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"parent_from_member" proposal
by Domagoj Saric 02 Oct '09

02 Oct '09

Sometimes your design contains the typical model<->view / data/logic<->gui separation of classes/objects but at the same time it is static enough that it does not require the also typical dynamic way of connecting the two worlds through pointers and/or signals/events and/or function pointers/callbacks and/or ... In other words: - the two corresponding objects ('model/logic' and 'view/gui') always exist in the same memory space/process - the 'model' always exists when the 'view' exists - one does not mind compile time coupling/compile time hit that will occur if the 'model' and the 'view' classes know which methods they must call on 'the other' object as opposed to knowing which slots to expose/signals to connect to. In such a scenario the typical 'dynamic connection/coupling' approach unnecessarily incurrs overhead both in terms of verbosity and efficiency...it is 'easier' if the 'model' holds the 'view' object by value (or a wrapper class holds them both or whatever other solution as long as their offset in memory is constant)...then the the 'model' knows its 'view' instance implicitly from its this pointer (only a positive offset is required) but the 'view' instance does not know its 'model' instance implicitly (using 'conventional' methods) although it is infact also only a matter of offset calculation from its this pointer (only a negative one in this situation)... Now, if we take into account that the 'model' class knows the name of its 'view' member it can 'create' a pointer-to-member to it thus enabling us to create a sort of an extended and templated version of the standard C offset macro (from stddef.h). Using this 'template offset' functor (called ParentFromMember here, provided by the 'model' class) the 'view' class/instance can now also get to its 'model' instance implicitly from its this pointer (without knowing exactly how or where it exists in relation to the 'model' instance). template <class T> struct DummyStorage { typedef typename std::tr1::aligned_storage < sizeof( T ), std::tr1::alignment_of<T>::value >::type type; }; template < class Parent, class Member, Member Parent::* pMember > class ParentFromMember { public: typedef typename std::tr1::remove_const<Parent>::type Parent; typedef typename std::tr1::remove_const<Member>::type Member; public: Parent & operator()( Member & member ) const { DummyStorage<Parent>::type const parentStorage; Parent const * const pDummyParent( reinterpret_cast<Parent const *>( &parentStorage ) ); ptrdiff_t const offset ( reinterpret_cast<char const *>( &( pDummyParent->*pMember ) ) - reinterpret_cast<char const *>( pDummyParent ) ); return *reinterpret_cast<Parent *>( reinterpret_cast<char *>( &member ) - offset ); } Parent const & operator()( Member const & member ) const { return operator()( const_cast<Member &>( member ) ); } }; ...the DummyStorage part is just 'added-paranoia'...the whole operator() function could (probably ?) be simplified to work just like the offset macro in MSVC's stddef.h (in fact, with MSVC, both approaches produce the same code)...: Parent & operator()( Member & member ) const { ptrdiff_t const offset( reinterpret_cast<ptrdiff_t>( &( reinterpret_cast<Parent const *>( 0 )->*pMember ) ) ); return *reinterpret_cast<Parent *>( reinterpret_cast<char *>( &member ) - offset ); } .... so if you have class View { void someViewFunc(); }; class Model { private: View v; public: typdef ParentFromMember<Model, View, &Model::v> ViewModel; void someModelFunc(); } void View::someViewFunc() { Model & myModel( Model::ViewModel()( *this ) ); myModel.someModelFunc(); } ... If this has any chance of not being against the standard and/or "by-the-book" conventions it could probably be augmented with additional debugging/paranoia checks (for example that classes that would use this would be required to derive from some utility class and/or hold the "Member" object in some templated wrapper that would add GUID-like headers in front of objects in memory to assert that the conversions were called on valid objects and things like that)... The whole approach could also be extended with utility classes like FusionContainerFromMember, ParentFromOptionalMember, MemberFromMember and such... One 'big' problem is that this breaks MSVC (tested with 9.0 SP1 and 10b1) with a compiler error (at the typedef line) when the Parent class (in this case the Model class) is a template class (it compiles fine with the online Comeau compiler). A workaround (for MSVC) that might come to mind is to place the typedef outside the body of the template Parent class (it can also be in a another class) but this no solution as template typedefs do not work and an out-of-body template would require public access to the member/encapsulation breakage...so far the only acceptable solution I could find for MSVC is to use a wrapper metafunction that returns the required ParentFromMember<> specialization... -- "That men do not learn very much from the lessons of history is the most important of all the lessons of history." Aldous Huxley

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[serialization]Double rounding bug?
by Mariusz Kwiczala 02 Oct '09

02 Oct '09

Hello, I found that for some small double value, serialization change last few digits.(it look like some rounding bug) Below is one example (I have more :) usually it is a number 0.00... or 0.00 with 19-20 digits after dot): -0.0070850229047457131 - double value -0.007085022904745714 - double value after save/read from xml file On my computer I have always assert in function DoubleTest(). Boost: version 1.39/boost_serialization-vc90-mt-gd-1_39.dll Compiler: VS2008 Could you verify below code on your computer (call DoubleTest())? Is it bug? Sample code: #pragma warning( push ) #pragma warning( disable : 4512 ) #include <boost/archive/xml_iarchive.hpp> #pragma warning( pop ) #include <boost/archive/xml_oarchive.hpp> #include <boost/serialization/vector.hpp> #include <boost/bind.hpp> #include <fstream> #include <boost/archive/xml_oarchive.hpp> #include <boost/archive/text_iarchive.hpp> #include <boost/archive/text_oarchive.hpp> #include <boost/serialization/vector.hpp> void LoadDoubleValue(DoubleValue& doubleValue, const char* fileName) { std::ifstream ifs(fileName); assert(ifs.good()); boost::archive:: xml_iarchive ia(ifs); ia >> BOOST_SERIALIZATION_NVP(doubleValue); } void SaveDoubleValue(DoubleValue& doubleValue, const char* fileName) { std::ofstream ofs(fileName); assert(ofs.good()); boost::archive::xml_oarchive oa(ofs); oa << BOOST_SERIALIZATION_NVP(doubleValue); } void DoubleTest() { DoubleValue doubleValue1; doubleValue1.m_value = -0.0070850229047457131; SaveDoubleValue(doubleValue1, "DoubleValue.xml"); DoubleValue doubleValue2; LoadDoubleValue(doubleValue2, "DoubleValue.xml"); //but from file is read -0.007085022904745714 assert(doubleValue1.m_value==doubleValue2.m_value); } Best regards, Mariusz

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[BoostCon 2010] Call for Participation
by Hartmut Kaiser 02 Oct '09

02 Oct '09

Please distribute! -------------------------------- 4th Annual Boost Conference 2010 -------------------------------- Aspen CO, USA, May 4-10, 2010, www.boostcon.com Call for participation ---------------------- We invite you to submit session proposals to the 4th Annual Boost Conference: BoostCon 2010 (Aspen CO, USA, May 10-14, 2010). Traditionally the main face-to-face event for all things Boost (www.boost.org) BoostCon 2010 will present leading speakers from the whole C++ community. From using the Boost libraries to writing and maintaining them, from evangelizing to deploying Boost within your organization, from infrastructure and process to vision and mission, and the new C++ Standard, BoostCon brings together the sessions, the colleagues, and the inspiration to support your work with C++ and Boost in particular for the next year. To reflect the breadth of the Boost community, the conference includes sessions aimed at two constituencies: Boost end-users and hard-core Boost library and tool developers. The program fosters interaction and engagement within and across those two groups, with an emphasis on hands-on, participatory sessions. Session topics -------------- Topics of interest include, but are not restricted to, the following: * General tutorial sessions introducing one or more Boost libraries * In-depth sessions on using specific Boost libraries * Case studies on using Boost * Experts panels * Advanced sessions on implementation techniques used within Boost libraries * C++0x and how it will change life for users and library writers * Development workshops to extend or enhance existing Boost libraries * Workshops on design process * Infrastructure workshops such as Build tools, Website, Testing * Concepts and Generic Programming * Hardware and infrastructure presentations focused on how libraries can make better use of the technology * Other topics likely to be of great interest to Boost users and developers Interactive and collaborative sessions are encouraged, as this is the nature of both the on-line Boost community and the style of learning and participation that has proven most successful at such events. Sessions can be tutorial based, with an emphasis on interaction and participant involvement, or workshop based, whether hands-on programming or paper-based, discussion-driven collaborative work. Session formats --------------- Presentations Presentations focus on a practitioner's ideas and experience with anything relevant to Boost and Boost users. Panels Panels feature three or four people presenting their ideas and experiences relating to Boost's relevant, controversial, emerging, or unresolved issues. Panels may be conducted in several ways, such as comparative, analytic, or historic. Tutorials Tutorials are sessions at which instructors teach conference participants specific Boost-relevant skills. Workshops Workshops provide an active arena for advancements in Boost- relevant topics. Workshops provide the opportunity for experienced practitioners to develop new ideas about a topic of common interest and experience. Author's Corner Presentations These were introduced at BoostCon 2008, and were a great success. They are short (30 minute) sessions, focusing on tips on usage and design. In addition, we're looking to uncover the hidden design gems in Boost libraries. Tool Vendors Presentations We actively encourage tool vendors and ISP's to submit proposals for a special Tool Vendors Session Track aimed at products related to Boost and C++ (compilers, libraries, tools, etc.). Other formats may also be of interest. Don't hold back a proposal just because it doesn't fit into a pigeonhole. Submitting a proposal --------------------- Standard Sessions are 90 minutes. You may submit a proposal for fractions or multiples of 90-minutes. Fractional proposals will be grouped into 90 minute sessions covering related topics. Longer sessions, such as tutorials and classes, will be assigned 90 minute, three hour (i.e. half day), or six hour (i.e. full day) time slots. Please include: * The working title. * Type of session: presentation, panel, tutorial, workshop, authors corner, vendor track, other. * A paragraph or two describing the topic covered, suitable for the conference web site. * Proposed length: 10-20 minute short talks, 45 minutes, 90 minutes, half day, full day. * Alternate lengths, if you are willing to make adjustments: 10-20 minute short-talks, 45 minutes, 90 minutes, half-day, full day. * Audience: users, developers, both. * Level: basic, intermediate, advanced. * A biography, suitable for the conference web site. * Your contact information (will not be made public). Submission details ------------------ All submissions have to be done through the EasyChair conference management system: http://www.easychair.org/conferences/?conf=boostcon10. If you have not already registered at EasyChair, you will need to do so in order to submit your proposal. All submissions will go through a peer review process. Authors are invited (but are not required) to submit PDF versions of full papers of up to 10 pages in ACM conference proceedings format (see http://www.acm.org/sigs/publications/proceedings-templates) The full papers are not required unless you want them published in the proceedings. All accepted proposals will be made available in the Association for Computing Machinery (ACM) Digital Library (approval pending). Best papers, after further reviews, will be considered to be book chapters or journal articles in a renowned journal. The session materials go on the BoostCon website and will be available to attendees. For general information on the BoostCon 2010 paper submission or the scope of technical papers solicited, please refer to the conference website at www.boostcon.com. For any other questions about the submission process or paper format, please contact the Program Committee at boostcon10(a)easychair.com. If you have any technical problems with EasyChair, please contact EasyChair for help. Note: Presenters must agree to grant a non-exclusive perpetual license to publish submitted materials, either electronically or in print, in any media related to BoostCon. Important dates --------------- Proposal submissions due: Dec 10th, 2009. Proposals decisions sent (tentative program available): Jan 15th, 2010. Fully scheduled program available: Feb 5th, 2010. Session materials due: Apr 15th, 2010. Hartmut Kaiser, email: hartmut.kaiser(a)gmail.com (Program Committee Chair) David Abrahams, email: dave(a)boostpro.com (Conference Chair) On behalf of the conference organizers

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[rdb] 0.0.10 + documentation
by Jean-Louis Leroy 01 Oct '09

01 Oct '09

I have uploaded a new revision to the vault. The only /visible/ change in the API is the syntax for the insert...select statement. It was `insert_into(table)(cols)(select(...))`, it is now `insert_into(table)(cols).select(...). The syntax engine is beginning to look more and more like a compile-time finite state machine. And there is the beginning of a documentation ! you can view it here : http://www.yorel.be/boost/libs/rdb/doc/html/index.html The tutorial is 2/3 complete for this phase (i.e. sans prepared statements). The structure of the doc is strongly influenced by Fusion's - no wonder, I spent so much time in it ;-) While I like the overall structure, I wonder if the Fusion style is appropriate for a tool that is not so much into meta-programming (well at least on the outside). I documented insert_into in this fashion (see http://www.yorel.be/boost/libs/rdb/doc/html/rdb/sql_subsystem/statements/in…) for a test. If you have opinions, please voice them. J-L

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[mpl] Can we generate this type in a simpler way?
by vicente.botet 01 Oct '09

01 Oct '09

Hi, I want to generate the following type R1::mth1_<T1, R3::mth1_<T3, C::mth1_> > > from mpl::vector<mpl::pair<R1, T1>, mpl::pair<R3, T3>, C and mth1_? I have started with this template <typename SequenceOfPairs, typename E, ??? MTH> struct generator { typedef ??? type; }; but I don't know what MTH'can be, because we have 3 different mth1_. So I have reached to make a specific mth1_generator (for the specific symbol 'mth1_') template <typename SequenceOfPairs, typename E> struct mth1_generator { typedef ??? type; // The details of the type are ommited using 'mth1' }; satisfying mth1_generate<mpl::vector<mpl::pair<R1, T1>, mpl::pair<R3, T3>, C>::type is equal to R1::mth1_<T1, R3::mth1_<T3, C::mth1_> > > ? As aal the mthX_generator follow the same structure, I have defined a macro DEFINE_GENERATOR which will define the specific generator for a symbol MTH #define DEFINE_GENERATOR(MTH) \ template <typename SequenceOfPairs, typename E> struct MTH##_generator { typedef ??? type; // The details of the type are ommited suing now MTH. } So the user will just have to do DEFINE_GENERATOR(mth1); Can I do it in a simpler way using some kind of traits or this is an inherent preprocessor problem? Thanks for clarifications, _____________________ Vicente Juan Botet Escribá

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[mpl]haskell-like list comprehension
by Larry Evans 01 Oct '09

01 Oct '09

A recent post about variadic fusion: http://article.gmane.org/gmane.comp.lib.boost.devel/194407 contained, in the test driver attachment, a pair of templates: test test_impl These two templates were used to, in effect, test a cross product from the domains {0...24,0...24}. This was a use-case for something like haskell's list comprehension: http://www.haskell.org/haskellwiki/List_comprehension There's now a prototype of an mpl list_comprehension class in the boost vault: http://www.boostpro.com/vault/index.php?directory=variadic_templates& the output from the file is: { 9000, 9010, 9020} { 9000, 9010, 9021} { 9000, 9011, 9020} { 9000, 9011, 9021} { 9000, 9012, 9020} { 9000, 9012, 9021} { 9001, 9010, 9020} { 9001, 9010, 9021} { 9001, 9011, 9020} { 9001, 9011, 9021} { 9001, 9012, 9020} { 9001, 9012, 9021}

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[Asio] Why does Boost Asio only allow 64 buffers to be sent/recei ved using scatter/gather?
by Stephens Patrick 01 Oct '09

01 Oct '09

Hi all, Apologies if this question should be directed at an Asio-specific list but I could not see one. I originally posted on the users list so trying the developers list now. I am curious why the Boost Asio library specifies a maximum of 64 buffers can be used for scatter/gather operations? I would like to gain a better understanding as to why this value was used. The documentation (http://www.boost.org/doc/libs/1_40_0/doc/html/boost_asio/overview/implement ation.html), and the code backs it up, seems to specify that the maximum allowed will be 'min(64, IOV_MAX)' for linux implementations. Was this value (64) chosen for some particular reason? What would the consequences be of using IOV_MAX if it was greater than 64? I see that the Windows NT, 2000, XP, 2003 and Vista implementation also has a limit of 64 so is this something limited by the OS or to keep it consistent across all the Asio implementations? I had a look around to see if there was a restriction under Windows but the only documentation I could find (http://msdn.microsoft.com/en-us/library/ms742203%28VS.85%29.aspx) mentions that it is restricted to a value of 16 under Windows 95, 98 and ME, which does tally with what the Asio documentation states in the link above. Thanks for any help, Pat. This email, including any attachment, is a confidential communication intended solely for the use of the individual or entity to whom it is addressed. It contains information which is private and may be proprietary or covered by legal professional privilege. If you have received this email in error, please notify the sender upon receipt, and immediately delete it from your system. Anything contained in this email that is not connected with the businesses of this company is neither endorsed by nor is the liability of this company. Whilst we have taken reasonable precautions to ensure that any attachment to this email has been swept for viruses, we cannot accept liability for any damage sustained as a result of software viruses, and would advise that you carry out your own virus checks before opening any attachment.

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[mpl] set_c with enums
by Domagoj Saric 01 Oct '09

01 Oct '09

void aFunction() { enum AnEnum { First, Second, Third, Fourth }; typedef boost::mpl::set_c<AnEnum, First, Fourth, Third> AnEnumSubSet; bool const exists ( boost::mpl::has_key < AnEnumSubSet, boost::mpl::integral_c<AnEnum, Second> >::value ); } the above code fails to compile in MSVC++ 9.0 SP1 and 10.0b1 with the following error(s): error C2440: 'specialization' : cannot convert from 'int' to 'aFunction::AnEnum' if the AnEnumSubSet definition is changed to use ...set_c<int... everything compiles and works properly (the has_key statement can still use the enum)...everything also works properly (with an enum) when using vector_c and contains instead of set_c and has_key... -- "That men do not learn very much from the lessons of history is the most important of all the lessons of history." Aldous Huxley

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[mpl] at<AssocSeq,Key,Default>
by Domagoj Saric 01 Oct '09

01 Oct '09

the mpl::at<AssocSeq,Key,Default> version for associative containers (still) exists in the documentation but (still) not in the sources (1.40 official ones)... -- "That men do not learn very much from the lessons of history is the most important of all the lessons of history." Aldous Huxley

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How can new members can start contributing to this group?
by Manoj Sharma 01 Oct '09

01 Oct '09

Hi Friends, I have 5 years of development experience on C++ on Solaris. I am new to Boost and want to be active member of this group. Please suggest me how can I proceed to start contributing to this group. Thanks, Manoj Keep up with people you care about with Yahoo! India Mail. Learn how. http://in.overview.mail.yahoo.com/connectmore

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