August 2005 - Boost-users - lists.boost.org

1.33 pointer to object serialization
by Chris Coleman 07 Aug '05

07 Aug '05

Hi, I'm having trouble with serializing an object through a pointer to it. The code below works in 1.32, but in 1.33 it gives the errors below. I am using Mac OS X 10.4.2, gcc 4.0. I've had a look at the headers, but my template programming isn't good enough to make too much sense of them. It seems that there is a check to ensure T is not a pointer on line 549 of oserializer.hpp, which is the reason the static assert is failing? Is it correct that objects shouldn't be serializable by pointers to them, or not? Cheers Chris gps_position* p_g = new gps_position(35, 59, 24.567f); oa << p_g; // causes the error's below g++ -o test test.cpp -lboost_serialization-d-1_33 /usr/local/include/boost/archive/detail/oserializer.hpp: In function 'void boost::archive::save(Archive&, T&) [with Archive = boost::archive::text_oarchive, T = gps_position*]': /usr/local/include/boost/archive/basic_text_oarchive.hpp:78: instantiated from 'void boost::archive::basic_text_oarchive<Archive>::save_override(T&, int) [with T = gps_position*, Archive = boost::archive::text_oarchive]' /usr/local/include/boost/archive/detail/interface_oarchive.hpp:85: instantiated from 'Archive& boost::archive::detail::interface_oarchive<Archive>::operator<<(T&) [with T = gps_position*, Archive = boost::archive::text_oarchive]' hash_test.cpp:130: instantiated from here /usr/local/include/boost/archive/detail/oserializer.hpp:560: error: invalid application of 'sizeof' to incomplete type 'boost::STATIC_ASSERTION_FAILURE<false>' This message has been checked for viruses but the contents of an attachment may still contain software viruses, which could damage your computer system: you are advised to perform your own checks. Email communications with the University of Nottingham may be monitored as permitted by UK legislation.

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Problem compiling regex lib.
by Thaddeus Olczyk 07 Aug '05

07 Aug '05

kept it simple: ------------------------ #include <boost/regex.hpp> int main(int argc,char argv[]) { return 1; } --------- So all it does is try to compile the headers for the regex lib. Here is the output. ------------------------------ g++ -I/cy/f/Programs/development/boost_1_32_0/nocygwin/include/boost-1_32 -ansi -pedantic -Wall -O2 -c main.cpp -o main.o In file included from /cy/f/Programs/development/boost_1_32_0/nocygwin/include/boost-1_32/boost/regex/regex_traits.hpp:32, from /cy/f/Programs/development/boost_1_32_0/nocygwin/include/boost-1_32/boost/regex/v4/regex.hpp:57, from /cy/f/Programs/development/boost_1_32_0/nocygwin/include/boost-1_32/boost/regex.hpp:34, from main.cpp:1: /cy/f/Programs/development/boost_1_32_0/nocygwin/include/boost-1_32/boost/regex/v4/regex_traits.hpp:827: error: overflow in constant expression /cy/f/Programs/development/boost_1_32_0/nocygwin/include/boost-1_32/boost/regex/v4/regex_traits.hpp:840: error: overflow in constant expression -- Thad

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Spirit parser - using a skip scanner and file_iterator
by Phil Endecott 06 Aug '05

06 Aug '05

Dear Boost Spirit experts, I've been using Spirit for a few weeks and it is one of the most impressive things I've seen for a long time. Thanks to everyone who has made this possible. Its main problem, as far as I can see, is that the error messages are almost entirely incomprehensible. This is not unusual for C++; the compiler (gcc in my case) has a share of the blame too. The result, in my case, is not venturing much beyond the structures used in the examples from the (excellent) documentation, and debugging by trial and error. Anyway, I am trying to write a parser that will: - Use a file_iterator to parse a file. - Skip comments using #-to-end-of-line syntax. - Skip whitespace. - Recognise a simple language. I can do the main part of the parser (the language); the problem is with the comment skipper. I think that using file_iterator might be making it more complicated, though I have also failed to get a char* version to compile. Following the suggestions at http://spirit.sourceforge.net/distrib/spirit_1_8_2/libs/spirit/doc/file_ite… I have written the following test program: #include <string> #include <boost/spirit.hpp> #include <boost/spirit/actor.hpp> #include <boost/spirit/iterator/file_iterator.hpp> using namespace std; using namespace boost::spirit; int main(int argc, char* argv[]) { string fn = argv[1]; typedef file_iterator<char> iterator_t; typedef scanner<iterator_t> scanner_t; typedef rule<scanner_t> rule_t; rule_t skip = comment_p("#") | space_p ; rule_t language = * ch_p('X') ; iterator_t first(fn.c_str()); if (!first) { cout << "Unable to open " << fn << endl; exit(1); } iterator_t last = first.make_end(); parse_info<iterator_t> info = parse(first, last, language, skip); } The errors are attached below. Can anyone spot what I need to change? My feeling is that I need a different type for skip, i.e. not rule_t, and I'm pretty sure that I need a definition for scanner_t that mentions skip. I've tried various combinations and got different, equally verbose and incomprehensible, error messages. I'm using Boost 1.32.0 with gcc 3.3.6 on Debian Linux. Many thanks in advance for any suggestions. Phil. $ g++ -Wall -O -o spirit_test spirit_test.cc /usr/include/boost/spirit/core/non_terminal/impl/rule.ipp: In member function ` typename boost::spirit::parser_result<DerivedT, ScannerT>::type boost::spirit::impl::rule_base<DerivedT, EmbedT, T0, T1, T2>::parse_main(const ScannerT&) const [with ScannerT = boost::spirit::scanner<boost::spirit::file_iterator<char, boost::spirit::fileiter_impl::std_file_iterator<char> >, boost::spirit::scanner_policies<boost::spirit::skip_parser_iteration_policy<boost::spirit::rule<main(int, char**)::scanner_t, boost::spirit::nil_t, boost::spirit::nil_t>, boost::spirit::iteration_policy>, boost::spirit::match_policy, boost::spirit::action_policy> >, DerivedT = boost::spirit::rule<main(int, char**)::scanner_t, boost::spirit::nil_t, boost::spirit::nil_t>, EmbedT = const boost::spirit::rule<main(int, char**)::scanner_t, boost::spirit::nil_t, boost::spirit::nil_t>&, T0 = main(int, char**)::scanner_t, T1 = boost::spirit::nil_t, T2 = boost::spirit::nil_t]': /usr/include/boost/spirit/core/non_terminal/impl/rule.ipp:171: instantiated from `typename boost::spirit::parser_result<DerivedT, ScannerT>::type boost::spirit::impl::rule_base<DerivedT, EmbedT, T0, T1, T2>::parse(const ScannerT&) const [with ScannerT = boost::spirit::scanner<boost::spirit::file_iterator<char, boost::spirit::fileiter_impl::std_file_iterator<char> >, boost::spirit::scanner_policies<boost::spirit::skip_parser_iteration_policy<boost::spirit::rule<main(int, char**)::scanner_t, boost::spirit::nil_t, boost::spirit::nil_t>, boost::spirit::iteration_policy>, boost::spirit::match_policy, boost::spirit::action_policy> >, DerivedT = boost::spirit::rule<main(int, char**)::scanner_t, boost::spirit::nil_t, boost::spirit::nil_t>, EmbedT = const boost::spirit::rule<main(int, char**)::scanner_t, boost::spirit::nil_t, boost::spirit::nil_t>&, T0 = main(int, char**)::scanner_t, T1 = boost::spirit::nil_t, T2 = boost::spirit::nil_t]' /usr/include/boost/spirit/core/scanner/impl/skipper.ipp:107: instantiated from `static boost::spirit::parse_info<IteratorT> boost::spirit::impl::phrase_parser<SkipT>::parse(const IteratorT&, const IteratorT&, const ParserT&, const SkipT&) [with IteratorT = boost::spirit::file_iterator<char, boost::spirit::fileiter_impl::std_file_iterator<char> >, ParserT = boost::spirit::rule<main(int, char**)::scanner_t, boost::spirit::nil_t, boost::spirit::nil_t>, SkipT = boost::spirit::rule<main(int, char**)::scanner_t, boost::spirit::nil_t, boost::spirit::nil_t>]' /usr/include/boost/spirit/core/scanner/impl/skipper.ipp:154: instantiated from `boost::spirit::parse_info<IteratorT> boost::spirit::parse(const IteratorT&, const IteratorT&, const boost::spirit::parser<DerivedT>&, const boost::spirit::parser<SkipT>&) [with IteratorT = main(int, char**)::iterator_t, ParserT = boost::spirit::rule<main(int, char**)::scanner_t, boost::spirit::nil_t, boost::spirit::nil_t>, SkipT = boost::spirit::rule<main(int, char**)::scanner_t, boost::spirit::nil_t, boost::spirit::nil_t>]' spirit_test.cc:29: instantiated from here /usr/include/boost/spirit/core/non_terminal/impl/rule.ipp:189: error: no matching function for call to ` boost::spirit::impl::abstract_parser<main(int, char**)::scanner_t, boost::spirit::nil_t>::do_parse_virtual(const boost::spirit::scanner<boost::spirit::file_iterator<char, boost::spirit::fileiter_impl::std_file_iterator<char> >, boost::spirit::scanner_policies<boost::spirit::skip_parser_iteration_policy<boost::spirit::rule<main(int, char**)::scanner_t, boost::spirit::nil_t, boost::spirit::nil_t>, boost::spirit::iteration_policy>, boost::spirit::match_policy, boost::spirit::action_policy> >&)' /usr/include/boost/spirit/core/non_terminal/impl/rule.ipp:213: error: candidates are: typename boost::spirit::match_result<MatchPolicyT, T>::type boost::spirit::impl::abstract_parser<ScannerT, AttrT>::do_parse_virtual(const ScannerT&) const [with ScannerT = main(int, char**)::scanner_t, AttrT = boost::spirit::nil_t] /usr/include/boost/spirit/core/non_terminal/impl/rule.ipp: In member function ` typename boost::spirit::parser_result<DerivedT, ScannerT>::type boost::spirit::impl::rule_base<DerivedT, EmbedT, T0, T1, T2>::parse_main(const ScannerT&) const [with ScannerT = boost::spirit::scanner<boost::spirit::file_iterator<char, boost::spirit::fileiter_impl::std_file_iterator<char> >, boost::spirit::scanner_policies<boost::spirit::no_skipper_iteration_policy<boost::spirit::skip_parser_iteration_policy<boost::spirit::rule<main(int, char**)::scanner_t, boost::spirit::nil_t, boost::spirit::nil_t>, boost::spirit::iteration_policy> >, boost::spirit::match_policy, boost::spirit::action_policy> >, DerivedT = boost::spirit::rule<main(int, char**)::scanner_t, boost::spirit::nil_t, boost::spirit::nil_t>, EmbedT = const boost::spirit::rule<main(int, char**)::scanner_t, boost::spirit::nil_t, boost::spirit::nil_t>&, T0 = main(int, char**)::scanner_t, T1 = boost::spirit::nil_t, T2 = boost::spirit::nil_t]': /usr/include/boost/spirit/core/non_terminal/impl/rule.ipp:171: instantiated from `typename boost::spirit::parser_result<DerivedT, ScannerT>::type boost::spirit::impl::rule_base<DerivedT, EmbedT, T0, T1, T2>::parse(const ScannerT&) const [with ScannerT = boost::spirit::scanner<boost::spirit::file_iterator<char, boost::spirit::fileiter_impl::std_file_iterator<char> >, boost::spirit::scanner_policies<boost::spirit::no_skipper_iteration_policy<boost::spirit::skip_parser_iteration_policy<boost::spirit::rule<main(int, char**)::scanner_t, boost::spirit::nil_t, boost::spirit::nil_t>, boost::spirit::iteration_policy> >, boost::spirit::match_policy, boost::spirit::action_policy> >, DerivedT = boost::spirit::rule<main(int, char**)::scanner_t, boost::spirit::nil_t, boost::spirit::nil_t>, EmbedT = const boost::spirit::rule<main(int, char**)::scanner_t, boost::spirit::nil_t, boost::spirit::nil_t>&, T0 = main(int, char**)::scanner_t, T1 = boost::spirit::nil_t, T2 = boost::spirit::nil_t]' /usr/include/boost/spirit/core/scanner/impl/skipper.ipp:42: instantiated from `void boost::spirit::impl::skipper_skip(const ST&, const ScannerT&, const boost::spirit::skipper_iteration_policy<BaseT>&) [with ST = boost::spirit::rule<main(int, char**)::scanner_t, boost::spirit::nil_t, boost::spirit::nil_t>, ScannerT = boost::spirit::scanner<boost::spirit::file_iterator<char, boost::spirit::fileiter_impl::std_file_iterator<char> >, boost::spirit::scanner_policies<boost::spirit::skip_parser_iteration_policy<boost::spirit::rule<main(int, char**)::scanner_t, boost::spirit::nil_t, boost::spirit::nil_t>, boost::spirit::iteration_policy>, boost::spirit::match_policy, boost::spirit::action_policy> >, BaseT = boost::spirit::iteration_policy]' /usr/include/boost/spirit/core/scanner/skipper.hpp:114: instantiated from `void boost::spirit::skip_parser_iteration_policy<ParserT, BaseT>::skip(const ScannerT&) const [with ScannerT = boost::spirit::scanner<boost::spirit::file_iterator<char, boost::spirit::fileiter_impl::std_file_iterator<char> >, boost::spirit::scanner_policies<boost::spirit::skip_parser_iteration_policy<boost::spirit::rule<main(int, char**)::scanner_t, boost::spirit::nil_t, boost::spirit::nil_t>, boost::spirit::iteration_policy>, boost::spirit::match_policy, boost::spirit::action_policy> >, ParserT = boost::spirit::rule<main(int, char**)::scanner_t, boost::spirit::nil_t, boost::spirit::nil_t>, BaseT = boost::spirit::iteration_policy]' /usr/include/boost/spirit/core/scanner/impl/skipper.ipp:108: instantiated from `static boost::spirit::parse_info<IteratorT> boost::spirit::impl::phrase_parser<SkipT>::parse(const IteratorT&, const IteratorT&, const ParserT&, const SkipT&) [with IteratorT = boost::spirit::file_iterator<char, boost::spirit::fileiter_impl::std_file_iterator<char> >, ParserT = boost::spirit::rule<main(int, char**)::scanner_t, boost::spirit::nil_t, boost::spirit::nil_t>, SkipT = boost::spirit::rule<main(int, char**)::scanner_t, boost::spirit::nil_t, boost::spirit::nil_t>]' /usr/include/boost/spirit/core/scanner/impl/skipper.ipp:154: instantiated from `boost::spirit::parse_info<IteratorT> boost::spirit::parse(const IteratorT&, const IteratorT&, const boost::spirit::parser<DerivedT>&, const boost::spirit::parser<SkipT>&) [with IteratorT = main(int, char**)::iterator_t, ParserT = boost::spirit::rule<main(int, char**)::scanner_t, boost::spirit::nil_t, boost::spirit::nil_t>, SkipT = boost::spirit::rule<main(int, char**)::scanner_t, boost::spirit::nil_t, boost::spirit::nil_t>]' spirit_test.cc:29: instantiated from here /usr/include/boost/spirit/core/non_terminal/impl/rule.ipp:189: error: no matching function for call to ` boost::spirit::impl::abstract_parser<main(int, char**)::scanner_t, boost::spirit::nil_t>::do_parse_virtual(const boost::spirit::scanner<boost::spirit::file_iterator<char, boost::spirit::fileiter_impl::std_file_iterator<char> >, boost::spirit::scanner_policies<boost::spirit::no_skipper_iteration_policy<boost::spirit::skip_parser_iteration_policy<boost::spirit::rule<main(int, char**)::scanner_t, boost::spirit::nil_t, boost::spirit::nil_t>, boost::spirit::iteration_policy> >, boost::spirit::match_policy, boost::spirit::action_policy> >&)' /usr/include/boost/spirit/core/non_terminal/impl/rule.ipp:213: error: candidates are: typename boost::spirit::match_result<MatchPolicyT, T>::type boost::spirit::impl::abstract_parser<ScannerT, AttrT>::do_parse_virtual(const ScannerT&) const [with ScannerT = main(int, char**)::scanner_t, AttrT = boost::spirit::nil_t]

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Maybe a problem with boost::object_pool?
by Labour, Matthieu (MLPRO SF) 06 Aug '05

06 Aug '05

Hi I have a simple program running on Linux. The program implements an Active Object and uses boost::object_pool and boost::thread It cores when sending lots of messages Here is the message I get when running gdb #0 0x0804b840 in boost::simple_segregated_storage<unsigned int>::ordered_free (this=0x988b4d0, chunk=0x988bf2c) at simple_segregated_storage.hpp:46 46 { return *(static_cast<void **>(ptr)); } There are 2 threads. One thread creates Objects using boost::object_pool and enqueues them into a stl queue. The other Thread dequeues the stl queue and call MyObject::handle. static boost::object_pool<MyEvent>* _pool; Class MyObject{ Public: void handle(){ //do something _pool->destroy(this); } }; _pool = new boost::object_pool<MyObject>(1000); MyObject* obj = _pool.construct(); Queue.putq(obj); I would appreciate any thoughts/help Thank you very much -------------------------------------------------------- If you are not an intended recipient of this e-mail, please notify the sender, delete it and do not read, act upon, print, disclose, copy, retain or redistribute it. Click here for important additional terms relating to this e-mail. http://www.ml.com/email_terms/ --------------------------------------------------------

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Re: [Boost-users] [1.33.0] Release candidate #1 is available
by Richard Jennings 06 Aug '05

06 Aug '05

I'm getting a compile error with my code to do with the boost::is_abstract class for compilers that don't support type_traits/is_abstract, i.e. those that have BOOST_NO_IS_ABSTRACT defined, BCB 5.6.4 in my case. Serialization/is_abstract.hpp defines an is_abstract class if BOOST_NO_IS_ABSTRACT is defined rather than including type_traits/is_abstract.hpp. With 1.33 RC1 type_traits/is_abstract.hpp now defines an is_abstract class if BOOST_NO_IS_ABSTRACT is defined, which it didn't use to do. Thus the class boost::is_abstract is multiply defined. Minimal code to reproduce the error is: #include <boost/type_traits.hpp> #include <boost/serialization/is_abstract.hpp> int main(int argc, char* argv[]) { return 0; } Compile that with BCB5.6.4 and you get: [C++ Error] is_abstract.hpp(32): E2238 Multiple declaration for 'is_abstract<T>' [C++ Error] is_abstract.hpp(130): E2344 Earlier declaration of 'is_abstract<T>' The first is serialization/is_abstract.hpp the second is type_traits/is_abstract.hpp. Perhaps serialization/is_abstract.hpp could check for type_traits/is_abstract.hpp having already been included or perhaps the serialization version is not now needed? Richard -----Original Message----- From: boost-users-bounces(a)lists.boost.org [mailto:boost-users-bounces@lists.boost.org] On Behalf Of Doug Gregor Sent: 01 August 2005 18:04 To: boost-users(a)lists.boost.org Subject: [Boost-users] [1.33.0] Release candidate #1 is available Boost 1.33.0 release candidate #1 is now available here: http://www.osl.iu.edu/~dgregor/boost-1.33.0/ There are two sets of files important for this release: - boost_1_33_0_rc1.*: The actual release candidate - boost_1_33_0_(docbook|fo|man).*: The documentation in other formats Please download and unpack the archives, browse the documentation, try the release with your favorite compiler, etc. Thanks! Doug Gregor 1.33.0 Release Manager _______________________________________________ Boost-users mailing list Boost-users(a)lists.boost.org http://lists.boost.org/mailman/listinfo.cgi/boost-users

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Floating point exception in simple_segregated_storage (boost::pool)
by Shriram V 05 Aug '05

05 Aug '05

Hi, I am trying to use simple_segregated_storage<>, but I am getting "Floating point exception" in simple_segregated_storage.hpp:194 This is the code that I used. Am I going wrong anywhere? Is it necessary to upgrade to 1_32? Or is it some thing else? Code: ===== <snip> #include <cstdlib> #include <boost/pool/simple_segregated_storage.hpp> #include <iostream> int main() { using namespace std; std::size_t size = 10 * 1024; void* ptr = malloc(size); // cout << ptr << endl; boost::simple_segregated_storage<char> T; T.add_ordered_block(ptr, size, 1024); //← Floating point exception here. cout << T.malloc() << endl; return 0; } </snip> simple_segregated_storage.hpp:194 ================================= <snip> char * old = static_cast<char *>(block) </snip> This code was compiled as: ========================== g++ --version: (GCC) 3.3.2 g++ -Wall -Werror -g3 -pedantic -I/home/include/boost-1_31 -o smem.o -c smem.cpp g++ -o smem smem.o Boost: ====== Version: 1_31 Please guide. Regards, -Shriram

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BGL: conversion from vertex_iterator to vertex_descriptor possible?
by Rene Meier 05 Aug '05

05 Aug '05

Hello, I would like to do some topology modification, depending on bundled properties of the vertices. So i use: std::pair<vertex_iterator, vertex_iterator> vertices(const adjacency_list& g) to get an iterator range for all vertices, then i make a loop over all vertices, search for the properties, maybe i store the iterators of some vertices for later use, but the main problem is: I can not these iterators in functions like: std::pair<edge_descriptor, bool> add_edge(vertex_descriptor u, vertex_descriptor v, adjacency_list& g) void remove_vertex(vertex_descriptor u, adjacency_list& g) void clear_vertex(vertex_descriptor u, adjacency_list& g) and so on... Thats why i would like to know how to convert an vertex_iterator to an vertex_descriptor? Thanks, Rene -- René Meier Institut für Pharmazeutische Chemie Martin-Luther-Universität Halle email: rene.meier(a)pharmazie.uni-halle.de Wolfgang-Langenbeck-Str. 4 phone: (49)345 55-25043 06120 Halle (Saale) fax: (49)345 55-27355 Petition für ein Softwarepatent-Freies Europa: http://www.ffii.org/index.de.html

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[mpl] how to find out whether a function is implemented
by Zeljko Vrba 05 Aug '05

05 Aug '05

I hope the MPL label is right. At least the question has *some* relevance to metaprogramming. Basically, I need to find out whether a certain function F over a certain type is defined, and if yes, take its address. Input: the type T, and function NAME F. Output: pointer to F if Ret F(T, T& or T const&; or two arguments) is defined, 0 otherwise. The function can return anything, including void. Variations in input: - the function may take T, T&, or T const& - if possible, the method should work for user-defined operators (my C++ is a bit rusty in this area - is it at all possible to take an address of an overloaded operator?) I guess the F would then be named, e.g. 'operator<' ? If the general case is hard to work out, it's OK to have the solution just for Ret F(T const&) and Ret F(T const&, T const&). I hope the question is clear enough :) Thanks for your time and answers.

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question: boost::array does not have compile time checked access
by gast128 05 Aug '05

05 Aug '05

Dear all, I was wondering why boost::array did not offer compile time checked access to its contents, something like a.get<1>(), a similar interface like tuple. Otherwise I see not much enhancement compared to an ordinary std::vector. Wkr, me

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Question concerning boost::tuples::length (1.32)
by Daniel Krügler 05 Aug '05

05 Aug '05

(OK, this is my third try. I got problems with (re)subscriptions **although** I am subscribed since years...) Dear Boosters, its quite a while that I could participate in this newsgroup, so maybe my request is ol' stuff and has been answered 100 times. In case of that I apologize for the following question: I observe that boost::tuple::length in version 1.32 exist two template specializations for empty tuples, namely template<> struct length<tuple<> > { BOOST_STATIC_CONSTANT(int, value = 0); }; template<> struct length<null_type> { BOOST_STATIC_CONSTANT(int, value = 0); }; which lead to the unexpected effect that e.g. typedef const tuple<> ConstEmptyTuple; int k = length<ConstEmptyTuple>::value; (modulo namespace issues) does not compile. The reason is obvious, because deduction of boost::tuples::length<ConstEmptyTuple> extracts "const tuple<>", which leads to the generic template definition: template<class T> struct length { BOOST_STATIC_CONSTANT(int, value = 1 + length<typename T::tail_type>::value); }; which does not compile in this case, because const oost::tuples::tuple<> has no tail_type. Similar situations arise for const null_type arguments and corresponding volatile variants thereof. To my humble opinion tuples::length should work independent of cv qualification of the template arguments, but this route should of course be gone in accordance to similar situations of "template predicates" in boost::mp/type_traits. One further indirection and usage of boost::remove_cv<T> could simply resolve the described problem, such as: // Define length_impl + 2 specialisation for tuple<> and null_type as // currently done for length namespace details { template <typename T> struct length_impl { .. // as before; }; template <> struct length_impl<null_type> { .. // as before; }; template <> struct length_impl<tuple<null_type, ...> > { .. // as before; }; } // One single - not specialized - length template handling all cases: template <typename T> struct length { static const int value = details::length_impl< typename ::boost::remove_cv<T>::type >::value; }; What do you think? Greetings from Bremen, Daniel Krügler

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