July 2016 - Boost - lists.boost.org

[contract] Friend functions
by Lorenzo Caminiti 19 Jul '16

19 Jul '16

Hello all, I would like to discuss contracts for friend functions and specifically how they are handled in Boost.Contract. Consider the following example: class a; class b; class data { ... friend bool deep_equal(a*, b*); bool equal(data const&); }; class a { ... friend bool deep_equal(a*, b*); data data_; }; class b { ... friend bool deep_equal(a*, b*); data data_; }; bool deep_equal(a* x, b* y) { return x->data_.equal(y->data_); } Via friendship, deep_equal can be considered to extend a and b public interfaces, but not data's public interface (in fact, deep_equal does not take instance of data as an argument). Therefore, it is reasonable to think that deep_equal should check a and b class invariants (if so... in which order?), but not data's class invariants. As discussed in N4160, that would probably require some new language feature to specify which subset of friend functions also extend a class public interface. Plus such a feature should identify some preferred order in which class invariants should be checked for a friend function that extends public interfaces of multiple classes. That seems rather complicated so I think a language proposal (like N1962) is better off going with the general rule that friends functions do not check class invariants (even if that might not always be ideal in all cases): bool deep_equal(a* x, b* y) [[requires: x && y]] // Does not check a and b (and c) invariants... even if arguably it should. { return x->data_.equal(y->data_); } In Boost.Contract: bool deep_equal(a* x, b* y) { boost::contract::guard c = boost::contract::function() .precondition([&] { BOOST_CONTRACT_ASSERT(x && y); }) ; // Does not check a and b (and c) invariants... even if arguably it should. return x->data_.equal(y->data_); } Maybe programmers could manually check a and b invariants (but then also from the function body when it throws) when those checks are truly essential for friend function: bool deep_equal(a* x, b* x) [[requires: x && y]] // Check a and b invariants in that order (if contract writes decide to), does not check c invariants. [[requires: x->invariant() && y->invariant()] [[ensures: x->invariant() && y->invariant()] { try { return x->data_.equal(y->data_); } catch(...) { [[assert: x->invariant() && y->invariant()]]; throw; } } (That seems somewhat verbose... plus it assumes that class invariants are somehow specified in a `bool invariant() const function (that can be private), or using a set of [[invariant: ...]] attributes that automatically generate such a callable `bool invariant() const` function.) This is possible in Boost.Contract: bool deep_equal(a* x, b* y) { boost::contract::guard c = boost::contract::function() .precondition([&] { BOOST_CONTRACT_ASSERT(x && y); }) ; // Check a and b invariants in that order (if contract writers decide to), does not check c invariants. boost::contract::guard inv_x = boost::contract::public_function(*x); boost::contract::guard inv_y = boost::contract::public_function(*y); return x->data_.equal(y->data_); } Finally, note that in this case preconditions are checked before entry invariants (while usually public functions check preconditions after entry invariants). That is desirable/needed for friend functions because the class object is not *this (which is always well defined and therefore subject to no precondition). For friend functions, the class object can be any computation of the friend function arguments and those arguments must be validated by preconditions before they can be used to access the class object. In the examples above, the arguments are checked to be not null by preconditions so they can be safely dereferenced to get the objects *x and *y (and in general the computations required might be even much more complex than dereferencing pointers). Thank you. --Lorenzo

1 0

[contract] Without the macros
by Lorenzo Caminiti 19 Jul '16

19 Jul '16

Hello all, In the last few years my professional and personal lives changed quite a bit limiting my ability to contribute to Boost. However, in my spare time I slowing continued to revise Boost.Contract hoping to be able to commit it to a Boost release someday (after the library was accepted 3+ years ago... https://groups.google.com/forum/?fromgroups=#!topic/boost-list/jQ7OjAmos_Y) While doing so I realized that leveraging C++11 lambda functions, Boost.Contract could be re-implemented without its crazy macros that alter C++ function declaration syntax. Boost.Contract still remains the only C++ library that implements *all* features of Contract Programming (a.k.a., Design by Contract or DbC): subcontracting, class invariants (also static and volatile), postconditions (with old and return values), preconditions, customizable actions on assertion failure (terminate, throw, etc.), optional assertion compilation, disable assertion checking while already checking other assertions (to avoid infinite recursion), etc. Furthermore, in its new incarnation Boost.Contract no longer uses crazy macros so it is easier to use, faster to compile, and gives readable compiler errors. For example: #include <boost/contract.hpp> int inc(int& x) { int result; boost::contract::old_ptr<int> old_x = BOOST_CONTRACT_OLDOF(x); boost::contract::guard c = boost::contract::function() .precondition([&] { BOOST_CONTRACT_ASSERT(x < std::numeric_limits<int>::max()); }) .postcondition([&] { BOOST_CONTRACT_ASSERT(x == *old_x + 1); BOOST_CONTRACT_ASSERT(result == *old_x); }) ; return result = x++; // Function body. } Or with subcontracting: #include <boost/contract.hpp> #include <vector> template<typename T> class pushable; // Arbitrary base to demo subcontracting. template<typename T> class vector #define BASES public pushable<T> : BASES { public: typedef BOOST_CONTRACT_BASE_TYPES(BASES) base_types; // Subcontracting. #undef BASES void invariant() const { // Checked in AND with base class invariants. BOOST_CONTRACT_ASSERT(size() <= capacity()); // Line 25. } virtual void push_back(T const& value, boost::contract::virtual_* v = 0) /* override */ { boost::contract::old_ptr<unsigned> old_size = BOOST_CONTRACT_OLDOF(v, size()); // Old values. boost::contract::guard c = boost::contract::public_function< override_push_back>(v, &vector::push_back, this, value) .precondition([&] { // Checked in OR with base preconditions. BOOST_CONTRACT_ASSERT(size() < max_size()); // Line 35. }) .postcondition([&] { // Checked in AND with base postconditions. BOOST_CONTRACT_ASSERT(size() == *old_size + 1); // Line 38. }) ; vect_.push_back(value); // Function body. } BOOST_CONTRACT_OVERRIDE(push_back) // For `override_push_back`. // Could program contracts for those as well. unsigned size() const { return vect_.size(); } unsigned max_size() const { return vect_.max_size(); } unsigned capacity() const { return vect_.capacity(); } private: std::vector<T> vect_; }; Full documentation and examples at: https://lcaminiti.github.io/boost-contract What do you think? Thanks, --Lorenzo P.S. The library can also be used without C++11 lambda functions (or any C++11 specific feature) but programmers have to write a fare amount of extra code to program the precondition and postcondition functors (using non-local functions, Boost.LocalFunction, Boost.Funsion, Boost.Lambda, or some other approach) so that might not useful in practice.

6 14

[graph] Compilation error with adjacency_list and C++11
by Sebastien Loriot (GeometryFactory) 18 Jul '16

18 Jul '16

Hello, the program below does not compile at least with g++ 5.3.1 and clang++ 3.5.2-1 when using c++11 standard. If I comment line #1 it compiles. If I change #2 to undirectedS it compiles. Is there anything wrong in my code or is it a problem in boost's? Thanks, Sebastien. #include <boost/graph/adjacency_list.hpp> struct A { A(){} A(const A& ){} // #1 A& operator=(const A&){return *this;} }; typedef boost::adjacency_list<boost::listS, boost::vecS, boost::directedS, //#2 A > Graph; int main() { Graph g; boost::add_vertex(g); return 0; }

2 2

[type_index] Interest in dynamic_cast emulation?
by Chris Glover 17 Jul '16

17 Jul '16

Hi, I reached for Boost.TypeIndex the other day expecting to find a kind of dynamic_cast I could use in the absence of Rtti. I didn't find it, so I wrote something to emulate it using type_index internally. It's working, but before I go too far and clean this up and possibly submit a pull request, I would like to gauge if there's interest in such a thing or if there's some fundamental reason why it doesn't exist. So, thoughts? Thanks, -- chris

5 8

[contract] Strong exception safety guarantees
by Lorenzo Caminiti 15 Jul '16

15 Jul '16

Hello all, I've been considering adding a .except(...) construct to Boost.Contract that will allow to specify conditions to check at function exit but when the function body throws (in contrast to postconditions that are checked at function exit but only when the function body does not throw). I think .except(...) could be used to assert strong exception safety guarantees... (note that class invariants are already checked at exit of public functions and also when the public function bodies throw, but invariants are suited to assert only basic, and not strong, exception safety guarantees). That might help addressing a point made in P0147R0 under the "Contracts and Exceptions" section: ``Some operations make stronger exception safety claims. In particular, they claim that an exception thrown from a member function will leave the state of an object unchanged from its state on function entry. If we invalidate postconditions on exceptions, we appear to have no mechanism to describe strong exception safety.'' For example, the following swap ensures to leave its arguments unchanged when it throws: void swap(std::string& a, std::string& b) { boost::contract::old_ptr<std::string> old_a = BOOST_CONTRACT_OLDOF(a); boost::contract::old_ptr<std::string> old_b = BOOST_CONTRACT_OLDOF(b); boost::contract::guard c = boost::contract::function() .postcondition([&] { // Checked at function exit but only if body does not throw. BOOST_CONTRACT_ASSERT(a == *old_b); BOOST_CONTRACT_ASSERT(b == *old_a); }) .except([&] { // Checked if body throws (strong exception safety guarantees). BOOST_CONTRACT_ASSERT(a == *old_a); BOOST_CONTRACT_ASSERT(b == *old_b); }) ; ... // Body implementation (which might throw). } Would this be beneficial? Thanks, --Lorenzo

2 5

smartptr maintained
by Karolin Varner 15 Jul '16

15 Jul '16

Hi, is smartptr still being maintained? There are four pull requests, one more than a year old. Best, Karolin Varner

2 3

[graph] A* implementation doesn't follow the algorithm
by Nick Lamprianidis 14 Jul '16

14 Jul '16

For the A* algorithm holds that when a new vertex v is reached through a shorter path, then v is added to the open set. But looking at the boost graph's A* implementation, which is based on the BFS algorithm, one can see that a target vertex is added to the priority queue, regardless of whether the relevant edge is being relaxed. This creates the following situation: The execution starts and you get to a point where you know you cannot reach the goal: no vertices with finite cost in the priority queue. Normally, you would expect that the priority queue is empty and thus the execution ends. Instead, the execution continues, since the priority queue is filled with all those vertices (with infinite cost) that got added for no reason. In an application where the state of a target vertex v gets set when an associated edge is being relaxed, a problem arises. In the situation mentioned above, uninitialized vertices reach the visitor's examine_vertex method. Unless you know what's really happening, so you can take care to add a test condition to exit, it leaves you wondering what's going wrong. I propose that you either change the implementation or at least update the documentation (pseudocode). -- Nick Lamprianidis http://paign10.me

3 2

[log][regression] Error with Boost.Lob build jamfile breaks MinGW regression tester in develop
by Ion Gaztañaga 13 Jul '16

13 Jul '16

Hi, My develop branch regression runner fails whereas the master one works fine. The develop runner fails with all Mingw targets (msvc 7.1 works fine), with this error: ************************************ # Starting tests ("c:\boost\develop\boost_bb\src\engine\bin.ntx86\bjam.exe" "-sBOOST_BUILD_PATH=c:\boost\develop;c:\boost\develop\boost_bb\src" "-sBOOST_ROOT=c:\boost\develop\boost_root" "--boost=c:\boost\develop\boost_root" "--boost-root=c:\boost\develop\boost_root" "--boost-build=c:\boost\develop\boost_bb\src" "--debug-configuration" -l300 toolset=gcc-6.1c++14 -d2 preserve-test-targets=off --dump-tests -j3 --abbreviate-paths debug-symbols=off -m64 "--build-dir=c:\boost\develop\results" >>"c:\boost\develop\results\bjam.log" 2>&1)... c:\boost\develop\boost_root\status> "c:\boost\develop\boost_bb\src\engine\bin.ntx86\bjam.exe" "-sBOOST_BUILD_PATH=c:\boost\develop;c:\boost\develop\boost_bb\src" "-sBOOST_ROOT=c:\boost\develop\boost_root" "--boost=c:\boost\develop\boost_root" "--boost-root=c:\boost\develop\boost_root" "--boost-build=c:\boost\develop\boost_bb\src" "--debug-configuration" -l300 toolset=gcc-6.1c++14 -d2 preserve-test-targets=off --dump-tests -j3 --abbreviate-paths debug-symbols=off -m64 "--build-dir=c:\boost\develop\results" 1>>"c:\boost\develop\results\bjam.log" 2>&1 # Running Boost.Build tests Traceback (most recent call last): File "run.py", line 71, in <module> runner(root) File "c:\boost\develop\boost_regression_src\regression.py", line 287, in __init__ self.main() File "c:\boost\develop\boost_regression_src\regression.py", line 624, in main getattr(self,action_m)() File "c:\boost\develop\boost_regression_src\regression.py", line 589, in command_regression self.command_test() File "c:\boost\develop\boost_regression_src\regression.py", line 368, in command_test self.command_test_boost_build() File "c:\boost\develop\boost_regression_src\regression.py", line 410, in command_test_boost_build "boost/bin.v2/libs/any/test/any_test.test")); WindowsError: [Error 3] The system cannot find the path specified: 'c:\\boost\\develop\\results\\boost/bin.v2/libs/any/test/any_test.test/*.*' ************************************ That path ("..libs/any/test/any_test.test/) is hardcoded in regression.py, but it's not generated in my bin.v2 so it's reasonable an error saying that the system can't find the path ;-) It seems that error occurs before boost.build tests, as bjam.log shows: ************************************ C:/boost/develop/boost_bb/src/build\targets.jam:1077: in evaluate-requirements from module targets error: Can not evaluate conditional properties <conditional>@Jamfile<C:\boost\develop\boost_root>%Jamfile<C:\boost\develop\boost_root>.handle-static-runtime <conditional>@Jamfile<C:\boost\develop\boost_root>%boostcpp.deduce-address-model <conditional>@Jamfile<C:\boost\develop\boost_root>%boostcpp.deduce-architecture <conditional>@Jamfile<C:\boost\develop\boost_root\libs\log\build>%Jamfile<C:\boost\develop\boost_root\libs\log\build>.check-instruction-set <conditional>@Jamfile<C:\boost\develop\boost_root\libs\log\build>%Jamfile<C:\boost\develop\boost_root\libs\log\build>.check-message-compiler <conditional>@Jamfile<C:\boost\develop\boost_root\libs\log\build>%Jamfile<C:\boost\develop\boost_root\libs\log\build>.check-pthread-mutex-robust <conditional>@Jamfile<C:\boost\develop\boost_root\libs\log\build>%Jamfile<C:\boost\develop\boost_root\libs\log\build>.check-visibility <conditional>@Jamfile<C:\boost\develop\boost_root\libs\log\build>%Jamfile<C:\boost\develop\boost_root\libs\log\build>.select-arch-specific-sources <conditional>@Jamfile<C:\boost\develop\boost_root\libs\log\build>%Jamfile<C:\boost\develop\boost_root\libs\log\build>.select-platform-specific-sources <conditional>@Jamfile<C:\boost\develop\boost_root\libs\log\build>%Jamfile<C:\boost\develop\boost_root\libs\log\build>.select-regex-backend <link>shared:<define>BOOST_LOG_DLL <target-os>cygwin:<define>BOOST_USE_WINDOWS_H <target-os>cygwin:<define>NOMINMAX <target-os>cygwin:<define>SECURITY_WIN32 <target-os>cygwin:<define>WIN32_LEAN_AND_MEAN <target-os>cygwin:<define>__USE_W32_SOCKETS <target-os>cygwin:<library>/boost/log//advapi32 <target-os>cygwin:<library>/boost/log//mswsock <target-os>cygwin:<library>/boost/log//ws2_32 <target-os>freebsd:<library>/boost/log//rt <target-os>hpux:<define>_XOPEN_SOURCE=600 <target-os>hpux:<library>/boost/log//ipv6 <target-os>linux:<define>_XOPEN_SOURCE=600 <target-os>linux:<library>/boost/log//rt <target-os>qnxnto:<library>/boost/log//socket <target-os>solaris:<define>_XOPEN_SOURCE=500 <target-os>solaris:<define>__EXTENSIONS__ <target-os>solaris:<library>/boost/log//nsl <target-os>solaris:<library>/boost/log//socket <target-os>windows:<define>BOOST_USE_WINDOWS_H <target-os>windows:<define>NOMINMAX <target-os>windows:<define>SECURITY_WIN32 <target-os>windows:<define>WIN32_LEAN_AND_MEAN <target-os>windows:<library>/boost/log//advapi32 <target-os>windows:<library>/boost/log//mswsock <target-os>windows:<library>/boost/log//ws2_32 <threading>multi:<library>/boost/atomic//boost_atomic <threading>multi:<library>/boost/thread//boost_thread <threading>single:<define>BOOST_LOG_NO_THREADS <toolset>clang:<cxxflags>-ftemplate-depth-1024 <toolset>como-linux:<define>_GNU_SOURCE=1 <toolset>como:<link>static <toolset>darwin:<cxxflags>-ftemplate-depth-1024 <toolset>gcc,<target-os>cygwin:<linkflags>-Wl,--enable-auto-import <toolset>gcc,<target-os>windows:<linkflags>-Wl,--enable-auto-import <toolset>gcc:<cxxflags>-fno-strict-aliasing <toolset>gcc:<cxxflags>-ftemplate-depth-1024 <toolset>intel-darwin:<cxxflags>-wd177,780,2196,1782,193,304,981,1418,411,734,279 <toolset>intel-linux:<cxxflags>-wd177,780,2196,1782,193,304,981,1418,411,734,279 <toolset>intel-win:<cxxflags>/Qwd177,780,2196,1782,193,304,981,1418,411,734,279 <toolset>intel-win:<define>_CRT_SECURE_NO_DEPRECATE <toolset>intel-win:<define>_CRT_SECURE_NO_WARNINGS <toolset>intel-win:<define>_SCL_SECURE_NO_DEPRECATE <toolset>intel-win:<define>_SCL_SECURE_NO_WARNINGS <toolset>msvc,<runtime-link>shared:<threading>multi <toolset>msvc:<cxxflags>/bigobj <toolset>msvc:<cxxflags>/wd4003 <toolset>msvc:<cxxflags>/wd4456 <toolset>msvc:<cxxflags>/wd4459 <toolset>msvc:<cxxflags>/wd4503 <toolset>msvc:<define>_CRT_SECURE_NO_DEPRECATE <toolset>msvc:<define>_CRT_SECURE_NO_WARNINGS <toolset>msvc:<define>_SCL_SECURE_NO_DEPRECATE <toolset>msvc:<define>_SCL_SECURE_NO_WARNINGS <toolset>pgi:<library>/boost/log//rt C:/boost/develop/boost_bb/src/build\targets.jam:1112: in common-properties2 from module targets C:/boost/develop/boost_bb/src/build\targets.jam:977: in targets.common-properties from module targets C:/boost/develop/boost_bb/src/build\targets.jam:1303: in class(a)basic-target.generate from module object(typed-target)@1504 C:/boost/develop/boost_bb/src/build\targets.jam:774: in generate-really from module object(main-target)@49045 C:/boost/develop/boost_bb/src/build\targets.jam:746: in class(a)main-target.generate from module object(main-target)@49045 C:/boost/develop/boost_bb/src/build\targets.jam:895: in targets.generate-from-reference from module targets C:/boost/develop/boost_bb/src/build\targets.jam:1266: in generate-dependencies from module object(typed-target)@14269 C:/boost/develop/boost_bb/src/build\targets.jam:1320: in class(a)basic-target.generate from module object(typed-target)@14269 C:/boost/develop/boost_bb/src/build\targets.jam:774: in generate-really from module object(main-target)@49008 C:/boost/develop/boost_bb/src/build\targets.jam:746: in class(a)main-target.generate from module object(main-target)@49008 C:/boost/develop/boost_bb/src/build\targets.jam:895: in targets.generate-from-reference from module targets C:/boost/develop/boost_bb/src/build\targets.jam:1266: in generate-dependencies from module object(alias-target-class)@36618 C:/boost/develop/boost_bb/src/build\targets.jam:1323: in class(a)basic-target.generate from module object(alias-target-class)@36618 C:/boost/develop/boost_bb/src/build\targets.jam:774: in generate-really from module object(main-target)@36634 C:/boost/develop/boost_bb/src/build\targets.jam:746: in class(a)main-target.generate from module object(main-target)@36634 C:/boost/develop/boost_bb/src/build\targets.jam:272: in class(a)project-target.generate from module object(project-target)@2141 c:/boost/develop/boost_bb/src\build-system.jam:714: in load from module build-system C:\boost\develop\boost_bb\src/kernel\modules.jam:295: in import from module modules C:\boost\develop\boost_bb\src/kernel/bootstrap.jam:139: in boost-build from module C:\boost\develop\boost_root\boost-build.jam:17: in module scope from module ************************************ I can't see why this Jamfile from Boost.Log is accepted when MSVC-7.1 is the target but fails when MinGW is the selected target. I could neither t deduce what is the failing piece of the configuration. The same error happens with a wide range of MINGW targets: GCC-3.4, GCC-4.1, GCC-4.2, GCC-4.3, GCC-4.4, GCC-4.5, GCC-4.6, GCC-4.7, GCC-4.8, GCC-4.9, GCC-5.1, GCC-5.2, GCC-5.3 and GCC-6.1. Any clue on what can be happening and how can it be fixed? Attached regression logs for a failed MINGW regression with GCC 6.1. Best, Ion

3 8

[regression][winapi] Tests not being run
by Andrey Semashev 11 Jul '16

11 Jul '16

Hi, I wrote about it before, but now the problem becomes more weird. The problem is that the tests for Boost.WinAPI are not being run for some reason. What's weird is that now there is one test in the matrix (http://www.boost.org/development/tests/develop/developer/winapi.html) that isn't part of the Boost.WinAPI test suite. I assume that entry is part of the formal checks for the library conformance, since it is present for all libraries. Could someone please have a look why the tests for Boost.WinAPI are not being executed? PS: The link for the __boost_check_library__ entry is broken: https://github.com/boostorg/winapi/blob/developstatus/boost_check_library.py I believe, there's a slash missing between develop and status, and also the repository name should be boost rather than winapi.

2 2

[TypeErasure] Merging pull-requests
by Deniz Bahadir 11 Jul '16

11 Jul '16

Hello everyone, Hello Steven, a view weeks ago I reported some bugs of Boost.TypeErasure [1,2] and provided pull-requests [3,4] which fix these. I just wanted to bring these to attention so that they might get merged and find their way into the next Boost release. Thanks, Deniz PS: There is another open pull-request [5] (by John Maddock) which seems to be even more urgent. [1] https://svn.boost.org/trac/boost/ticket/12291 [2] https://svn.boost.org/trac/boost/ticket/12292 [3] https://github.com/boostorg/type_erasure/pull/9 [4] https://github.com/boostorg/type_erasure/pull/10 [5] https://github.com/boostorg/type_erasure/pull/11 -- BENOCS GmbH Dipl.-Inform. Deniz Bahadir Winterfeldtstr. 21 10781 Berlin Germany Phone: +49 - 30 / 577 0004-22 Email: deniz.bahadir(a)benocs.com www.benocs.com Board of Management: Michael Wolz, Dr.-Ing. Oliver Holschke, Dr.-Ing. Ingmar Poese Commercial Register: Amtsgericht Bonn HRB 19378

2 1