September 2011 - Boost - lists.boost.org

[conversion] review
by Gordon Woodhull 03 Sep '11

03 Sep '11

Hi all, Here is my review of the Conversion library. I like the idea of a uniform configurable casting operator, whether it's called convert_to, static_cast, convert_cast, or extrinsic_cast. If I had to write a conversion function, I would rather write it as an overload of a general-purpose converter, rather than giving it some ugly typeA2TypeB name. And I would rather find out what header to include and use a generic function rather than using such some specific name. I vote to accept the library (although obviously as Review Manager I'll follow the wishes of all reviewers). Part of the reason I took on the challenge of managing this review is that the library is something people don't know they need. I think uniformity of interface is a good enough reason to use the library, but when would you need a truly generic conversion function as this library offers? Or more to the point, what does it mean to have a "shadow conversion space" for types that don't know about each other? We would hope that libraries are generic enough so that their types can be adapted to work with each other (prime example: Polygon & Geometry). But it's the sad truth that most libraries are not designed this way, and any non-header library can't be designed this way. So that's where Conversion steps in to make combining those libraries cleaner. As we've already discussed, the Achille's Heel of this library is that it requires all compilation units to agree on what conversions they will use, to avoid ODR violations. In practice this probably means that users would have to maintain their own conversion setup headers, which is annoying. But it's hard to imagine an openly configurable global utility that doesn't suffer from some version of this problem. John Bytheway's suggestion of tagging libraries with type keys is an interesting idea. I think Vicente also mentioned the possibility of a scheme that would cause linker errors instead of ODR violations, which would be an improvement. (FWIW I suggested something involving #error but of course that would only work within a CU.) In my mind it is very clear that a templated function<T>(x) will probably return a T and I don't find it necessary that the proposed function has to use the preposition "to". But that's because I'm very aware that the explicit template argument must be the return type, which is understandably not clear to everyone. While the recursive features of this library look interesting and useful, I wonder if there isn't a more general way to do this. I keep thinking it's an awful lot like fusion::copy or Marsden's Traversals. Well, that's enough for now. I hope later today to post summaries of some comments I received off-list and maybe get those people to join the conversion. (You know who you are!) Cheers, Gordon

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[type traits] Extension to operator detection -> choose your preferred naming
by Frédéric Bron 03 Sep '11

03 Sep '11

It is time to include the type trait extension to the official boost trunk. These traits can detect if you can use a given operator with given arguments. For example: has_plus<double, int>::value is true because the following program compiles without error: double lhs; int rhs; lhs+rhs; We have come to three proposed lists of names (A, B and C): https://svn.boost.org/trac/boost/wiki/GuideLines/Naming/OperatorTraitNames I have included the corresponding names of standard keywords, standard function objects from <functional>, boost Proto and boost Operators. Please give your preference between A, B and C before Sept. 5th. Regards, Frédéric

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[preprocessor]BOOST_PP_CHECK_2 with wrong number args
by Larry Evans 02 Sep '11

02 Sep '11

boost/preprocessor/detail/check.hpp in boost version 1.47.0 contains: # if ~BOOST_PP_CONFIG_FLAGS() & BOOST_PP_CONFIG_MSVC() && ~BOOST_PP_CONFIG_FLAGS() & BOOST_PP_CONFIG_DMC() # define BOOST_PP_CHECK_D(x, type) BOOST_PP_CHECK_1(BOOST_PP_CAT(BOOST_PP_CHECK_RESULT_, type x)) # define BOOST_PP_CHECK_1(chk) BOOST_PP_CHECK_2(chk) # define BOOST_PP_CHECK_2(res, _) res # elif BOOST_PP_CONFIG_FLAGS() & BOOST_PP_CONFIG_MSVC() The above shows BOOST_PP_CHECK_2 is called with 1 argument on rhs of BOOST_CHECK_1; yet, the arity is 2, as shown on the next line. This results in the errors reported here: http://article.gmane.org/gmane.comp.lib.boost.devel/222795 when that line is changed to: # define BOOST_PP_CHECK_1(chk) BOOST_PP_CHECK_2(chk,_) the reported error goes away; however, several other errors occur about too many instead of too few arguments passed to BOOST_PP_CHECK_2. Is this a BOOST_PP bug? If not; how can the errors reported in: http://article.gmane.org/gmane.comp.lib.boost.devel/222795 be avoided? TIA. -regards, Larry

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[Boost.serialization] - Json Serialization (Marshalling and unmarshalling)
by Demetrio Car 02 Sep '11

02 Sep '11

I need some example of how to serialize/deserilize from Json format to Object and from Object to Json. I used this example http://www.boost.org/doc/libs/1_47_0/libs/serialization/doc/index.html, but it only serialize to a simple text. In my project, for other requirenments, I am using boost library with success. I am almost sure that I do need some other specific library like Json-Spirit or standard QT library (QScriptEngine). Any simple example will be very appreciate. This is an example of the Json files I must serialized to a class. [{"DscTipoEstrutura":"Unidade de Neg\u00f3cio","FlgAtivo":true,"IdDominio":1,"IdTipoEstrutura":1,"NroOrdem":0},{"DscTipoEstrutura":"Regi\u00e3o","FlgAtivo":true,"IdDominio":1,"IdTipoEstrutura":2,"NroOrdem":1},{"DscTipoEstrutura":"Distrito","FlgAtivo":true,"IdDominio":1,"IdTipoEstrutura":3,"NroOrdem":2}] Ps.: I found http://www.codeproject.com/KB/recipes/JSON_Spirit.aspx and http://boost-spirit.com/repository/applications/show_contents.php similiar to I need but, because I am C++ begnnier, I couldn't understand them neither run the example after some couple of hours. I need some simple example.

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Acknowledgement for Certs 4 Less
by Dave Abrahams 02 Sep '11

02 Sep '11

All--- For some time now, Boost has been using the CA-signed wildcard SSL certificate that was very generously donated by Certs 4 Less. I promised them, in return, that Boost would acknowledge them on our website, as we have done in the past for other donors. We acquired the certificate so we could accept e-payments for BoostCon, but in the end we decided to pay EventBrite to take payments for us... so as far as I know, the cert is only being used at the moment for https://svn.boost.org Two questions: 1. Where does the acknowledgement belong? 2. Can someone who knows how put it there? P.S. I would be very happy not to get separate answers to those, if someone who knows how to edit the website *and* an appropriate placement for the acknowledgement could just take care of it ;-) Thanks, -- Dave Abrahams BoostPro Computing http://www.boostpro.com

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Version 10 of Boost.Algorithm available
by Marshall Clow 02 Sep '11

02 Sep '11

Changes since -009 * Predicate versions of the search functions have been removed. * Search functions now work for raw pointers * Now use tr1/unordered_map everywhere - this should make (most versions) of gcc happy. * Now including <climits> in search.hpp, which defines CHAR_BIT. * Fixed a bug in boyer_moore::create_suffix_table, which caused the search to fail sometimes. * The skip table is now templated on the value_type being searched on, rather than the iterator type. * Documentation has been updated (more to come here) Thanks to Mikhail Levin, TONGARI, and Sebastian for bug reports. Since the vault is gone, I've put the code here: http://dl.dropbox.com/u/11048326/Boost.Algorithm-010.zip -- Marshall Marshall Clow Idio Software <mailto:mclow.lists@gmail.com> A.D. 1517: Martin Luther nails his 95 Theses to the church door and is promptly moderated down to (-1, Flamebait). -- Yu Suzuki

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[review] conversion - Kevlin's comments
by Gordon Woodhull 02 Sep '11

02 Sep '11

Hi Vicente, all - I got this comment from Kevlin Henney, author of lexical_cast: On Sep 1, 2011, at 11:45 AM, Kevlin Henney <kevlin(a)curbralan.com> wrote: > I was looking through the docs and they seem to offer a solution to a common family of conversion problems. Based on casual reading, it feels a little more complex and requires a higher-entry level of knowledge than would be appropriate for many of the people who actually need this functionality. These are initial impressions only, so don't read too much into them. The eternal battle between power and simplicity. :-) Cheers, Gordon

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[proto] Can't use functions in expressions?
by John Maddock 02 Sep '11

02 Sep '11

So.... I have a function that returns an expression template of proto::tag::function type, like so: template <class Exp>\ typename proto::result_of::make_expr<\ proto::tag::function\ , detail::BOOST_JOIN(func, _funct)<typename detail::backend_type<Exp>::type>\ , detail::big_number_exp<Exp>\ >::type const \ func(const detail::big_number_exp<Exp>& arg)\ {\ return proto::make_expr<proto::tag::function>(\ detail::BOOST_JOIN(func, _funct)<typename detail::backend_type<Exp>::type>() \ , arg \ );\ }\ and it all works fine, until I try and use the result of such a function call in an expression: sqrt(arg) + arg yeilds: 1>m:\data\boost\sandbox\big_number\libs\math\ide\extended_real\scrap\scrap.cpp(25): error C2893: Failed to specialize function template 'const boost::proto::detail::enable_binary<boost::proto::domainns_::deduce_domain,boost::proto::detail::not_a_grammar,boost::mpl::or_<boost::proto::is_extension<T>,boost::proto::is_extension<Right>>,boost::proto::tag::plus,const Left,const Right>::type boost::proto::exprns_::operator +(const Left &,const Right &)' 1> With the following template arguments: 1> 'boost::math::detail::big_number_exp<Expr>' 1> with 1> [ 1> Expr=boost::proto::exprns_::basic_expr<boost::proto::tag::function,boost::proto::argsns_::list2<boost::math::detail::big_number_exp<boost::proto::exprns_::basic_expr<boost::proto::tag::terminal,boost::proto::argsns_::term<boost::math::detail::sqrt_funct<boost::math::mpfr_real_backend<50>>>,0>>,boost::math::detail::big_number_exp<boost::proto::exprns_::expr<boost::proto::tag::terminal,boost::proto::argsns_::term<boost::math::big_number<boost::math::mpfr_real_backend<50>> *>,0>>>,2> 1> ] 1> 'boost::math::mpfr_real_50' So I figured I needed to update my grammar, so I tried adding this case: template<> struct big_number_grammar_cases::case_<proto::tag::function> : proto::function< proto::_ > {}; But still no joy (same error message). Any ideas on what I'm doing wrong? BTW I couldn't find any examples of using proto::function in a grammar, it wasn't obvious to me what it's template arguments should be, or indeed whether this actually enabled the function call operator rather than my use case? Thanks, John.

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Basic boost::mpl::max_element question.
by Yves Dolce 02 Sep '11

02 Sep '11

Hi everyone, Once past the basic understanding of C++ metaprogramming (factorial, vector/typeslist, .), I must confess I have a hard time using max_element in my particular scenario. And I have not found a lot of samples on the net. Consider this "repro" first: template <unsigned char L> struct Level { static const unsigned char value = L; }; template <class LEVEL> struct CTA { typedef LEVEL Level_t; }; typedef boost::fusion::vector<CTA1, CTA2, CTA3, CTA4> CTAS; Now, using max_element, I'd like to pick the one CTAn for which CTn::Level_t::value is the biggest. Can you enlighten me? Thanks! An MPL/FUSION beginner. J

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[TypeTraits] A patch for clang's intrinsics (was: [type_traits] is_enum on scoped enums doesn't works as expected)
by Michel MORIN 01 Sep '11

01 Sep '11

John Maddock wrote: >> Boost.TypeTraits does not use intrinsics for clang yet. >> (c.f. https://svn.boost.org/trac/boost/changeset/72725) >> >> >> this explains why it is not working now. Is someone working on this issue? > > Not me, we need a Clang expert to look into it - or at least someone with > access to Clang to take care of the testing - someone did submit a patch to > enable intrinsic support for Clang, but it broke more things than it fixed > so it got reverted :-( Let's proceed step by step. As a first step, I made a patch to use clang's intrinsics except problematic intrinsics (i.e. `is_pod` and `is_empty`). All the tests run successfully on gcc-4.4, 4.5, 4.6, clang (trunk) and Mac OS X Lion's clang (Apple clang version 2.1). Regards, Michel

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