January 2009 - Boost - lists.preview.boost.org

Futures - Reviews Needed (January 5, 2009)
by Tom Brinkman 19 Jan '09

19 Jan '09

Futures Join the review and discussion starting January 5, 2009. I need commitments for reviews from threading experts on the two Futures library candidates. Braddock Gaskill - http://braddock.com/~braddock/future Anthony Williams - http://www.justsoftwaresolutions.co.uk/files/n2561_future.hpp Early comments are welcome.

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Lazy list
by Zachary Turner 19 Jan '09

19 Jan '09

It occured to me that boost is lacking a true lazy list. I feel like this should be possible to implement on most compilers, although I doubt I have the metaprogramming expertise to be able to implement such a data structure myself. But nonetheless I think this would be extremely useful. Lazy lists are basically lists that don't store the actual values of the list, instead they store a -function- that is called each time the next element of the list is requested, and the result of that list is returned. Most likely there is a caching mechanism as well, so that accessing recently accessed (or preceding) elements would return a cached value if it had already been accessed. I guess it would not cache arbitrarily large amounts of elements though for memory usage reasons, otherwise it would defeat the whole purpose, which is the ability to expose truly infinite sequences to the user in the form of a list. Has this been considered before, and can anyone think of any technical limitations that would prevent such a class to be written?

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[filesystem] operator == performance
by Konstantin Litvinenko 19 Jan '09

19 Jan '09

Hi! I am developing an application with very intensive boost::filesystem::path usage. At certain moment application start to be slowly and I start profiler. Profiler shows me that std::map<fs:path, ....> is painfully slow due path::operator <() that do lexicographical compare , that do void iterator_helper<Path>::do_increment( iterator & itr ) that is really slow. So I have replaced std::map on boost::unordered_map.. and didn't get expected performance gain. Profiles show me that path::operator <() hit count 200000 and now only 100000. That tooooo much. Further investigation shows that problem was path::operator ==() used in unordered_map. I understand that operator == can be implemented using strict weak ordering concept, but for filesystem::path. Why not implement it as: bool path::operator == (const path& lhs, const path& rhs) const { return lhs.string() == rhs.string(); } ?

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Re: [boost] [SVN Configuration] Request an additional MIME type to support Scalable Vector Graphics (SVG)
by Jeroen N. Witmond 19 Jan '09

19 Jan '09

Peter Foley wrote on 2007-08-23 11:52:25 GMT: > Should I simply update my local configuration file to include the line: > > *.svg = svn:eol-style=native; svn:mime-type=image/svg+xml > > Any advice would be greatly appreciated. With this autoprop set, `svn add` gets into trouble (at least for me) adding a file with extension .svg. I had to change the svn:mime-type to text/svg+xml to get it to work. Regards, Jeroen.

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utility class: lazy data type
by Zachary Turner 19 Jan '09

19 Jan '09

I wrote this class to support lazy evaluation and caching of values. It seems like it would be useful for inclusion as a miscellaneous class in boost. It seems like this pattern occurs pretty often in practice, it's even the fundamental implementation method for singletons, and at least I often have tons of boost::optionals in my code, with get accessors on the classes that check if there's a value, if not call a fetch function, and then return the value. It's cleaner to just call get every single time and not worry about it. I don't consider myself a guru, so suggestions on how to make it better are, of course, appreciated. template<class T> class lazy { public: explicit lazy(function<T ()> fetch) : _fetch(fetch) { } T get() { if (!_cached) _cached = _fetch(); return _cached.get(); } private: optional<T> _cached; function<T ()> _fetch; }; Perhaps such a class is too trivial to be included, but here it is nonetheless.

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[interthreads] Library under development v0.3
by vicente.botet 19 Jan '09

19 Jan '09

Hi, I have add the fork_after function to Boost.InterThreads. The prototype allows to execute asynchronously N functions and execute asynchronously a function that depends on the completion of N functions. bith::shared_launcher ae; BOOST_AUTO(actT, bith::fork_all(ae, fct1, fct2)); BOOST_AUTO(act, bith::fork_after(ae, fct3, actT)); act.wait(); bith::shared_launcher is an asynchronous executor (AE) that executes asynchronously a function on a new thread. bith::fork_all request the AE to execute asynchronously each function. It returns a fusion tuple of the asynchronous completion token (ACT) associated the the ae. bith::fork_after request the AE to execute a function asynchronously once each one of ACTs in the dependency tuple parameter are ready. It is similar to the async_with_dependencies proposed Peter Dimov. I have used for that Boost.Future (Anthony proposal). I've added also some act traits, as value type, is movable, has_future_if, has_thread_if. The library is available at Boost Sandbox: https://svn.boost.org/svn/boost/sandbox/interthreads and Boost Vault: http://www.boostpro.com/vault/index.php?action=downloadfile&filename=intert… Includes every thing on the Sandbox + Html documentation + Boost.Futures + Boost.ThreadPool adaptations I'd appreciate it if people could take a look, test it on their compiler and give me some feedback. Best regrads, Vicente _____________________ Vicente Juan Botet Escribá

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BoostCon'09 Registration Now Open
by David Abrahams 18 Jan '09

18 Jan '09

Greetings, Boosters and former BoostCon attendees The third annual Boost conference (BoostCon), featuring a keynote address by Andrei Alexandrescu, will take place May 3-8 2009 in Aspen, Colorado. The conference is now open for registration! Please go to http://www.boostcon.com/registration and reserve your place at the year's premier C++ event today. -- Dave Abrahams BoostPro Computing http://www.boostpro.com

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Boost Library Authors: BoostCon submission deadline approaching
by Hartmut Kaiser 18 Jan '09

18 Jan '09

Hi all, at last year's BoostCon, one of the highlights was the authors corner track. These were 20-30 minute sessions held by Boost library authors talking about their libraries. Most of the attendees of those sessions found them to be very interesting and useful. At this year's BoostCon we would like to have a similar track again. Unfortunately by now we don't have any related submissions. So I thought I explicitly encourage boost authors who are planning to be in Austin this year to consider giving a 30 minute introductory talk about their libraries. This is not a huge effort in terms of preparation, but adds a lot to the conference. You can find the details about BoostCon and the submission process here: http://www.boostcon.com/program/call-for-sessions. Please spread the word! Regards Hartmut Program Chair

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[uitility/result_of] CodeGear support of result_of
by joaquin＠tid.es 18 Jan '09

18 Jan '09

Hi, Seemingly, CodeGear does not support boost::result_of http://tinyurl.com/8onbjj I propose that this is officially recognized so that including <boost/utility/result_of.hpp> results in BOOST_NO_RESULT_OF being defined rather than the current compile error. This will benefit those result_of-dependent libraries honoring BOOST_NO_RESULT_OF (vg. Boost.Parameter). Joaquín M López Muñoz Telefónica, Investigación y Desarrollo||* *

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[any] Will it be in C++0x?
by Andrey Semashev 17 Jan '09

17 Jan '09

Suddenly, it occurred to me that STL does not provide an instrument for dynamic typed variables (or variants). I didn't see such a tool in TR1 either. So, are there any plans to include such a tool in C++0x? Boost.Any seems to me a very simple, yet very useful example of utility of that kind. It would be great if STL provided a similar instrument out of box.

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