August 2007 - Boost - lists.preview.boost.org

Proposed addition to the iterator library for iterating over all tuples.
by Alex Mendes da Costa 19 Jun '09

19 Jun '09

Hi folks: I quite often have to write code to do the following: Given N sequences, generate all the N-tuples s.t. the i'th element in each tuple is drawn from the i'th sequence. For example, if sequence S1 is { 1, 2, 3 } and sequence S2 is { 10, 20 }, I need to generate these tuples: (1, 10), (2, 10), (1, 20), (2, 20). I think this problem could be solved elegantly with a iterator similar to zip_iterator. I have some questions: (1) Is there already a way to do this in boost? (2) If not, would this be a worthwhile addition to the iterator library? (3) If so, could I contribute code for this, or must the existing library owners write it? (4) If so, how would I go about getting my code added? Most of the docs seem to be about submitting entire libraries, rather than extensions to existing libraries. Thanks, Alex

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[IOStreams] Opinion on test case needed
by Frank Birbacher 06 Jan '08

06 Jan '08

Hi! I had problems using iostreams::stream<file_descriptor> with Windows and MSVC 8 Express. The file_descriptor had a bug and failed seeking. But the error had gone unnoticed. Because of this I wrote a test case for this in hope to discover an error in IOStreams (source: see below). I did not discover one. Instead the test runs fine on linux/gcc 4.1.2 but fails on Windows/MSVC8Express (test run: see below). I based the test on "Standard C++ IOStreams and Locales" (Langer&Kreft), Section 1.3 "The Stream State". And I found the IOStreams library is just using std::iostream for handling the errors. So is MSVC buggy in this regard? Or am I missing something? Source of test case in Trac SVN Browser: http://svn.boost.org/trac/boost/browser/sandbox-branches/birbacher/fix_iost… Result of test case on platform Windows/MSVC 8 Express: > ...using <p..\..\..\bin.v2\libs\iostreams\test\error_test.test\msvc-8.0express\debug>error_test.exe... > testing.capture-output ..\..\..\bin.v2\libs\iostreams\test\error_test.test\msvc-8.0express\debug\error_test.run > ====== BEGIN OUTPUT ====== > Running 12 test cases... > error_test.cpp(81): error in "wrap_nothrow <&test_seekg>": exception thrown by function(stream) > error_test.cpp(66): error in "wrap_nothrow <&test_seekg>": stream still good > error_test.cpp(68): error in "wrap_nothrow <&test_seekg>": stream did not set badbit > error_test.cpp(69): error in "wrap_nothrow <&test_seekg>": stream did not fail > error_test.cpp(71): error in "wrap_nothrow <&test_seekg>": stream does not report failure by operator ! > error_test.cpp(73): error in "wrap_nothrow <&test_seekg>": stream does not report failure by operator void* > error_test.cpp(66): error in "wrap_throw <&test_seekg>": stream still good > error_test.cpp(68): error in "wrap_throw <&test_seekg>": stream did not set badbit > error_test.cpp(69): error in "wrap_throw <&test_seekg>": stream did not fail > error_test.cpp(71): error in "wrap_throw <&test_seekg>": stream does not report failure by operator ! > error_test.cpp(73): error in "wrap_throw <&test_seekg>": stream does not report failure by operator void* > unknown location(0): fatal error in "wrap_throw_delayed<&test_seekg>": std::runtime_error: bad seek > error_test.cpp(73): last checkpoint > error_test.cpp(81): error in "wrap_nothrow <&test_seekp>": exception thrown by function(stream) > error_test.cpp(66): error in "wrap_nothrow <&test_seekp>": stream still good > error_test.cpp(68): error in "wrap_nothrow <&test_seekp>": stream did not set badbit > error_test.cpp(69): error in "wrap_nothrow <&test_seekp>": stream did not fail > error_test.cpp(71): error in "wrap_nothrow <&test_seekp>": stream does not report failure by operator ! > error_test.cpp(73): error in "wrap_nothrow <&test_seekp>": stream does not report failure by operator void* > error_test.cpp(66): error in "wrap_throw <&test_seekp>": stream still good > error_test.cpp(68): error in "wrap_throw <&test_seekp>": stream did not set badbit > error_test.cpp(69): error in "wrap_throw <&test_seekp>": stream did not fail > error_test.cpp(71): error in "wrap_throw <&test_seekp>": stream does not report failure by operator ! > error_test.cpp(73): error in "wrap_throw <&test_seekp>": stream does not report failure by operator void* > unknown location(0): fatal error in "wrap_throw_delayed<&test_seekp>": std::runtime_error: bad seek > error_test.cpp(73): last checkpoint > > *** 24 failures detected in test suite "Master Test Suite" > > EXIT STATUS: 201 > ====== END OUTPUT ====== Any opinions on this? Any suggestions on what to do about it? Frank

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[fusion] list/detail/at_impl.hpp, Suggest recrusive elem_at_c instead of recursive apply
by Larry Evans 24 Oct '07

24 Oct '07

In boost/fusion/.../list/detail/at_impl.hpp the apply is recursive; however, the only reason for the recursion is to "find the right element type". The other reason for apply is the same as that of the apply in.../vector/detail/at_impl.hpp. "find the right element type" in vector's at_impl is done with mpl::at. The similarity between list and vector at_impl would be more apparent if: template <typename Sequence, int N> struct elem_at_c { typedef typename mpl::eval_if< mpl::bool_<N == 0> , mpl::identity<typename Sequence::car_type> , elem_at_c<typename Sequence::cdr_type, N-1> >::type type; }; were used to find the right element type. Then the frist part of list::at_impl::apply would be: template <typename Sequence, typename N> struct apply { typedef elem_at_c<Sequence, N::value> element; typedef typename mpl::eval_if< is_const<Sequence> , detail::cref_result<element> , detail::ref_result<element> >::type type; which is very similar to the counterpart in vector: template <typename Sequence, typename N> struct apply { typedef mpl::at<typename Sequence::types, N> element; typedef typename mpl::eval_if< is_const<Sequence> , detail::cref_result<element> , detail::ref_result<element> >::type type;

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[soc] Boost.extension/reflection project advances
by Mariano Gabriel Consoni 16 Oct '07

16 Oct '07

Hi Community...! As some of you may know, I'm working on a SoC project called "Boost.extensions and reflection". This mail is just to keep you informed about the project advances. At this time, we have very good news. The library is now near completion, and we expect submitting it for revision in the next days. We've been worked the last two weeks in the following tasks: - Code style: continued improving the code style according Boost guidelines. - Build: improved the Jamfiles to work well in more platforms. - Boost::function: migrated some code to (optionally) use boost::function. - Benchmarks: made new benchmarks to test the new integrations. - Performance analysis: documented the results of the benchmarks. - Preprocessor: replaced a lot of boiler-plate code with (optional) boost::preprocessor macros. - Dependencies flags: documented the optional dependencies and how to enable them. As I have finished all the tasks planned in my proposal (and a lot more :) ) I will advance to Reflection part and Jeremy (Pack, original author) will finish some remaining tasks of Extension. Bye! -- Mariano

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[ANN] Xpressive 2.0 pre
by Eric Niebler 12 Oct '07

12 Oct '07

It's a poorly kept secret that I've been adding new features to Xpressive on CVS HEAD for a while now. So here are the features already implemented (documentation forthcoming) for Xpressive 2.0: << Semantic Actions >> Specify code to execute when parts of a regex match, a-la Spirit's semantic actions. Eg.: if you want to parse a string of name/value pairs into a std::map, you might: std::map<std::string, int> result; std::string str("aaa=>1 bbb=>23 ccc=>456"); // Like "(\\w+)=>(\\d+)": sregex pair = ( (s1= +_w) >> "=>" >> (s2= +_d) ) [ ref(result)[s1] = as<int>(s2) ]; sregex rx = pair >> *(+_s >> pair); if(regex_match(str, rx)) { assert(result["aaa"] == 1); assert(result["bbb"] == 23); assert(result["ccc"] == 456); } The actions are placed on a queue and executed in order only when the regex match succeeds. << Custom Assertions >> Use the check() function to create a boolean predicate that can participate in the match. Here's a regex that recognizes two integers only if the first is less than the second: sregex rx = ( (s1= +_d) >> ' ' >> (s2= +_d) ) [ check( as<int>(s1) < as<int>(s2) ) ]; Unlike actions, predicates execute immediately. You can also define the predicate out-of-line as a function object. << Dynamic Regex Grammars with Named Regexes >> Using regex_compiler, you can map a name to a regex object, and then refer to that regex from another by name. In this way, you can build grammars from regexes at runtime. sregex_compiler comp; sregex rx = comp.compile("^bar(?$RE)baz$"); comp.compile("(?$RE=)\\d+ \\d+"); There's an alternate syntax for associating a name with a regex that you can use to nest a static regex in a dynamic one. Eg., the last line above could be: comp["RE"] = +_d >> ' ' >> +_d; With these changes, you can now nest static and dynamic regexes within each other freely, giving you lots of flexibility to build grammars and modify them on the fly. << Named Captures >> For dynamic regular expressions, you can create a named capture with (?P<name> ...). You can refer back to the named capture with (?P=name). In substitution strings (for use with regex_replace()), you can refer back to a named capture with \\g<name> when using the format_perl or format_all flags. And more .... I'd like to give props to Dave Jenkins who has been doing m4d things with this stuff already, and who has given me a laundry list of other features he'd like. The new features are only available in CVS HEAD, for now. Feedback is welcome. -- Eric Niebler Boost Consulting www.boost-consulting.com

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Boost threadsafe singleton?
by Robert Ramey 21 Sep '07

21 Sep '07

I'm review the serialization library with the eye of making it threadsafe. I think that very useful in this effort would be lightweight threadsafe singleton. There are tons of cyberbits spilled on this topic - but much to my suprise and disappointment, no boost library for this purpose. Someone please tell me its here but that I just haven't found it. Robert Ramey

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Variable Preprocess Metaprogramming?
by Atry 20 Sep '07

20 Sep '07

As we known, there is a preprocess metaprogramming library in boost, but it is not flexible enough. we are unable to define an custom preprocess loop(something like #for or #while ?), and we are also unable to use recursion. I have an idea to do that, C/C++ allows recursion of #include, so we can put the codes we want to evaluate repeatedly to a head, and include itself depends on a preprocess condition. But if we wrote code below, we would meet a error of macro redefinition. /**** foo.hpp ****/ #if FOO < 10 // do something with I # define FOO FOO + 1 # include "foo.hpp" #endif /**** foo.hpp ****/ /**** bar.hpp ****/ #define FOO 0 #include "foo.hpp" /**** bar.hpp ****/ The problem is that an macro must not depends on itself. Thus, to change a preprocess variant, I use a bit of #if to transfer value of a macro to some temporary macro. see my code below: /**** begin_set_value.hpp ****/ #if (BOOST_VPP_VALUE & (1 << 0)) == 0 #define BOOST_VPP_TEMPORARY_BIT_0 0 #else #define BOOST_VPP_TEMPORARY_BIT_0 1 #endif #if (BOOST_VPP_VALUE & (1 << 1)) == 0 #define BOOST_VPP_TEMPORARY_BIT_1 0 #else #define BOOST_VPP_TEMPORARY_BIT_1 1 #endif /* ... */ #if (BOOST_VPP_VALUE & (1 << 30)) == 0 #define BOOST_VPP_TEMPORARY_BIT_30 0 #else #define BOOST_VPP_TEMPORARY_BIT_30 1 #endif #if (BOOST_VPP_VALUE & (1 << 31)) == 0 #define BOOST_VPP_TEMPORARY_BIT_31 0 #else #define BOOST_VPP_TEMPORARY_BIT_31 1 #endif #undef BOOST_VPP_VALUE #define BOOST_VPP_VALUE \ (BOOST_VPP_TEMPORARY_BIT_0 << 0 ) \ + (BOOST_VPP_TEMPORARY_BIT_1 << 1 ) \ + (BOOST_VPP_TEMPORARY_BIT_2 << 2 ) \ + (BOOST_VPP_TEMPORARY_BIT_3 << 3 ) \ /* ... */ \ + (BOOST_VPP_TEMPORARY_BIT_29 << 29 ) \ + (BOOST_VPP_TEMPORARY_BIT_30 << 30 ) \ + (BOOST_VPP_TEMPORARY_BIT_31 << 31 ) \ /*BOOST_VPP_VALUE*/ /**** begin_set_value.hpp ****/ Now, the BOOST_VPP_VALUE is depends on some of BOOST_VPP_TEMPORARY_BIT_n, and can be used to change the former macro: #define FOO 0 #define BOOST_VPP_VALUE FOO #include "begin_set_value.hpp" #undef FOO #define FOO (BOOST_VPP_VALUE + 1) But, FOO depends on BOOST_VPP_TEMPORARY_BIT_ns, and can not be change again, the solution is that A must a variant depends on some other BIT_n definition instead of directly depends on BOOST_VPP_VALUE. Actually, I implements an variant stack to allocate and release these variant. I think the concept of variable preprocess is useful, if Boost.Typeof or Boost.Bind use that, these code they need would be less than copying same codes. I have upload a sample on vault, file name is variable_preprocess.zip. http://boost-consulting.com/vault/index.php?&direction=0&order=&directory=P… http://boost-consulting.com/vault/index.php?action=downloadfile&filename=va… All code is validated by wave, thank you for your attention.

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Threadsafe singleton - questions
by Robert Ramey 19 Sep '07

19 Sep '07

I'm going through the documentation and now have some questions. I would hope that the documentation could be expanded to include answers to these questions. a) reference is made to a "lease" which sounds like a mutex to me. But its not obvious to me how this should be used. How does the compare with the pattern that I am more familiar with class s : singlton mutex m_mutex ... my_function(...){ scoped_lock(m_mutex); ... } OK - I've looked again and I think its clear to me how this is to be used. We need a tutorial here !!!! b) reference is made to boost::restricted which I couldn't find anywhere. Robert Ramey

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[SVN Configuration] Request an additional MIME type to support Scalable Vector Graphics (SVG)
by Peter Foley 17 Sep '07

17 Sep '07

To upload Scalable Vector Graphics (SVG) images to the Sandbox do I simply update my local subversion configuration (as mentioned here http://tinyurl.com/2zqoqm) to include the MIME details for SVG files or will something need to be updated on the server as well? As mentioned at http://tinyurl.com/2dteq2 RFC 3023 (http://www.ietf.org/rfc/rfc3023.txt) has this to say about the SVG MIME type: ---------- RFC info on SVG ------------- 8.19 Image/svg+xml Content-type: image/svg+xml <?xml version="1.0" ?> Scalable Vector Graphics (SVG) documents are XML documents whose content describes graphical information, as defined by [SVG]. As a format based on XML, SVG documents SHOULD use the '+xml' suffix convention in their MIME content-type identifier. However, no content type has yet been registered for SVG and so this media type should not be used until such registration has been completed. ---------- END RFC info on SVG ------------- Should I simply update my local configuration file to include the line: *.svg = svn:eol-style=native; svn:mime-type=image/svg+xml Any advice would be greatly appreciated. Thanks, Peter.

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Development and Release Practices
by Beman Dawes 14 Sep '07

14 Sep '07

A draft "Development and Release Practices" document is up on the Wiki: http://www.crystalclearsoftware.com/cgi-bin/boost_wiki/wiki.pl?Development_… Comments welcomed! The proposed process refinements are meant to complement the parallel ongoing efforts to improve our tools, but don't depend on any tool improvements. Thus we can get started as soon as we reach sufficient consensus. That said, I think tools are very important, and hope we can rapidly make improvements in both process and tools. --Beman

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