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[array] array_cast helper function
by herve martin 15 Mar '09

15 Mar '09

Hi, I would present here a new helper function which could take place in the boost array package since it is related to C-array. the array_cast() function aims at making cast into C array more friendly than when using the esoteric syntax T(&)[N]. It can help also to check some consistency in size between original type and resulting C array. For some reason reference on C array is almost never used by developers even if a reference on C array encapsulates more information than just a pointer on the 1st element. A striking example is that the dynamic allocation of an array using the new syntax returns a pointer on first element ( int *ptr = new int[10]; ) although I would expect getting a pointer on an array ( int (*ptr)[10] = new int[10]; - this syntax fails but is more conform to what we could expect, even if I must admit that the second syntax is not really intuitive -). array_cast() could make reference on C array more common. The main benefit of array reference is that the size information of the array is encapsulated in the reference type. In the previous 'new' example, when writing { int *ptr = new int[10]; } we have to keep track of the array size by some other way which is not really smart (#define for example). array_cast() use will allow the following syntax: { int (&carray)[10] = array_cast<int>( *new int[10] ); } which is equivalent to: { int (&carray)[10] = *(int(*)[10]) new int[10] ); } Size of the C array can be retrieved just with operation sizeof(carray) In working with array reference rather than with pointer on element array we could imagine some generic algorithm whose implementation could be optimized according to the array size. array_cast() profits also from boost::math::static_gcd function and checks consistency between sizes. for example the following code will raise a static assert since type sizes are not consistent. {{{ struct { char d1; char d2; char d3; } toto; long (&carray)[1] = array_cast<long>( toto ); }}} Indeed, sizeof( toto ) is rarely equal to sizeof( long[1] ). 3 main functions are defined for array_cast(): array<T,N>( INPUT& data) array<T>( INPUT& data) array<N>( INPUT& data) and its derivatives for const, volatile and const volatile lvalues. for more details, take a look at the source code array_cast.hpp<http://www.boostpro.com/vault/index.php?action=downloadfile&filename=array_…>in the boost vault repository and let me know if there is any interest to include it in boost::array. thanks, herve

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Re: [boost] [Boost-users] Maintenace Guidelines wiki page
by vicente.botet 15 Mar '09

15 Mar '09

----- Original Message ----- From: "Tomas Puverle" <Tomas.Puverle(a)morganstanley.com> To: <boost-users(a)lists.boost.org> Sent: Sunday, November 23, 2008 4:31 AM Subject: Re: [Boost-users] Maintenace Guidelines wiki page > >> I have started the Maintenace Guidelines wiki page. >> >> You can access it directly >> https://svn.boost.org/trac/boost/wiki/Guidelines/MaintenanceGuidelines >> >> or via https://svn.boost.org/trac/boost/wiki >> >> Guidelines >> * Maintenance Guidelines >> >> There page need to be completed and surely reworked but this is an starting >> point. >> >> Please be free to improve the page directly or post your comments or > suggestions to this list. >> >> Hopping this goes on the right direction, > > Vincente, > > A few ideas: How will you evaluate that your proposal is actually successful > and being followed by the boost developers? Hi, First this is proposal for guidelines. So people will be after all free to follow some of them or not. I'm expecting from people like you to improve it so it could be followed by more people. > Also, check out Daniel Walker's idea in the Boost.Range thread on boost.devel > about not having the engineers in charge of their own QA. Daniel Walker's idea " Perhaps a procedural solution that could avert this problem in the future is to quarantine the test cases. Authors can maintain commit privileges to their libraries on trunk, but only a select group of independent guardians have commit privileges to the test cases. That way there is a guarantee that libraries pass the same tests from one release to another. If an author would like to make a change that would break a test case, he or she would need to present the change to the list and submit a patch to the test case sentinels. This would be a fairly simple quality assurance protocol: engineers aren't allowed to do their own QA." This is already considered on the guidelines insome way. "Preserve the test from the preceding versions [author] The test from the preceding versions should not be changed when the author modifies its library. These not changed tests are a probe of compatibility with the preceding version. When these test must be changed they indicate a breaking user code issue. So instead of changing them add new ones stating explicitly on which version they were included. Old tests that should fail can be moved to the compile_fail or run_fail tests on the Jamfile. " The Daniel proposal implies some changes in the writing rights of the authors. I prefer to let this point out of these guidelines. Of course I think that this is a good idea. There is another guideline that could be used by the Boost comunity to check the author has not changed the old test cases. "Inspect announced modifications [author, user, RM] The use of the diff file will help to inspect that the modifications introduced have been correctly included on the documentation and a good test coverage has been done. This will result in a non official mini-review of the library. " I will add to check that the old testcases have not been changed. > Finally, please consider the idea of "core" and "new" release cycles, where the > components in "core" have much more stringent requirements on how and when they > are allowed to change. IMO this is out of the scope of the guidelines. Note that at the end it is up to the author to make the modification he/she consider pertinent. Could you send what you have in mind in the form of guidelines? > Finally, do you think it may have been better to start this thread on > boost.devel? I belived that i did it on both. I'm answering to both each time. Should I start a new thread including the guidelines contents? Vicente

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Boost Lite Version
by Jean-Sebastien Stoezel 14 Mar '09

14 Mar '09

Hi, I have been using Boot for desktop applications and I'm very happy with it. It allows me to write portable and reusable code on all the platforms I've been supporting. I also develop C++ applications for small embedded devices, that have very limited ROM and RAM capabilities (several hundreds of kilo bytes of ROM and dozens of kilobytes of RAM). The Boost libraries cannot be used as is for these devices, since the OSes (RTOS I should say) that run on these devices are not supported by Boost. Then my code for these devices is not as portable and reusable as I which it would be. I've developed my own accross-platform generic interface for these devices and it's starting to look like Boost... Except it's not Boost and it's still very proprietary, in the niche sense. I am very interested in having a (real) lite version of Boost for these embedded devices, even if it only consists of stub functions. Is there already an on going effort to do this? Again, the idea is a lite version, something that would fit in less than 30% of the memory of a microcontroller. Jean-Sebastien

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[math] calculate derivative automatically.
by Dongfei Yin 14 Mar '09

14 Mar '09

Hi Bruno, > But I can help you if you want of course.I think the first step for you would be to > learn about Boost.Proto as it's really the tool needed for that. Learn > how to search/replace patterns in an expression. Thank your for your guidance, I am really appreciate your help. I am now going to learn about Boost.Proto. If I have some problem, we can talk about it. Dongfei.

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[geometry] area, length, centroid, behavior
by Barend Gehrels 13 Mar '09

13 Mar '09

I would like to hear the opinion of potential geometry users on the list about the following. For the three geometries, point, linestring (= sequence of points), polygon: What should the generic "area" algorithm return for point and linestring? - 0 (zero) - compiler error (so this function is not defined for them at all) - exception Personally I would feel for 0 (zero) because you can then request the "area" in a generic collection, regardless of what is inside. What should the generic "length" algorithm return for polygon? - 0 (zero) - its perimeter - compiler error - exception What should the generic "centroid" algorithm return for point and linestring? - the point / the average its points - compiler error - exception and for an invalid polygon (e.g. no points at all, or not closed)? - exception - return "false" (if centroid is passed as a reference parameter) - ? (we've not always the compiler error option here because points are usually stored in a runtime collection) Thanks, Barend

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is_virtual_base_of ?
by Robert Ramey 13 Mar '09

13 Mar '09

Is there an implementation of the type trait is_virtual_base_of<D, B> anywhere? If not is there a way to make such a thing? Robert Ramey

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Preview 4 of the Generic Geometry Library (ggl)
by Barend Gehrels 13 Mar '09

13 Mar '09

Dear list, It is a pleasure for us to present the fourth preview of the Generic Geometry Library. This time we've added the library to the SVN repository at boost, https://svn.boost.org/svn/boost/sandbox/ggl To store the library under a proper name, "ggl" is used, which stands for Generic Geometry Library. Before this we called it just Geometry Library, but we think Generic is appropriate from this version on. The first three previews were sent to this list in January, March and October 2008. Since then everything has been revised and reworked again, based on comments from the list. Thanks for all your comments! Concepts are now applied for all geometries. Algorithms now take any geometry fulfilling the concepts, and automatically take the right version of the underlying implementation. Ranges are now used instead of .begin()/end(). Tag dispatching is used instead of SFINAE. Transformations: previously these were just explained as an example, now transformations are included in the library, either to go from one coordinate system to another (for example from spherical to cartesian3D) or to translate/rotate/scale/map points from one Cartesian system to another, or otherwise. Map projections: included is an extensive addition with nearly 100 map projections. Those are not programmed by ourselves but automatically converted from C (PROJ4) into a our template-based approach, fitting with the geometry library, especially in the transformations explained above. License-wise this is possible. We're not sure about if this would fit in the Boost Library Collection, if there is interest in it, or that it might be "too much" for it, so we would be glad to hear your opinions. For more change descriptions, see the page on status and preview from the documentation (link below). The Generic Geometry Library is accessible from Boost SVN, mentioned above, or can be downloaded as well from http://geometrylibrary.geodan.nl Especially the examples, such as the custom point example and custom line string example show nicely how the library handles custom geometries and how they can be used inside the generic algorithms. We welcome any type of comment, opinion, cooperation, merge or join. Barend Gehrels, Amsterdam Bruno Lalande, Paris

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GSoC 2009 Status
by troy d. straszheim 13 Mar '09

13 Mar '09

All- Our application to be a mentoring organization for the fourth year is in, I'm idling on the gsoc channel and watching things develop. We'll know soon if boost is accepted again this year, and at that time we'll be able to start getting our mentors into the system. Meanwhile there is a (currently empty) wiki page for project ideas: https://svn.boost.org/trac/boost/wiki/soc2009 Please feel free to post your gsoc ideas there. I believe there will be a stage soon where students will see that we are a potential mentoring organization and will peruse this list, looking for things that interest them... so have at it. -t

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[accumulator] reset?
by Neal Becker 13 Mar '09

13 Mar '09

I don't suppose accumulators implement a reset?

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[math] calculate derivative automatically.
by Dongfei Yin 13 Mar '09

13 Mar '09

> I personally signaled my interest for something much more general than > only derivatives. But as Dongfei's goal seems to be focused in that > direction Hi Bruno, Actually, I do interesting in simplifying, not only derivative. If you have good idea, we can work it out together if you don't mind. Some times, a expression is simply for computer but not for human. compromising is always needed, and it is hard to make a choice. But as you said, just for compile-time integral value, things become easier. Like the volume of hypersphere, when N = 2, after simplified, computation will be reduced a lot. Dongfei.

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