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[ValueRef] Interest in a new library for immutable values with internal sharing?
by THOMAS JORDAN 20 Apr '15

20 Apr '15

Hi, I'd like to gauge whether there might be any interest in a new Boost library comprising a generic, non-intrusive, wrapper class for creating immutable/const values with sharing of the underlying object via internal reference counting. This new class would be called ValueRef (or possibly just Value), and it would effectively provide an assignable/swappable 'reference'/handle to shared, const values. It can be considered an effective alternative to the commonly used shared-pointer-to-const idiom, providing cleaner and more explicit value semantics, whilst also hiding calls to 'new' as an internal implementation detail. In a nutshell, ValueRef adapts a regular type T to give a new type ValueRef<T> with const T value semantics and uses reference counting of an underlying object on the heap internally to reduce copying overhead. ValueRef will spawn off a new copy of the wrapped object (if necessary) if the ValueRef is assigned another ValueRef or another object of type T. Const functions of T do not incur any overhead of counter access or copy and are invoked by either * or -> syntax. Forwarding constructors are provided which permit the wrapped value to be constructed in place, and conversion operator allows inter-operation with values of the unwrapped type. ValueRef also provides the common relational operators. I have so far implemented a rough (C++03-only so far) version of this (based on a stripped down version of Adobe::copy_on_write library) and a test suite and it seems to work okay. Example usage: /* type of ValueRef wrapped std::vector<int> */ typedef ValueRef<std::vector<int> > ValueRefVecType; /* create vector of 10 elements via forwarding constructor */ ValueRefVecType valueRefVector1(10,1); /* non-mutating/const op */ assert( valueRefVector1->size() == 10 ); /* non-mutating/const op */ assert( (*valueRefVector1)[0] == 1 ); /* error - compilation failure occurs calling a non-const op */ (*valueRefVector)[0] = 2; /* copy ctor */ ValueRefVecType valueRefVector2(valueRefVector1); /* test for equality */ assert( valueRefVector1 == valueRefVector2 ); /* test for equality (implicit conversion) */ assert( valueRefVector2 == std::vector<int>(10,1) ); /* valueRefVector1 and valueRefVector2 share same std::vector */ assert( valueRefVector1.identity(valueRefVector2) ); /* ref count is no longer one */ assert( !valueRefVector1.unique_instance() ); /* new value */ valueRefVector1 = std::vector<int>(5); /* non-mutating/const */ assert( valueRefVector1->size() == 5 ); /* test for equality - value semantics */ assert( !(valueRefVector1 == valueRefVector2) ); /* valueRefVector1 and valueRefVector2 do not share same std::vector */ assert( !valueRefVector1.identity(valueRefVector2) ); I am not aware of anything else current that provides this functionality. Regards, Tom

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[release] Python 3 build problems
by Daniel James 20 Apr '15

20 Apr '15

Hi, Is there anyone who can write a brief description of the build problem with python 3 for the release notes? We probably should say something. thanks, Daniel

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[regex] Support for Perl's (*SKIP)
by Sei Lisa 20 Apr '15

20 Apr '15

I'd like to see support for Perl's (*SKIP) regex verb in Boost. There are a number of verbs, but that one has an interesting and frequent use case: it enables searching for an expression but only outside of some contexts. There is a page called "The best regex trick" with details about the process and a number of examples. I can't link to it as this is my first message (I attempted before but it was rejected). It explains how to do it with and without (*SKIP). I've seen several questions in Stack Overflow asking how to accomplish that task, so it seems it's quite frequent to run into that need. Let's say for example that we want to find the string 'foo' as an identifier in C. This is a crude example of a Perl regex that does it (a real one might need to be more elaborate; in particular, backslashes for line continuation are not considered): (?x-s) (?# free spacing, dot doesn't match newline) (?://.*+ (?# eat single-line comment text) |/\*[\S\s]*?\*/ (?# eat multi-line comment text) |"(?:\\.|[^"\n])*+" (?# eat string text) )(*SKIP)(?!) (?# skip these) |\bfoo\b (?# match this) regex::search will match that expression only when foo is present outside of a string or comment. Without (*SKIP), it can be done only by calling regex::search multiple times, using an expression like this: (?-s)//.*+|/\*[\S\s]*?\*/|"(?:\\.|[^"\n])*+"|(\bfoo\b) and ignoring every match where group 1 wasn't matched. That's presumed to be slower, and certainly more inconvenient for the programmer. Support for this particular use case would be a great feature to have in the regex engine. Sei

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[master] Open for 1.59?
by Joaquin M Lopez Munoz 20 Apr '15

20 Apr '15

Is master already open for commits towards Boost 1.59? Thank you, Joaquín M López Muñoz Telefónica

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[config] BOOST_SYMBOL_VISIBLE on MinGW
by Robert Ramey 20 Apr '15

20 Apr '15

I made adjustments so that the serialization library on Develop branch will build with default visibilty = hidden. There is a little more to this than one would think. Basically I used BOOST_SYMBOL_VISIBLE on all "exported" classes (and their base classes) and BOOST_ARCHIVE_DECL ( defined as either BOOST_ARCHIVE_IMPORT or BOOST_ARCHIVE_EXPORT) on exported/visible member functions. This seems to give me what I need in that things build and test for gcc, clang, MSVC. EXCEPT for gcc under MinGW. see http://www.boost.org/development/tests/develop/developer/output/MinGW-32%20… The message seems to indicate to me that I should have BOOST_SYMBOL_VISIBLE on the class declaration - which seemed to resolve similar compilation errors with GCC on other platforms. Poking around config/compiler/gcc.hpp and config/plaform/w32.hpp It seems to me that this scheme things look OK - that is it looks that BOOST_SYMBOL_VISIBILITY should be defined as __attribute__((__visibility__("default"))) I'm also puzzled by the fact that the linker craps out only on this on declaration. Any help appreciated. Robert Ramey -- View this message in context: http://boost.2283326.n4.nabble.com/config-BOOST-SYMBOL-VISIBLE-on-MinGW-tp4… Sent from the Boost - Dev mailing list archive at Nabble.com.

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[container][stable_vector] What does reserve() do for stable_vector
by Arindam Mukherjee 19 Apr '15

19 Apr '15

Consider the following code. #include <string> #include <boost/container/stable_vector.hpp> #include <iostream> int main() { boost::container::stable_vector<std::string> vec; vec.reserve(10); std::cout << "capacity = " << vec.capacity() << '\n'; } On running this (on g++ and Linux), the output is: capacity = 4294967286 (that's 2^32 - 10) If replace boost::container::stable_vector with std::vector above, the output is: capacity = 10 I know it could as well have been capacity = 20, or capacity = 64 or whatever but that's still sane behavior. What capacity() returns for stable_vector seems to be (2^32 - N), N being the requested capacity. I didn't see such a definition of capacity in the docs: http://www.boost.org/doc/libs/1_56_0/doc/html/boost/container/stable_vector… Thanks, Arindam

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[type_traits] Testing for copy constructor
by Edward Diener 19 Apr '15

19 Apr '15

Does one use has_trivial_copy or has_nothrow_copy to determine if a class has a copy constructor or not ? I am writing some code that can do different things depending on whether a particular class has a copy constructor or does not have a copy constructor. I do not really care whether the copy constructor is a compiler generated copy constructor or not.

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Feedback on Boost.Http
by Vinícius dos Santos Oliveira 18 Apr '15

18 Apr '15

I recently submitted an HTTP server library to Boost Incubator and I'd appreciate feedback: http://rrsd.com/blincubator.com/bi_library/http/?gform_post_id=1460 I intend to submit to Boost later. This is the library that I developed during GSoC 2014 and I made several improvements (new features, bug fixes, better and extended documentation...) after the end of GSoC. There are a few improvements that I still want to do, but none of them would be a barrier for Boost integration, in my opinion. This library doesn't have a builtin request router, opposed to several libraries out there, then you can use whatever routing style you wish (tree-based, middleware-based, no router...). Also, it follows Boost active style, then you can build your own scheduler around it (prioritize requests from certain IPs, defer acceptance of new connections during server high load, reuse prior constructed objects...). The library follows Asio threading model, then you also choose whether you will handle all requests from the same thread (useful for embedded devices) or multiples ones. The library is fully async, then one thread is not a problem. It has a powerful and flexible file server API, supporting range-based requests, conditional requests, support for ETags and so on. After the GSoC, I had the chance to add tests for asynchronous abstractions and now the implementation is much more trustable and stable. The choice to reuse an existing HTTP parser (the Node.js's C parser) also helps a lot. The simple message-based API helps to support HTTP pipelining, allocation fine tuning and much more. Besides HTTP pipelining, HTTP chunking (and other modern features like 100-continue and HTTP Upgrade) are also supported. There are zero reviews/comments on Boost Incubator right now and I'd love to see more eyes on this lib that does better on many fronts than previous choices. Benchmark is one item that I still need to tackle, btw. But I hope to see good results here too. -- Vinícius dos Santos Oliveira https://about.me/vinipsmaker

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[tools] How to use 1.58.0/bjam --toolset=sun for specified stdlib feature?
by Sergey Sprogis 18 Apr '15

18 Apr '15

Running boost regression unit tests I found it convenient to direct output from every single tested library into a separate logfile. To do that, my testing script (bash) at first extracts the list of all <library>/test lines from status/Jamfile.v2, and puts them into another test_suites.txt file. Then it runs all extracted test suites like this: my_res_dir= `pwd` for dir in `cat test_suites.txt`; do dir1=`echo $dir | sed "s/\//\./g"` cd $BOOST_ROOT/libs/$dir bjam --toolset=sun variant=release > $my_res_dir/$dir1.log 2>&1 done All that worked fine until boost-1.58 in which tools/build/src/tools/sun.jam file was modified so that instead of single standard library it now allows the possibility of using any of 5 available libraries. The question is, how exactly should I define bjam's options in my bash script shown above, if for example, I want to use gnu library in c++03 mode? The proper code inside sun.jam file looks like this: feature.extend stdlib : gnu ; feature.compose <stdlib>gnu : <cxxflags>-std=c++03 <linkflags>-std=c++03 ; but how should I tell to bjam to use this specific library? Thanks, Sergey

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[build] [boost 1.58] Error when compiling with MSVC-7.1
by Ion Gaztañaga 18 Apr '15

18 Apr '15

Hi, I just tried the newly released version with this toolset (I don't think many will use and support it, but still useful). Output when building move from boost/libs/move/test: ..\..\..\b2.exe toolset=msvc-7.1 variant=debug C:/Data/Libs/boost/tools/build/src/tools\msvc.jam:1075: in configure-really *** argument error * rule generate-setup-cmd ( version : command : parent : options * : cpu : global-setup : default-global-setup-options : default-setup ) * called with: ( 7.1 : C:\Program Files (x86)\Microsoft Visual Studio .NET 2003\Vc7\bin : C:\Program Files (x86)\Microsoft Visual Studio .NET 2003\Vc7 : <command>C:\Program Files (x86)\Microsoft Visual Studio .NET 2003\Vc7\bin\cl.exe : i386 : : x86 : vcvars32.bat ) * missing argument global-setup C:/Data/Libs/boost/tools/build/src/tools\msvc.jam:809:see definition of rule 'generate-setup-cmd' being called C:/Data/Libs/boost/tools/build/src/tools\msvc.jam:201: in configure C:/Data/Libs/boost/tools/build/src/tools\msvc.jam:153: in msvc.init C:/Data/Libs/boost/tools/build/src/build\toolset.jam:43: in toolset.using C:/Data/Libs/boost/tools/build/src\build-system.jam:461: in process-explicit-toolset-requests C:/Data/Libs/boost/tools/build/src\build-system.jam:527: in load C:\Data\Libs\boost\tools\build\src/kernel\modules.jam:289: in import C:\Data\Libs\boost\tools\build\src/kernel/bootstrap.jam:139: in boost-build C:\Data\Libs\boost\boost-build.jam:17: in module scope I've found a workaround adding this to user-config.jam, in case anyone needs a workaround: using msvc : 7.1 : : <setup>"C:/Program Files (x86)/Microsoft Visual Studio .NET 2003/Vc7/bin/vcvars32.bat" ; Of course that path is in a 64-bit Windows OS, adjust it to your installed path. Best, Ion

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