September 2010 - Boost - lists.preview.boost.org

bad include guards
by Steven Watanabe 26 Jan '17

26 Jan '17

AMDG The following pairs of files have identical include guards ./boost/concept_check/general.hpp ./boost/concept/detail/msvc.hpp ./boost/concept_check/msvc.hpp ./boost/concept/detail/msvc.hpp ./boost/filesystem/cerrno.hpp ./boost/cerrno.hpp ./boost/interprocess/containers/tree.hpp ./boost/interprocess/containers/detail/tree.hpp ./boost/mpl/min_max.hpp ./boost/mpl/max.hpp ./boost/mpl/vector/aux_/front.hpp ./boost/mpl/list/aux_/front.hpp ./boost/multi_index/identity_fwd.hpp ./boost/multi_index/identity.hpp ./boost/python/pointee.hpp ./boost/python/detail/pointee.hpp ./boost/spirit/phoenix/closures.hpp ./boost/lambda/closures.hpp ./boost/xpressive/proto/v1_/proto_typeof.hpp ./boost/xpressive/proto/proto_typeof.hpp ./libs/config/test/boost_no_dep_nested_class.ipp ./libs/config/test/boost_has_vc6_mem_templ.ipp ./libs/config/test/boost_no_mem_templates.ipp ./libs/config/test/boost_has_vc6_mem_templ.ipp ./libs/config/test/boost_no_std_allocator.ipp ./libs/config/test/boost_has_vc6_mem_templ.ipp ./libs/conversion/test.hpp ./libs/any/test.hpp ./libs/interprocess/example/print_container.hpp ./libs/interprocess/example/printcontainer.hpp ./libs/interprocess/test/expand_bwd_test_template.hpp ./libs/interprocess/test/allocation_test_template.hpp ./libs/interprocess/test/printcontainer.hpp ./libs/interprocess/example/printcontainer.hpp ./libs/interprocess/test/print_container.hpp ./libs/interprocess/example/printcontainer.hpp ./libs/iostreams/test/detail/utf8_codecvt_facet.hpp ./boost/detail/utf8_codecvt_facet.hpp ./libs/regex/test/regress/test_regex_search.hpp ./libs/regex/test/regress/test_partial_match.hpp ./libs/serialization/test/C.hpp ./libs/serialization/test/A.hpp ./libs/xpressive/perf/regex_comparison.hpp ./libs/regex/performance/regex_comparison.hpp ./tools/inspect/time_string.hpp ./tools/common/time_string.hpp In Christ, Steven Watanabe

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Why no non-null smart pointers?
by Ross MacGregor 29 Apr '14

29 Apr '14

I just created a very small smart pointer libary for our project. It will contain two types of shared pointers: SharedHandle and NullableSharedHandle. SharedHandle will be a shared pointer that cannot be null by ensuring a non-null construction while NullableSharedHandle will basically be a typedef for boost::shared_ptr. I firmly believe that code can be made more reliable by minimizing the use of nullable pointers. To this end, I think it is important that we start using non-null pointer types. Ideally the compiler would be able to understand a non-null pointer and catch bugs at compile time, but I think we can still improve things with a few runtime checks. If we make sure that a shared pointer is constructed with a non-null pointer and ban any reset() type methods, we guarentee that it points to something. This can be beneficial for the following reasons: 1. Any function that uses this type will no longer be burdened with precondition checks to make sure variables of this type are not null. 2. It's type is simply more explicit and better explains its function. 3. Moving the non-null check to the creation phase will reduce the possibility of encountering null pointer exceptions at runtime (assuming there are many more pointer references than constructor calls). So my little pointer library seems to make a lot of sense, but if so why hasn't this simple smart pointer variation made it into boost yet? Has this been discussed somewhere already? My search on non-null smart pointers is not revealing much discussion on the topic. Regards, Ross

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De Bruijn Bind (alternate bind syntax) Interest?
by David Sankel 24 Jun '13

24 Jun '13

Hello all, I've been working on an alternate bind syntax based on De Bruijn indices[1]. The syntax is very simple, yet the terms are very powerful. Here is an example of a function const that takes in an argument c and returns another function that, for all input, returns c: //λx.λy.x = λλ1 with De Bruijn indices. auto const_ = abs<1>( abs<1>( var<1,0>() ) ); More examples, further explanation, and an implementation are available here[2]. I'm thinking that this library could also be useful as a core for more syntax heavy bind variations. David [1] http://en.wikipedia.org/wiki/De_Bruijn_index [2] http://bitbucket.org/camior/de-bruijn-bind/ -- David Sankel Sankel Software www.sankelsoftware.com 585 617 4748 (Office)

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[parameter] std proposal
by Lorenzo Caminiti 07 Jan '13

07 Jan '13

Hello all, Is there a C++ standard proposal for named parameter addition? I am looking for an "N-paper" for named parameters similar to N2081 for concepts, or N1962 for contracts. Thank you. -- Sent from my mobile device Lorenzo

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[#pragma once]
by Sid Sacek 18 Nov '12

18 Nov '12

I've worked with the MSVC, Sun and GCC compilers. Each one of them supports #pragma once. Is there any reason to wrap this pragma within #ifdefs? Are there any compilers out there today that don't support this #pragma? #if defined( _MSC_VER ) && ( _MSC_VER >= 1020 ) # pragma once #endif Could we change this coding pattern so that it no longer looks like MSVC is being selfish? -Sid Sacek

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[config] explicit call of operator templates / msvc bug workaround
by Stefan Strasser 10 Oct '12

10 Oct '12

Hi, is there already a macro in Boost.Config that allows you to insert the "template" keyword in the following code for those compilers that require it? struct functor{ template<class T> void operator()(); }; template<class F> void g(F f){ f.template operator()<int>(); //(1) works with GCC and comeau f.operator()<int>(); //(2) works with MSVC } this apparently only applies to operator calls. MSVC accepts both (1) and (2) for regular functions. (instantiating the operator template with an object of type T as argument, like mpl::for_each does, is not an option. I can't construct T.) thanks, Stefan

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[interprocess] message_queue hangs when another process dies
by Sergei Politov 03 Nov '11

03 Nov '11

Hi, I have found the following problem with message_queue on win32 (MSVC 2008 + Windows Vista). Suppose we have 2 processes, one sends messages to queue, another reads them. When reading process dies (for instance using End process) during message_queue.receive the another process hangs in send. As I found during investigation, it tries to lock interprocess mutex, but it is already locked by dead process. So this message queue instance becomes unusable. I attached the example. Steps to reproduce: 1) Start "mq.exe s" (i.e. with argument s) It outs: sender: $PID 2) Start mq.exe without arguments. It outs: receiver: $PID 0 1 2 3 4 This time sender outs: send done: 3) At this point the message queue is empty and receiver waits for messages. End it with Task Manager. 4) Enter some number in sender console and press Enter. 5) The sender hangs in message_queue.send Best Regards, Sergei

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[serialization] or [spirit] JSON Archives
by Fernando Pelliccioni 08 Sep '11

08 Sep '11

Hi, After experimenting with Spirit.Qi to make a JSON parser, I had the need for a serializer. First, I thought I could serialize my model of JSON (json:: value, json: object, etc.), but that was not compatible with boost::serialization. I am currently writing a ARCHIVE for Boost Serialization, but I'm finding some problems in order to implement JSON correctly. The question is, does anyone know about some files to Boost Serialization already finished? I've seen the Archive made by Esteve Fernandez, but do not serve my purpose, because I just need JSON. I would like to develop a JSON parser which in turn is a compatible Boost Serialization serializer . Any ideas? Thanks and regards, Fernando Pelliccioni.

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[Opaque] Request for interest in Opaque typedefs library emulation
by vicente.botet 27 Jul '11

27 Jul '11

Hi, I have started to play with a class to define opaque typedefs on funcdamental types. It is based on the C++ proposal " Progress toward Opaque Typedefs for C++0X" by Walter E. Brown http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2005/n1891.pdf and http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2004/n1706.pdf Please take a look on the preceding links to understand the motivation. Boost.Sericalization provide a BOOST_STRONG_TYPEDEF already, but in my opinon the implementation is not complete,as only the order operators are defined (But maybe I'm wrong). Evidently it can not provide everything we can have with a language approach, but IMO this could yet be useful. The library include two class templates (CRTP) to define opaque types: * public_opaque_type<OT,UT> : implicit conversion from OT to UT * private_opaque_type<OT,UT> : no conversion from OT to UT An opaque type (OT) is a new type, different from the underlying type (UT) and other OT. It defines explicit constructor from the UT, and defines all the operators the UT support but this time applied to the OT. To define a new OT with this mixin classes struct serial_number: public_opaque_type<serial_number, unsigned> { BOOST_OPAQUE_PUPLIC_FORWARD_CONSTRUCTORS(serial_number,unsigned); }; struct game_score: private_opaque_type<game_score, unsigned> { BOOST_OPAQUE_PRIVATE_FORWARD_CONSTRUCTORS(game_score,unsigned); }; In addition, defines macros that make this simpler BOOST_OPAQUE_PUBLIC_TYPEDEF(unsigned, serial_number); BOOST_OPAQUE_PRIVATE_TYPEDEF(unsigned, game_score); Next follows the definition of the public_opaque_type template <typename Final, typename T> class public_opaque_type : boost::totally_ordered< Final , boost::integer_arithmetic< Final , boost::bitwise< Final , boost::unit_steppable< Final , boost::totally_ordered< T, Final // public specific conversions , boost::integer_arithmetic< T, Final // public specific conversions , boost::bitwise< T, Final // public specific conversions > > > > > > > { protected: T val_; typedef public_opaque_type opaque_type; public: typedef T underlying_type; explicit public_opaque_type(const T v) : val_(v) {}; public_opaque_type() {}; public_opaque_type(const opaque_type & rhs) : val_(rhs.val_) {} public_opaque_type & operator=(const opaque_type & rhs) { val_ = rhs.val_; return *this; } public_opaque_type & operator=(const T rhs) { val_ = rhs; return *this; } T const& underlying() const { return val_; } T& underlying() { return val_; } operator const T & () const { return val_; } operator T & () { return val_; } #if 0 bool operator==(const opaque_type & rhs) const { return val_ == rhs.val_; } #endif bool operator<(const Final & rhs) const { return val_ < rhs.val_; } Final& operator+=(const Final & rhs) { val_ += rhs.val_; return static_cast<Final&>(*this); } Final& operator-=(const Final & rhs) { val_ -= rhs.val_; return static_cast<Final&>(*this); } ... }; I have started to make some tests and it works well for the moment. Limitations: * As we can not specialize the behaviour of static_cast/dynamic_cast the library sould provide two specific casts opaque_static_cast and opaque_dynamic_static_cast (Not yet implemented). * As operator.() can not be overloaded, it works transparently only for underlying types that don't defines member functions (C++ fundamental types, as int, char, ...). For the others an explicit use of the underlying() member function is needed :( * Others I have not catched yet :( Do you think it is worth continuing? Please, let me know if you see a error on the design. _____________________ Vicente Juan Botet Escribá http://viboes.blogspot.com/

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[mpl] string to type conversion
by Bartosz Marcinkiewicz 19 Jun '11

19 Jun '11

Hello, I would like to have a macro which could be used like this: STRING_TO_TYPE( MyType ) which would yield: typedef mpl::string<'M','y','T','y','p','e'> MyType_id_t; Any ideas how to implement something like that? Thanks for any help, bma. -- Bartosz Marcinkiewicz tel. (+48) 516 034 243 e-mail: bma(a)epcon.pl, bartosz.marcinkiewicz(a)epcon.pl EPCON Sp. z o.o. www.epcon.pl adres: 53-407 Wrocław, ul. Gajowicka 114/116 tel. (+48) 71 361 75 55 ext.36 fax (+48) 71 361 74 44 NIP PL 899-24-92-498 KRS 0000190187 REGON 932963731 Kapitał zakładowy: 500 000 PLN

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Re: [boost] [date_time] Time zone improvements
by Rutger ter Borg 25 May '11

25 May '11

Jeff Garland wrote: > Very cool :-) One question -- is there a portable solution where a user > could deploy a files onto a Windows system or is it a Unix only solution? > I'm fine with incorporating a *nix only solution because what your > suggesting will be a nice solution for *nix platforms, but it will need to > be clear that it's not portable. I don't see why it wouldn't be possible to deploy the (big-endian) binary files to any platform. Getting it into this binary form (using zone info compiler zic) may be harder to do cross-platform, but cygwin may help here. [snip] > As the primary maintainer of Boost date-time I can say with certainty that > there is interest in this functionality -- it's long been on my todo list > and I haven't had time to get to it. You can email me privately and we > can discuss all the details of how to get your code incorporated. I'll do! Regards, Rutger

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accurate sum accumulator (kahan)
by Gaetano Mendola 27 Apr '11

27 Apr '11

Hi all, I had to implement in terms of boost accumulators the Kahan summation algorithm. I will paste at the end of this message the accumulator, the feature and the extractor source code. This accumulator reduces the numerical error obtained with standard sequential sum, as example the sum of 1e6f elements equal to 1e-6f should give 1.0f, this is the results obtained with sum and sum_kahan: tag::sum: 1.009038925 tag::sum_kahan: 1.000000000 I'm not sure if that sum_kahan is worth to be inserted in the accumulators provided with boost, I'm not an expert of boost:accumulators (I just followed the guide to make this new accumulator) so not sure if you prefer to have a fast_sum and an accurate_sum instead of sum and sum_kahan. Regards Gaetano Mendola // File kahan_sum.hpp #ifndef KAHAN_SUM #define KAHAN_SUM #include <boost/accumulators/framework/accumulator_base.hpp> #include <boost/accumulators/framework/parameters/sample.hpp> #include <boost/numeric/conversion/cast.hpp> namespace boost { namespace accumulators { namespace impl { template<typename Sample> struct sum_kahan_accumulator : accumulator_base { typedef Sample result_type; template<typename Args> sum_kahan_accumulator(Args const & args) : sum(args[sample | Sample()]), compensation(boost::numeric_cast<Sample>(0.0)) { } template<typename Args> void operator ()(Args const & args) { const Sample myTemp1 = args[sample] - this->compensation; const Sample myTemp2 = this->sum + myTemp1; this->compensation = (myTemp2 - this->sum) - myTemp1; this->sum = myTemp2; } result_type result(dont_care) const { return this->sum; } private: Sample sum; Sample compensation; }; }}} namespace boost { namespace accumulators { namespace tag { struct sum_kahan : depends_on< > { typedef impl::sum_kahan_accumulator< mpl::_1 > impl; }; }}} namespace boost { namespace accumulators { namespace extract { extractor< tag::sum_kahan > const sum_kahan = {}; } using extract::sum_kahan; }} #endif

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D-style scope guards?
by Martin Christiansson 07 Mar '11

07 Mar '11

Hi, I have used the good old scopeguard in the past and recently done some experiments with the Boost.ScopeExit library. Still I feel that the clean scope statements in D is missing. It will not be possible to do an equally clean solution without having the same features in the language itself, but I could reach as far as this example that reuses the ScopeExit library: void foo() { GUARDED_SCOPE_BEGIN GUARDED_SCOPE_EXIT() { cout << "Returning from foo()" << endl; } GUARDED_SCOPE_EXIT_END GUARDED_SCOPE_SUCCESS() { cout << "foo(): No Errors occurred!" << endl; } GUARDED_SCOPE_SUCCESS_END GUARDED_SCOPE_FAILURE() { cout << "foo(): Exception caught!" << endl; } GUARDED_SCOPE_FAILURE_END GUARDED_SCOPE_END } The GUARDED_SCOPE_BEGIN macro declares one boolean guard to handle return from several levels of nested scopes and one boolean to guard the current scope from exceptions (will be shadowed in nested scopes). GUARDED_SCOPE_END will set the exception_thrown guard to false before that variable is used by the GUARDED_SCOPE_*() destructors. The latter is actually reused ScopeExit code with an added wrapper with a single if-statement. GUARDED_SCOPE_EXIT() will allways run on scope exit. GUARDED_SCOPE_SUCCESS() will only run if the function is exited with wrapper for return keyword (GUARDED_SCOPE_RETURN). The wrapper must be used since it updates the hidden guard variables. Using plain "return" will behave as if exception was thrown. GUARDED_SCOPE_FAILURE() will run when exception is thrown. There is also a separate GUARDED_SCOPE_NESTED_BEGIN that is supposed to be used for all nested scopes. A reference is kept to the return_called variable in the top-level-scope (variable declared by GUARDED_SCOPE_BEGIN). The biggest issue here is that any extra closing curly bracket inserted between GUARDED_SCOPE_*-definitions and GUARDED_SCOPE_END will cause destructors to run before update of guard variable. Could happen if someone thinks it "looks better" without understanding how stuff works. That kind of error will behave as if exception was thrown. Is this something to investigate further? Messy or potentially useful? Suggestions for improvements? I've appended the contents of my small test program at the end of this email. Can be tested by inserting GUARDED_SCOPE_RETURN() and "throw exception();". Regards, /Martin ----------- #include <iostream> #include <exception> #include <boost/scope_exit.hpp> using namespace std; #define GUARDED_SCOPE_BEGIN bool return_called = false; { bool& return_called_ref = return_called; bool exception_thrown = true; #define GUARDED_SCOPE_NESTED_BEGIN { bool& return_called_ref = return_called; bool exception_thrown = true; #define GUARDED_SCOPE_END exception_thrown = false; (void) return_called_ref; } #define GUARDED_SCOPE_RETURN(rc) { return_called_ref = true; return rc; } #define GUARDED_SCOPE_EXIT(Seq) BOOST_SCOPE_EXIT(Seq) #define GUARDED_SCOPE_EXIT_END BOOST_SCOPE_EXIT_END #define GUARDED_SCOPE_SUCCESS(Seq) BOOST_SCOPE_EXIT( (&return_called_ref) (&exception_thrown) Seq) { if(return_called_ref || !exception_thrown) #define GUARDED_SCOPE_SUCCESS_END } BOOST_SCOPE_EXIT_END #define GUARDED_SCOPE_FAILURE(Seq) BOOST_SCOPE_EXIT( (&return_called_ref) (&exception_thrown) Seq) { if(!return_called_ref && exception_thrown) #define GUARDED_SCOPE_FAILURE_END } BOOST_SCOPE_EXIT_END void foo() { GUARDED_SCOPE_BEGIN GUARDED_SCOPE_EXIT() { cout << "Returning from foo()" << endl; } GUARDED_SCOPE_EXIT_END GUARDED_SCOPE_SUCCESS() { cout << "foo(): No Errors occurred!" << endl; } GUARDED_SCOPE_SUCCESS_END GUARDED_SCOPE_FAILURE() { cout << "foo(): Exception caught!" << endl; } GUARDED_SCOPE_FAILURE_END do { GUARDED_SCOPE_NESTED_BEGIN GUARDED_SCOPE_FAILURE() { cout << "Inner scope: Exception caught!" << endl; } GUARDED_SCOPE_FAILURE_END GUARDED_SCOPE_SUCCESS() { cout << "Inner scope: No Errors occurred!" << endl; } GUARDED_SCOPE_SUCCESS_END GUARDED_SCOPE_END } while(0); GUARDED_SCOPE_END } int main() { try { foo(); } catch(exception& e) { cout << "main(): Caught exception: " << e.what() << endl; return -1; } cout << "main(): No Errors occurred!" << endl; return 0; }

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[scope_exit] MSVC error C2355: 'this' : can only be referenced inside non-static member functions
by Lorenzo Caminiti 01 Mar '11

01 Mar '11

Hello all, I am trying to use Boost.ScopeExit parameter binding mechanism to implement Boost.LocalFunction. To do so, I need to use some internal ScopeExit code to detect the type of `this` and bind its value to the local function declaration. The following code works on GCC but not on MSVC... This appears to be a MSVC 2008 bug: http://connect.microsoft.com/VisualStudio/feedback/details/331418/erroneous… 1) Can anyone please try this code on MSVC versions later than 2008 to see if it was fixed? 2) Do you know of a workaround for this problem? // File: lf03.cpp #include <boost/scope_exit.hpp> struct c { void f() { typedef void (*this_t)(int this_ ); #if defined(BOOST_MSVC) // for MSVC typedef boost::type_of::msvc_typeid_wrapper< sizeof(*boost::type_of::encode_start( #else // for GCC typedef __typeof__( boost::type_of::ensure_obj( #endif boost::scope_exit::aux::wrap( boost::scope_exit::aux::deref( this, (this_t)0 ) ) ) #if defined(BOOST_MSVC) // for MSVC )>::type #else // for GCC ) #endif this_w; } }; int main() { c cc; cc.f(); return 0; } I get this error on MSVC 2008 but the code compiles just fine on GCC: Microsoft (R) 32-bit C/C++ Optimizing Compiler Version 14.00.50727.42 for 80x86 Copyright (C) Microsoft Corporation. All rights reserved. lf03.cpp using native typeof lf03.cpp(17) : error C2355: 'this' : can only be referenced inside non-static member functions lf03.cpp(22) : error C2955: 'boost::type_of::msvc_typeid_wrapper' : use of class template requires template argument list C:\Program Files\boost\boost_1_42\boost/typeof/msvc/typeof_impl.hpp(212) : see declaration of 'boost::type_of::msvc_typeid_wrapper' Thank you very much. -- Lorenzo

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[serialization] boost/serialization/path.hpp
by Johan Råde 21 Feb '11

21 Feb '11

There is no boost/serialization/path.hpp. I suggest the following: ---------------------------------------------------------------------------------------------------------------- #ifndef BOOST_SERIALIZATION_PATH_HPP #define BOOST_SERIALIZATION_PATH_HPP // MS compatible compilers support #pragma once #if defined(_MSC_VER) && (_MSC_VER >= 1020) #pragma once #endif #include <boost/config.hpp> #include <boost/filesystem/path.hpp> #include <boost/serialization/level.hpp> BOOST_CLASS_IMPLEMENTATION(boost::filesystem::path, boost::serialization::primitive_type) #ifndef BOOST_NO_STD_WSTRING BOOST_CLASS_IMPLEMENTATION(boost::filesystem::wpath, boost::serialization::primitive_type) #endif namespace boost { namespace serialization { template<class Archive, class String, class Traits> void serialize(Archive& ar, boost::filesystem::basic_path<String, Traits>& p, const unsigned int version) { String s; if(Archive::is_saving::value) s = p.string(); ar & boost::serialization::make_nvp("string", s); if(Archive::is_loading::value) p = s; } }} #endif //-------------------------------------------------------------------------------------------------------------- Comments? Any suggested improvements? --Johan Råde

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[C++0x] Emulation of scoped enums
by Beman Dawes 16 Feb '11

16 Feb '11

The improved type safety of the C++0x scoped enum feature is attractive, so I'd like to start using it as it becomes available in compilers. See http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2007/n2347.pdf for a description. Note that the committee changed the name from strongly typed enums to scoped enums. See the attached for a boost/detail header that provides macro wrappers that use scoped enums if available, otherwise fall back on C++03 namespaces and unscoped enums. It lets a library write: BOOST_SCOPED_ENUM_START(algae) { green, red, cyan }; BOOST_SCOPED_ENUM_END ... BOOST_SCOPED_ENUM(algae) sample( algae::red ); void func(BOOST_SCOPED_ENUM(algae)); and then a user can write: sample = algae::green; func( algae::cyan ); Comments or suggestions appreciated, --Beman // scoped_enum_emulation.hpp ---------------------------------------------------------// // Copyright Beman Dawes, 2009 // Distributed under the Boost Software License, Version 1.0. // See http://www.boost.org/LICENSE_1_0.txt // Generates C++0x scoped enums if the feature is present, otherwise emulates C++0x // scoped enums with C++03 namespaces and enums. The Boost.Config BOOST_NO_SCOPED_ENUMS // macro is used to detect feature support. // // Caution: only the syntax is emulated; the semantics are not emulated and // the syntax emulation doesn't include being able to specify the underlying type. // // See http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2007/n2347.pdf for a // description of the feature. Note that the committee changed the name from // strongly typed enums to scoped enums. // // Sample usage: // // BOOST_SCOPED_ENUM_START(algae) { green, red, cyan }; BOOST_SCOPED_ENUM_END // ... // BOOST_SCOPED_ENUM(algae) sample( algae::red ); // void foo( BOOST_SCOPED_ENUM(algae) color ); // ... // sample = algae::green; // foo( algae::cyan ); #ifndef BOOST_SCOPED_ENUM_EMULATION_HPP #define BOOST_SCOPED_ENUM_EMULATION_HPP #include <boost/config.hpp> #ifndef BOOST_NO_SCOPED_ENUMS # define BOOST_SCOPED_ENUM_START(name) enum class name # define BOOST_SCOPED_ENUM_END # define BOOST_SCOPED_ENUM(name) name #else # define BOOST_SCOPED_ENUM_START(name) namespace name { enum enum_t # define BOOST_SCOPED_ENUM_END } # define BOOST_SCOPED_ENUM(name) name::enum_t #endif #endif // BOOST_SCOPED_ENUM_EMULATION_HPP

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[process] How to run test cases
by Boris 23 Jan '11

23 Jan '11

As Boost.Process 0.3 has been released it would be great if the test cases are run on various platforms. So far I've tested Boost.Process on WinXP with MSVC 9.0, Cygwin with g++ 3.4.4 and Solaris with g++ 3.4.6 and Sun C++ 5.9. To make it as easy as possible for others to run the test cases here's a short description of how to proceed. Nearly all test cases depend on a program called "helpers". This program is built first and is started by many test cases as a child process. In order to find the program "helpers" the test cases must know its location. As there is no way to get the location at runtime it is hardcoded in the file libs/process/test/misc.hpp. As the location differs depending on what compiler is used YOU MUST CHECK FIRST THE PATH IN libs/process/test/misc.hpp! Otherwise most of the test cases will fail as they look for a program "helpers" in the wrong directory. As of today only those paths are correct and have been tested which are set for Windows, Cygwin and Solaris. Only after you have checked and maybe updated the path in libs/process/test/misc.hpp you should try to build and run the test cases: WinXP/MSVC 9.0 ************** With MSVC 9.0 you only need to open the Visual Studio 2008 Command Prompt, change to the directory with the test cases and run bjam: C:\boost_1_36_0\libs\process\test> ..\..\..\bjam.exe -q Cygwin/GCC 3.4.4 **************** On Cygwin it's important to know if the Boost libraries have been built for the POSIX or Windows API. By default Boost libraries on Cygwin use the Windows API. With the Windows API the Boost.Process test cases are not passed successfully though (there are compiler errors where I'm not sure currently if they are a Boost.Process problem and how they could be fixed). If you want to run the test cases on Cygwin you must (re-)build the Boost libraries to use the POSIX API: $ cd ~/boost_1_36_0 $ ./bjam cxxflags=-DBOOST_POSIX_API Afterwards you can run the test cases: $ cd ~/boost_1_36_0/libs/process/test $ ../../../bjam cxxflags=-DBOOST_POSIX_API -q Solaris/GCC 3.4.6 ***************** At first you have to put the following line in ~/user-config.jam: using gcc : : : <linker-type>sun ; Then start building the Boost libraries: $ cd ~/boost_1_36_0 $ ./bjam --toolset=gcc cxxflags=-mcpu=ultrasparc For the test cases to be passed successfully you must update Boost.Test. Change line 624 in ~/boost_1_36_0/boost/test/impl/execution_monitor.ipp temporarily to: - , m_CHLD_action( SIGCHLD, catch_system_errors, attach_dbg, alt_stack ) + , m_CHLD_action( SIGCHLD, false, attach_dbg, alt_stack ) It is important that the second parameter is false as the signal SIGCHLD should not be handled by the execution monitor and should not be reported as an error. Afterwards the test cases can be run: $ cd ~/boost_1_36_0/libs/process/test $ ../../../bjam --toolset=gcc cxxflags=-mcpu=ultrasparc -q Solaris/Sun C++ 5.9 ******************* Build the Boost libraries with the sun toolset: $ cd ~/boost_1_36_0 $ ./bjam --toolset=sun stdlib=sun-stlport For the test cases to be passed successfully you must update Boost.Test. Change line 624 in ~/boost_1_36_0/boost/test/impl/execution_monitor.ipp temporarily to: - , m_CHLD_action( SIGCHLD, catch_system_errors, attach_dbg, alt_stack ) + , m_CHLD_action( SIGCHLD, false, attach_dbg, alt_stack ) It is important that the second parameter is false as the signal SIGCHLD should not be handled by the execution monitor and should not be reported as an error. If you run the test cases now you'll get this compiler error for one test case: "../../../boost/asio/detail/socket_ops.hpp", line 218: Error: Cannot assign void* to char*. "../../../boost/asio/detail/socket_ops.hpp", line 229: Error: Cannot assign void* to char*. "../../../boost/asio/detail/descriptor_ops.hpp", line 66: Error: Cannot assign void* to char*. "../../../boost/asio/detail/descriptor_ops.hpp", line 72: Error: Cannot assign void* to char*. The bug has been reported to the Boost.Asio mailing list. If you want to build that one test case, too, you need to fix the two files in Boost.Asio 1.36.0 yourself. All the test cases can be built and run with: $ cd ~/boost_1_36_0/libs/process/test $ ../../../bjam --toolset=sun stdlib=sun-stlport -q

4 9

[SoC] BGL project idea
by Gautam Sewani 03 Jan '11

03 Jan '11

Hi, I am a Computer Science student hoping to contribute to Boost for this year's summer of code. I had a few questions regarding the BGL project idea (https://svn.boost.org/trac/boost/wiki/SoC2010#Boost.Graph) for SOC 2010. 1. I can think of only a few places where the suggested algorithms will be used. Does the community think that these algorithms are used frequently enough to put them in a library? How important does the community consider this project? 2. Will the project proposal be expected to include the API design? Thanks and Regards Gautam

5 29

[GIL] [patch] read multipage TIFF files
by Robert Pollak 29 Nov '10

29 Nov '10

Hello, the following patch (against the current trunk) allows to read any page of a multipage TIFF file, by optionally specifying the zero-based directory number. (The correct term for a TIFF page is "directory".) It adds a "dirnum" to the relevant functions, and uses the corresponding libtiff functionality. The "dirnum" default value is 0 for compatibility with present callers. Additionally, it defines the function tiff_get_directory_count to get the number of directories in the TIFF file. Please give me some feedback or consider applying the patch. This patch would close the corresponding feature request https://svn.boost.org/trac/boost/ticket/2373 . Credits go to Roland Richter, whose code the patch is based on. Best Regards, Robert Pollak Index: boost/gil/extension/io/tiff_io.hpp =================================================================== --- boost/gil/extension/io/tiff_io.hpp (revision 64065) +++ boost/gil/extension/io/tiff_io.hpp (working copy) @@ -122,9 +122,13 @@ protected: TIFF *_tp; public: - tiff_reader(const char* filename) { + tiff_reader(const char* filename,tdir_t dirnum=0) { io_error_if((_tp=TIFFOpen(filename,"r"))==NULL, "tiff_reader: fail to open file"); + if(dirnum>0) { + io_error_if(TIFFSetDirectory(_tp,dirnum)!=1, + "tiff_reader: fail to set directory"); + } } ~tiff_reader() { TIFFClose(_tp); } template <typename View> @@ -171,10 +175,10 @@ private: CC _cc; public: - tiff_reader_color_convert(const char* filename) : - tiff_reader(filename) {} - tiff_reader_color_convert(const char* filename,CC cc_in) : - tiff_reader(filename),_cc(cc_in) {} + tiff_reader_color_convert(const char* filename,tdir_t dirnum=0) : + tiff_reader(filename,dirnum) {} + tiff_reader_color_convert(const char* filename,CC cc_in,tdir_t dirnum=0) : + tiff_reader(filename,dirnum),_cc(cc_in) {} template <typename View> void apply(const View& view) { point2<std::ptrdiff_t> dims=get_dimensions(); @@ -336,18 +340,34 @@ }; /// \ingroup TIFF_IO +/// \brief Returns the number of directories in the TIFF file +inline int tiff_get_directory_count(const char* filename) { + TIFF *tif; + io_error_if((tif=TIFFOpen(filename,"r"))==NULL, + "tiff_get_count: fail to open file"); + + int dircount = 0; + do { + dircount++; + } while (TIFFReadDirectory(tif)); + + TIFFClose(tif); + return dircount; +} + +/// \ingroup TIFF_IO /// \brief Returns the width and height of the TIFF file at the specified location. /// Throws std::ios_base::failure if the location does not correspond to a valid TIFF file -inline point2<std::ptrdiff_t> tiff_read_dimensions(const char* filename) { - detail::tiff_reader m(filename); +inline point2<std::ptrdiff_t> tiff_read_dimensions(const char* filename,tdir_t dirnum=0) { + detail::tiff_reader m(filename,dirnum); return m.get_dimensions(); } /// \ingroup TIFF_IO /// \brief Returns the width and height of the TIFF file at the specified location. /// Throws std::ios_base::failure if the location does not correspond to a valid TIFF file -inline point2<std::ptrdiff_t> tiff_read_dimensions(const std::string& filename) { - return tiff_read_dimensions(filename.c_str()); +inline point2<std::ptrdiff_t> tiff_read_dimensions(const std::string& filename,tdir_t dirnum=0) { + return tiff_read_dimensions(filename.c_str(),dirnum); } /// \ingroup TIFF_IO @@ -356,17 +376,17 @@ /// Throws std::ios_base::failure if the file is not a valid TIFF file, or if its color space or channel depth are not /// compatible with the ones specified by View, or if its dimensions don't match the ones of the view. template <typename View> -inline void tiff_read_view(const char* filename,const View& view) { +inline void tiff_read_view(const char* filename,const View& view,tdir_t dirnum=0) { BOOST_STATIC_ASSERT(tiff_read_support<View>::is_supported); - detail::tiff_reader m(filename); + detail::tiff_reader m(filename,dirnum); m.apply(view); } /// \ingroup TIFF_IO /// \brief Loads the image specified by the given tiff image file name into the given view. template <typename View> -inline void tiff_read_view(const std::string& filename,const View& view) { - tiff_read_view(filename.c_str(),view); +inline void tiff_read_view(const std::string& filename,const View& view,tdir_t dirnum=0) { + tiff_read_view(filename.c_str(),view,dirnum); } /// \ingroup TIFF_IO @@ -375,25 +395,25 @@ /// Throws std::ios_base::failure if the file is not a valid TIFF file, or if its color space or channel depth are not /// compatible with the ones specified by Image template <typename Image> -void tiff_read_image(const char* filename,Image& im) { +void tiff_read_image(const char* filename,Image& im,tdir_t dirnum=0) { BOOST_STATIC_ASSERT(tiff_read_support<typename Image::view_t>::is_supported); - detail::tiff_reader m(filename); + detail::tiff_reader m(filename,dirnum); m.read_image(im); } /// \ingroup TIFF_IO /// \brief Allocates a new image whose dimensions are determined by the given tiff image file, and loads the pixels into it. template <typename Image> -inline void tiff_read_image(const std::string& filename,Image& im) { - tiff_read_image(filename.c_str(),im); +inline void tiff_read_image(const std::string& filename,Image& im,tdir_t dirnum=0) { + tiff_read_image(filename.c_str(),im,dirnum); } /// \ingroup TIFF_IO /// \brief Loads and color-converts the image specified by the given tiff image file name into the given view. /// Throws std::ios_base::failure if the file is not a valid TIFF file, or if its dimensions don't match the ones of the view. template <typename View,typename CC> -inline void tiff_read_and_convert_view(const char* filename,const View& view,CC cc) { - detail::tiff_reader_color_convert<CC> m(filename,cc); +inline void tiff_read_and_convert_view(const char* filename,const View& view,CC cc,tdir_t dirnum=0) { + detail::tiff_reader_color_convert<CC> m(filename,cc,dirnum); m.apply(view); } @@ -401,31 +421,31 @@ /// \brief Loads and color-converts the image specified by the given tiff image file name into the given view. /// Throws std::ios_base::failure if the file is not a valid TIFF file, or if its dimensions don't match the ones of the view. template <typename View> -inline void tiff_read_and_convert_view(const char* filename,const View& view) { - detail::tiff_reader_color_convert<default_color_converter> m(filename,default_color_converter()); +inline void tiff_read_and_convert_view(const char* filename,const View& view,tdir_t dirnum=0) { + detail::tiff_reader_color_convert<default_color_converter> m(filename,default_color_converter(),dirnum); m.apply(view); } /// \ingroup TIFF_IO /// \brief Loads and color-converts the image specified by the given tiff image file name into the given view. template <typename View,typename CC> -inline void tiff_read_and_convert_view(const std::string& filename,const View& view,CC cc) { - tiff_read_and_convert_view(filename.c_str(),view,cc); +inline void tiff_read_and_convert_view(const std::string& filename,const View& view,CC cc,tdir_t dirnum=0) { + tiff_read_and_convert_view(filename.c_str(),view,cc,dirnum); } /// \ingroup TIFF_IO /// \brief Loads and color-converts the image specified by the given tiff image file name into the given view. template <typename View> -inline void tiff_read_and_convert_view(const std::string& filename,const View& view) { - tiff_read_and_convert_view(filename.c_str(),view); +inline void tiff_read_and_convert_view(const std::string& filename,const View& view,tdir_t dirnum=0) { + tiff_read_and_convert_view(filename.c_str(),view,dirnum); } /// \ingroup TIFF_IO /// \brief Allocates a new image whose dimensions are determined by the given tiff image file, loads and color-converts the pixels into it. /// Throws std::ios_base::failure if the file is not a valid TIFF file template <typename Image,typename CC> -void tiff_read_and_convert_image(const char* filename,Image& im,CC cc) { - detail::tiff_reader_color_convert<CC> m(filename,cc); +void tiff_read_and_convert_image(const char* filename,Image& im,CC cc,tdir_t dirnum=0) { + detail::tiff_reader_color_convert<CC> m(filename,cc,dirnum); m.read_image(im); } @@ -433,23 +453,23 @@ /// \brief Allocates a new image whose dimensions are determined by the given tiff image file, loads and color-converts the pixels into it. /// Throws std::ios_base::failure if the file is not a valid TIFF file template <typename Image> -void tiff_read_and_convert_image(const char* filename,Image& im) { - detail::tiff_reader_color_convert<default_color_converter> m(filename,default_color_converter()); +void tiff_read_and_convert_image(const char* filename,Image& im,tdir_t dirnum=0) { + detail::tiff_reader_color_convert<default_color_converter> m(filename,default_color_converter(),dirnum); m.read_image(im); } /// \ingroup TIFF_IO /// \brief Allocates a new image whose dimensions are determined by the given tiff image file, loads and color-converts the pixels into it. template <typename Image,typename CC> -inline void tiff_read_and_convert_image(const std::string& filename,Image& im,CC cc) { - tiff_read_and_convert_image(filename.c_str(),im,cc); +inline void tiff_read_and_convert_image(const std::string& filename,Image& im,CC cc,tdir_t dirnum=0) { + tiff_read_and_convert_image(filename.c_str(),im,cc,dirnum); } /// \ingroup TIFF_IO /// \brief Allocates a new image whose dimensions are determined by the given tiff image file, loads and color-converts the pixels into it. template <typename Image> -inline void tiff_read_and_convert_image(const std::string& filename,Image& im) { - tiff_read_and_convert_image(filename.c_str(),im); +inline void tiff_read_and_convert_image(const std::string& filename,Image& im,tdir_t dirnum=0) { + tiff_read_and_convert_image(filename.c_str(),im,dirnum); } /// \ingroup TIFF_IO

2 7

[guidelines] why template errors suck
by Eric Niebler 26 Nov '10

26 Nov '10

This is borderline self-promotion and I fretted posting this. But we a community of advanced C++ library developers and I'd really like feedback about these issues. And they really do involve Boost library development. If we could reach agreement about these techniques, we might want to integrate them into Boost's coding guidelines. http://www.reddit.com/r/programming/comments/diddg/expressive_c_why_templat… Comments? -- Eric Niebler BoostPro Computing http://www.boostpro.com

24 136

LLVM license compatibility with BSL
by vicente.botet 19 Nov '10

19 Nov '10

Hi, I have found quite useful to adapt the test for llvm/libc++ ratio/chrono to test Boost.Ratio and Boost.Chrono. But Anthony has signaled me that maybe there is a compatibility problem with the license included in these files. //===----------------------------------------------------------------------===// // // The LLVM Compiler Infrastructure // // This file is distributed under the University of Illinois Open Source // License. See LICENSE.TXT for details. // //===----------------------------------------------------------------------===// Is the LLVM License (http://llvm.org/docs/DeveloperPolicy.html#license) compatible with the Boost Software License? Can we include files with this comment on a Boost library? Best, _____________________ Vicente Juan Botet Escribá http://viboes.blogspot.com/

11 22

Interest in B-tree library for Boost?
by Beman Dawes 17 Nov '10

17 Nov '10

A Boost B-tree library would provide disk-based associative containers that scale all the way from really, really, small to really, really, large. B-trees perform well on hardware ranging from ancient floppy disk drives all the way up to humongous disk arrays. They are the technology behind most high-performance disk file systems and databases. If you don't know what a B-tree is, or think that "B-tree" is an abbreviation for "Binary tree", you might want to read the Wikipedia B-Tree article: http://en.wikipedia.org/wiki/B-tree. Knuth and other computer science texts also supply descriptions. See http://mysite.verizon.net/beman/btree/index.html for a more complete description of the proposed library. A preliminary implementation is available. Download http://mysite.verizon.net/beman/btree/btree-preview-1.zip, and unpack into a current Boost distribution. A few existing Jamfiles will be overwritten. The only compilers tested and working so far are VC++ 10 and GCC/MinGW 4.5. You can view the library online at http://github.com/Beman/Boost-Btree There is no detailed documentation yet, but if you know how to use std::map and other standard library associative containers, you already know most of what you need to know. Critical differences are documented in the Library Characteristics section of the index.html page referenced above. Initial timing tests have been very encouraging. The time test compares the btree_map implementation to std::map. As expected, a btree_map is many times slower than a std::map, given a cold operating system file cache and constraining the btree_map's caching to a minimum. But at the other extreme, when the O/S file cache is warm and the btree_map's cache is as large as the file, the btree_map is very similar in speed to std::map.The btree library's code is still very new, so timings and everything else may be subject to lots of revision. Any interest? --Beman

14 37

[gsoc] Boost.Process done
by Boris Schaeling 31 Oct '10

31 Oct '10

Here are the results of the Boost.Process project within this year's Google Summer of Code program: We have a complete library to manage system processes now! If you like to play around with the library download the ZIP file from <http://www.highscore.de/boost/gsoc2010/process.zip>. As it's a header-only library simply copy the files to your Boost folder. If you like to quickly check the documentation click on <http://www.highscore.de/boost/gsoc2010/>. The library is now complete and basically ready for a review. As there have been so many Boost.Process drafts before (after all the first version was created 2006) this library's version number is 0.4. This will somehow make it possible to refer to the various drafts if it's necessary. For now I would appreciate if the library's test cases are run on as many platforms as possible. After copying the files from the ZIP file to the Boost folder change to libs/process/test/ and run bjam - that's all! What has been changed? * All previous Boost.Process drafts including Ilya's 2008 version from the vault have been thoroughly studied to create a better version. From the multiple Boost.Process drafts which have been floating around since 2006 we took the best ideas and created a new unified version. * The design and implementation of the library have been simplified. The library's API is smaller, and the implementation is easier to understand. It should be possible to benefit from this library as quickly as possible. Even developers who have no experience in managing system processes should be able to do so easily. * There are no POSIX and Windows specific classes anymore (posix_context, posix_child, win32_context, win32_child etc. have been dropped). Instead of trying to support each and every feature platforms provide extension points have been defined. They enable library users to "link in" those platform specific features they are interested in. * For the first time there is full support for synchronous and asynchronous operations. While asynchronous operations are built on top of Boost.Asio synchronous operations can be utilized without that library. Developers don't need to include any Boost.Asio headers and don't need to learn about Boost.Asio if they don't need asynchronous operations. * Stream behaviors define if and how standard streams can be used by a child process. While the various stream behaviors were defined as an enumeration or a boost::variant in previous Boost.Process drafts they are now implemented as classes. This makes it possible for developers to create new stream behaviors. * The code to start child processes on POSIX platforms has been carefully adapted to support multi-threaded applications (it turned out that this code was wrong in all Boost.Process drafts so far). The documentation explains what you need to take care of if you want to create child processes in a multi-threaded application on POSIX platforms. * The documentation is new and has been shortened and simplified. There is a user guide which can be read in 10 minutes and introduces all the major features of the library. The documentation is now also based on Quickbook. * The test cases have been restructured to simplify them. They can now be run without patching Boost.Test and without setting a path to a helper executable in the source files - it's now all automatic. They are all passed successfully with MSVC 9 (2008) and g++ 4.2.1. What is currently missing? * Pipelines are not (yet) supported. If you have been using boost::process::launch_pipeline() there is nothing in this Boost.Process draft you can use instead. Depending on feedback this feature will be added again (there was simply no time yet to do this). We hope that after four years, two Google Summer of Code programs and countless drafts this new version will finally become the official Boost.Process library so many have been waiting for. Boris and Felipe

18 182

[constrained_value] Constrained Value review results
by Gordon Woodhull 29 Oct '10

29 Oct '10

Greetings, Substituting for Jeff Garland, I am pleased to present the results from the constrained_value review. The library is available at http://rk.dl.pl/f/constrained_value.zip The documentation is at http://rk.dl.pl/r/constrained_value Enjoy! Gordon 1. History The idea for a constrained value library goes back to at least 2004; Christopher Diggins proposed a mini-library at that time. In 2007 Joe Gottman suggested that Jeff Garland's constrained_value.hpp in date_time could be a top-level library. Concurrently, Robert Kawulak (henceforth RK) was working on his own library for the purpose, which he also started in 2004, unaware of the others. RK announced his library on November 11, 2007. Discussion continued into 2008; on June 19, RK announced his library was ready for review and it was put in the queue. The review began on December 1 2008 and continued until around December 15 (with some trailing discussion of the definition of invariant and why exceptions should not be used to check invariants). Gordon Woodhull reviewed the thread's 260 messages in the summer of 2010 and produced this report, dividing the issues raised between those where there was consensus on a change, those where no resolution was found, and those where the author and requesters (mostly) agreed that no change was needed. 2. Votes Eight people voted for acceptance of the library; there were no "no" votes. However, many people stated conditions on acceptance. Thanks to Chris (indy271828(a)sympatico.ca) Vicente Botet, Zach Laine, John Maddock, Thorsten Ottosen, Stjepan Rajko, Daryle Walker, and Gordon Woodhull for providing reviews. (In addition, Paul Bristow provided a review which looks like a yes but does not explicitly say so.) Thanks also to David Abrahams, Kim Barrett, Neal Becker, Paul Bristow, Edward Diener, Jeff Flinn, Joe Gottman, Mathias Guanard, Mika Heiskanen, Giovanni Pierro Deretta, Thomas Klimpel, Michael Marcin, OvermindDL1, John Phillips, raindog, Ravi (lists_ravi(a)lavabit.com) Johan Råde, Sebastian Redl, Peter Simons, Steven Watanabe, Utku Yaman, and Deane Yang for participating in a very active discussion. 3. Issues to be Addressed Floating point By far the most contentious issue in the review was the statement in the library documentation that floating point is not supported, and a few reviewers made fixing this a condition on acceptance. The issue is that the x87 math instructions (which are the default for 32-bit Intel compiles) utilize 80-bit registers which are then rounded down to 64 bits when a double value is written to memory. This can cause two values which were not equal to become equal later, with fairly unpredictable behavior depending on optimization and what code intervenes between calculating a value and comparing it. One solution is simply not to use the x87 math instructions by enabling the SSE2 math instructions instead. However, users may want the extra precision, and there is no way for a library to control this option. A few reviewers confused this issue with the frequent need for fuzzy comparison with epsilon; it was shown that the bug can still appear with epsilon-based comparisons. Jeff Garland points out that the Boost Numeric Interval library, http://www.boost.org/doc/libs/1_42_0/libs/numeric/interval/doc/interval.htm has also dealt with the x87 and NaN problems. It uses the round-trip-to-memory approach for x87. There is potential to create constraints for constrained_value using numeric::interval, and perhaps any other fixes for floating point belong in that library. Many solutions were proposed; after debate there were four left standing: * Force the new value to be written to memory Kim Barrett suggested the following function, noting that it should not force a memory write unless the value is in a register. inline double exact(double const& x) { return *const_cast<double const volatile*>(&x); } Gordon Woodhull has tested this against example provided by Thomas Klimpel in a message titled "floating point FUD" of January 23, 2010 (http://article.gmane.org/gmane.comp.lib.boost.devel/198817) and it does work. However, many people objected to this solution because of efficiency concerns: it requires a round-trip to memory (or at least to cache) for every assignment. * Only allow >= or <= for floating point types, and make sure the bounds are truncated 80- to 64-bit truncation can cause two values to become equal, but if one of them is already truncated, it cannot cause them to swap order. Since it is likely that the value will be changed much more frequently than the bound, it would suffice to apply truncation just to the bounds when they are set, e.g. with the exact() function above. However it does not seem that this solution can work if the bounds are dynamically calculated; the library supports bounds being returned by an inlined function. Johan Råde also suggested that it might be possible to implement < and > in terms of <= and >= and the std::nextafter function. * Force the processor to use 64-bit precision Johan Råde mentions a floating point control register which could be used in http://article.gmane.org/gmane.comp.lib.boost.devel/183760 There were also mentions of possible assembly code solutions, but none were provided and this was generally unpopular because it requires someone very knowledgeable to maintain it. John Phillips argued that reducing the precision will "lose significance faster than expected". * Another interesting solution was suggested by Stjepan Rajko: that the test might not be the same as the invariant. This is what testing with epsilon would guarantee. If the value passes the test it is guaranteed to satisfy the invariant, but only the test and not the invariant is in code. So some values might be rejected which are okay, but no bad value is accepted. RK felt that any floating point solution should be implemented separately from constrained_value, because he does not have the expertise. But he should be willing to document the scope of the problem better, including the SSE2 compiler flags that avoid the problem altogether. The first solution (truncation of the value) does not seem to require any changes to the library. Truncating the bounds might require some extra customization points. NaN Another problem with floating point is NaN, which compares false with everything. It might be okay if the bounds inclusion test always returned false. But the closed range is implemented as !(x < lower) && !(upper < x). Stjepan Rajko suggested that it should always be compare(lower, x) && compare(x, upper) where compare is < for excluded bounds and <= for included. It seems like this solution would work well for floats but not necessarily for user-defined types, which might only define operator<(). Substitutability with the underlying type A few people requested the ability to set a compiler flag in order to substitute the constrained_value with the underlying type. This is not exactly possible, unless the user is willing to explicitly extract the value using static_cast<T>(cv). The library does provide unconstrained<> which in most cases optimizes away, but the interface is not perfectly compatible with the underlying type. Constraints not copied when operators used The use of operators invokes implicit conversion to the underlying type, which means that in a statement like constrained_value x(10, constraint(...)), y(-x); y ends up with uninitialized constraints. Steven Watanabe suggested that the operators could be overloaded, but RK argued that the behavior would be application-specific: "For some applications returning a constrained value would be OK (but again there is the problem that the constraint may reject the modified value) while for others it's better to return the underlying type." Constrained strings Jeff Garland offered that he has written constrained_string classes for allowing values from a set of strings, and for validation against a regex. RK said he might add a constraint type which validates against set<T>, and affirmed that a regex validator would be nice too. Bounding on only one side Utku Yaman and others requested a way to bound integers on only one side. RK noted that you could set one of the bounds to the maximum or minimum possible integer, but this is verbose. Default arguments would be confusing, and RK thought maybe he would supply lower_saturating_int and upper_saturating_int. Note that there is a more general problem, especially if floating point is allowed. (Also consider e.g. fixed point, rational.) Recoverable error policy - error policy changing the value There were some objections to the error policy taking three parameters - the new value, the member value, and the constraint. Does it really need to change the member value? Yes, RK explained, because this is a recoverable error policy. Vicente Botet asked that the concept be called RecoverableErrorPolicy. Serialization Neal Becker requested support for serialization. RK agreed this is worth looking into and pointed out a couple of difficulties. One, a way to not serialize empty (or static) policies is needed. Two, non-default constructible types such as odd_number might require use of load_construct_data() / save_construct_data() instead of serialize(). Rename bounded_int This class name does not convey the fact that the bounds are specified at compile time. Neal Becker suggested compile_time_bounded or static_bounded. RK says the first name is too long, and the second might imply that the bounds are static members (which is also a legitimate use case). sizeof static constrained types == sizeof underlying type Assuming that the empty base class optimization is being applied correctly, which seems to be the case, if the constraint and the error policy are empty, the size of the constrained value should be the same as the size of the underlying type. However, this was not the case on all platforms, at least at the time of the review. The library should include sizeof tests in its test suite so that potential users know if there is unexpected overhead on their platform. Specify static bounds as open<0>, closed<100> for bounded<> and bounded_int<> Requested by Vicente Botet. If possible, this would reduce the number of template arguments and would be more clear than the current bounds exclusion boolean parameters. Some default constructions may throw If zero does not satisfy the constraint, then a default-constructed constrained value may throw an exception. (There are other examples, like non-empty string.) Many reviewers requested a means to provide a default value, which can be done by wrapping the underlying type, but RK felt a default value class was out of scope. At the very least this should be documented and probably an example given. Examples Vicente Botet requested: * an example showing how to create a constrained class by derivation and/or containment which adds/removes methods from the constrained value interface * a date example where changing the month affects the bounds for the day. * example of static bounding on only one side * example of bounds calculated at runtime by a function ("runtime dynamic bounding") Others: * example of constraints with static members - allows shared mutable constraints with no overhead per instance. Tests! Many reviewers were offended that there were no tests in the review version. RK said he would write some. Documentation * document the concepts and provide tests with concept archetypes. It turns out that these are documented briefly in the doxygen documentation of constrained<> at http://tinyurl.com/39v8o6r, but many reviewers were expecting a section in the main document. * Stjepan Rajko pointed out that the constraint can't depend on mutable members of the underlying type, and wondered if there were other implicit requirements, such as the way copy construction or swapping works. He requested these be documented. * Gordon Woodhull suggests a section on space efficiency and which configurations should allow the size to be optimized to the same size as the underlying type, and spelling out in each example what the cost in space is. * Thorsten Ottosen requested benchmarks of non-checking unconstrained against just using the underlying type. RK offered that he had looked at the generated assembly on some platforms. 4. Unresolved debates Error policy is allowed to change constraint Vicente Botet objected to the "bounded object with memory" example, which tracks extremal values by setting the bounds to include any new values. And Thorsten Ottosen objected to the inefficiency of change_constraint using construct-and-swap: it's not necessary to swap the constraint unless it might be changed by the error policy. This seems to be an example of a monitored value, which RK does not want to write himself, so does it belong in this library? RK argued that it does no harm, so why not allow? Double-checking and disabling assertions A number of people were concerned with the inefficiency of first checking the constraint, and then also asserting that the constraint is satisfied after the assignment has happened or the error handler has been called. But RK argued that it was necessary to check the invariant to make sure that the assignment operator and the error handler are doing their job. Besides, it is possible to disable the asserts with either BOOST_DISABLE_ASSERTS or NDEBUG. There was some discussion of adding an assert policy or a specific macro (with no clear conclusion). Disabling checks There is unconstrained, which offers a way to replace one constrained type with an unconstrained type, but Chris (indy271828(a)sympatico.ca) requested a way to disable all checks with a single macro. It might not be good enough to use a single error policy and select between throwing version and an assign-anyway version, because the compiler won't always optimize this away. More members, less free functions Thorsten Ottosen thought that any functions which change the state of the object should be members, not free functions. In particular, change_constraint might be less efficient than possible because the construct-and-swap requires copying the constraint. This does seem to be partly an ideological debate. Specific classes instead of a general super-template Vicente Botet requested that the interface use specific classes instead of typedefs: currently many of the specializations, like bounded<>, are metafunctions that apply some parameters to the generic constrained_value and return a new type, and then the specific operations are free functions. Instead these could be full classes with member functions. RK argued that this would result in unnecessary duplication. Way to disable the arithmetic operators Vicente Botet requested a solution in code or in documentation for users who don't want the arithmetic operators defined. 5. Ideas not requiring any action Monitored Values Stjepan Rajko suggested (and Vicente Botet expanded on the idea) that constrained value is really a special case of a more general "monitored value" class, in which a monitor policy decides how to handle any assignment. So constrained value would be a monitored value where the monitor policy checks a constraint, possibly calls an error policy, and then asserts the constraint. RK did not want to implement this and resisted suggestions to allow the assertion to be disabled in order to allow this use case, because without an invariant, it's not really a constrained value. But he suggested that monitored value could be implemented by someone else and constrained value could be re-implemented in terms of it. "Monitored value" might not be the best name for the general class, because "monitor" suggests something passive, rather than something which controls the outcome of assignment. A way to run a function on a constrained value Stjepan Rajko requested a way to make a copy of the value, run a function on it, and then reassign back, preferring the syntax call_using_copy(f, x) to x = f(x). But he notes this could be written as a free function. Multiple ranges Edward Diener requested a way to supply multiple ranges, but agreed that the syntax would be unattractive. Assertions instead of exceptions Thorsten Ottosen requested a way to have only assertions and no exceptions, and RK pointed out that this can be done either by specifying an error policy which asserts, or even with an assign-anyway error policy, which leaves the invariant checking in place. Exclude bounds parameter Vicente Botet found it confusing that bounded_int takes false to mean include bounds and true to mean exclude the bounds. RK explained that this is an artifact of the way within_bounds is templated on a type which can be either a compile-time or a runtime value, e.g. mpl::true_ or bool; this technique means there can be no default argument to the constructor and thus the more common option must be false, the default constructed value of bool. Constraints between several variables. Vicente Botet suggested a sort of constrained_tuple where if you set one field it would affect the constraints for the other fields. E.g. a date object where the month and year would affect the valid range for the day. With the current interface you'd have to set the whole date at once. Constrained values as sets of instances Exploring the problem domain, Vicente Botet suggested another possible implementation of constrained value where the constrained value type keeps track of which instances satisfy the constraint. This class would offer a split operation which moves any instances which satisfy a more specific constraint into the new set. Changing the constraint would similarly return the set of instances which are now excluded.

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Thoughts for a GUI (Primitives) Library
by Gwenio 20 Oct '10

20 Oct '10

As it stands, neither Boost nor C++ has any support for GUI applications. Therefore I am suggesting a library that provides the bare minimum required to create a GUI application. My thoughts on what this library would contain are as follows: - Types for controls (contexts bound to the extent of their parent) and windows (contexts that remain separate from their parents). - An event handler class that is passed when controls and windows are created that contains all information needed to handle events for the new context. - Functions for generating events (if applicable) and (a) function(s) to initiate message handling (unless the event loop is run in its own thread like in Java). - Functions to access and manipulate the data of the contexts (size, position, z-order, ect). - Miscellaneous other types used for support (such as for screen positions). - A way to retrieve the native concept of a window/control. As you can see, there are no controls/widgets/ect defined, either from the library or using the native versions. Such things can be added later, if people can ever agree on how they should be implemented. It needs a lot of refining, but I believe this covers the *minimum* support that is needed for a GUI.

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