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Re: [boost] [Boost-users] [review][constrained_value] Review of Constrained Value Library begins today
by Mika Heiskanen 25 Dec '08

25 Dec '08

Mathias Gaunard wrote: > Mika Heiskanen wrote: > >> If the value must be checked beforehand, why bother using a constrained >> type at all? > > Because it performs checking in debug mode to make sure the invariant is > indeed true. I do not believe boost should accept a library which would only work in debug mode. I believe boost is mostly about runtime libraries, not about debugging aids. --> Mika Heiskanen

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[shared_ptr] A smarter smart pointer proposal for dynamic libraries
by J.D. Herron 25 Dec '08

25 Dec '08

I have a suggestion for the shared pointer implementation to overcome a severe limitation it has currently regarding dynamically unloaded libraries. I posted a little while back regarding this problem which is illustrated with the following example from a Microsoft Windows environment. I have a simple factory interface like so: class Factory { public: virtual shared_ptr<int> GetIntSharedPtr() = 0; virtual int * GetIntRawPtr() = 0; }; I implement a factory DLL to provide one of these factories that has an exported function GetFactory() like so: /// implementation of the Factory interface class TestFactory : public Factory { public: virtual shared_ptr<int> GetIntSharedPtr() { return shared_ptr<int>( new int(5) ); } virtual int * GetIntRawPtr() { return new int(0); } }; /// Library instance of the factory implementation TestFactory g_Factory; /// Exported function to return the factory for this library _declspec(dllexport) extern "C" Factory & GetFactory() { return g_Factory; } This is compiled into a library named "TestFactory.dll". Now I create a simple command line application that does the following: /// Typedefinition for for the GetFactory exported function typedef Factory & (_cdecl * GetFactory)(); int main() { // dynamically load the TestFactory library HMODULE hFactoryDll = ::LoadLibrary( "TestFactory.dll" ); // get the GetFactory() interface from the loaded library GetFactory pfnGetFactory = ::GetProcAddress( hFactoryDll, "GetFactory" ); // Acquire the factory object Factory & factory = pfnGetFactory(); // Call the factory interfaces to get dynamically allocated integers int * pRawInt = factory.GetIntRawPtr(); shared_ptr<int> spInt = factory.GetIntSharedPtr(); // everything is fine so far, now unload the factory library ::FreeLibrary( hFactoryDll ); // deallocating the raw pointer recieved from the factory works just fine delete pRawInt; // THIS WORKS! // However due to the reasons outlined below, releasing the shared_ptr causes // an access violation spInt.reset() // THIS CRASHES! } The basic problem is that the shared_ptr implementation uses virtual functions in the sp_counted_base class that gets generated in the factory dll since it is a template instantiation and once that factory dll is unloaded the virtual function tables for all shared_ptrs it generated are now garbage. In my opinion the virtual function implementation in the template is an unnecessary design flaw that creates this limitation. I also think the reference counter just simply does too much. I would propose an alternative design that eliminated the use of virtual functions in template generated base classes and let the outer smart pointer class handle the deallocation chores and make the reference counter just a simple reference counter. This could eliminate the limitation illustrated in this simple and very common use case. Ignoring a bunch of stuff right now like custom deallocators, weak references, some basic members like assignment, etc., here is a simple reference counted smart pointer that is able to handle this library unloading example without a problem just as you could do with a raw pointer: /// reference counter THAT ONLY REFERENCE COUNTS AND HAS NO VTABLE class SimpleRefCounter { public: /// Constructor initializes reference count to 0 SimpleRefCounter( long count = 0 ) : m_Count(count) {} /// Increments the reference count and returns it long Increment() { return ::InterlockedIncrement( &m_Count ); } /// Decrements the reference count and returns it long Decrement() { return ::InterlockedDecrement( &m_Count ); } /// Returns the current reference count long Count() const { return m_Count; } private: long m_Count; }; /// Simple smart pointer template that handles the deallocation chores and therefor /// can be used safely across dynamic dll boundaries template < typename _type > class SmarterPtr { public: /// Default constructor creates a null pointer SmarterPtr() : m_pValue( NULL ), m_pRefCounter( NULL ) {} /// Constructor taking an allocated value to manage SmarterPtr( _type * p_pValue ) : m_pValue( p_pValue ) { m_pRefCounter = new SimpleRefCounter( 1 ); } /// Copy constructor SmarterPtr( const SmarterPtr & p_Original ) : m_pValue( p_Original.m_pValue ), m_pRefCounter( p_Original.m_pRefCounter ) { m_pRefCounter->Increment(); } /// Destructor releases ~SmarterPtr() { reset(); } /// Resets the managed pointer to the passed in one releasing the /// currently managed pointer and deallocating if necessary void reset( _type * pNewValue = NULL ) { if ( pNewValue != m_pValue ) { if ( m_pValue && 0 == m_pRefCounter->Decrement() ) { // need to deallocate current value delete m_pValue; delete m_pRefCounter; // ignore weak ref for now m_pValue = NULL; m_pRefCounter = NULL; } if ( pNewValue ) { m_pRefCounter = new SimpleRefCounter( 1 ); m_pValue = pNewValue; } } } private: _type * m_pValue; SimpleRefCounter * m_pRefCounter; }; Again the key is no VTABLE and deallocation handled by the exposed templates. Why shouldn't shared_ptr move to an equivalent model so it can be used across dynamic dll boundaries safely? J.D.

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Is program_options unmaintained?
by Peter Simons 24 Dec '08

24 Dec '08

Hi, a couple of weeks ago, I reported a bug in the program_options library to the author, Vladimir Prus, but received no response. Then I tried reporting the problem on the boost-users mailing list, but didn't receive a response either. Since then, I've seen at least one other poster on the boost-users list wondering about this library, but did not receive a no response either. Does anyone still maintain the program_options library? More generally speaking, what is the procedure if it turns out that a Boost library *is* unmaintained? Take care, Peter

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[test] Floating point comparison update
by Gennadiy Rozental 24 Dec '08

24 Dec '08

Hi, I've checked in 2 changes to the floating point comparison tools. 1. BOOST_CHECK_CLOSE now can compare values of different types: BOOST_CHECK_CLOSE( 2, 2.1, 6 ); // compare and and double BOOST_CHECK_CLOSE( 2.1, 2, 6 ); // compare double and int BOOST_CHECK_CLOSE( 2.1, 2.f, 6 ); // compare double and float 2. Floating point comparison tools now report difference if any: BOOST_CHECK_CLOSE( 2, 2.1, 3 ) will lead to: difference{4.7619%} between 2{2} and 2.1{2.1} exceeds 3% BOOST_CHECK_CLOSE_FRACTION( 2, 2.1, 0.04 ) will lead to: difference{0.047619} between 2{2} and 2.1{2.1} exceeds 0.04 Any comments appreciated, Gennadiy

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Re: [boost] [uuid] Interface
by Vladimir Batov 24 Dec '08

24 Dec '08

It seems I did it again. :--( Just noticed that I misread the following excerpt of Scott's email. Apologies and corrections further below. >> Take, for example, a map<string, uuid>. No default constructor means >> that you can't use operator[], First, my preference is to *have* the default constructor -- we disagree on its behavior as I'd like the default constructor to *be part* of the constructors family (constructing a valid object) and you insist on the default constructor being an exception. The latter is not how the language interprets the default constructor. Therefore, me not happy. IMHO that deviation of the meaning from the letter of the language is unacceptible. Second, even if I cannot use operator[], so what? std::fstream has no default constructor. std::list has no operator[], std::vector has no push_front(). That did not stop anyone from using those classes. What the lack of those "features" achieved instead is that it most likely saved a few people from shooting themselves in a foot. Best, V.

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[asio] overlapped_ptr issue
by Sergei Politov 23 Dec '08

23 Dec '08

Hi, I sent the following letter to asio mail list some time ago: ======================================= I have found the following problem with overlapped_ptr. There is complete method in win_iocp_overlapped_ptr: void complete(const boost::system::error_code& ec, std::size_t bytes_transferred) { if (ptr_) { ptr_->io_service_.post_completion(ptr_, 0, 0); ptr_ = 0; } } As you can see, post_completion does not uses arguments of complete. So it notifies handler with invalid values. ======================================= But I did not receive response from Chris. Where should I submit a ticket? Best Regards, Sergei

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Asio AcceptEx failing with error 121 on Windows with multiple network connections
by Stuart A. Malone 23 Dec '08

23 Dec '08

Hi folks, I'm working with the Boost Asio library from Boost 1.37 on Mac and Windows, and have encountered a problem that only occurs on Windows, and only when the computer has multiple network connections (such as both wired ethernet and WiFi). I started with the "HTTP Server" example code for a simple single- threaded server. I'm running the server on address 0.0.0.0 with port number 0 so that it listens on all network interfaces and allows the OS to select the port number. The server works fine on a Mac with multiple network connections. And on Windows, the default (wired ethernet) connection works fine, too. But if I try to connect to the Windows server over the non-default (WiFi) connection, there is about a 20 second pause and the server exits with error 121, "The semaphore timeout period has expired." I've done some poking around under the debugger, and it appears that the origin of this error is the AcceptEx call in the async_accept<> function in win_iocp_socket_service.hpp, line 2129. While this call does not fail directly since it is an asynchronous call, the error code eventually turns up in the accept_operation::do_completion_impl function in win_iocp_socket_service.hpp, line 1908. I don't really know enough about either Boost Asio or Windows networking to figure out much more on my own. Does anyone have an insight into the source of this problem, or suggestions on how I might go about tracking it down further? Best wishes, --Stuart A. Malone Llamagraphics, Inc. Makers of Life Balance personal coaching software http://www.llamagraphics.com/

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[type_traits] patch for gccxml
by Neal Becker 23 Dec '08

23 Dec '08

Please apply this patch to support current gccxml. The issue is that gccxml will claim to be gcc4.3, but it is really based on gcc4.2, and doesn't support the additional intrinsics (__is_enum, in particular). diff -r 13bbd7c5c6d0 boost/type_traits/intrinsics.hpp --- a/boost/type_traits/intrinsics.hpp Mon Dec 01 07:41:09 2008 -0500 +++ b/boost/type_traits/intrinsics.hpp Tue Dec 23 09:15:32 2008 -0500 @@ -126,7 +126,7 @@ # define BOOST_HAS_TYPE_TRAITS_INTRINSICS #endif -#if defined(__GNUC__) && ((__GNUC__ > 4) || ((__GNUC__ == 4) && (__GNUC_MINOR__ >= 3))) +#if defined(__GNUC__) && ((__GNUC__ > 4) || ((__GNUC__ == 4) && (__GNUC_MINOR__ >= 3) && !defined(__GCCXML__))) # include <boost/type_traits/is_same.hpp> # include <boost/type_traits/is_reference.hpp> # include <boost/type_traits/is_volatile.hpp>

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Tests are a mess
by Gennaro Prota 23 Dec '08

23 Dec '08

Few questions: * BGD-Ubuntu is among tested platforms for release, but not for trunk. How is a poor fellow supposed to test on trunk first? * Same as above for BGD-Windows, with the fellow getting poorer and poorer * Are RW_WinXP_VC and RW_WinXP_VCrtl the same? * Can anyone please have a look at the trunk failures for HP-UX_ia64_aCC? For a bunch of libraries I've looked at it gives an Unsatisfied symbol "boost::exception_detail::refcount_ptr<..." What's that? Compiler bug, misconfiguration, phase of the moon? Sorry, but if this is the status quo I'm just going to merge to branches/release and be done with it. -- Genny

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[unique_ptr] So how is it used differently?
by Sid Sacek 23 Dec '08

23 Dec '08

Thank you, I didn't realize it was already a part of the latest boost library. What I'm curious about is two things... 1) When would I choose unique_ptr<> over auto_ptr<> ? And 2) When would I choose unique_ptr<> over scoped_ptr<> ? Can somebody please provide some coding differences? If these coding examples are already documented someplace, can you please direct me to them? Thank you very much in advance. -Sid Sacek -----Original Message----- From: boost-bounces(a)lists.boost.org [mailto:boost-bounces@lists.boost.org] On Behalf Of OvermindDL1 Sent: Sunday, December 21, 2008 6:01 AM To: boost(a)lists.boost.org Subject: Re: [boost] unique_ptr, was: Composing non copyable and movable classes On Sat, Dec 20, 2008 at 3:10 PM, Sid Sacek <heavyreign(a)optonline.net> wrote: > > I tried to locate the mentioned unique_ptr<> classes for testing, but am > unable to locate them. > > Can somebody point me in the right direction please? This is the only unique_ptr I know of: http://www.boost.org/doc/libs/1_35_0/doc/html/interprocess/interprocess_smar t_ptr.html#interprocess.interprocess_smart_ptr.unique_ptr _______________________________________________ Unsubscribe & other changes: http://lists.boost.org/mailman/listinfo.cgi/boost

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Computer Properties
by Sid Sacek 23 Dec '08

23 Dec '08

Is there a boost library that provides information like: 1) Number of CPU cores ? 2) Total amount of system RAM ? 3) Other system and hardware basics ? Regards, -Sid Sacek

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"thread's copy constructor is inaccessible" BUG in solaris.
by Maruvekere, Praveen (Contractor) 23 Dec '08

23 Dec '08

Hi , I have done the temporary fix to build the boost 1.37.0 as told in one of the solaris user forum thread http://forums.sun.com/thread.jspa?threadID=5326640 <http://forums.sun.com/thread.jspa?threadID=5326640> for the below said error sun.compile.c++ bin.v2/libs/thread/build/sun-5.9/release/link-static/threading-multi/thr ead.o "./boost/thread/detail/thread.hpp", line 344: Error, inaccessible: boost::thread::thread(boost::thread&) is not accessible from boost::move(boost::detail::thread_move_t<boost::thread>). 1 Error(s) detected. Do I need a patch to fix this? -PM-

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[uuid] Interface
by Andy Tompkins 22 Dec '08

22 Dec '08

Here is what I see the interface looking like based on feedback from the review so far. It would, of course, be split into different header files. namespace boost { namespace uuids { class uuid : boost::totally_ordered<uuid> { // no default constructor private: uuid(); public: typedef ... value_type; // will only represent one octet typedef ... iterator; typedef ... const_iterator; typedef ... difference_type; typedef ... size_type; enum variant_type { variant_unknown, variant_ncs, variant_rfc_4122, variant_microsoft }; enum version_type { version_unknown, version_1 = 1, version_2 = 2, version_3 = 3, version_4 = 4, version_5 = 5, version_time_based = version_1, version_dce_security = version_2, version_name_based_md5 = version_3, version_random_number_based = version_4 version_name_based_sha1 = version_4 }; public: // valid expression // generator() - result type must be convertible to a uuid template <typename Generator> explicit uuid(Generator & generator); // assert(std::distance(begin, end) >= 16); template <typename ByteInputIterator> uuid(ByteInputIterator begin, ByteInputIterator end); iterator begin(); iterator end(); const_iterator begin() const; const_iterator end() const; bool is_nil() const; operator unspecified_bool_type() const; // return !is_nil(); static size_type size(); // always return 16 bool operator==(uuid const& rhs) const; bool operator<(uuid const& rhs) const; variant_type variant() const; version_type version() const; }; void swap(uuid & lhs, uuid & rhs); std::size_t hash_value(uuid const& u); // removed get/set_showbraces (does anybody want/use them?) template <typename ch, typename char_traits> std::basic_ostream<ch, char_traits>& operator<<(std::basic_ostream<ch, char_traits>& os, uuid const& u); template <typename ch, typename char_traits> std::basic_istream<ch, char_traits>& operator>>(std::basic_istream<ch, char_traits>& os, uuid& u); class nil_generator // always generates a nil uuid { public: typedef uuid result_type; uuid operator()(); }; uuid nil(); // easy to use function - should it be included? template <typename RandomGenerator = boost::mt19937> class random_generator { public: typedef uuid result_type; random_generator(); explicit random_generator(RandomGenerator & gen); explicit random_generator(RandomGenerator * gen); uuid operator()(); }; // I guess technically a transformer since it does not have a zero argument // operator() class name_based_generator // uses sha1 hash { public: typedef uuid result_type; explicit name_based_generator(uuid const& namespace_uuid); template <typename ch, typename char_traits, typename allocator> uuid operator()(std::basic_string<ch, char_traits, allocator> const& name); uuid operator()(const char* name); // use std::strlen uuid operator()(const wchar_t* name); // use std::wcslen template <typename ByteInputIterator> uuid operator()(ByteInputIterator begin, ByteInputIterator end); }; class windows_generator // uses UuidCreate { public: typedef uuid result_type; uuid operator()(); }; class linux_generator // used uuid_generate { public: typedef uuid result_type; uuid operator()(); }; // on windows - will typedef to windows_generator // on linux - will typedef to linix_generator typedef ... native_generator; } //namespace uuids using uuids::uuid; // so nobody has to type boost::uuids::uuid } //namespace boost BOOST_CLASS_IMPLEMENTATION(boost::uuids::uuid, boost::serialization::primitive_type) /* uuid Generator concept Notation: X - a type that is a model of uuid generator x - an object of type X Associated Types: Result Type - X::result_type - this must be convertable to boost::uuids::uuid Valid Expressions: x() - return a boost::uuids::uuid */ Regards, Andy Tompkins

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[boost.build] should we not define _SECURE_SCL=0 by default for all msvc toolsets
by Thorsten Ottosen 22 Dec '08

22 Dec '08

Dear all, Is there are reason why we do not compile with this flag set by default? Are there any users of Boost out there which actually wants the securuty mode turned on? If not, then I suggest that we change the build settings. Thanks in advance -Thorsten

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Processor traits
by Antoine de Maricourt 22 Dec '08

22 Dec '08

Hi, is there in boost a trait to describe current target capabilities, i.e. processor's available instruction set, size of registers (32, 64, ... bits) and any other usefull feature? To give an example, I'd like to write code like the following one, with different versions of the same function depending on target capabilities. Regards, Antoine. --- namespace detail { template <typename T, unsigned D, typename P = current_target_trait> struct _popcount; template <> struct _popcount<__m128i, 128, ssse3> { int operator()(const __m128i& x) { static const __m128i M = { 0x0f0f0f0f0f0f0f0fULL, 0x0f0f0f0f0f0f0f0fULL }; static const __m128i C = { 0x0302020102010100ULL, 0x0403030203020201ULL }; __m128i y = _mm_add_epi16 (_mm_shuffle_epi8 (C, _mm_and_si128 (x, M)), _mm_shuffle_epi8 (C, _mm_and_si128 (_mm_srai_epi16 (x, 4), M))); return _mm_cvtsi128_si32 (_mm_sad_epu8 (_mm_hadd_epi16 (y, y), _mm_setzero_si128())); } }; // Count bits in the low 64-bit quad word template <> struct _popcount<__m128i, 64, ssse3> { int operator()(const __m128i& x) { static const __m128i M = { 0x0f0f0f0f0f0f0f0fULL, 0x0f0f0f0f0f0f0f0fULL }; static const __m128i C = { 0x0302020102010100ULL, 0x0403030203020201ULL }; __m128i y = _mm_shuffle_epi8 (C, _mm_and_si128 (_mm_unpacklo_epi32 (x, _mm_srai_epi16 (x, 4)), M)); return _mm_cvtsi128_si32 (_mm_sad_epu8 (_mm_hadd_epi16 (y, y), _mm_setzero_si128())); } }; } template <typename T> int popcount (const T& data) { return detail::_popcount<T,sizeof(data)*8>()(data); }

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Re: [boost] interest in properties library
by Daniel Oberhoff 22 Dec '08

22 Dec '08

> Hello, Daniel. > > Saturday, December 20, 2008 at 4:29:53 PM you wrote: > > DO> What I still want to do is enable simpler syntax and maybe signals > DO> triggered by property and other goodies, but that is actually > rather > DO> simple to do, using bind and/or lambda. > > Some time ago I showed another way to define properties for the class. > I think what this way quite simpler. Take a look: > > > Hi. I saw this in the list. I like the notational simplicity, but it does it allow run-time addressing of properties (i.e. scripting, setting properties from config files) and accessing properties without knowing the full type? The latter becomes important when you don't want to include headers for everything or load additional classes through plugins. I have also found some properties stuff in the sandbox, especially one that nice handles property graphs, but none fulfilled the above requirements. So maybe this is too specialized? I thought it would be a great way to allow scriptable access to properties of classes that are not known at compile time, and thereby allow easy runtime setup of a modular system. Thanks for the replies though, some interesting thoughts. Daniel

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[config] gcc and <unordered_set> vs <ext/hash_set>
by John Maddock 22 Dec '08

22 Dec '08

Folks, Dave A. asked for a config macro to detect the presence of std conforming <unordered_set> and <unordered_map>. However, I've run into an unexpected issue: it appears that with gcc-4.3.x you cannot include both <unordered_set> and <ext/hash_set> as attempting to do so leads to endless errors inside the <ext/*> headers :-( Including either one of the headers is just fine though. So... how should we handled this? Not define BOOST_HAS_HASH when <unordered_set> *is* available? As far as I can tell the only library effected by this change would be Boost.Serialization which would lose has_set support in gcc's c++0x mode. How do folks feel about that? Regards, John.

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[smart_ptr] shared_ptr::before(), owner_less, etc.
by Frank Mori Hess 22 Dec '08

22 Dec '08

-----BEGIN PGP SIGNED MESSAGE----- Hash: SHA1 If I provide a patch that adds support for before() methods to boost::shared_ptr and weak_ptr, and a boost::owner_less (as described in n2637) would it be considered? I don't plan to change the semantics of boost::shared_ptr::operator<(), I just want to make it slightly easier to write code that will be portable across boost::shared_ptr and the upcoming std::shared_ptr. -----BEGIN PGP SIGNATURE----- Version: GnuPG v1.4.6 (GNU/Linux) iD8DBQFJSv/f5vihyNWuA4URAuCbAKDQc5/ufv01thvyrLUScX2GpiXMZACgkzII +6c/b6ZJ9e5oee7O9DWxI6Q= =Ggbl -----END PGP SIGNATURE-----

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Re: [boost] interest in properties library
by Daniel Oberhoff 21 Dec '08

21 Dec '08

> On Sat, Dec 20, 2008 at 5:29 AM, Daniel Oberhoff > <daniel.oberhoff_at_[hidden]> wrote: > > HasPropertiesBase<VariantTypes> * foo = new Foo; > > foo->set_property("a", 1); > > int a = get<int>( foo->get_property( "a" ) ); > > If this is your typical use case, I would implement properties > non-intrusively in a separate property_database: > > property_database pd; > boost::shared_ptr<Foo> foo(new Foo); > pd.set<int>(foo,"a"); > > The property_database class is essentially a > std::map<boost::weak_ptr<void>,std::map<std::string,boost::any>>, and > you'd dynamic_cast<void *> the pointers passed to set and get. > Interesting approach. If you need non-intrusiveness. Though if intrusiveness is not a problem I think my approach is better, because a) you bind the properties explicitly to the class and thus have much less setup work to do and b) it automatically manages many properties along the inheritance graph. > > Another thought, you can also use tag types to make the properties > compile-time type-safe. See the similar system used in > http://www.boost.org/doc/libs/1_37_0/libs/exception/doc/boost-exception.html > . > In that case the syntax could be: > > typedef property<struct tag_a,int> prop_a; > pd.set(prop_a(42),foo); > int p=pd.get<prop_a>(foo); > Well, I use boost::variant, the other option is boost::any. The variant makes it possible to inspect the type at runtime and automate conversions, while the boost:.any would give you type safety. I admit your approach would be more efficient, but I designed this with scriptability in mind, which is also why I use strings as keys. Also it looks like your approach does not allow addressing properties at run-time. Daniel

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Re: [boost] interest in properties library
by Daniel Oberhoff 21 Dec '08

21 Dec '08

> Daniel Oberhoff wrote: > > > HasPropertiesBase<VariantTypes> * foo = new Foo; > > foo->set_property("a", 1); > > int a = get<int>( foo->get_property( "a" ) ); > > And I suppose if it's not an int, it throws? > For proprieties, it might be better to provide lexical conversion to > the > target type, so that it always succeeds (modulo allocation errors). > > Anyway, I'm not too sure this is very useful. > It's just a std::map<std::string, some_variant_type>. Does that really > deserve its own class? > well, this was the simpler case. by using variants and defining proper visitors conversions can be made automatically, like using lexical_cast, which is what I wanted to do soon (I alread do the simple conversions, just learned about lexical cast now). But the point of the lib is actually, that you don't need to know the type of the class, plus that you have arbitrary setter/getter methods. Also properties from classes along the inheritance graph get concatenated into a single interface. Daniel

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[crypto] Bug in md5
by Konstantin Litvinenko 21 Dec '08

21 Dec '08

Hi All! I just tried crypto library from the vault and immediately hit a bug :) in message_digest.hpp template<class Context> std::string message_digest<Context>::to_string() const { // !!!BUG!!! Should be context_type::digest_length * 2 + 1 char buf[context_type::digest_length * 2]; for (int i = 0; i < context_type::digest_length; ++i) std::sprintf(buf + i * 2, "%02x", static_cast<const unsigned char*>(digest())[i]); return std::string(buf, context_type::digest_length * 2); }

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Composing non copyable and movable classes
by vicente.botet 21 Dec '08

21 Dec '08

Hi, Imagine a class X which contains several noncopyable and movable members Ci mi;. class X : noncopyable { C1 m1; C2 m2; // ... Ck mk; // ... }; Very often a class is made movable by storing a pointer to some implementation data on a shared_ptr. Without allocator this means a heap new/delete. If the class accept allocators this means an allocate/deallocate on the allocator. class Mi : noncopyable { struct implementation_data; shared_ptr<implementation_data> data_; // ... }; The question is how to make X movable efficiently. The first way is to move each one of the movable objects one by one. This could be expensive if the number of members is high. In addition X can have also member that are not movable. The second approach is to use the same technique, store a pointer to the data on a shared_pointer, and move on one operation all the members via the pointer. class X : noncopyable { struct implementation_data { C1 m1; C1 m2; // ... C1 mk; }; shared_ptr<implementation_data> data_; public: // ... }; In this case the class X don't need any more that its members be movable. In order to avoid the allocation/deallocation of the respective classes Ci, it would be interesting to have a class which is not copyable and not movable and that owns the implementation class nonmovable_Ci : noncopyable { struct implementation_data; implementation_data data_; // ... }; Except the movable support, the nonmovable_Ci class share with Ci the same functionality. But is not related to Ci by inheritance. Both classes model a common concept. Of course this can not be applied if the implementation_data must be hidden in some .cpp file (pimpl idiom). The consequence is the classes and functions that should work with both implementations need to be templated. This allows the class X to allocate all the data at once. class X : noncopyable { struct implementation_data { nonmovable_C1 m1; nonmovable_C1 m2; // ... nonmovable_C1 mk; }; shared_ptr<implementation_data> data_; public: // ... }; I think that this separation is in line with the C++ principle "you don't pay for what you don't use". Any thoughts? Vicente

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Re: [boost] interest in properties library
by Daniel Oberhoff 20 Dec '08

20 Dec '08

> On Fri, Dec 19, 2008 at 5:50 AM, Daniel Oberhoff < > daniel.oberhoff_at_[hidden]> wrote: > > Hi, > > > > I am thinking about submitting a library proposal and would like > to query > > wether there is any interest in such a library and chance of > success of such > > a proposal. > > > > The basic idea is to implement the possibility to decorate a class > with > > named properties, such that given a pointer to an instance > properties can be > > accessed by name rather than using set/get methods. Also the type > of the > > instance should not need to be known at compile time, other than > that it > > derives from a suitable base class describing the property > mechanisms. > > > > There is a rough implementation existing and used in a product > environment. > > Setting and getting is done using appropriate boost functions. Type > > resolution is done using RTTI (especially dynamic cast). Complex > inheritance > > hierarchies are supported through virtual inheritance from the > base class, > > such that several classes along the hierarchy can contribute > property slots. > > CRTP and static initialization is used to register properties. > Convenient > > setter/getter function generators are provided as is a mechanism > to access > > nested properties using dot notation. > > I'm not sure I follow exactly what you mean, could you give a small > example > of the interface and usage? It sounds like you are referring to > something > along the lines of C# properties though I don't immediately see what > you are > using dynamic casting for or what exactly this provides as a benefit > over > get/set methods. Thanks. sorry, forgot the examples. so, to enable properties for a class: class Foo : public HasProperties<VariantTypes, foo> { protected: typedef HasProperties<VariantTypes, foo> PBase; typedef Foo This; static void init_properties() { PBase::add_ivar_property_rw( "a", &This::a ); } private: int a; }; usage: HasPropertiesBase<VariantTypes> * foo = new Foo; foo->set_property("a", 1); int a = get<int>( foo->get_property( "a" ) ); Here VariantTyped is a mpl::sequence Furthermore it still works when a class has several such properties activated classes along its inheritance ancestors, and all properties can be acessed unless there is a name conflict, in which case classes further down override properties from its ancestors, though this could be handled differently. What I still want to do is enable simpler syntax and maybe signals triggered by property and other goodies, but that is actually rather simple to do, using bind and/or lambda. Best Daniel

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Re: [boost] [boost.build] should we not define _SECURE_SCL=0bydefault for all msvc toolsets
by raindog＠macrohmasheen.com 20 Dec '08

20 Dec '08

I read about people running into them frequently enough on internal discussion aliases at microsoft (where I work) and recall just last week I believe someone who ran into a perf issue on this newgroup while writing a sorting algorithm ------Original Message------ From: Emil Dotchevski Sender: To: boost(a)lists.boost.org ReplyTo: boost(a)lists.boost.org Sent: Dec 20, 2008 12:13 AM Subject: Re: [boost] [boost.build] should we not define _SECURE_SCL=0bydefault for all msvc toolsets On Fri, Dec 19, 2008 at 10:34 PM, <raindog(a)macrohmasheen.com> wrote: > The checks are however a huge performance hit that people tend to be caught by surprise with. Not my experience. The checks do affect performance, but rarely enough to get on my radar. I do like having them on by default. Emil Dotchevski Reverge Studios, Inc. http://www.revergestudios.com/reblog/index.php?n=ReCode _______________________________________________ Unsubscribe & other changes: http://lists.boost.org/mailman/listinfo.cgi/boost Sent from my Verizon Wireless BlackBerry

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[Test] should we consider to turn off argument deduction for 2nd template parameter
by Thorsten Ottosen 20 Dec '08

20 Dec '08

Hi Genndiy, When I write code like BOOST_CHECK_CLOSE( a->conditionals().sum(), 2., 0.001f ); I tend to get a compilation error the first time, because I wrote BOOST_CHECK_CLOSE( a->conditionals().sum(), 2, 0.001f ); I think that many users are not helped very much by the resulting error messages deep inside the test library. Maybe we should consider to turn off deduction for the second argument with template< class T > bool operator()( T l, mpl::identity<T>::type r, ... ); ? Any thoughts. -Thorsten

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