraries where T* might imply ownership you might use optional<T&> to imply no ownership and some temporary validity. Perhaps we should define a new "smart pointer" called dumb_ptr<T> which can't be assigned into auto_ptr,unique_ptr,shared_ptr, or any pointer type which implies ownership. Maybe I'm missing something, but I don't see the justification. Chris

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Re: [boost] [optional] generates unnessesary code for trivial types
by Andrzej Krzemienski 09 Feb '12

09 Feb '12

> optional< T& > is a useful thing when you want to apply operators (such as > relation operators or streaming) to the referred value. In generic code you > don't have to specialize for pointers to do the right thing. I'm going to use > this property in my Boost.Log library. Andrey, would you mind giving us a short example of how you want to use an optional reference? I am in the middle of designing the new optional interface for TR2, and came to the conclusion that in order to avoid counter-intuitive semantics for optional reference assignment, I had better remove it at all; that is, optional references are to be limited: they should provide no assignment. You could still use optional values and optional references in generic code but with reduced interface: template <typename T> // T is a ref or a value void use( std::tr2::optional<T> opt, T nval ) { if (opt) { std::cout << *out; // fine *opt = nval; // fine, assigning T's not optionals opt = nval; // invalid if T is a ref opt = opt; // invalid if T is a ref } if (needToRebindAReference()) { opt.emplace(nval); // valid - always rebinds } }; Would such a limited interface as I described above be enough for your generic usage of optional? Regards, &rzej

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Simple boost polygon boolean OR doesn't work: help needed
by Praveen Vs 09 Feb '12

09 Feb '12

Hi, Below is code for doing a boolean OR operation. I'm not sure of the mistake I'm doing here. The output generated is wrong. I'm not using the operator+() becaue of the compile issue on MSVC2010. #include <boost/polygon/polygon.hpp> namespace gtl = boost::polygon; using namespace gtl; using namespace boost::polygon::operators; using namespace std; typedef gtl::polygon_set_data<double> CPolygonSet; typedef gtl::polygon_data<double> CPolygon; static void test_boost_polygons() { CPolygonSet polyset1, polyset2, rset; CPolygon polygon1, polygon2; typedef gtl::polygon_traits<CPolygon>::point_type CPoint; vector<CPoint> poly1Points, poly2Points; poly1Points.push_back(gtl::construct<CPoint>(0.0000, 0.0000)); poly1Points.push_back(gtl::construct<CPoint>(50.0000, 50.0000)); poly1Points.push_back(gtl::construct<CPoint>(100.0000, -50.0000)); poly1Points.push_back(gtl::construct<CPoint>(50.0000, -50.0000)); poly2Points.push_back(gtl::construct<CPoint>(50.0000, 0.0000)); poly2Points.push_back(gtl::construct<CPoint>(100.0000, 50.0000)); poly2Points.push_back(gtl::construct<CPoint>(150.0000, -50.0000)); polygon1.set(poly1Points.begin(), poly1Points.end()); polygon2.set(poly2Points.begin(), poly2Points.end()); vector<CPolygon> polygonArray1, polygonArray2; polygonArray1.push_back(polygon1); polygonArray2.push_back(polygon2); polyset1.insert(polygonArray1.begin(), polygonArray1.end()); polyset2.insert(polygonArray2.begin(), polygonArray2.end()); gtl::arbitrary_boolean_op<CPolygonSet::coordinate_type> bop; bop.execute(rset, polyset1.begin(), polyset1.end(), polyset2.begin(), polyset2.end(), 0); vector<CPolygon> polys; rset.get(polys); for(unsigned int i = 0; i < polys.size(); ++i) { CPolygon::iterator_type it = polys[i].begin(); for(; it != polys[i].end(); ++it) { cout<<"("<<(*it).x()<<", "<<(*it).y()<<")"<<endl; } } } void main() { test_boost_polygons(); } -- -praveen

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GSoC idea on Geometry library
by sultana rashid 08 Feb '12

08 Feb '12

Hello, I have several ideas on some libraries.Today I present on Geometry library. *1.Conics:* I did not found *conics* in Geometry library.Ellipse,parabola,hyperbola concept is very useful in geometry.Can Boost add some functionality of conics? as: 1.Area determination of conics 2.Foci determination 3.Major-minor axis 4.Determine whether a point on a conic 5.Focal length,center determination etc... etc... Or at least add something on Conic in Concept section? If this idea seems useful to you,please let me know.I will describe details on what I want to do about Conic section in Geometry library. *2. **Convex HUll: *There is only one algorithm implemented .We can implement *Gift wrapping*<http://en.wikipedia.org/wiki/Gift_wrapping_algorithm> *O*(*nh*) ; *Divide and conquer* *O*(*n* log *n*) or *Chan's algorithm*<http://en.wikipedia.org/wiki/Chan%27s_algorithm> *O*(*n* log *h*). Jarvis march ,Chan's algo are output sensitive.These are useful when we can assume that the result will not be too large. Thanking you, Sultana

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Manually marking noexcept for a constructor
by Daryle Walker 08 Feb '12

08 Feb '12

I realized that my proposed C++11 update for base_from_member should propagate noexcept. But how do I manually specify the noexcept status of an inner constructor? (Beta versions of C++11 may just have core language changes but not the library changes, so I shouldn't rely on is_nothrow_XXX_constructible just like not relying on std::forward.) I originally thought of: class MyType{ MyInnerType x;public: MyType() noexcept( noexcept(MyInnerType()) );}; This expression includes the inner default constructor call, but it also secretly includes a destructor call (for MyInnerType), and therefore includes it in the calculations! But how about: class MyType2{ MyInnerType x;public: MyType2() noexcept( noexcept(new (std::nothrow) MyInnerType()) );}; Hopefully this, or something like it, includes the constructor call, without calling a destructor. I think the C++11 version of nothrow_t-new is marked noexcept, and I hope the complete new call doesn't hide the constructor call. Daryle W.

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MSVC 2010 Compile error for polygon_set_data
by Praveen Vs 08 Feb '12

08 Feb '12

Hi, Below code gives a compile error in MSVC2010. Any ideas whats the issue? #include <boost/polygon/polygon.hpp> namespace gtl = boost::polygon; using namespace gtl; using namespace boost::polygon::operators; using namespace std; typedef gtl::polygon_set_data<double> CPolygonSet; static void test_boost_polygons() { CPolygonSet polyset1, polyset2, rset; rset = polyset1 + polyset2; } void main() { test_boost_polygons(); } Error: ===== \boost\polygon\polygon_45_set_data.hpp(1458): error C2825: 'iT': must be a class or namespace when followed by '::' 1>\boost\polygon\polygon_45_set_data.hpp(1524) : see reference to function template instantiation 'void boost::polygon::get_error_rects_shell<cT,const boost::polygon::point_data<T>*>(cT &,cT &,iT,iT)' being compiled 1>with 1>[ 1> cT=stlp_std::vector<boost::polygon::rectangle_data<Unit2>>, 1> T=double, 1> iT=const boost::polygon::point_data<double> * 1>] 1>\boost\polygon\polygon_45_set_data.hpp(1621) : see reference to function template instantiation 'void boost::polygon::get_error_rects<stlp_std::vector<_Tp>,boost::polygon::polygon_45_with_holes_data<T>>(cT &,cT &,const pT &)' being compiled 1>with 1>[ 1> _Tp=boost::polygon::rectangle_data<Unit2>, 1> T=double, 1> cT=stlp_std::vector<boost::polygon::rectangle_data<Unit2>>, 1> pT=boost::polygon::polygon_45_with_holes_data<double> 1>] 1>\boost\polygon\detail/polygon_set_view.hpp(102) : see reference to function template instantiation 'void boost::polygon::polygon_45_set_data<Unit>::applyAdaptiveBoolean_<0>(boost::polygon::polygon_45_set_data<Unit> &,const boost::polygon::polygon_45_set_data<Unit> &) const' being compiled 1>with 1>[ 1> Unit=double 1>]

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[utility] Don't mind if I "change" base_from_member?
by Daryle Walker 08 Feb '12

08 Feb '12

Since the suggested trick of using GCC (4.6) from MacPorts as a Darwin GCC worked, I've tried out my first C++11 update: base_from member. It's very straightforward. //$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$Index: boost/utility/base_from_member.hpp===================================================================--- boost/utility/base_from_member.hpp (revision 76917)+++ boost/utility/base_from_member.hpp (working copy)@@ -1,6 +1,6 @@ // boost utility/base_from_member.hpp header file --------------------------// -// Copyright 2001, 2003, 2004 Daryle Walker. Use, modification, and+// Copyright 2001, 2003, 2004, 2012 Daryle Walker. Use, modification, and // distribution are subject to the Boost Software License, Version 1.0. (See // accompanying file LICENSE_1_0.txt or a copy at // <http://www.boost.org/LICENSE_1_0.txt>.)@@ -10,6 +10,7 @@ #ifndef BOOST_UTILITY_BASE_FROM_MEMBER_HPP #define BOOST_UTILITY_BASE_FROM_MEMBER_HPP +#include <boost/config.hpp> #include <boost/preprocessor/arithmetic/inc.hpp> #include <boost/preprocessor/repetition/enum_binary_params.hpp> #include <boost/preprocessor/repetition/enum_params.hpp>@@ -68,12 +69,19 @@ protected: MemberType member; +#if defined(BOOST_HAS_RVALUE_REFS) && defined(BOOST_HAS_VARIADIC_TMPL)+ template <typename ...T>+ explicit BOOST_CONSTEXPR base_from_member( T&& ...x )+ : member( static_cast<T&&>(x)... ) // some libs don't have std::forward+ {}+#else base_from_member() : member() {} BOOST_PP_REPEAT_FROM_TO( 1, BOOST_PP_INC(BOOST_BASE_FROM_MEMBER_MAX_ARITY), BOOST_PRIVATE_CTR_DEF, _ )+#endif }; // boost::base_from_member //$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$ I don't use std::forward because I've heard that some beta C++11 modes implement the core-language ideas needed (r-value references) but not the library changes (i.e. std::move and std::forward), and I didn't want to find (and conditionally?) #include another header. What I got will work just fine, right? Do the constructors need any marking besides "explicit" and "constexpr"? (I believe the "constexpr" will be safely ignored if the forwarded constructor isn't "constexpr" itself without a compile-time error. It was designed that way, right?) I'll just update the documentation and commit the change, then. Daryle W.

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docs on new build system?
by Neal Becker 07 Feb '12

07 Feb '12

I am testing 1_49_0_beta1. I see my usual build failed, saying 'warning: mismatched versions of Boost.Build engine and core'. Taking a wild guess, tried cd tools/build/v2 sh ./bootstrap.sh sudo ./b2 install --prefix=/usr/local I see I now have a new bjam, and something called 'b2'. Should I be reading some new docs on how to use this stuff? Are there some docs? My old build procedure: bjam -sHAVE_ICU=1 -sEXPAT_INCLUDE=/usr -sEXPAT_LIBPATH=/usr/lib64 -- layout=tagged threading=single,multi stage Seems to be proceeding normally (so far)

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[hash] regular behaviour of hash function for double values
by Kai Schroeder 07 Feb '12

07 Feb '12

Hi, the following code: double fStart = 31337; double fEnd = 65536; double fStep = fStart - fEnd; fStep /= 512; for (int i = 0; i < 512; i++) { std::cout << std::hex << boost::hash<double>()(fStart + i * fStep) << std::endl; } leads to the output of surprisingly regular hash values (see end of mail). This seems to occur mainly if a power of two number of points is sampled equidistantly within an interval. Especially since some hash table implementations (e.g. intel's threading building blocks) only use the last few bits to determine the bucket, this can lead to very bad caching behaviour for the rather common case of regularly sampled points (equidistant samplings of power of 2 are e.g. common in computer graphics and numerical algorithms). Are you aware of this? Would you consider it a bug? Best regards, Kai Schroeder Output of code using Boost 1.48 (similar behaviour can be observed for other start and end values and other power of 2 step counts): ff9f20000000000f e5042f900000000f 52f13f200000000f 297ac8b00000000f 48721e400000000f 2f9b8dd00000000f 3df0b1600000000f d19cf2f00000000f 9201c800000000f 9409aa100000000f 7cb3fba00000000f d7a42b300000000f b15982c00000000f 5f7900500000000f e0ba85e00000000f 255ee5700000000f cec119000000000f 955bd6900000000f 6a58f4200000000f 843a37b00000000f 590797400000000f 7e8db4d00000000f 1721b6600000000f 37acf9f00000000f df5f65800000000f 88b1a5100000000f 494a0a00000000f bb1082300000000f 1ea62bc00000000f ...

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unordered_map 32bit VS 64bit
by Avikam Bara-nes 07 Feb '12

07 Feb '12

Hi, I'm porting a project from Linux 32bit to Linux 64bit. While doing so I notice that I have a dramatic performance degradation with unordered_map. My platform is Ubuntu 10.4.3 64bit running on Intel Xeon X3220 but, I tested similar program on WindowsXP SP2 64bit which running on Intel i5 and I get the same degradation. My boost version is 1_46_1. I use the following program in order to test unordered_map - Hop I didn't make any copy mistakes :-). #include <stdio.h> #include <sys/time.h> #include <boost/unordered_map.hpp> int main(int argc, char *argv[]) { struct timeval tv_before, tv_after; boost::unordered_map<boost::int_32_t, boost::int32_t> boost_map; boost_map[1] = 2; boost_map[3] = 4; gettimeofday(&tv_before, NULL); for(int i = ; i < 100000; i++) boost_map.find(1); gettimeofday(&tv_after, NULL); printf("Boost time is %f \n", (double)(((tv_after.tv_sec - tv_before.tv_sec) * 1000000 + (double)(tv_after.tv_usec - tv_before.tv_usec)) / 100000)); return 0; } I use the following compile commands: 64bit - g++ -O3 perf_test -o perf_test_64bit 32bit - g++ -m32 -O3 perf_test -o perf_test_32bit When I run the 32bit program I get 0.5 sec When I run the 64bit program I get 1.54 sec Any ideas ???

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