October 2009 - Boost - lists.boost.org

[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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Re: [boost] On the Road to Aspen (BoostCon 2010)
by pete＠pcbartlett.com 01 Oct '09

01 Oct '09

On Tue 29/09/09 12:22 , Joel de Guzman <joel(a)boost-consulting.com> wrote: > Edouard A. wrote: > > Hi Joel, > > > > You can also create a twitter account and link your Facebook page > to this > > twitter account, mirroring all your facebook status updates to > your twitter > > account. > > > > This increases visibility and give the possibility to your fans to > choose > > the medium they like to follow you. > Thanks, Edouard. Done. BoostCon Facebook Linked to > Twitter (@BoostCon) > http://www.twitter.com/BoostCon Many users of Boost are in corporate environments. Many corporate environments block access to Facebook and/or Twitter (mine blocks both) domains. It'd be great therefore if Boost didn't move too much content there if equivalent

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Double free from UTF
by janm-boost-devel＠transactionware.com 01 Oct '09

01 Oct '09

Hi, I am seeing a double free when using boost-test on: - FreeBSD 7.2-STABLE, amd64 (gcc 4.2.1) with boost 1.39 - Mac OSX 10.6.1, x86_64 (XCode 3.2, gcc 4.2) with boost 1.40 I don't see the problem on Windows XP with Visual C++ 2005 Express. A simple test case is below, just run. The _malloc_options is to make the system malloc() fill memory with 0xa5 on allocation and 0x5a on deallocation. #define BOOST_TEST_MAIN #include <boost/test/included/unit_test.hpp> #include <stdlib.h> const char* _malloc_options = "J"; BOOST_AUTO_TEST_CASE(broken) { BOOST_CHECK(true); } Output: Running 1 test case... *** No errors detected zsh: bus error (core dumped) ./a.out Stack Trace: #0 0x0000000800b1bdee in free () from /lib/libc.so.7 #1 0x000000000043e51c in boost::unit_test::framework_impl::clear (this=0x55ad20) at framework.ipp:133 #2 0x000000000043e652 in ~framework_impl (this=0x55ad20) at framework.ipp:122 #3 0x00000000004110c6 in __tcf_1 () at framework.ipp:222 #4 0x0000000800b6dbb6 in __cxa_finalize () from /lib/libc.so.7 #5 0x0000000800b1f7c7 in exit () from /lib/libc.so.7 #6 0x0000000000404595 in _start () Any ideas? Thanks, Jan Mikkelsen

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Interest in flat_iterator for nested containers?
by Christoph Heindl 01 Oct '09

01 Oct '09

Hi, is there any interest in an iterator that provides a flat view of nested containers? For example ---------- using namespace boost::assign; typedef std::list<int> inner_container_type; typedef std::vector<inner_container_type> outer_container_type; outer_container_type elements(6); elements[1] += 1,2,3; elements[2] += 4,5; elements[4] += 6; BOOST_CHECK(std::equal( make_flat_iterator(elements.begin(), elements.end()), make_flat_iterator(elements.end(), elements.end()), list_of(1)(2)(3)(4)(5)(6).begin()) ); ---------- If so, I'll be glad to share my code with the boost community. I attach my current state of development and a single test suite. The current state of development contains a class named flat_iterator, a make_flat_iterator function and a set of meta-functions to derive required types. flat_iterator derives from boost::iterator_adaptor. It derives an inner_iterator type from the passed iterator to be adapted (outer_iterator type). The value_type of outer_iterator is required to model STL container concept. The value_type passed to boost::iterator_adaptor is const-qualified if the reference type of the outer_iterator or inner_iterator type is const-qualified (please see question 1 below). The traversal category of flat_iterator is bidirectional if the the outer_iterator and inner_iterator type are at least bidirectional. It models forward traversal else (question 2). flat_iterators can be stacked over each other to recursively flatten a hierarchy of arbitrary levels. ---------- using namespace boost::assign; typedef std::list<int> level_0; typedef std::vector<level_0> level_1; typedef std::vector<level_1> level_2; level_2 elements(10); elements[2] += list_of(1)(2); elements[4] += list_of(3)(4); typedef flat_iterator<level_2::iterator> flat_iterator_outer; typedef flat_iterator<flat_iterator_outer> flat_iterator_inner; flat_iterator_outer outer_begin(elements.begin(), elements.end()); flat_iterator_outer outer_end(elements.end(), elements.end()); flat_iterator_inner inner_begin(outer_begin, outer_end); flat_iterator_inner inner_end(outer_end, outer_end); BOOST_CHECK(std::equal(inner_begin, inner_end, list_of(1)(2)(3)(4).begin())); ---------- Open questions: * Currently the the value_type passed to boost::iterator_adaptor is const qualified based on required reference type of the outer_iterator, which renders the code for input iterators unusable, right? What's the best way to achieve const correctness? * The traversal category of flat_iterator is supposed to be the 'greatest common divisor' of the inner and outer iterator type. Is there a meta-function in boost that provides that type? Currently bidirectional traversal is chosen if both, inner and outer iterator, are at least of bidirectional traversal. Else forward traversal is chosen (which is of course incorrect when incrementable is passed). * Stacking flat_iterators to flatten out a hierarchy of arbitrary levels is possible but currently requires a lot of typing. I think that applying some recursive meta-functions to generate a correct iterator types for such situations should be possible but is beyond my current knowledge of meta-programming. Kind regards, Christoph

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boost::variant and "Current Approach: Temporary Heap Backup" vs "An Initial Solution: Double Storage"
by Peter Foelsche 01 Oct '09

01 Oct '09

1) boost::variant and "Current Approach: Temporary Heap Backup" vs "An Initial Solution: Double Storage" Please provide both solutions. A potential heap allocation may prevent certain application areas. 2) I also do not understand that exception safety requires that the variant is never empty (e.g. empty() returning always false). What is the use of calling the constructor (of which type btw?) if somebody creates an unintialized variant variable? Or: In the following piece of code is the std::string constructor being called? boost::variant<std::string, int> s; Thanks Peter

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