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[conversion] How to repere assignement to a variable? (was [property] interest in C# like properties for C++?)
by vicente.botet 26 Oct '09

26 Oct '09

Hi, in the thread about C# like properties we were talking about the advantage to be able to repere assignation to properties. I said that, another way to repare the assignments is to use a free function assign_to, like we use the free function swap, or the cast family functions. assign_to(a.p_X, 1); assign_to call by default the assignment operator. If we want transitive assignation a = b = c; we could do assign_to(a, assign_to(b, c)); and if we find this not really readable we can try with tie(a) = tie(b) = c; tie is a template function returning an ca_wrapper. template <typename T> ca_wrapper <T> tie(T& r) { return ca_wrapper<T>(r); } ca_wrapper is responsable to transforming the assignation and operator conversion on a call to assign_to and no more. template <typename T> class ca_wrapper { T& ref_; public: ca_wrapper(T& r) : ref_(r) {} template <typename U> T& operator =(U const& u) { return assign_to(ref_, u); } template <typename U> operator U() { return convert_to(ref_, u); } }; The advantage of having a specific function is that we can specialize the assign_to function for unrelated classes. The Boost.Conversion library (on the review schedule) defines two free functions convert_to and assign_to which by default use the conversion operator and the assignment. We can see convert_to as a getter and assign_to as a setter. The major advantage is that with a uniform syntax, the user can however specialize them to do conversion and assignations between unrelated types. I don't know if tie is a good name to manage with assignation of a variable, I have taken the name from the Boost.Tuple? Regards, _____________________ Vicente Juan Botet Escribá P.S. tie and ca_wrapper are new features of Boost.Conversion v.0.3

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boost design details
by wildinto wildinto 26 Oct '09

26 Oct '09

hi all, because i'm studying the generic programming, i just want to study boost to get the most useful skills, but i can't find any design details about boost. such as boost bind, so, anyone who can tell where i can find the design details about the design of each boost lib ? thanks very much! best regards, Thunder

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[BGL] [Property Map] PropertyGraph concept
by Cosimo Calabrese 26 Oct '09

26 Oct '09

Hi to all, I've taked a look to the PropertyGraph concept, and it defines the following valid expression: get(p, g, x) and its return type: boost::property_traits<Map>::*value_type* Also the docs of Property Map library says that the get() function return the property *by value*, making a copy of the property. But looking to the \boost\graph\detail\adjacency_list.hpp file, I've noticed that the return value of the get function is: typename boost::property_traits< typename boost::property_map<typename Config::graph_type, Property>::type >::*reference* Why this difference? Or they are the same think? Which is the correct specific? Thanks in advance, Cosimo Calabrese.

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[RegEx] Performance degradation since 1.36
by Dave Vest 26 Oct '09

26 Oct '09

I've just downloaded boost 1.40, compiled the libraries, and re-compiled our application. Part of our application uses regular expressions extensively to search through source code and the performance appears to be up to 5 x slower in release mode than with the 1.36 libraries. Boost source (no modifications) compiled with Visual Studio 2008 on Win 7. (Note: 1.36 was compiled with VS 2008 on Win Vista.) bjam debug release --with-thread --with-regex --with-date_time link=static Regex creation: boost::regex::flag_type flags = boost::regex::perl | boost::regex::optimize | boost::regex::icase); boost::regex * pengine = new boost::regex(strSampleExpression, flags); .. Regex use: boost::regex_iterator<char const*> itMatch(pszStr, pszStr + nStrLen, *pengine); boost::regex_iterator<char const*> itEnd; if ( itMatch != itEnd ) { . } A simple for(int i=0;i<100000;++i) loop test shows huge differences. Any ideas why 1.40 is so much slower? Some change in default traits or some documentation note I've missed?

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[PBGL] Distributed BFS example : input and outpu
by Sandeep Gupta 26 Oct '09

26 Oct '09

Hello, I am trying to understand how the example libs/graph_parallel/example/breadth_first_search.cpp works. I am not able to understand (neither find any documentation for it) the input and output of the program. To the best of my understanding a valid input to this program is graph/test/ weighted_graph.gr. What's the format for the input. And why does the output of BFS dependent upon the number of process in the mpirun argument. Would greatly appreciate any explanation or relevant pointers. -thanks Sandeep

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[Test] Building with Comeau C/C++ 4.3.10.1 fails
by Mateusz Loskot 25 Oct '09

25 Oct '09

Hi, Where can I find current status what Boost libraries compile using Comeau C/C++ compiler? I've tried to build Boost.Test and it fails. Is this a known issue? Should I submit a ticket with detailed errors log? Best regards, -- Mateusz Loskot, http://mateusz.loskot.net

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tuple<T,T,...> generator meta-function
by Emre Turkay 23 Oct '09

23 Oct '09

Hi folks, How can I do this in a better way? template <typename T, size_t N> struct make_tuple { }; template <typename T> struct make_tuple<T, 1> { typedef boost::tuple<T> type; }; template <typename T> struct make_tuple<T, 2> { typedef boost::tuple<T, T> type; }; template <typename T> struct make_tuple<T, 3> { typedef boost::tuple<T, T, T> type; }; template <typename T> struct make_tuple<T, 4> { typedef boost::tuple<T, T, T, T> type; }; // ... Thanks, emre

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Re: [boost] [property] interest in C# like properties for C++?
by Stefan Strasser 23 Oct '09

23 Oct '09

Not trying to beat a dead horse, but this is yet another reason to keep the parenthesis syntax: name().size() -- Ursprüngl. Mitteil. -- Betreff: Re: [boost] [property] interest in C# like properties for C++? Von: Olaf van der Spek <olafvdspek(a)gmail.com> Datum: 23.10.2009 07:44 On Fri, Oct 23, 2009 at 1:30 AM, Edward Diener <eldiener(a)tropicsoft.com> wrote: > Of course you can support reference properties along with value properties. > It is just very hard, if not impossible, to support both kinds using the > same template class. So really one would not a separate template class to > support reference properties. Maybe I should've said class reference. Take std::string for example. I'd be very interested if you've got code that supports for example name.size() where name is your reference property class. name->size() is no problem, but I'd like to have name.size(). Olaf _______________________________________________ Unsubscribe & other changes: http://lists.boost.org/mailman/listinfo.cgi/boost

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[random] seeding with arbitrary integers
by Steven Watanabe 23 Oct '09

23 Oct '09

AMDG Currently, some PRNGs cannot be seeded with certain values. For example, the seed for linear_congruential cannot be a multiple of the modulus if the offset is zero. lagged_fibonacci also cannot be seeded with 0, because it uses minstd_rand0. Since linear_congruential already tries to wrap the seed to fit in the range, I'd like to change it so that any seed works. The other generator that needs to be changed is linear_feedback_shift. linear_feedback_shift cannot be seeded with a small integer. What I've done is to add the minimum value to the seed, if the seed is too small. I'm not sure that this is a good solution, since this means that there are a few (and only a few) seeds that result in identical generators. Thoughts? Would it be better to wrap the values to make them fit in range instead? At least this would be consistent with linear_congruential. I've attached a patch with these changes and test cases. See also: http://svn.boost.org/trac/boost/ticket/3516 which prompted this investigation. In Christ, Steven Watanabe

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[asio] help windows.h not littering namespace
by Bjoern Thiel 23 Oct '09

23 Oct '09

Hallo, in socket_types.hpp instead of ... # if defined(__CYGWIN__) # if !defined(__USE_W32_SOCKETS) # error You must add -D__USE_W32_SOCKETS to your compiler options. # endif // !defined(__USE_W32_SOCKETS) # if !defined(NOMINMAX) # define NOMINMAX 1 # endif // !defined(NOMINMAX) # endif // defined(__CYGWIN__) # include <winsock2.h> ... I suggest something like ... # if defined(__CYGWIN__) # if !defined(__USE_W32_SOCKETS) # error You must add -D__USE_W32_SOCKETS to your compiler options. # endif // !defined(__USE_W32_SOCKETS) # endif // defined(__CYGWIN__) # if !defined(NOMINMAX) # define NOMINMAX 1 # define BOOST_NOMINMAX_DEFINED 1 # endif // !defined(NOMINMAX) # include <winsock2.h> # if defined(BOOST_NOMINMAX_DEFINED) # undef NOMINMAX # undef BOOST_NOMINMAX_DEFINED # endif // defined(BOOST_NOMINMAX_DEFINED) ... Thanks. Bjoern Thiel

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