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RE: [Boost-Users] A strange question-)
by Aleksey Gurtovoy 13 Nov '02

13 Nov '02

Sam Gentile wrote: > I went there and indeed it can't get any simpler - at least > in theory-) > Read the document > C:\Boost\boost_1_29_0\libs\type_traits\c++_type_traits.htm > and its quite > simple: > > template <typename T> > struct is_void > { static const bool value = false; }; > > template <> > struct is_void<void> > { static const bool value = true; }; > > That's exactly what I want to show. So I go to the header files and > instead: > > //* is a type T void - is_void<T> > > BOOST_TT_AUX_BOOL_TRAIT_DEF1(is_void,T,false) > > BOOST_TT_AUX_BOOL_TRAIT_SPEC1(is_void,void,true) > > > > Huh? So I look in bool_trait_def.hpp: > > #define BOOST_TT_AUX_BOOL_TRAIT_DEF1(trait,T,C) \ > > template< typename T > struct trait \ > > : mpl::bool_c< C > \ > > { \ > > BOOST_TT_AUX_BOOL_TRAIT_VALUE_DECL(C) \ > > BOOST_MPL_AUX_LAMBDA_SUPPORT(1,trait,(T)) \ > > }; \ Well, the original code doesn't have all these excessive newlines ;), but yes, basically that's how it's implemented. > Argh! Why is it done like this? This makes it much more > complicated and unreadable than it has to be. Why are macros > being used everywhere? Practical engineering matters. If you consider that the fact that there are ~60 trait templates in the library and every time when a new version of a compiler comes out, or when somebody starts porting the library to a new platform, there is a chance that you need to change half of those definitions, from, for instance, template <typename T> struct is_void : mpl::bool_c<false> { }; to template <typename T> struct is_void { BOOST_STATIC_CONSTANT(bool, value = false); typedef mpl::bool_c<value> type; }; it might all make sense, after all :). Something along the lines of both of the above scenarios has actually happened, a couple of times. It's not the whole picture yet, but IMO it's enough of the motivation already, so I won't go too deep into details :). Hope this answers your question, Aleksey

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1.29.1 release timeframe?
by Johan Nilsson 13 Nov '02

13 Nov '02

As the topic says. I do realize that there can be no absolute dates specified, I'd just like to get a hint on whether it's something within the matter of weeks, months or whatever. Thanks // Johan

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RE: [Boost-Users] Q: Boost Python / weave / swig
by Aleksey Gurtovoy 13 Nov '02

13 Nov '02

Claudius Schnörr wrote: > I would like to build a python-interface for a C++-template library I > wrote. > > After looking around a bit, besides Boost-python I found swig > and weave, which seem to have a similar purpose in mind!?! > > I would appreciate it if someone could provide some comparing > hints/links/information about these various solutions (I'm new to all > these packages). > How do they differ in terms of > - the learning curve, > - their capabilities and > - their foci ? > Have you seen this one - http://www.boost.org/libs/python/doc/comparisons.html? It's more than 1 year old, though, so things might have changed since then. In general, it's better to ask Boost.Python-related questions here - http://mail.python.org/mailman/listinfo/c++-sig. For one, you are much likely to get a quicker response :). Aleksey

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Can not gunzip bjam.exe.gz
by Mike Wilson 13 Nov '02

13 Nov '02

Hi, In Cygwin (version 2.125.2.10) I've tried to $ gunzip bjam.exe but get gunzip: bjam.exe.gz: not in gzip format (downloaded http://boost.sourceforge.net/jam-executables/bin.cygwinx86/bjam.exe.gz which was 143,050 bytes in size (x3 tries) ) My WinZip (V8.1) can't read it either. In fact I can't seem to read several of the .gz files that can be downloaded (but I did manage the Windows .zip version). Can anybody give me a clue as to what is wrong ? Mike Wilson

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Erasing an element in shared_ptr
by cadiolis 12 Nov '02

12 Nov '02

I know that the destructor of shared_ptr will call delete for its contents, but what about erasing a member using the standard erase() function in vector?

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RE: [Boost-Users] set thread priority
by Mark Storer 12 Nov '02

12 Nov '02

I'd think a relatively simple implementation would be to simply support them when possible, and otherwise turn all such calls into no-ops. Coming up with a range of priority values that would be portable shouldn't be too terribly difficult either. --Mark Storer Software Engineer Cardiff Software #include <disclaimer> typedef std::disclaimer<Cardiff> Discard;

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using ublas to solve linear systems?
by deane_yang 12 Nov '02

12 Nov '02

I'm trying to see if I can use ublas to solve a linear system of equations. Digging through the documentation, I find a description of a function called 'solve" that says "Solves a linear equation for a triangular matrix." There is also a formula, B = solve(A, B, tag) <------> B <- A-1 B But I just don't know what any of this means (even though I am a mathematician and quite fluent in linear algebra). So a) can ublas be used (without me implementing any additional algorithms) to solve a linear system of equations? b) what exactly does the function solve do?

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RE: [Boost-Users] BUG: counted_base::release
by Per Kristensen 12 Nov '02

12 Nov '02

This is a constructed test case which should illustrate the problem. The bug is only a problem if you access data members of the counted_based object after the call to delete. So you can live happy without knowing anything about the bug if you never do that. //sourcecode begin #include "boost/shared_ptr.hpp" #include "boost/weak_ptr.hpp" class foo { public: void setWeak(boost::shared_ptr<foo> s) { w = s; } private: boost::weak_ptr<foo> w; //the desctuction of this member will delete the counted_based object }; class deleter { public: deleter() :lock(0) {} ~deleter() { assert(lock==0); //assert if destructor is called when we are executing } void operator() (foo *p) { ++lock; //lock the object from destruction within this operation delete p; --lock;//unlock the object } private: int lock; }; void main() { boost::shared_ptr<foo> s(new foo,deleter()); s->setWeak(s); s.reset(); } //source code end -----Original Message----- From: Peter Dimov [mailto:pdimov@mmltd.net] Sent: 11. november 2002 21:43 To: Boost-Users(a)yahoogroups.com Subject: Re: [Boost-Users] BUG: counted_base::release From: "perkristensennettest" <per.kristensen(a)nettest.com> > To me it seems like a bug, that the weak_count in > counted_base::release is decremented before the call to dispose. See > below [...] > > If the call to dispose() indirectly calls weak_release there is an > error as weak_release will decrement the --weak_count and may > destruct the counted_base object. This will happen if you have an > class C with a member of type weak_ptr<C>. Do you have a test case that breaks? Info: < http://www.boost.org> Wiki: < http://www.crystalclearsoftware.com/cgi-bin/boost_wiki/wiki.pl> Unsubscribe: <mailto:boost-users-unsubscribe@yahoogroups.com> Your use of Yahoo! Groups is subject to the Yahoo! Terms of Service <http://docs.yahoo.com/info/terms/> . [Non-text portions of this message have been removed]

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uBLAS Matrix Multiplication
by Hickman, Greg 12 Nov '02

12 Nov '02

Why isn't there an overloaded matrix_expression operator* (const matrix_expression&, const matrix_expression&); for peforming matrix multiplication? Greg Hickman

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compose function objects
by daniel szymanski 11 Nov '02

11 Nov '02

hi, i've a question regarding the compose function objects. i was wondering if there is something like compose_f_x_gy etc? i know there's only the compose_f_gx_hy function object. but then i would need g(x) = x, so my question: is there another way to get the same result like using g(x) = x or writing a compose_f_x_gx? thanks, daniel

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