July 2012 - Boost - lists.boost.org

C++11 decltype/SFINAE puzzler
by Eric Niebler 13 Aug '12

13 Aug '12

I'm running into a usability problem with the extended SFINAE rules that could effect best practice for all new C++ libraries. I'm hoping some clever person in the Boost community can help me. I find that in highly generic code, using decltype to define the return type of functions is very handy. Dave A. suggested a RETURNS macro to simplify this idiom: <https://groups.google.com/d/msg/boost-devel-archive/OzJ5Ft3pSnU/b_Ter9bgNqAJ> It's used like this: template<typename T> auto foo( T && t ) RETURNS( some-expression-using-t ); This is great and I use it a lot. Now, imagine you have a library of such functions calling other such functions: function A calls B calls ... calls Y, calls Z, all of which use decltype to declare their return types. Now, the user calls A passing a variable t for which the expression in Z's return type calculation makes no sense. Extended SFINAE kicks in, and Z simply disappears. Since Z has disappeared, the expression in Y's return type makes no sense, so Y disappears, too. And so on up the chain. The end result is that the user is presented with an error like: "no viable function A, template substitution failed." The user is given no information about which function in the chain failed to compile, or why. This is a serious usability problem! So, my question is: what can be done about this? Can we get the benefit of automatic type deduction in return types without causing SFINAE to drop functions from the overload set? Is there another trick we can use to report errors meaningfully when APIs are misused? The only solution I can think of is turn all the free functions in the chain into function objects and then using std::result_of to compute return types for them instead of using decltype directly. That means Dave's (very convenient!) RETURNS macro shouldn't be used, which is a bummer. (I think it also means that we need a noexcept_of template that computes the noexcept of an expression without causing the expression to appear in the function declaration, but that depends on how <http://llvm.org/bugs/show_bug.cgi?id=13286> gets resolved.) All suggestions welcome, -- Eric Niebler BoostPro Computing http://www.boostpro.com

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[graph] interest in resumable dijkstra?
by Alex Hagen-Zanker 13 Aug '12

13 Aug '12

Dear boost-list, I placed the BGL algorithm of the dijkstra_shortest_path in a class, with the creation and initialization part separate from the main algorithm. This allows interrupting, resetting and resuming the algorithm. Would this be of interest to anybody? The following function call: dijkstra_shortest_path(graph, orig, parameter_pack); is separated into: auto dijkstra = make_dijkstra(graph, parameter_pack); dijkstra.init_from_origin(orig /*, optional_visitor*/); dijkstra.expand(/*optional_visitor*/); The make_dijkstra() function reads all parameters from the parameter_pack including color_map and priority_queue Visitors interrupt the calculation using a do_intterrupt() callback instead of throwing an exception. The function expand() can be called repeatedly, each time with another visitor. The implementation requires C++11, because of auto and lambda's, it also relies on the following patch: https://svn.boost.org/trac/boost/ticket/7130. To see for yourself: http://people.pwf.cam.ac.uk/ahh34/dijkstra_test.zip I am interested to hear your opinion. With kind regards, Alex

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[1.51][Wave] Last minute commit
by Hartmut Kaiser 07 Aug '12

07 Aug '12

Hey, I would like to ask for permission to commit rev 79783 to the release branch (see attached patch). This fixes a bug introduced only recently and will fix the current regressions (see here: http://tinyurl.com/c44ql68, for instance). The patch is for Wave only and does not touch any of the other Boost libraries. Regards Hartmut --------------- http://boost-spirit.com http://stellar.cct.lsu.edu

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[review] Multiprecision review (June 8th - 17th, 2012)
by Jeffrey Lee Hellrung, Jr. 07 Aug '12

07 Aug '12

Okay, it's that time. Apologies for not sending a reminder, but there had been a lot of pre-review comments over the last week or so, so I think this has been on at least some people's radar. The original review announcement is given below. On Tue, May 29, 2012 at 2:08 PM, Jeffrey Lee Hellrung, Jr. < jeffrey.hellrung(a)gmail.com> wrote: > Hi all, > > The review of the proposed Boost.Multiprecision library authored by John > Maddock and Christopher Kormanyos has been scheduled for > > June 8th - June 17th, 2012 > > and will be managed by myself. > > From the Introduction: > > -------- > "The Multiprecision Library provides *User-defined* integer, rational and > floating-point C++ types which try to emulate as closely as practicable the > C++ built-in types, but provide for more range and precision. Depending > upon the number type, precision may be arbitrarily large (limited only by > available memory), fixed at compile time values, for example 50 decimal > digits, or a variable controlled at run-time by member functions. The types > are expression-template-enabled for better performance than naive > user-defined types." > -------- > > And from the original formal review request from John: > > -------- > Features: > > * Expression template enabled front end. > * Support for Integer, Rational and Floating Point types. > > Supported Integer backends: > > * GMP. > * Libtommath. > * cpp_int. > > cpp_int is an all C++ Boost licensed backend, supports both arbitrary > precision types (with Allocator support), and signed and unsigned fixed > precision types (with no memory allocation). > > There are also some integer specific functions - for Miller Rabin testing, > bit fiddling, random numbers. Plus interoperability with Boost.Rational > (though that loses the expression template frontend). > > Supported Rational Backends: > > * GMP > * libtommath > * cpp_int (as above) > > Supported Floating point backends: > > * GMP > * MPFR > * cpp_dec_float > > cpp_dec_float is an all C++ Boost licensed type, adapted from Christopher > Kormanyos' e_float code (published in TOMS last year). > > All the floating point types, have full std lib support (cos sin exp, pow > etc), as well as full interoperability with Boost.Math. > > There's nothing in principal to prevent extension to complex numbers and > interval arithmetic types (plus any other number types I've forgotten!), > but I've run out of energy for now ;-) > > Code is in the sandbox under /big_number/. > > Docs can be viewed online here: > http://svn.boost.org/svn/boost/sandbox/big_number/libs/multiprecision/doc/h… > -------- > Any review discussion should take place on the developers' list ( boost(a)lists.boost.org) and anyone may submit a formal review, either publicly to the entire list or privately to just myself. As usual, please consider the following questions in your formal review: 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, most importantly, please explicitly answer the following question: Do you think the library should be accepted as a Boost library? Lastly, please consider that John and Christopher have compiled a TODO list [1] based on pre-review comments. Feel free to comment on the priority and necessity of such TODO items, and whether any might be show-stoppers or warrant conditional acceptance of the library. Thanks in advance; looking forward to the discussion! - Jeff (& John & Christopher) [1] http://svn.boost.org/svn/boost/sandbox/big_number/libs/multiprecision/doc/h…

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[type_erasure] Review started (July 18-27, 2012)
by Lorenzo Caminiti 06 Aug '12

06 Aug '12

Hello all, *** The review of Steven Watanabe's proposed Boost.TypeErasure library begins on July 18, 2012 and ends on July 27, 2012. *** THE LIBRARY C++ provides runtime polymorphism through virtual functions. They are a very useful feature, but they do have some limitations. * They are intrusive. In generic programming, we can design an interface which allows third-party types to be adapted to it. * They require dynamic memory management. Of course, most of the problems can be avoided by using an appropriate smart pointer type. Even so, it still acts like a pointer rather than a value. * Virtual functions' ability to apply multiple independent concepts to a single object is limited. The Boost.TypeErasure library solves these problems allowing us to mirror static generic programming at runtime. Library source: http://svn.boost.org/svn/boost/sandbox/type_erasure/ Pre-built documentation: http://steven_watanabe.users.sourceforge.net/type_erasure/libs/type_erasure/ You can also download archives with pre-built documentation from: http://sourceforge.net/projects/steven-watanabe.u/files/ YOUR REVIEW Please submit a review to the mailing-list by replying to this email ("[boost] [type_erasure] Review ..." should be in the subject). Please state clearly whether you think this library should be accepted as a Boost library. Other questions you may want to consider: 1. What is your evaluation of the design? 2. What is your evaluation of the implementation? 3. What is your evaluation of the documentation? 4. What is your evaluation of the potential usefulness of the library? 5. Did you try to use the library? With what compiler? Did you have any problems? 6. How much effort did you put into your evaluation? A glance? A quick reading? In-depth study? 7. Are you knowledgeable about the problem domain? Thanks in advance to all who participate in the review discussion -- I'm looking forward to it! The review manager. --Lorenzo

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Formal review request: TypeIndex library
by Antony Polukhin 05 Aug '12

05 Aug '12

Hi, I'd like to ask to add Boost.TypeIndex to review queue. Introduction TypeIndex is an extended C++11 type_index library, that * works with disabled RTTI * can store const-volatile-reference info about types (if user requested it) * has all the functionality of std::type_index * has portable across compilers and platforms functionality for getting demangled type names * works across modules/shared libraries * does not require C++11 to work Docs: http://apolukhin.github.com/type_index/index.html Git: https://github.com/apolukhin/type_index Sources (zipped): https://github.com/apolukhin/type_index/zipball/master Git contains `patched` folder with TypeIndex'ed (and untested) versions of some existing boost libraries (Boost.Any, Boost.Graph, Boost.Math, Boost.MSM, Boost.PropertyMap, Boost.PropertyTree). Those libraries now do not require RTTI to compile. More libraries could be added to this list. Previous threads (checking interest): * Is there interest in typeid(TYPE).name() like function that does not require RTTI http://lists.boost.org/Archives/boost/2012/05/193491.php * [boost] Is there interest in copyable type_info that does not require RTTI (was: Is there interest in typeid(TYPE).name() like function that does not require RTTI) http://lists.boost.org/Archives/boost/2012/05/193519.php * [boost] [type_index] C++03 implementation in boost? http://lists.boost.org/Archives/boost/2012/07/194627.php P.S.: Additional thanks to Agustín K-ballo Bergé for pointing out and fixing some bugs. P.P.S.: It would be great to schedule review to the end of September. -- Best regards, Antony Polukhin

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[rational] with optional over/underflow checking
by Dan Searles 04 Aug '12

04 Aug '12

Hello, Would there be any interest in a modified "rational" class template/header that optionally allows for an exception be generated if there is under/overflow during any of the operations? I have been developing such a template, where the new defaulted bool template parameter would generate the class exactly as before to preserve the original stable implementation, and to support unlimited-precision integer where over/underflow would not be possible. Setting the new template parameter to true, however would generate code that adds the over/underflow checking. I have also generated new test driver code (BTW test code referenced by the documentation does not appear to exist, or at least the link is broken). rational.hpp has been around and stable for quite some time, so there may be a desire to keep it unchanged, but its original function (and indeed its original source code) can be maintained through the template system. If such a class were to be included in boost, what would be the best submission method?

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Announce: Boost 1.50 installer for 32-bit Windows now available
by John Wiegley 02 Aug '12

02 Aug '12

With apologies to the community for not finding the time to release Windows installers for 1.48 and 1.49, we now have an installer for 1.50 available for immediate download: http://www.boostpro.com/download The version installs 32-bit libraries and/or DLLs for the following compilers: Visual C++ 8.0 (Visual Studio 2005) Visual C++ 9.0 (Visual Studio 2008) Visual C++ 10.0 (Visual Studio 2010) We are dropping support for Visual C++ 7.1 as of this time, unless someone wishes to contract us to bring it back. Also, although I have prepared a 64-bit installer, I have not yet found a solution for integrating it with the existing installer. If anyone with NSIS scripting experience would be willing to assist me, we'd be happy to provide a free installer which installs both 32-bit and 64-bit Boost libraries for applicable Windows platforms. Enjoy! -- John Wiegley BoostPro Computing Software Development Training http://www.boostpro.com Clang/LLVM/EDG Compilers C++ Boost

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[type_erasure] Review ends today July 27, 2012
by Lorenzo Caminiti 01 Aug '12

01 Aug '12

Hello all, On Mon, Jul 23, 2012 at 9:09 AM, Lorenzo Caminiti <lorcaminiti(a)gmail.com> wrote: > On Wed, Jul 18, 2012 at 1:13 AM, Lorenzo Caminiti <lorcaminiti(a)gmail.com> wrote: >> *** The review of Steven Watanabe's proposed Boost.TypeErasure library >> begins on July 18, 2012 and ends on July 27, 2012. *** > > *** Boost.TypeErasure review ends in 5 days. Please submit your reviews :D *** *** Boost.TypeErasure review ends today July 27, 2012. If you are planning to submit a review, please do so as soon as possible. *** Thank you to everyone who has commented on the library and submitted a review so far! The review manager, --Lorenzo P.S. I am considering extending the review until end of day Sunday July 29, 2012... I will keep you posted. > There have been interesting discussions on the library on the ML but I > have not received any official review yet :( Especially if you are a > user of Boost Any, Function, and Any Iterator, you definitely want to > take a look at Type Erasure as it generalizes solutions provided by > those other libraries. > > Thank you. > > The review manager. > --Lorenzo > >> THE LIBRARY >> >> C++ provides runtime polymorphism through virtual functions. They are >> a very useful feature, but they do have some limitations. >> * They are intrusive. In generic programming, we can design an >> interface which allows third-party types to be adapted to it. >> * They require dynamic memory management. Of course, most of the >> problems can be avoided by using an appropriate smart pointer type. >> Even so, it still acts like a pointer rather than a value. >> * Virtual functions' ability to apply multiple independent concepts to >> a single object is limited. >> The Boost.TypeErasure library solves these problems allowing us to >> mirror static generic programming at runtime. >> >> Library source: >> http://svn.boost.org/svn/boost/sandbox/type_erasure/ >> >> Pre-built documentation: >> http://steven_watanabe.users.sourceforge.net/type_erasure/libs/type_erasure/ >> >> You can also download archives with pre-built documentation from: >> http://sourceforge.net/projects/steven-watanabe.u/files/ >> >> YOUR REVIEW >> >> Please submit a review to the mailing-list by replying to this email >> ("[boost] [type_erasure] Review ..." should be in the subject). >> >> Please state clearly whether you think this library should be accepted >> as a Boost library. >> >> Other questions you may want to consider: >> 1. What is your evaluation of the design? >> 2. What is your evaluation of the implementation? >> 3. What is your evaluation of the documentation? >> 4. What is your evaluation of the potential usefulness of the library? >> 5. Did you try to use the library? With what compiler? Did you have >> any problems? >> 6. How much effort did you put into your evaluation? A glance? A >> quick reading? In-depth study? >> 7. Are you knowledgeable about the problem domain? >> >> Thanks in advance to all who participate in the review discussion -- >> I'm looking forward to it!

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Review Request: Endian
by David Stone 01 Aug '12

01 Aug '12

A few months back I posted a proposal for an endian conversion library: http://lists.boost.org/Archives/boost/2012/04/191931.php I believe my library is now in a finished state, and I would like to have it considered for inclusion into Boost. A zip file containing everything can be found here: https://bitbucket.org/davidstone/endian/get/tip.zip or you can just browse the repository here: https://bitbucket.org/davidstone/endian/ The only file that users need to be concerned with is endian.hpp. endian.cpp contains performance + correctness tests, and example.cpp is a very short example program on how to use the library that opens up a file, reads in a number that was written in big-endian format, and prints it to the user's screen in host format. There is no special compiling / linking instructions (people who wish to test the program can simply compile endian.cpp). Included is a SCons script that allows easy compilation with gcc or clang with many warnings + optimizations turned on. My programs all compile cleanly at very high warning levels in these compilers because I know many users compile their own projects at such a setting, and I don't want a library file causing noise. I included the documentation in index.html, but I'm not quite sure on how to correctly format things.

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