December 2008 - Boost - lists.boost.org

BoostCon 2009: Call for Participation
by Hartmut Kaiser 13 Dec '08

13 Dec '08

Hi all, before we all relax into the holidays I wanted to remind you all about next year's Boost Conference in Aspen, CO, USA, May 3-9. Even if all important dates are listed in the attached Call for Participation, I'll list them here once again: Proposals for submissions due: January 10th 2009. Proposals acceptances sent (tentative program available): February 10th, 2009 Fully scheduled program available: March 1st, 2009 Session materials due: April 1st 2009. IOW, you might want to use some of your free time during the next weeks to think about a possible contribution. It really doesn't take much time to come up with a short abstract! Let's make sure BoostCon 2009 will be a major C++ event! Happy holidays! Regards Hartmut Program Committee Chair BoostCon 2009

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[thread] reset a thread_specific_ptr by this pointer
by Pengcheng Song 13 Dec '08

13 Dec '08

Hi All, I was experimenting with the boost.threads library and especially boost::thread_specific_ptr. However, I ran into problems trying to reset the thread_specific_ptr by the this pointer (see the code below). // ========= beginning of code ============= #include <iostream> #include <boost/thread/thread.hpp> #include <boost/thread/mutex.hpp> #include <boost/thread/tss.hpp> boost::mutex mutex_; class A { private: double x_; static boost::thread_specific_ptr ptr_; public: A(double x=0) : x_(x) {} void operator()() { if (0==ptr_.get()) { ptr_.reset(this); } boost::mutex::scoped_lock lock(mutex_); std::cout << "x_=" << x_ << std::endl; } }; boost::thread_specific_ptr A::ptr_; int main() { boost::thread thrd1( A(1) ); boost::thread thrd2( A(2) ); thrd1.join(); thrd2.join(); return 0; } // ======= end of code ========= This compiled fine with boost_1_36 (binary from boostPro) under VC9 with multithreaded debug DLL code generation. But when I ran it under the debug mode, I got the following error message: Debug Assertion Failed. Expression: _BLOCK_TYPE_IS_VALID(pHead->nBlockUse) I searched the web and this seemed to be a memory problem. And I noticed that it failed to call the destructor of thread_specific_ptr. Is my code legal? Or one is not supposed to reset a thread_specific_ptr to this pointer? Your feedback would be greatly appreciated. Pengcheng Song -- View this message in context: http://www.nabble.com/-thread--reset-a-thread_specific_ptr-by-this-pointer-… Sent from the Boost - Dev mailing list archive at Nabble.com.

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[iterators] how about an identity_iterator or generate_iterator?
by Dean Michael Berris 12 Dec '08

12 Dec '08

Hi, Has anybody found a need for an "identity_iterator"? Something that you can initialize to a value and returns that value every time it's referenced? It could model a random access iterator, and a default constructed version will mark an "end" of the identity_iterator. Something to the effect of: template <class Type> struct identity_iterator { identity_iterator(size_t count = 0) : v_(), count_(count) {} identity_iterator(const identity_iterator & o) : v_(o.v_), count_(o.count_) {} Type operator*() { return v_; } identity_iterator & operator++() { ++count_; *this; } identity_iterator & operator++(int) { ++count_; *this; } bool operator==(identity_iterator const & rhs) { return (this->count_ == rhs.count_); } bool operator<(identity_iterator const & rhs) { return (this->count_ < rhs.count_); } // ... and other required iterator nested types private: Type v_; size_t count_; }; Or even a "generate_iterator" which takes a nullary function object of signature "tuple<bool, T>()" where bool indicates whether it's at the end? It can be modeled as an input iterator. Something like: template <class T> struct generate_iterator { generate_iterator() : f_(), at_end(true) { } generate_iterator(function<tuple<bool, T>() > f) : f_(f), at_end(false) { } // copy constructor, swap, assignment, etc. T operator* () { T return_; tie(at_end, return_) = f_(); return return_; } // other required nested types private: function<tuple<bool, T>()> f_; bool at_end; }; Or is there already something out there which allows these iterator semantics? -- Dean Michael C. Berris Software Engineer, Friendster, Inc.

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Re: [boost] [review][constrained_value] Review of Constrained Value Library begins today
by Kim Barrett 12 Dec '08

12 Dec '08

At 2:23 PM +0100 12/6/08, Robert Kawulak wrote: >... maybe the problem >could be somehow solved if we have a function float exact(float) that, given a >floating point value (that may have greater precision because of caching in a >register), returns a value that is truncated (has exactly the precision of >float, not greater). I think that something along the lines of the following will likely work: inline double exact(double x) { struct { volatile double x; } xx = { x }; return xx.x; } The idea is to force the value to make a round trip through a memory location of the "correct" size. The use of volatile should prevent the compiler from optimizing away the trip through memory. If worried about whether a compiler will really do what's needed here, then I think the only other option is inline assembler to produce the equivalent behavior. Looking through the x86 instruction set, I don't see any other way to cause the desired rounding.

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[Graph] random_access_iterator_property_map
by remi.chateauneu＠gmx.de 12 Dec '08

12 Dec '08

Hi, I try to use random_access_iterator_property_map following the example here: http://www.boost.org/doc/libs/1_37_0/libs/graph/doc/using_property_maps.html I have exactly the same problem mentioned here, on 2003-01-04 : http://www.mail-archive.com/boost@lists.boost.org/msg02627.html The interesting thing is that the documentation is still not updated, and there are still occurences of this class: /usr/include/boost/graph/detail/self_avoiding_walk.hpp: SAW_visitor< random_access_iterator_property_map<Tri*,Tri,Tri&>, /usr/include/boost/graph/detail/self_avoiding_walk.hpp: HList, random_access_iterator_property_map<Iter*,Iter,Iter&> > /usr/include/boost/graph/detail/self_avoiding_walk.hpp: typedef random_access_iterator_property_map<Tri*,Tri,Tri&> TriD; /usr/include/boost/graph/detail/self_avoiding_walk.hpp: typedef random_access_iterator_property_map<Iter*,Iter,Iter&> IterD; Is it a mistake from me, or ? Thanks

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[ref] provide unref( T& )?
by Thorsten Ottosen 11 Dec '08

11 Dec '08

Hi, To be able to call a function object wrapped in boost::reference_wrapper<T>, we need something like the following: template< class T > inline typename boost::unwrap_reference<T>::type& unref( T& value ) { return static_cast<typename boost::unwrap_reference<Fun>::type&>(value); } which can then be used like template< class Fun > int algorithm( Fun fun ) { return unref(fun)(42); } any objections to adding this to ref.hpp? -Thorsten

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[variant]compile-time-checked boost::get<T>?
by Arno Schödl 11 Dec '08

11 Dec '08

Hello, I just replaced our own union implementation by boost::variant and was surprised that boost::get<T> does not compile-time check T. IMHO, boost::get<T> should only compile if T is a possible member of the variant. We implemented this with an enable_if without much difficulty. As a further extension, boost::get<S> where S is a base class of a T contained in the variant, should also work. I believe this would also be implementable with enable_if/disable_if, but we have not done it, so no guarantee. Arno -- Dr. Arno Schoedl · aschoedl(a)think-cell.com Technical Director think-cell Software GmbH · Invalidenstr. 34 · 10115 Berlin, Germany http://www.think-cell.com · phone +49-30-666473-10 · toll-free (US) +1-800-891-8091 Directors: Dr. Markus Hannebauer, Dr. Arno Schoedl · Amtsgericht Charlottenburg, HRB 85229

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[constrained_value] need help with runtime error
by Neal Becker 11 Dec '08

11 Dec '08

This code has an error: #include <boost/numeric/ublas/vector.hpp> #include <boost/constrained_value.hpp> namespace cv = boost::constrained_value; namespace ublas = boost::numeric::ublas; typedef cv::bounded<int>::type val_t; typedef cv::bounded<int>::type::constraint_type constraint_type; int main() { int min = -200; int max = 200; val_t init (10, constraint_type (min, max)); ublas::vector<val_t> v (10, init); ublas::vector<val_t> w = -v; } This code will throw an exception. The last line invokes: ublas/functional.hpp:70 (scalar_negate), which for some reason calls constrained.hpp:224, which is: constrained(const value_type & v) That is, initialize only the value, not the constraint! Any ideas?

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[review][constrained_value] Review of Constrained Value Library begins today
by Jeff Garland 11 Dec '08

11 Dec '08

Hi all, The review of the Robert Kawulak's Constrained Value library begins today December 1, 2008, and will end on December 10th -- I will be the review manager. Please post reviews to the developer list. Here's the library synopsis: The Boost Constrained Value library contains class templates useful for creating constrained objects. A simple example is an object representing an hour of a day, for which only integers from the range [0, 23] are valid values. bounded_int<int, 0, 23>::type hour; hour = 20; // OK hour = 26; // exception! Behavior in case of assignment of an invalid value can be customized. The library has a policy-based design to allow for flexibility in defining constraints and behavior in case of assignment of invalid values. Policies may be configured at compile-time for maximum efficiency or may be changeable at runtime if such dynamic functionality is needed. The library can be downloaded from the here: http://rk.go.pl/f/constrained_value.zip The documentation is also available online here: http://rk.go.pl/r/constrained_value --------------------------------------------------- Please state in your review, whether you think the library should be accepted as a Boost library. Additionally, please consider the following aspects in your review of the library: - What is your evaluation of the design? - What is your evaluation of the implementation? - What is your evaluation of the documentation? - What is your evaluation of the potential usefulness of the library? - Did you try to use the library? With what compiler? Did you have any problems? - How much effort did you put into your evaluation? A glance? A quick reading? In-depth study? - Are you knowledgeable about the problem domain? Thanks, Jeff

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[review][constrained_value] Review of Constrained Value Library begins today
by Jeff Garland 11 Dec '08

11 Dec '08

Hi all, The review of the Robert Kawulak's Constrained Value library begins today December 1, 2008, and will end on December 10th -- I will be the review manager. Please post reviews to the developer list. Here's the library synopsis: The Boost Constrained Value library contains class templates useful for creating constrained objects. A simple example is an object representing an hour of a day, for which only integers from the range [0, 23] are valid values. bounded_int<int, 0, 23>::type hour; hour = 20; // OK hour = 26; // exception! Behavior in case of assignment of an invalid value can be customized. The library has a policy-based design to allow for flexibility in defining constraints and behavior in case of assignment of invalid values. Policies may be configured at compile-time for maximum efficiency or may be changeable at runtime if such dynamic functionality is needed. The library can be downloaded from the here: http://rk.go.pl/f/constrained_value.zip The documentation is also available online here: http://rk.go.pl/r/constrained_value --------------------------------------------------- Please state in your review, whether you think the library should be accepted as a Boost library. Additionally, please consider the following aspects in your review of the library: - What is your evaluation of the design? - What is your evaluation of the implementation? - What is your evaluation of the documentation? - What is your evaluation of the potential usefulness of the library? - Did you try to use the library? With what compiler? Did you have any problems? - How much effort did you put into your evaluation? A glance? A quick reading? In-depth study? - Are you knowledgeable about the problem domain? Thanks, Jeff

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