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[type_map] Interest in container indexed by type?
by Tony D 08 Nov '05

08 Nov '05

Hi people, A couple years ago I wrote a container indexed by type, which I've come to consider a basic building block for reusable code. Effectively, code can use "type_maps" to handle an arbitrary structure, without needing to know member identifiers, and gets the speed benefit of compile-time access resolution. A simple implementation follows: namespace NS { namespace Private { class no_type2 { }; class no_type3 { }; class no_type4 { }; class no_type5 { }; template <typename T> class type_map_base { public: void operator=(const T& t) { t_ = t; } operator const T&() const { return t_; } private: T t_; }; template<> class type_map_base<no_type2> { }; template<> class type_map_base<no_type3> { }; template<> class type_map_base<no_type4> { }; template<> class type_map_base<no_type5> { }; } template <typename T1, typename T2 = Private::no_type2, typename T3 = Private::no_type3, typename T4 = Private::no_type4, typename T5 = Private::no_type5> class type_map : public Private::type_map_base<T1>, public Private::type_map_base<T2>, public Private::type_map_base<T3>, public Private::type_map_base<T4>, public Private::type_map_base<T5> { public: using Private::type_map_base<T1>::operator=; using Private::type_map_base<T2>::operator=; using Private::type_map_base<T3>::operator=; using Private::type_map_base<T4>::operator=; using Private::type_map_base<T5>::operator=; }; } // sample usage... #include <iostream> #include <string> using namespace std; int main() { NS::type_map<int, string> tmid; tmid = 3; tmid = "hello"; string s = tmid; cout << (int)tmid << ' ' << (string)tmid << ' ' << s << endl; cout << sizeof(tmid) << " vs " << sizeof(int) << '+' << sizeof(string) << endl; } I've found typemaps useful for writing things like a logging system that allows arbitrary criterion for cataloging errors. To store several data items of the same type, simply wrap each instance in a distinct class (possibly using the template w/ unique number idiom). Implementation note: the empty base class optimisation makes it practical to have a single template, avoiding typelists (mpl sequences), preprocessing etc.. Cheers, Tony ___________________________________________________________ How much free photo storage do you get? Store your holiday snaps for FREE with Yahoo! Photos http://uk.photos.yahoo.com

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[range] Inconsistent range_iterator metafunction
by David Abrahams 08 Nov '05

08 Nov '05

I note the following: typedef std::vector<int> vint; typedef int aint[4]; range_iterator<vint const>::type ==> std::vector<int>::iterator range_iterator<aint const>::type ==> int const* It seems like it should be range_iterator<vint const>::type ==> std::vector<int>::const_iterator I know we discussed this before. Thorsten, are you planning to make this change? -- Dave Abrahams Boost Consulting www.boost-consulting.com

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compiler_status_2
by Robert Ramey 07 Nov '05

07 Nov '05

I've recently uploaded the program compiler_status_2.cpp to the vault. It was there before but due to things beyond our control files in the vault were lost so I uploaded it again. Previously it had a respectable number of downloads. The difference between the version and the official compiler_status.cpp is that the table generated displays results of all the builds rather than just one. I find it very helpful since different compilers require different builds (static/dynamic, etc) and I also occasionally build for release. This lets me easily see which problems are associated with particular build settings. It also allows me to leave all my build/test results permantently on my machine. Every time I run a test the table is updated and I can see all my tests at once. I had hoped that these improvements might be incorporated into the "official" version. I still hope that this or something like it can occur. Its not a huge issue for me as it has worked well for me as is but I think this "superset" of the original would be valuable to others. Robert Ramey

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[iostreams] Why devices must be copy-constructible?
by Alberto Ganesh Barbati 07 Nov '05

07 Nov '05

Hi, I started using the iostreams library for a pet project. I thinks it's a great piece of software. However, I immediately stumbled in what I think it may be a defect. Consider this simple source device: #include <boost/iostreams/stream.hpp> struct Source : boost::noncopyable { typedef char char_type; typedef boost::iostreams::source_tag category; Source(int); // ctor std::streamsize read(char* s, std::streamsize n) { // implementation here } private: /* ... private members here */ }; int main() { boost::iostreams::stream<Source> s(0); } the boost::noncopyable up there has been put because the device keeps handles to OS resources whose duplication can be very expensive. I was amazed that the code above doesn't compile. This is the error message reported by VC7.1: C:\lib\Boost\include\boost-1_33\boost\iostreams\detail\wrap_unwrap.hpp(52) : error C2558: struct 'Source' : no copy constructor available or copy constructor is declared 'explicit' (full error message is very long and is reported, for reference, at the end of the message) It seems that a device must be copy-constructibile. In particular, the code above makes at least three short-lived copies of the device. Question is: why? I believe this requirement is unintended and not due to a conscious design choice, my arguments are: 1) it's not documented, there is no mention of such requirement in http://www.boost.org/libs/iostreams/doc/concepts/device.html 2) it's unnatural and I believe my case (where copying the device could be expensive) occurs more often in practice than the opposite case 3) from the error messages it seems that a copy is only required as a side-effect of the template machinery used in BOOST_IOSTREAMS_FORWARD. In fact, the offending line detail\wrap_unwrap.hpp(52) is: inline T wrap(const T& t BOOST_IOSTREAMS_DISABLE_IF_STREAM(T)) { return t; } that requires T to be copy-constructible. Am I missing something? Thanks in advance, Ganesh ----- full error messaage follows C:\lib\Boost\include\boost-1_33\boost\iostreams\detail\wrap_unwrap.hpp(52) : error C2558: struct 'Source' : no copy constructor available or copy constructor is declared 'explicit' C:\lib\Boost\include\boost-1_33\boost\iostreams\stream_buffer.hpp(90) : see reference to function template instantiation 'T boost::iostreams::detail::wrap<T>(const T &,boost::disable_if_c<B,void>::type *)' being compiled with [ T=Source, B=false ] C:\lib\Boost\include\boost-1_33\boost\iostreams\stream_buffer.hpp(90) : while compiling class-template member function 'void boost::iostreams::stream_buffer<T,Tr,Alloc>::open(const T &,int,int)' with [ T=Source, Tr=std::char_traits<char>, Alloc=std::allocator<char> ] C:\lib\Boost\include\boost-1_33\boost\utility\base_from_member.hpp(69) : see reference to class template instantiation 'boost::iostreams::stream_buffer<T,Tr,Alloc>' being compiled with [ T=Source, Tr=std::char_traits<char>, Alloc=std::allocator<char> ] C:\lib\Boost\include\boost-1_33\boost\iostreams\stream.hpp(61) : see reference to class template instantiation 'boost::base_from_member<MemberType>' being compiled with [ MemberType=boost::iostreams::stream_buffer<Source,std::char_traits<char>,std::allocator<char>> ] C:\lib\Boost\include\boost-1_33\boost\iostreams\stream.hpp(98) : see reference to class template instantiation 'boost::iostreams::detail::stream_base<Device,Tr,Alloc>' being compiled with [ Device=Source, Tr=std::char_traits<char>, Alloc=std::allocator<char> ] TestVc2.cpp(26) : see reference to class template instantiation 'boost::iostreams::stream<Device>' being compiled with [ Device=Source ]

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bjam question
by Robert Ramey 07 Nov '05

07 Nov '05

I have made some tests to compare serialization of different types of data different archives and to compare against raw i/o. So far so good. Now I would like to alter my test/Jamfile to achieve the following: a) I would like to run a command after the test run to display the size of the test executable. b) I would like to run a command (gprof) after the test for certain tests. I would hope that the output of these post processing command would appear in the output log of the standard output. c) I would like to inhibit the running of these tests when the build is in debug mode. d) I intend to uses these in my own environment as this would impose extra burden on testing and I don't really need to run this stuff except for once in a while. However, I'm am curious how one achieves the effect of the config_info test on the main test matrix whereby the test passes but still produces a link to the test output. Robert Ramey

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Re: [boost] Global object initialization [was: Phoenix-2 prerelease]
by David Abrahams 07 Nov '05

07 Nov '05

Joel de Guzman <joel(a)boost-consulting.com> writes: > Any links to the thread? No, we've been doing this offline. I'll try to forward something to you. >> 1. The placeholders are statically initialized const POD objects in >> an unnamed namespace and you have likely ODR violation when used >> by templates in multiple translation units. >> 2. The placeholders are dynamically initialized references in an >> unnamed namespace and you risk undefined behavior when they are >> used without initialization due to initialization order issues >> 3. The placeholders are dynamically initialized objects in an >> unnamed >> namespace, and you have likely ODR violation *and* initialization >> order issues >> Seems from the doc like you have #3, which is the worst of both >> worlds. No? > > Actually it is 4: > > 4. The placeholders are dynamically initialized *const* objects in > namespace phoenix That's essentially 1, in that you get a different object in each TU and are likely to end up with an ODR violation. > Well, we can easilly make them PODs, so: > > 5. The placeholders are statically initialized *const* POD objects > in namespace phoenix Same problem. > So, question: how does this code below constitute ODR violation? > > namespace x // named > { > T const pod = T(); // T is a POD > } It does not. You need two translation units and a template, instantiated in each one, that uses your object "pod." > is this link relevant?: > http://lists.boost.org/Archives/boost/2004/06/67159.php Precisely. > how about: > http://lists.boost.org/Archives/boost/2001/05/12609.php I don't think so. Internal linkage doesn't save you from an ODR violation. -- Dave Abrahams Boost Consulting www.boost-consulting.com

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Re: [boost] Gender neutral documentation
by brangdon＠cix.compulink.co.uk 07 Nov '05

07 Nov '05

In-Reply-To: <uacgkh76q.fsf(a)boost-consulting.com> dave(a)boost-consulting.com (David Abrahams) wrote (abridged): > Angus' version is better. > > This means that if Bind is unneeded the user can discard it > completely. > > Of course, "this" needs an antecedent :) > > > For example, if Bind is unneeded the user can discard it > completely. > > is much more to the point. But "is unneeded" again fails to say who doesn't need it, and hence fails to say why it isn't needed. It's vague. I think clarity and precision are more important than good grammar or political correctness. -- Dave Harris, Nottingham, UK.

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[test] --catch_system_errors=no doesn't work with minimal test
by David Abrahams 07 Nov '05

07 Nov '05

When using boost/test/minimal.hpp, it doesn't respond to the presence of --catch_system_errors=no, which makes it unreasonably difficult to debug problems on Windows. All I get is an exception caught by the test library, with all of the info about the real cause of the error lost, which is absolutely unhelpful. It seems to me that the minimal configuration ought to at least be useful for writing and debugging simple test cases. -- Dave Abrahams Boost Consulting www.boost-consulting.com

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[mpl] apply as a placeholder expression?
by Eric Niebler 07 Nov '05

07 Nov '05

I have an MPL sequence of metafunction classes. I want to apply<> each with mpl::transform. So I did this: struct metafnclass { template<typename T> struct apply { typedef T type; }; }; typedef mpl::vector<metafnclass, metafnclass> metafnclasses; typedef mpl::transform< metafnclasses , mpl::apply<mpl::_1, int> >::type transmetafnclasses; This fails horribly, and I don't know why. If I add an indirection like this: template<typename T,typename U> struct indirect_apply : mpl::apply<T, U> {}; typedef mpl::transform< metafnclasses , indirect_apply<mpl::_1, int> >::type transmetafnclasses; then it works fine. Why should that be? Is something getting evaluated too eagerly? -- Eric Niebler Boost Consulting www.boost-consulting.com

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multi_index problem in VC 7.1
by Brock Peabody 07 Nov '05

07 Nov '05

If I try to compile the very first example in multi index I get the following error: c:\Program Files\Microsoft Visual Studio .NET 2003\Vc7\include\boost\multi_index\detail\node_type.hpp(56) : error C2903: 'node_class' : symbol is neither a class template nor a function template I get this with 1.33 and 1.32. I've tried many different compiler options. Here is my latest command line: /Ox /D "WIN32" /D "NDEBUG" /D "_CONSOLE" /D "NOMINMAX" /D "_AFXDLL" /D "_MBCS" /FD /EHsc /MD /GS /Fo"Release/" /Fd"Release/vc70.pdb" /W3 /nologo /c /Wp64 /Zi /TP I've dug around a bit and I can't make any sense of this problem. Has anyone else seen this? The exact code I'm compiling is: #include <boost/multi_index/key_extractors.hpp> #include <boost/multi_index_container.hpp> #include <string> struct employee { int id; std::string name; employee(int id,const std::string& name):id(id),name(name){} bool operator<(const employee& e)const{return id<e.id;} }; using namespace boost::multi_index; // define a multiply indexed set with indices by id and name typedef multi_index_container< employee, indexed_by< // sort by employee::operator< ordered_unique<identity<employee> >, // sort by less<string> on name ordered_non_unique<member<employee,std::string,&employee::name> > > > employee_set; employee_set e; Thanks!

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