February 2017 - Boost - lists.boost.org

Functional programming in boost
by Abhishek Kumar 16 Feb '17

16 Feb '17

Hello I am a Computer Science senior from India. I have been doing functional programming for quite some time and have also used C++ for different projects. I recently came across BOOST libraries for supporting functional programming in C++. I want to contribute to one of the BOOST libraries maybe PHOENIX. Are there any open issues or plans in this direction, in which I might help? Thanks Abhishek Kumar

1 0

[release] 1.64.0 deadline for new libraries approaching
by Rene Rivera 16 Feb '17

16 Feb '17

One week from today master will close for commits of new libraries. Thanks, -- The Boost Release Team -- -- Rene Rivera -- Grafik - Don't Assume Anything -- Robot Dreams - http://robot-dreams.net -- rrivera/acm.org (msn) - grafikrobot/aim,yahoo,skype,efnet,gmail

1 0

[safe_numerics] Review coming in March
by Andrzej Krzemienski 16 Feb '17

16 Feb '17

Hi Everyone, This is to inform you ahead of time that the formal review of Robert Ramey's Safe Numerics library will be held in about two weeks: March 2 - March 11. Boost Numerics is a set of drop-in replacements for the built-in integer types, which make the guarantee that the results of operations are either correct according to the rules of integer arithmetic or report a diagnosable error (rather than offering modulo arithmetic results, or resulting in undefined behavior, or returning incorrect results as in the case of signed vs. unsigned comparisons). The library can be found on GitHub: https://github.com/robertramey/safe_numerics/ Online docs: http://htmlpreview.github.io/?https://github.com/robertramey/safe_numerics/… Even before the formal review starts, you can provide your review on Boost Library Incubator: http://blincubator.com/reviews/?library_id=426 It will also be included in the final verdict. I will be making the official announcement on March 2. Andrzej Krzemienski, review manager.

1 0

Is there any interest in non-owning pointer-like types?
by Joseph Thomson 14 Feb '17

14 Feb '17

For some time, I have been developing a pair of non-owning pointer-like types that I am currently calling `observer_ptr` and `observer`. I had planned to propose their addition to the C++ standard library, but I have been informed by the author of the original `observer_ptr` proposal <http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2014/n4282.pdf> that the ISO C++ committee has rejected his proposal and made clear that it feels there is no place in the standard library for such types, believing that this role is filled to a satisfactory degree by regular pointers. I wholeheartedly disagree with this assessment, so I am bringing my proposal here instead. The `observer_ptr<T>` class template is a pointer-like type that does not do any resource management, and is intended to be used in place of `T*` wherever `T*` is used as a non-owning reference to an object of type `T`. `observer_ptr<T>` has three main advantages over `T*`: 1. `T&` is implicitly convertible to `observer_ptr<T>` which, unlike `T*`, makes it *type-safe*. `T*` can represent things that are not conceptually objects of type `T`: arrays, strings, iterators. No implicit conversion from `T*` means that these things cannot implicitly convert to `observer_ptr<T>`. Pointers aren't even required to point to valid objects (e.g. a past-the-end iterator). Conversely, in a well-formed program, `T&` is *always* a valid object of type `T`. 2. `observer_ptr<T>` documents its purpose. This is really a side-effect of it being type-safe (a type should have a single, specific purpose), but it's worth mentioning. Conversely, when you see `T*`, it may not be immediately obvious what it represents. 3. `observer_ptr<T>` has a minimal interface, which makes it harder to misuse than `T*`; for example, `observer_ptr<T>` has no pointer arithmetic operators, no array subscript operator, no conversion to `void*`. The `observer<T>` class template is a counterpart to `observer_ptr<T>` that has *no null state*; it cannot be default constructed, constructed from `nullptr_t` or constructed from `T*`, and it does not contextually convert to `bool`. The only way to create an `observer<T>` is from `T&`. This allows a "not null" precondition to be enforced at compile-time, rather than having to worry about pointers being null at run-time. Just to give you an idea of the current syntax, here is a simple tree node type (where the nodes do not own their children) implemented using `observer_ptr` and `observer`: class node { public: node() = default; node(node const&) = delete; node& operator=(node const&) = delete; node(node&&) = delete; node& operator=(node&&) = delete; void set_parent(observer_ptr<node> new_parent) { if (parent) parent->remove_child(*this); parent = new_parent; if (parent) parent->add_child(*this); } observer_ptr<node> get_parent() const { return parent; } size_t get_child_count() const { return children.size(); } observer<node> get_child(size_t index) const { return children[index]; } private: observer_ptr<node> parent; vector<observer<node>> children; void add_child(observer<node> child) { children.push_back(child); } void remove_child(observer<node> child) { children.erase(find(begin(children), end(children), child)); } }; And a contrived usage example: node a, b, c; b.set_parent(a); // conversion from `T&` c.set_parent(b); observer_ptr<node> x = c.get_parent(); if (x) // conversion to `bool` { observer<node> y = x->get_child(0); assert(y == c); // comparison with `T&` y->set_parent(a); b.set_parent(y); // conversion from `observer<T>` to `observer_ptr<T>` } A project with a working implementation <https://github.com/hpesoj/cpp-observer/blob/master/api/observer.hpp> and full test suite <https://github.com/hpesoj/cpp-observer/blob/master/tests/observer_tests.cpp> can be found here <https://github.com/hpesoj/cpp-observer>. Regards, Joseph

16 35

What is http://downloads.sourceforge.net/boost/boost_1_63_0.tar.bz2 ?
by Jonathan Wakely 14 Feb '17

14 Feb '17

The link http://downloads.sourceforge.net/boost/boost_1_63_0.tar.bz2 redirects to http://downloads.sourceforge.net/project/boost/boost/snapshots/master/boost… which seems to be a snapshot from master, and VERY different to the boost_1_63_0 release (which makes it a VERY misleading URL). How often is that snapshot updated? Shouldn't it have a different name if it's not boost_1_63_0.tar.bz2 but some completely different set of sources (which currently don't even build)? The Fedora Linux packages have been using that URL, for several years by the look of things. So I have no idea what arbitrary collection of changes we've been shipping instead of a proper release.

9 21

[test]redefinition of boost::unit_test::ut_detail::auto_test_unit_registrar
by Takatoshi Kondo 14 Feb '17

14 Feb '17

Hello, I'm using Boost.Test. When I define BOOST_AUTO_TEST_SUITE, I got a compile error 'redefinition of boost::unit_test::ut_detail::auto_test_unit_registrar' if the all following conditions are satisfied: 1. The test suite names are the same. 2. BOOST_AUTO_TEST_SUITE are defined in different files. 3. The files are included by one file. 4. BOOST_AUTO_TEST_SUITE are defined at the same line number. For example, main.cpp #define BOOST_TEST_MODULE test #include <boost/test/unit_test.hpp> #include "one.ipp" #include "two.ipp" one.ipp BOOST_AUTO_TEST_SUITE(a) BOOST_AUTO_TEST_CASE(tc1) { } BOOST_AUTO_TEST_SUITE_END() two.ipp BOOST_AUTO_TEST_SUITE(a) BOOST_AUTO_TEST_CASE(tc2) { } BOOST_AUTO_TEST_SUITE_END() Here is a live demo: http://melpon.org/wandbox/permlink/R459VQ6apnQfapyw If I insert a line the top of two.ipp, no errors are occurred. http://melpon.org/wandbox/permlink/jPRTstNDVb7agjXl According to the following document http://www.boost.org/doc/libs/1_63_0/libs/test/doc/html/boost_test/tests_or… "The same test suite can be restarted multiple times inside the same test file or in a different test files." The compile error is caused by the following line: https://github.com/boostorg/test/blob/develop/include/boost/test/unit_test_… If I replace BOOST_JOIN( BOOST_JOIN( test_name, _registrar ), __LINE__ ) \ with BOOST_JOIN( BOOST_JOIN( test_name, _registrar ), __COUNTER__ ) \ , then the error is disappeared. However, __COUNTER__ is not portable. I know that I can compile one.ipp and two.ipp separately, but I also want to have the option that include them from one file. Is there any good way to solve the error? Thanks, Takatoshi Kondo

2 2

Lazy Spirit Generators?
by Christof Donat 14 Feb '17

14 Feb '17

Hi, In a hobby project, I am using Spirit Karma generators. As far as I have understood Spirit Karma, it is not designed to work lazily in the iterator based interface. It takes an output iterator and writes to it until it has finished. What I am thinking of is a kind of generating range. E.g.: for(auto& char: generator_range(double_ << " + " << double_ << "i", context, c.real(), c.imag())) { // do whatever with the single characters returned by the generator } Is there something like that, which I simply have not found? Christof

3 2

Fit - Request for formal review
by Paul Fultz II 13 Feb '17

13 Feb '17

Hi, So I’ve made a lot of updates to the Fit library since last review. There are a few more changes I would like to make, but most of the work has been done. So, I would like to request for a formal review, and get it on the schedule soon. Vicente Botet was the review manager last time, I don’t know if he would be interested in being the review manager again. Is there perhaps someone else that would be interested in being review manager? https://github.com/pfultz2/Fit Thanks, Paul

1 1

boost::aligned_storage is not a POD.
by Vicente J. Botet Escriba 12 Feb '17

12 Feb '17

Hi, boost::aligned_storage is not a POD. I suspect it is because of the declared constructors private: // noncopyable aligned_storage(const aligned_storage&); aligned_storage& operator=(const aligned_storage&); public: // structors aligned_storage() { } ~aligned_storage() { } Was this intentional? Why aligned_storage is not copyable? Best, Vicente

2 2

[exception] error: looser throw specifier
by Niklas Angare 11 Feb '17

11 Feb '17

On QNX 6.6.0 with GCC 4.7.3 and Dinkumware library in -std=gnu++0x mode, I get the following error: ../libs/exception/test/throw_exception_test.cpp:21:1: error: looser throw specifier for 'virtual exception2::~exception2()' In file included from ../libs/exception/test/helper2.hpp:9:0, from ../libs/exception/test/throw_exception_test.cpp:6: ../boost/exception/exception.hpp:303:5: error: overriding 'virtual boost::exception::~exception() throw ()' libs/exception/test/throw_exception_test.cpp has these definitions: struct exception1: std::exception {}; struct exception2: std::exception, boost::exception {}; There is no error for exception1. Is the bug in the Boost library, the test, the compiler or the Dinkumware library? Other regression runners with GCC 4.7 don't get the error. My regression test runner is NA-QNX660-x86 so you can see all details in the result matrix. Regards, Niklas Angare

1 0