- Boost - lists.boost.org

[type_traits] has_member_function_callable_with
by Ion Gaztañaga 21 Sep '11

21 Sep '11

Hi to all, Trying to port C++11 code (allocator_traits) to C++03 (without decltype support), I needed to check at compile time if a member function can be called with some given parameters. Typical solutions I found on the net were based on specific signatures, say: const bool value = HAS_MEMBER_FUNCTION_FUNCNAME_WITH_SIGNATURE(MyClass, (int, char*)); However, it is not feasible to know the exact signature as I want to deal with conversions, const references, etc. Luckily, I found a very interesting explanation in Proto documentation: http://www.boost.org/doc/libs/1_47_0/doc/html/proto/appendices.html#boost_p… Based on this, I've tried to write my solution and I'd like to share it here with type traits experts, in case someone knows a better solution (see attached example). I know I don't take into account many issues for a truly generic utility (const member functions, etc.) but please let me know if you find this example interesting. Best, Ion

4 6

[BGL] container_gen
by Cromwell Enage 21 Sep '11

21 Sep '11

Hi, all. After a bit of a programming hiatus, I've managed to follow up on our container_gen discussion we had last May, archived here: <http://article.gmane.org/gmane.comp.lib.boost.devel/219238> I've created a branch in the sandbox called utility-container_gen that places the metafunction in Boost.Utility, changes detail::is_random_access to is_random_access_selector, provides an is_unique_associative_selector metafunction, and changes adjacency_list and parallel_edge_traits to use said utilities. Plus, there's Quickbook documentation. I've tested a few example programs in the BGL to make sure they still work, but I feel that's far from being thorough. No selectors for Boost.Intrusive have been implemented, yet. Feedback welcome! Cromwell D. Enage

2 2

Re: [boost] [contract] syntax redesign
by Andrzej Krzemienski 21 Sep '11

21 Sep '11

> Comments are always welcome :) Hi Lorenzo, The number of examples is impressive. It is a pleasure to observe your library growing at this pace. I would like to suggest two things. I could not see from the examples, if the library is capable of supporting "function try blocks" in constructor and destructor definitions. This is what I mean. http://msdn.microsoft.com/en-us/library/e9etx778%28v=vs.71%29.aspx http://www.gotw.ca/gotw/066.htm Second, I have seen #ifndef pragmas in some of the examples, e.g., in the body of function myadvance_dispatch you have: { #ifndef CONTRACT_CONFIG_NO_LOOP_VARIANTS Distance n_max = n; #endif CONTRACT_LOOP( while(n++) ) { CONTRACT_LOOP_VARIANT( const( n_max, n ) n_max - n ) --i; } } I am not sure if the necessity to use this conditional code would occur often, but if so, perhaps the code would be slightly more clear if instead the conditional code would be wrapped in an additional macro, like MFC did with DEBUG_ONLY macro: { CONTRACT_CONFIG_LOOP_VARIANT_ONLY( Distance n_max = n ); CONTRACT_LOOP( while(n++) ) { CONTRACT_LOOP_VARIANT( const( n_max, n ) n_max - n ) --i; } } That is, macro CONTRACT_CONFIG_LOOP_VARIANT_ONLY is defined as: #ifndef CONTRACT_CONFIG_NO_LOOP_VARIANTS #define CONTRACT_CONFIG_LOOP_VARIANT_ONLY(ARG) ARG #else #define CONTRACT_CONFIG_LOOP_VARIANT_ONLY(ARG) #endif Although I am not sure if a similar trick would be possible with the definition like: CONTRACT_FUNCTION( template( typename T ) requires( Addable<T> #ifndef CONTRACT_CONFIG_NO_POSTCONDITIONS // Equality only for postconditions. , boost::EqualityComparable<T> #endif ) (T) (add) ( (T) x, (T) y ) postcondition( auto result = return, result == x + y ) ) { return x + y; } Regards, &rzej

3 2

[exception] get_error_info with dynamic libraries
by Pavel Lebedev 19 Sep '11

19 Sep '11

Hi, I believe there is a problem with boost::get_error_info when used to retrieve error info objects added to exceptions in a module (exe/dll) different from the one making the call to this function under MSVC++ 2010 SP1. The problem appears to be introduced in SVN revision 68792 with a fix for ticket #5178 that changed struct boost::exception_detail::type_info_ from storing a reference to type info to a pointer in member type_. There's an assertion in function boost::exception_detail::error_info_impl_container::get that checks these members for equality which now does pointer comparison instead of calling std::type_info::operator== (for the case of enabled RTTI). This fails when used on error info added in the different module from the one trying to access it because each module gets its own copy of std::type_info object for the same type with different addresses, even though std::type_info::operator= does string comparison of class names and would have returned true, as it did before this change. Other compilers/platforms that don't provide process-unique type info objects are most likely affected too. The following patch appears to fix this problem for me by reverting to compiler-provided way of comparing type info objects. Index: info.hpp =================================================================== --- info.hpp (revision 74465) +++ info.hpp (working copy) @@ -97,7 +97,7 @@ { shared_ptr<error_info_base> const & p = i->second; #ifndef BOOST_NO_RTTI - BOOST_ASSERT( BOOST_EXCEPTION_DYNAMIC_TYPEID(*p).type_==ti.type_ ); + BOOST_ASSERT( *BOOST_EXCEPTION_DYNAMIC_TYPEID(*p).type_==*ti.type_ ); #endif return p; } Is this fix correct? Thanks in advance. Pavel Lebedev

2 2

[utility] rvalue support in value_initialized
by "Claas H. Köhler" 19 Sep '11

19 Sep '11

Hi everybody! Recently I encountered a problem using the std:::unique_ptr within boost::spirit. The reason is apparently that value_initialized does not support rvalue assignment. Are there any plans to implement move semantics into value_initialized? Mainly I would be interested in making something like this work: std::unique_ptr<T> a= boost::get( boost::value_initialized< std::unique_ptr<T> >() ); Currently this fails due to the fact, that unique_ptr can be moved but not copied. Regards Claas

8 9

[move] [optional] Move constructors support
by Antony Polukhin 19 Sep '11

19 Sep '11

There is a feature request https://svn.boost.org/trac/boost/ticket/1841 with some patch. I'm just curious, when will be it applied? Shall this patch be applied, or some integration with Boost.Move must be done instead? Best regards, Antony Polukhin

1 0

Template metaprogramming libraries
by Ábel Sinkovics 19 Sep '11

19 Sep '11

Hi Boost developers, I am a PhD student at Eotvos Lorand University, Budapest. My research area covers C++ template metaprogramming. As part of my research I have developed four template metaprogram libraries based on Boost.MPL. On my conference appearances I was encouraged to submit my libraries to the Boost sandbox. Here is a short summary of the libraries: metaparse A tool for building embedded DSLs in C++. This is a compile-time parser generator library. Using it one can build parsers that take compile-time strings as input text and parse them as part of the C++ compilation process. One can think of it as using Spirit at compile-time. safe_printf Typesafe printf implementation using metaparse. It provides printf (sprintf, fprintf) functions taking the format string as a template argument and type-checking it at compile-time. It is a practical application of the metaparse library. metamonad Monad implementation for C++ template metaprograms. The library provides a framework for using monads in C++ at compile-time. The library provides an embedded language for C++ template metaprogramming similar to Haskell's do-notation. Using it, template metaprograms can be written with a syntax that resembles procedural code. Unlike the approach presented at this year's Boostcon, my library focuses on monads evaluated completely at compile-time. The library contains implementations for a number of monads available in Haskell (Maybe, Either, Reader, Writer, State, etc.). As an addition, the library contains a monad for error propagation in C ++ template metaprogramming. Based on the similarities of monadic error propagation and exception handling in runtime C++, the library provides an embedded language that resembles to exception handling. Using it, one can throw and catch "exceptions" at compile-time. metatest Unit testing library for C++ template metaprograms. If a metaprogram test case fails, it does not produce compilation error, but makes the result information available at runtime. Using this one can generate advanced reports and integrate the results into unit testing frameworks for runtime C++ code. The library contains code that integrates it with Boost.Test. The source code, unit tests and examples for the library are available at http://github.com/sabel83/mpllibs I've tested the libraries with the following compilers: - gcc 4.5 - clang 2.8 - Visual C++ 10 Full documentation of the libraries can be found at http://abel.web.elte.hu/mpllibs. Publications related to the libraries: http://abel.sinkovics.hu/?mod=kutat I would like to ask you for access to the Boost sandbox and I would appreciate all feedback from the Boost community. Best regards, Abel Sinkovics

13 31

De Brujin Bind and nested bind calls (was: Re: Template metaprogramming libraries)
by Thomas Heller 19 Sep '11

19 Sep '11

On Fri, Sep 16, 2011 at 7:09 PM, David Sankel <camior(a)gmail.com> wrote: > On Fri, Sep 16, 2011 at 6:30 AM, Thomas Heller > <thom.heller(a)googlemail.com>wrote: >> On Friday, September 16, 2011 06:17:00 AM David Sankel wrote: >> > On Fri, Sep 16, 2011 at 4:51 AM, Thomas Heller >> > <thom.heller(a)googlemail.com>wrote: >> > > On Thursday, September 15, 2011 12:31:50 PM David Sankel wrote: >> > <snip> >> > > <rant> >> > <snip> >> > > It should be noted though that phoenix users can get around >> > > > this somewhat by using _identifier syntax. >> > > > </rant> >> > > #include <boost/phoenix.hpp> >> > <snip> >> > auto flip = lambda(_a = _1)[bind(_a, _2, _1)]; >> > <snip> >> > > Thanks for your unqualified rant, David. >> > huh? >> >> Is this not what you were saying wasn't possible with phoenix? >> Having a De Brujin style syntax is perfectly possible in phoenix. It just >> hasn't been done yet cause, as you saw in my example, can be expressed by >> using phoenix local variables. > > Oh, my bad. When I said "_identifier syntax", I was referring to phoenix > local variables. I should have double-checked my phoenix vocab before I > wrote. > > Phoenix locals definitely help fill the coverage problem I referred to. I > don't know for sure, but I'd expect phoenix to cover all functions that can > be defined in lambda calculus. > > The reason I said that phoenix "somewhat" gets around the bind heritage > problems, which was obscure I admit, was because phoenix's use of > traditional bind syntax still leaves a semantic hole. Ok, misunderstanding on both sides, no offense intended. > If someone writes the following: > > template< typename F > > auto doSomething( F f ) -> decltype(...) > { > return bind( f, 15, _1) > } > > And then I call doSomething elsewhere like this, > > doSomething( bind( g, 12, _1, _2 ) ) > > , then the result is something most likely unexpected for the user who knows > what doSomething means (it returns a version of f that has 15 filled in as > its first argument (λx. λy. x(15,y))), but hasn't read its implementation. Now you got me interested, can you tell me how the DBB syntax solves this problem? Or is it just that your particular implementation solves it? FWIW, phoenix provides everything to introspect the given F and decide which action to take (wrap it into a lambda, "unlambda" it, leave it alone, etc.). One of the main design goals of the phoenix bind module was to be compatible to bind. So unlikely "bind" in its form will be changed. > Don't get me wrong, I think phoenix is an impressive feat. I'm just > advocating that we stop perpetuating the troubles caused by basing new > libraries on the traditional bind syntax. P.S.: I also like the DBB style syntax and think it would be a great addition, as JdG already mentioned, it is all implemented, what's missing is the frontend.

2 1

C++ Standards
by Jarrad Waterloo 19 Sep '11

19 Sep '11

What is the status of and where can one go for current information on TR2, decimal type and modules? Are these dead? Is the C++ standards body taking a 3-10 years siesta before starting on any of these or the next standard? Has there been any recent discussion on "stack trace", reflection, dll(s), overloading -> and other operators. There was a list of items in which there was not enough time to consider for this standard but potential for the next standard. I ask these questions because I found about the link to the C++ standards from the main page of the boost website. However that link has been rather quiet.

2 1

[fusion] boost::fusion::nil bug
by Jeroen Habraken 18 Sep '11

18 Sep '11

Hi, Clang 2.9 just pointed out what's probably an error in fusion in boost-trunk, the same one I ran into during the Conversion review yesterday it seems. Note that GCC doesn't complain even with -Wall -Wextra -pedantic. The error: In file included from fusion.cpp:1: In file included from boost-trunk/boost/fusion/include/vector.hpp:10: In file included from boost-trunk/boost/fusion/container/vector.hpp:11: In file included from boost-trunk/boost/fusion/container/vector/vector10.hpp:15: In file included from boost-trunk/boost/fusion/sequence/intrinsic/begin.hpp:17: In file included from boost-trunk/boost/fusion/sequence/intrinsic/detail/segmented_begin.hpp:11: In file included from boost-trunk/boost/fusion/iterator/segmented_iterator.hpp:13: In file included from boost-trunk/boost/fusion/container/list/cons.hpp:14: In file included from boost-trunk/boost/fusion/sequence/intrinsic/end.hpp:17: boost-trunk/boost/fusion/sequence/intrinsic/detail/segmented_end.hpp:33:70: error: invalid use of incomplete type 'fusion::nil' segmented_end_impl<Sequence, fusion::nil>::call(seq, fusion::nil())); ^~~~~~~~~~~~~ In file included from fusion.cpp:1: In file included from boost-trunk/boost/fusion/include/vector.hpp:10: In file included from boost-trunk/boost/fusion/container/vector.hpp:11: In file included from boost-trunk/boost/fusion/container/vector/vector10.hpp:15: In file included from boost-trunk/boost/fusion/sequence/intrinsic/begin.hpp:17: In file included from boost-trunk/boost/fusion/sequence/intrinsic/detail/segmented_begin.hpp:10: In file included from boost-trunk/boost/fusion/sequence/intrinsic/detail/segmented_begin_impl.hpp:11: boost-trunk/boost/fusion/container/list/cons_fwd.hpp:13:12: note: forward declaration of 'boost::fusion::nil' struct nil; ^ 1 error generated. The code to reproduce the error: #include <boost/fusion/include/vector.hpp> int main(int, char*[]) { return 0; } It seems nil is either only forward-declared or the include with the declaration is missing. Kind regards, Jeroen Habraken

4 6