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Library categories
by Vicente J. Botet Escriba 30 Nov '11

30 Nov '11

Hi, I was wondering if we can add other categories to the library catalog (http://www.boost.org/users/history/version_1_47_0.html) Here is a proposal Best, Vicente Domain Specific crc - Cyclic Redundancy Code, from Daryle Walker. units - Zero-overhead dimensional analysis and unit/quantity manipulation and conversion, from Matthias Schabel and Steven Watanabe. uuid - A universally unique identifier, from Andy Tompkins. Idioms base-from-member - Idiom to initialize a base class with a member, from Daryle Walker. compressed_pair - Empty member optimization, from John Maddock, Howard Hinnant, et al. Language Emulation: these are libraries are emulating a missing language feature exception - A library for transporting of arbitrary data in exception objects, and transporting of exceptions between threads (N2179), from Emil Dotchevski. move - Portable move semantics for C++03 and C++1 compilers, from Ion Gaztañaga scope_exit - Execute arbitrary code at scope exit, from Alexander Nasonov. typeof - Typeof operator emulation, from Arkadiy Vertleyb and Peder Holt. Patterns: libraries that implement a known pattern flyweight - Design pattern to manage large quantities of highly redundant objects, from Joaquín M López Muñoz. signals - managed signals & slots callback implementation, from Doug Gregor. signals2 - managed signals & slots callback implementation (thread-safe version 2), from Frank Mori Hess. State Machines meta state machine - High-performance expressive UML 2.0 finite state machines, from Christophe Henry. statechart - Arbitrarily complex finite state machines can be implemented in easily readable and maintainable C++ code, from Andreas Huber. System: libraries that are close to the underlying system chrono - Useful time utilities, from Howard Hinnant, Beman Dawes, Vicente J. Botet Escribá. date_time - Date-Time library from Jeff Garland. filesystem - Portable paths, iteration over directories, and other useful filesystem operations, from Beman Dawes. system - Operating system support, including the diagnostics support that will be part of the C++0x standard library, from Beman Dawes. I would add also the following to exixting categories Data structures optional - Discriminated-union wrapper for optional values, from Fernando Cacciola. tribool - 3-state boolean type library, from Doug Gregor. I have no suggestion for the following, so we can maintain them in Miscellaneous conversion - Polymorphic and lexical casts, from Dave Abrahams and Kevlin Henney. swap - Enhanced generic swap function, from Joseph Gauterin. timer - Event timer, progress timer, and progress display classes, from Beman Dawes. TR1 - An implementation of the Technical Report on C++ Library Extensions, using other Boost libraries as a basis, from John Maddock. utility - Class noncopyable plus checked_delete(), checked_array_delete(), next(), prior() function templates, plus base-from-member idiom, from Dave Abrahams and others. value_initialized - Wrapper for uniform-syntax value initialization, from Fernando Cacciola, based on the original idea of David Abrahams. The following libraries are already in another category lexical_cast - General literal text conversions, such as an int represented as a string, or vice-versa, from Kevlin Henney. numeric/conversion - Optimized Policy-based Numeric Conversions, from Fernando Cacciola. program_options - Access to configuration data given on command line, in config files and other sources, from Vladimir Prus.

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[rfc] lockfree API/naming suggestions
by Tim Blechmann 30 Nov '11

30 Nov '11

hi all, i am preparing boost.lockfree so that it can be merged to trunk. however i'd request some suggestions, concerning interface and names: ringbuffer naming: there is a fixed-sized single-producer/single-consumer wait-free queue, which is implemented as ringbuffer. the linux kernel uses the name `kfifo', the jack-audio-connection-kit refers to it as `ringbuffer', herlihy/shavit discuss it under the name `BoundedQueue'. the boost.lockfree implementation is currently named `ringbuffer', but i could rename it before merging it into trunk. suggestions: ringbuffer waitfree_queue spsc_queue bounded_queue personally i'd be in favor of `ringbuffer' (because i have been using this name for years) or `spsc_queue' (because it makes clear that it doesn't support multiple produces/consumers). but i'd be curious, what other people suggest. fifo/queue bounded push: fifo and queue can be configured to use a dynamically growing freelist for memory management. in this case, the `push' operations may block if the freelist is exhausted and a new node has to be allocated from the OS. currently this can be avoided by a per-class policy. however it would be reasonable to move this policy from a per-class to a per- call policy. so instead of: queue<T, boost::lockfree::bounded<true> > q; T t; q.push(t); one could write: queue<T> q; T t; q.push_nonblocking(t); however this would imply 3 flavors of `push' * push, which may block during memory allocation * push_unsafe, which is not thread-safe (but faster) * push_nonblocking, which is guaranteed not to hit the memory allocator. so i am not sure, whether this introduces too much complexity into the API. any thoughts/comments? thanks, tim

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installing 1.48 on debian squeeze
by Janek Kozicki 30 Nov '11

30 Nov '11

Hi, does anybody here know some not too complex way to install boost 1.48 on debian squeeze? Preferably using a .deb package. manual install is also acceptable, but in a way where it will not conflict with native installed boost 1.42. looking forward for your help -- Janek Kozicki http://janek.kozicki.pl/ |

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[spirit] scan_keyword: scan an InputIterator for a keyword.
by Vicente J. Botet Escriba 30 Nov '11

30 Nov '11

Hi, for chrono input I'm using a scan_keyword function that adapted from libc++ library (you can find the code in[1]). Next follows the interface: // scan_keyword // Scans [b, e) until a match is found in the basic_strings range // [kb, ke) or until it can be shown that there is no match in [kb, ke). // b will be incremented (visibly), consuming CharT until a match is found // or proved to not exist. A keyword may be "", in which will match anything. // If one keyword is a prefix of another, and the next CharT in the input // might match another keyword, the algorithm will attempt to find the longest // matching keyword. If the longer matching keyword ends up not matching, then // no keyword match is found. If no keyword match is found, ke is returned // and failbit is set in err. // Else an iterator pointing to the matching keyword is found. If more than // one keyword matches, an iterator to the first matching keyword is returned. // If on exit b == e, eofbit is set in err. // Examples: // Keywords: "a", "abb" // If the input is "a", the first keyword matches and eofbit is set. // If the input is "abc", no match is found and "ab" are consumed. template <class InputIterator, class ForwardIterator> ForwardIterator scan_keyword(InputIterator& b, InputIterator e, ForwardIterator kb, ForwardIterator ke, std::ios_base::iostate& err ); What is the better way to do that (or something similar) with Spirit/Lexer? Can we hope that the Spirit solution could perform much better? What about if the strings to parse are know at compile-time? [1] https://svn.boost.org/svn/boost/trunk/boost/chrono/detail/scan_keyword.hpp Best, Vicente

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temp_ptr<> - preventing use as a member
by Gottlob Frege 29 Nov '11

29 Nov '11

I'm trying to see if I can replace all raw pointers with suitable smart pointers that clearly describe the pointer's lifetime, sharing, etc. For example, a pointer passed into a function, that is only valid for the lifetime of the function call. A temp_ptr or callstack_ptr or ... some better name. So this pointer would need a copy constructor so it can be passed along into a function (I don't think requiring a ref to the pointer would be good; I'd rather pass by value). It would also need construction from a raw pointer, but to avoid having a temp_ptr being kept beyond the function call, it would not have assignment (from another temp_ptr). To prevent constructing one via the copy constructor that will be kept around, I can define a custom new operator but keep it private. The only thing, I think, that I can't prevent, is construction of a new wrapper struct that has a temp_ptr as a member (which is copy constructed in wrapper's constructor). Can anyone think of a way to prevent that? I think anyone that goes out of their way to make a wrapper struct gets what they deserve, so I don't really *need* to prevent all bad uses. But I can aslo imagine someone just using it improperly inside their class due to misunderstanding or whatever. And thoughts on the goal of specific smart pointers for all occasions? Tony

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[trac] please add component
by Akira Takahashi 29 Nov '11

29 Nov '11

Hi, I seems to so that the 1.48.0 library component is not registered in Trac(container, move, and locale). Please add component.

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[optional] std::tr2::optional
by Andrzej Krzemienski 29 Nov '11

29 Nov '11

Hi, I use boost::optional quite often, find it very useful, and cannot imagine that it could not get into TR2. I am considering writing a proposal for adding it myself (if it is possible to propose things without attending the committee meetings), but I would first want to know how boost::optional could be improved given the new features in C++11. I provide a list of modifications that I could think of. What is your opinion? * Conversion explicit conversion to bool should be declared as explicit. * Should exception safety guarantees for assignment operations be enforced? In boost::optional they only provide a basic guarantee. One option is to provide strong guarantee for types T which implement operator= with strong guarantee, and give basic guarantee for other cases Other option (not sure if it is possible) is to provide strong guarantee for all cases at the cost of run-time performance (heap allocation). * Add move operations optional<T> & operator=( optional<T> && ) noexcept( nothrow_move_constructible<T>::value ); optional<T> & operator=( T && ) noexcept( nothrow_move_constructible<T>::value ); * move operations for optional references? But I am not sure what optional references are for... * What are optional references for anyway? * it could add an rvalue reference overload for stored object access: T&& operator*( ) && However using this overload implies that the user is not checking if an optional has been initialized, so it may encourage a bad practice. * Are in-place factories necessary if we have perfect forwarding? Instead, we can provide a reset function and a "variadic constructor": template< typename ... Args > void reset( Args&& ...args ); template< typename ... Args > optional( Args&& ...args ); The constructor will clash with another optional constructor: optional<T>::optional( bool cond, const T& val ); but perhaps it is not needed if we have std::optional<T> std::make_optional( bool cond,const T& val ); and move construction of optionals? * noexcept default construction and destroy operations * constexpr default ctor * Use nullptr instead of boost::none? - this will make some uses of optional pointers harder, but will make usage more clear in other cases. Regards, &rzej

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Proposed Boost.Algorithms Review Ends
by Dave Abrahams 28 Nov '11

28 Nov '11

The review of Marshall Clow's proposed Boost.Algorithms submission officially ended yesterday, but if you get your review in before the end of the weekend, as review manager I'll probably consider it. So far we've had five votes, which is reasonable for something of this scale. Thanks everybody for your time and interest. I'll be posting the review results next week. Regards, Dave -- Dave Abrahams BoostPro Computing http://www.boostpro.com

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[msm] guard behavior if guard guards the transition MSM threats event as handled is that correct?
by Michael.Herchel＠rohde-schwarz.com 28 Nov '11

28 Nov '11

Hi Christophe, Regarding our compile-time problem in the past and therefore, the changes Richard made: Would it be also feasible to develop an additional backend that is derived from the MSM one, but only implements the process_event() method for each event and not in a generic template-based way? With this approach we could still use MSM out-of-box and not having the need for internal transition tables or having references from inner to outer state machines etc but still gain small compiler units. I understand that we will loose flexibility and creating new state machines becomes more work, but I think we could live with that. What is your opinion? Am I thinking too short? Thanks, Michael

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Fwd: [msm] guard behavior if guard guards the transition MSM threats event as handled is that correct ?
by Richard Szabo 28 Nov '11

28 Nov '11

Hi Christophe the attached example I think shows 2 problems. 1st is that the deferral of event3 is not happening. 2nd is that the no_transition function is never called. the output of the run is : MS1 Entering State: Idle by: event1 MS1 Leaving State: Idle by: event1 MS1 Entering State: SubRunning by: event1 FwdGuard: returns:1, event: event2 Processing BaseEvent Instance(event2) Setting guard false FwdGuard: returns:0, event: event3 FwdGuard: returns:0, event: event4 FwdGuard: returns:0, event: event5 MS1 Leaving State: SubRunning by: event5 MS1 Entering State: AfterSub by: event5 I think it shall be : MS1 Entering State: Idle by: event1 MS1 Leaving State: Idle by: event1 MS1 Entering State: SubRunning by: event1 FwdGuard: returns:1, event: event2 Processing BaseEvent Instance(event2) Setting guard false FwdGuard: returns:0, event: event3 FwdGuard: returns:0, event: event4 MS1 no_transition event (event4) MS1 Leaving State: SubRunning by: event5 MS1 Entering State: AfterSub by: event5 MS1 no_transition event (event3) So in this example event3 and event4 are never triggered a transition ... the Row < SubRunning , baseEvent , none , ProcessBaseEvent , FwdGuard > was guarded by the FwdGuard for these events. Is my expected behavior wrong ? If guard is executed but the transition actually is triggered because it is guarded out why this event treated as handled event ?. This 2 problems breaks my current nested state machine implementation because I'm using no_transition to forward the event to the outer state machine. I'm confused :(. Cheers Richie

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