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[TTI] Review for The Type Traits Introspection library by Edward Diener **extended**
by Joel Falcou 20 Jul '11

20 Jul '11

The Type Traits Introspection library by Edward Diener started friday 1st have been *extended* to july 17. Comments and reviews are welcome. =========== What is it? =========== The TTI library, which is an abbreviation for the 'Type Traits Introspection' library, allows a programmer to introspect at compile time the inner elements of a C++ type. The introspection process depends on specifying the name of the inner element by different macros for different types of elements, and then using a generated metafunction to determine whether that element exists within the enclosing type. The inner elements which can be introspected are type, class template, member data, member function, static member data, and static member function. The TTI library is based on the type_traits_ext portion of the Concept Traits Library, with improvements and additions, and also reproduces functionality ( without changing existing code ), for the purposes of completeness, from Boost.MPL regarding introspection of types and templates. The purpose of the library is to provide a consistent set of interfaces for doing compile-time introspection of a type, which other template metaprogrammers can use in their code. If you are at all interested in compile-time introspection of types, please take a look at the functionality of this library. =================== Getting the library =================== The library is available at http://svn.boost.org/svn/boost/sandbox/tti/. The HTML documentation is available at http://svn.boost.org/svn/boost/sandbox/tti/libs/tti/doc/html/index.html and the PDF documentation is available at http://svn.boost.org/svn/boost/sandbox/tti/libs/tti/doc/TypeTraitsIntrospec…. =================== Writing a Review =================== The reviews and all comments should be submitted to the developers list, and the email should have "[TTI] Review" at the beginning of the subject line to make sure it's not missed. Please explicitly state in your review whether the library should be accepted. The general review checklist: - What is your evaluation of the design? - What is your evaluation of the implementation? - What is your evaluation of the documentation? - What is your evaluation of the potential usefulness of the library? - Did you try to use the library? With what compiler? Did you have any problems? - How much effort did you put into your evaluation? A glance? A quick reading? In-depth study? - Are you knowledgeable about the problem domain? And finally, every review should answer this question: - Do you think the library should be accepted as a Boost library? Be sure to say this explicitly so that your other comments don't obscure your overall opinion.

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Limitations / Flaws with transformed_range
by John M. Dlugosz 20 Jul '11

20 Jul '11

I've already noted that the "transformed_range", the class behind boost::adaptors::transform, is not using result_of as documented but seems to be simply looking for result_type, period. I've found another issue, and I consider it a "flaw" because it is a Limitation due to oversight or an artificial restriction, and the deeper workings should handle these cases just fine. Let me explain in detail: The template< class F, class R > struct transformed_range : takes two arguments. The R argument is used for two purposes. It gives the iterator type that will be held, via range_iterator<R>::type. It also gives the exact type of the argument expected by the constructor. Now here is an example from my experiments / work-in-progress: template< class Range > inline transformed_range<ASCII_lower,const Range> operator|( const Range& r, const ASCII_lower_forwarder ) { return transformed_range<ASCII_lower,const Range>( ASCII_lower(), // The underlying transform iterators wants this internal::src_prep(typename std::tr1::is_pointer<Range>::type() ,r) // "source" style argument processing ); } The src_prep is similar to the supplied is_literal, and used for the same purpose. It will package a primitive array as a iterator_range, handing string literals and primitive array objects in the way I intend with respect to nul terminators. It differs from is_literal in several ways, but the idea is the same. Now I don't have to do anything to the Range parameter passed as the type argument to transformed_range, because even when I change the type of the massaged argument, it still has the same underlying iterator type. After all, it gets the iterators from the original range thing passed in. But, the massaged value of r is rejected by the constructor, because it has a different type. It doesn't need to be the same type! It has the same underlying iterator type and could be assigned to it, but the constructor is too strict. It would be a simple matter of passing another template argument to the constructor, as is commonly done with constructors or assignment, and take anything that "works" in that boost::begin and boost::end returns something that can be used to initialize the range_iterator. Copying the class to my own code and changing the constructor to: template <typename R2> transformed_range( F f, R2& r ) : base( boost::make_transform_iterator( boost::begin(r), f ), boost::make_transform_iterator( boost::end(r), f ) ) indeed makes it acceptable to the compiler. (At this point I also noticed that _some_ of the types within the class are qualified by boost::, but not all of them. I know that functions are qualified to prevent argument-dependant lookup, but it is odd that some of the types (or names used in other context) are qualified and sometimes they are not.)

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Re: [Boost-users] [!! SPAM] [wave] Trace output lines with single underscore
by Hartmut Kaiser 20 Jul '11

20 Jul '11

> Many of the rescanning lines in the Wave trace output for a macro I am > tracing show either just a single underscore ( _ ), where the output is > empty, or a number and and underscore ( 1_ ) where it is actually just the > number which is being output. What is the reason for the underscore ? IIRC, the _ is used as a (readable) representation for the (empty) placeholder token, which disappears from the final output, but is helpful for debugging purposes. Regards Hartmut --------------- http://boost-spirit.com

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Boost BCP namespace renaming : dispelling the FUD ?
by BernardH 19 Jul '11

19 Jul '11

Hi, When implementing a library, one might want to neither require nor prevent the library users to also use any version of Boost. I believed that BCP used with namespace renaming would allow the use of (namespace-renamed) Boost in the implementation of such a library without *any* concern about conflict at link time and / or rub-time errors if the library user chooses to also use another Boost version. However, I have been reading that Boost brings some symbols that cannot be renamed because they are out of any namespace, with "C" linkage[*]. This brings the following questions : 1) can a list all such names be found ? 2) To be *completely safe*, must I : 2.1) only avoid using those symbols in my library 2.2) avoid the boost libaries that provide such symbols 2.3) avoid boost libraries that depend on such symbols (how am I to find out which ?) 2.4) avoid boost libraries that depend on the boost libraries providing such symbols (easier to do than 2.3 with bcp, I believe). 2.5) Despair ! (i.e. forgo boost usage under such constraints). Boost is a great set of libraries, I think that it is a pity that a legitimate concern (not imposing a specific Boost version on users) would prevent it's use for implementing libraries : please, help me dispel the Fear, Uncertainty and Doubt over this use case ! Best Regards, Bernard [*] http://stackoverflow.com/questions/2907882/using-concurrently-2-versions-of…

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[wave] Trace output lines with single underscore
by Edward Diener 19 Jul '11

19 Jul '11

Many of the rescanning lines in the Wave trace output for a macro I am tracing show either just a single underscore ( _ ), where the output is empty, or a number and and underscore ( 1_ ) where it is actually just the number which is being output. What is the reason for the underscore ?

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[accumulator] median absolute deviation
by Phil Bouchard 19 Jul '11

19 Jul '11

Hi, I see the median absolute deviation (MAD) is not provided by the accumulator library. Perhaps this is a feature that could be added. Thanks, -Phil

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More on my result_type problem
by John M. Dlugosz 19 Jul '11

19 Jul '11

I see from the source code that the transform range is calling make_transform_iterator which takes two arguments, and that "If Reference is use_default then the reference member of transform_iterator is result_of<UnaryFunction(iterator_traits<Iterator>::reference)>::type." The documentation for result_of explains the need, and shows how to use a result template instead of a result_type simple type in this case. My code follow from the example: struct ASCII_lower { // tell details to result_of template, since VS8 doesn't support decltype keyword. template <typename> struct result; template<typename F, typename T> struct result<F(T)> { typedef T type; }; template< typename CharT > CharT operator() (const CharT& ch) const { if (ch >= 'A' && ch <= 'Z') return ch+0x20; return ch; // unchanged } }; But, I still get an error that result_type is not found! B:\boost/iterator/transform_iterator.hpp(42) : error C2039: 'result_type' : is not a member of 'vst::internal::ASCII_lower' B:\boost/mpl/eval_if.hpp(41) : see reference to class template instantiation 'boost::detail::function_object_result<UnaryFunc>' being compiled with [ UnaryFunc=vst::internal::ASCII_lower ] B:\boost/iterator/iterator_adaptor.hpp(172) : see reference to class template instantiation 'boost::mpl::eval_if<C,F1,F2>' being compiled with [ C=boost::is_same<boost::use_default,boost::use_default>, F1=boost::detail::function_object_result<vst::internal::ASCII_lower>, F2=boost::mpl::identity<boost::use_default> ] It appears to be using function_object_result, not result_of as documented. And that is: template <class UnaryFunc> struct function_object_result { typedef typename UnaryFunc::result_type type; }; which simply turns result_type into type to make eval_if happy, and doesn't do anything fancier. So, it doesn't work as documented, and neither provides another way of passing the parameter in (exposing more arguments from the underlying transform_iterator). Is that a bug, or what? —John

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[Preprocessor] Is it possible to expand recursively?
by TONGARI 19 Jul '11

19 Jul '11

Hello, I'd like to have a macro like: BUILD_HIERARCHY (a, (b,) (c, (d,) (e,) ) ) which should expand to: struct a {}; struct b: a {}; struct c: a {}; struct d: c {}; struct e: c {}; Is this possible at all? I have tried but with no luck, if this is impossible, please tell me so. TIA

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[spirit] warnings after upgrade to 1.47
by Diederick C. Niehorster 19 Jul '11

19 Jul '11

Dear all, After upgrading to boost 1.47, I got the attached enormous warning, ironically saying that names are too long, for a very simple use of boost.spirit. Code: #include <string> #include <vector> using namespace std; #include <boost/spirit/include/karma.hpp> namespace bsk = boost::spirit::karma; namespace bsa = boost::spirit::ascii; vector<string> vUnrecog; //... bsk::generate(ostream_iterator<char>(cout), "Init file options not recognized:\n" << (" \"" << bsa::string << '"' << bsk::eol) % "", vUnrecog); Is there something I am doing suboptimally or in an old way? (The code has been around for about 2 years now). Thanks and best, Dee

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Asio 1.6: compile error in signal_set_service with MSVC10
by Norbert Wenzel 19 Jul '11

19 Jul '11

Hi, I was just updating Boost from 1.46.1 to 1.47 and encountered a compile error inside Asio. Since there is no major outcry on this list I guess I've made an error anywhere in the upgrade process or my code. When compiling my static library that contains the networking code with (our only compiler) Visual Studio 2010 I get compile errors in asio/detail/impl/signal_set_service.ipp in line 74 saying 'boost::signal': use of class template requires template argument list As a remedy I simply defined BOOST_ASIO_DISABLE_SIGNAL, the code compiles fine and I did not recognize any problems at a first short test. I tried to make a simple example showing the error, but I was not able to reproduce this easily. So I thougt I ask what disabling signals means for Asio and if this is a valid workaround, or if I really should try to get this compile error fixed before working with 1.47. thanks, Norbert

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