November 2012 - Boost - lists.preview.boost.org

[mpl] Strange error using boost::mpl::eval_if
by Edward Diener 12 Nov '12

12 Nov '12

No doubt I have had some sort of C++ brain blockage but the following code using boost::mpl::eval_if gives an error and I cannot see how this would be. This is a simplified case of a more serious problem. --------------------------------------------------------------- #include <boost/mpl/bool.hpp> #include <boost/mpl/eval_if.hpp> template<class T,class C> struct AAA { static const bool value=true; typedef boost::mpl::bool_<value> type; }; template<class T> struct CCC { static const bool value=true; typedef boost::mpl::bool_<value> type; }; template<class T> struct BBB : CCC<T> { }; template<class T1,class T2,class T3,class T4> struct DDD : boost::mpl::eval_if < boost::mpl::false_, BBB<T1>, AAA<int,int> > { }; template < class T1, class T2 = int, class T3 = int, class T4 = int > struct EEE : DDD<T1,T2,T3,T4> { }; int main() { bool result = EEE<int,int>::value; return(result ? 1 : 0); } ----------------------------------------------------------------------- Compiling with gcc 4.6.0 in MingW under Windows I get: test_has_mem_fun.cpp: In function 'int main()': test_has_mem_fun.cpp:50:17: error: 'value' is not a member of 'EEE<int, int>' "g++" -ftemplate-depth-128 -O0 -fno-inline -Wall -pedantic -g -Wno-variadic-macros -std=c++0x -DBOOST_ALL_NO_LIB=1 -I"..\..\.." -c -o "..\..\..\bin.v2\libs\tti\test\test_has_mem_fun.test\gcc-mingw-4.6.0\debug\test_has_mem_fun.o" "test_has_mem_fun.cpp" ----------------------------------------------------------------------- I must be overlooking something obvious but I cannot see it. Any help showing me what is wrong would be appreciated.

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[iterator] [property_map] Enhancement proposals
by Louis Dionne 12 Nov '12

12 Nov '12

Dear boost, First of all, let me quickly introduce myself as this is my first post here: I am a 20 years old programming enthusiast with interest for metaprogramming, functional programming and library design. I also have a strong will to contribute to open source projects since I love the philosophy behind it and it is a great way to develop new skills and to work with talented people. The object of this message is to collect feedback on several enhancement proposals I have prepared for two existing libraries: [boost.iterator] [boost.iterator.accessor_iterator] The accessor_iterator is an iterator adaptor that returns a reference to a member of its pointee when dereferenced. I see it as another step in the direction of easier iterator composition, which has helped me writting less code in the past. [boost.iterator.chained_output_iterator] The chained_output_iterator is an iterator adaptor allowing to apply a functional transformation to a value before outputing it into another output iterator. It is much like a function_output_iterator that would forward its result to another output iterator. It allows for cool stuff like creating a pipeline of operations without having to create temporary storage. [boost.property_map] [boost.property_map.accessor_property_map] The accessor_property_map is a property map returning a reference to a member of the key it is given. It is much like the accessor_iterator for property maps. [boost.property_map.chained_property_map] The chained_property_map is a tool for property map composition. It takes two property maps and uses a value in the first one as a key in the second one to perform its put, get, and operator[] operations. [boost.property_map.property_traits] I feel like the boost/property_map/property_map.hpp header is a little bit bloated and not quite as modular as it could be. For now, I propose that we move the code dealing with property_traits into the boost/property_map/property_traits.hpp header and that we provide metafunctions to check for adherence to property map types. By providing an include in the boost/property_map/property_map.hpp header, backward compatibility is maintained and we simply increase modularity. All the code is available on github: https://github.com/ldionne/boost-submissions To see how each class can be used, you may look at the unit tests for the corresponding class. If anything is accepted, I will be pleased to write documentation and examples for the concerned feature and to integrate it into the existing documentation. Looking forward to your feedback, Louis Dionne

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Re: [boost] hierarchy_tree container
by Morgan Freeberg 10 Nov '12

10 Nov '12

Okay thanks Jose, that helps. My search through the libraries did not pick up on these. By the time I did that I already had the application behavior I wanted, so on my end this has been a refactoring process; I can take a look at these and see if I did that the right way, or if perhaps these could've provided the functionality I need. >From skimming over the documentation, my initial impression is that they're both very cool implementations which might help me in future work, but some of what I did here is falling somewhat outside of that is provided by these. If you're still interested, I can provide an approximation of the challenges met here: 1. From a rather large not-quite-completely-standard XML file, I needed to parse from top to bottom, understanding the structure being created as containers are declared, sub-containers & leafs are added in, and each construct is eventually terminated. The process that does this would need to store not only the instantiation of the tree container, but a vector/array of references to the ancestors of some "current node" being built. That is so that, as it encounters terminating tags, the internal logic can say...this is ended, now this is ended, now this is ended...essentially so that it can "outdent" again. I can see with treetree and st_tree this is do-able if I write some level of intermediate code that builds such an array and maintains it, as I know lots of "standard" XML readers already do. (This I know from my attempts to find one I could actually use in my project.) The issue that would arise here is, I'd still need to write and test that code, and the result would in turn be redundant with what I did here...so it seems these two libraries recognize the same structure mine does, but the scope of purpose is a little bit different. My container internalizes all this parentage information so that when you're reading data sequentially in this way, the client code only needs to track the depth by way of counting the opening and closing tags, then make a call to the container that essentially says "add this, at this depth." Implication being: As a child of whatever. The container internally tracks the concept of "we are currently defining children of so-and-so." 2. In a configuration file of my own making, I needed to pre-declare what the tree should look like. This is not XML, it's a list of statements that say "that class we already defined on line 3, here on line 9 we are defining a class that is a child of that." The method described above that is good for reading these pseudo-XML files, it would not work for that. What is needed here is either a sequential or random-access search by name...In this case you need to write code on top of my container, as well as on top of treetree and s_tree. So in this requirement, all three provide the same functionality. 3. I chose an enumerator/callback interface that works by way of numeric return codes, because I needed it for a variety of commands to be executed on the trees -- some do searches, some validate, some filter (search without terminate after find), et al. The point to dynamically constructing a tree was to be able to do integrity checks on it, and then execute some different application behavior on each node within what I could be sure was the same tree as what I had seen before. So for my particular implementation this is a big benefit, because I can use a chain-of-responsibility design pattern to associate each command with a name, an invoker, some help text, and then a callback routine that defines the behavior. Again, it seems those other two containers can meet the requirement, after intermediate code has been written to adapt them to this application-specific purpose, which in turn has been internalized in my container. Much shorter version: Enum/callback pair for listing the contents of the tree, with numeric return codes; two distinctly separate methods for getting the data in at run-time, one method for reading a streaming mechanism such as XML, the other method for specifically identifying the parent of a new node -- "child of that guy, you made before, over there." The test program I provided mixes those two methods up, so that it is demonstrated they can both work on the same container once it is instantiated. I'll run some tests with these and, if you're interested, provide you with a more fully-informed report on where there may & may not be full redundancy.

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filesystem::path passed to GTest's assertion leads to stack overflow because of infinite recursion
by Andrey Upadyshev 10 Nov '12

10 Nov '12

Hi all, I found an interesting bug with 'filesystem::path' used with GTest: https://svn.boost.org/trac/boost/ticket/7564 I just want to discuss the design of 'path' class which iterator contains the 'path' itself. Don't you think it's nice to fix thing? Best regards, Andrey Upadyshev P.S. Sorry if this is wrong mailing list. Just let me know and I'll repost the message to boost-users <boost-users(a)lists.boost.org> mailing list.

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[type_traits] templated type traits?
by Lorenzo Caminiti 10 Nov '12

10 Nov '12

Hi, Is there a way to inspect if a type is a template instantiaton (is_templated) and the type of the instantiated template parameters (arg1_type)? is_templated< std::vector<int> >::value // true is_templated< int >::value // false template_traits< std::vector<int> >::arg1_type // int Thanks, --Lorenzo

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[wave] add_macro_definition("TEST=") behaves different than #define TEST
by Klaus Gütter 10 Nov '12

10 Nov '12

Test1 posted below produces: INT SPACE EOF SPACE IDENTIFIER SEMICOLON NEWLINE EOF While Test2 produces: INT SPACE IDENTIFIER SEMICOLON NEWLINE EOF The EOF in the third line of Test1 output is produced by the TEST macro expansion. If this expected behaviour? I found this surprising. (MSVC10, Boost 1.51) Regards, Klaus ---- Code: typedef cpplexer::lex_token<> token_type; typedef context< string::iterator, cpplexer::lex_iterator<token_type> > lexer_context_type; void Test1() { string instring("int TEST x;\n"); lexer_context_type ctx(instring.begin(), instring.end(), ""); ctx.set_language(language_support(support_c99)); ctx.add_macro_definition("TEST="); for (lexer_context_type::iterator_type it = ctx.begin(); it != ctx.end(); ++it) cout << get_token_name(token_id(*it)) << endl; } void Test2() { string instring("#define TEST\nint TEST x;\n"); lexer_context_type ctx(instring.begin(), instring.end(), ""); ctx.set_language(language_support(support_c99)); for (lexer_context_type::iterator_type it = ctx.begin(); it != ctx.end(); ++it) cout << get_token_name(token_id(*it)) << endl; }

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[type_traits] is_complete<T> possible realization
by Antony Polukhin 09 Nov '12

09 Nov '12

Hi, Yesterday I had a need to detect, is class forward declared or is it complete. Here are some thoughts: template <class T, int Misc> struct is_complete { typedef char false_type; typedef int true_type; template <class T1> static typename boost::enable_if_c<sizeof(T1), true_type>::type test(int); template <class T1> static false_type test(...); enum ENU { value = ( sizeof(test<T>(0)) == sizeof(true_type) )}; }; 'Misc' parameter is required to work around compilers one time instantiation: struct incomplete; template <int N> struct incomplete_template; struct complete{}; struct complete_abstract{ virtual void foo() =0; }; void test(); void foo1() { cout << is_complete<incomplete, __LINE__>::value << is_complete<incomplete_template<0> , __LINE__>::value << is_complete<incomplete_template<1> , __LINE__>::value << is_complete<complete, __LINE__>::value << is_complete<complete_abstract, __LINE__>::value << endl; } struct incomplete{}; template <> struct incomplete_template<0>{}; void foo2() { cout << is_complete<incomplete, __LINE__>::value // Without second template parameter it would be still returning 0 << is_complete<incomplete_template<0> , __LINE__>::value << is_complete<incomplete_template<1> , __LINE__>::value << is_complete<complete, __LINE__>::value << is_complete<complete_abstract, __LINE__>::value << endl; } int main() { foo1(); // Outputs 00011 foo2(); // Outputs 11011 return 0; } I was thinking of changing 'Misc' parameter definition to something like this: template <class T, class... Misc> struct is_complete ; Than it can be used in template functions/classes just like this: template <class T, class... SomeClasses> void test_function() { is_complete<T, SomeClasses..., boost::mpl::int_<__LINE__> >::value; } So, Is there interest in such metafunction? Can somebody give advices how to improve it? (I`m not sure that implementation is portable, I`ve tested it only on GCC-4.6 and CLANG-3.0, MSVC compiler will be available only tomorrow) -- Best regards, Antony Polukhin

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Re: [boost] hierarchy_tree container
by Morgan Freeberg 09 Nov '12

09 Nov '12

> Subject: Re: [boost] hierarchy_tree container > On Tue, Nov 6, 2012 at 5:28 PM, Morgan Freeberg <mkfreeberg(a)hotmail.com> wrote: > > I have the logic for this nicely separated into a header that seems to meet all the Boost coding guidelines, although I know a peer review process would likely yield helpful improvements that aren't immediately obvious to me. The doc file I prepared goes into much greater detail how this all works...would there be interest in looking into such a thing? > > > yes, can you share the doc url ? > http://www.peekinthewell.net/boostsub/hierarchy_tree/

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[datetime] IANA Time Zone Database
by Maxim Yegorushkin 09 Nov '12

09 Nov '12

Hi Boost, I have files with timestamps in various timezones. I would like to be able to convert these timestamps, no matter what timezone they are in (I know the names of the timezones) to UTC timestamps. I looked through datatime library documentation and found date_time_zonespec.csv database which doesn't seem to support the notion of different rules for the same timezone depending on the date. For example, Russia used to have summer time but not any more. Another method seems to be passing a timezone specification string manually, which requires the user to figure what it should be for a particular date. In other words, given a timestamp and its timezone, I would like to be able to convert that timestamp into a UTC timestamp using conversion rules in force at that particular date in the past. Ideally, this would use IANA Time Zone Database or something similar. Is there a facility in boost to do just that? -- Maxim

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C++ announcements coming tomorrow
by Beman Dawes 09 Nov '12

09 Nov '12

Herb Sutter, the Convenor of the ISO C++ Standards Committee, will be making some announcements tomorrow likely to be of interest to C++ developers in general and Boosters in particular. The venue is a talk titled "The Future of C++" at the Microsoft Build Conference. While some of Herb's announcements will be specific to Microsoft, the key C++ initiatives involve Boost and the whole C++ community. Some of the ideas evolved from feedback Herb got at C++Now/BoostCon 2012 last May. I'll post a summary of the announcements tomorrow, but you can also watch the live stream at http://channel9.msdn.com at 12:45 PM Pacific time. For other time zones, see http://www.timeanddate.com/worldclock/fixedtime.html?iso=20121102T1945 --Beman PS: We don't usually post teasers like this on the Boost lists, but Herb asked that a notice be posted, and given the endless work he has put in on this over the summer, I couldn't say no.

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★ Boost, Bruce left a message for you
by Badoo 08 Nov '12

08 Nov '12

Bruce left a message for you Only you can see the sender and content of your message, and you can delete it anytime. You can instantly reply using our message exchange system: http://eu1.badoo.com/tortoise74/in/3i4doZuulPE/?lang_id=3&m=21&mid=509c4330… If the link in this message does not work, try copying and pasting it into your browser. This email is part of our delivery procedure for the message sent by Bruce. If you have received this email by mistake, please ignore it. The message will be deleted soon. Have fun! The Badoo Team You have received this email from Badoo Trading Limited (postal address below). http://eu1.badoo.com/impersonation.phtml?lang_id=3&email=boost%40lists.boos… Badoo Trading Limited is a limited company registered in England and Wales under CRN 7540255 with its registered office at Media Village, 131 - 151 Great Titchfield Street, London, W1W 5BB.

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[test]portability of data test cases and build issues
by Gennadiy Rozenal 08 Nov '12

08 Nov '12

Hi, I've been working on portability fixes for new features in boost.test. They now works fine with gcc 4.6 and 4.7 msvc-10.0 and msvc-11.0. My attempt with clang on linux lead to compiler crashing, but I see it passing in regression on darwin, so I am not sure on the status. I do still have some issues about portability and boost.build: 1. Boost.Build does not handle correctly target foo with sources residing in subdirectory foo under location of Jamfile. I had to rename directory boost/libs/test/test/test_datasets into test_datasets_src, because of that. 2. How do I tell that I want to pass compilation to gcc in toolset gcc-4.7 only? I've tried <toolset>gcc-4.7:<cxxflags>-std=c++11 and <toolset>gcc-4.7.2:<cxxflags>-std=c++11 and either one does not work. <toolset>gcc:<cxxflags>-std=c++11 does work, but I want to pass different options for different versions of gcc. 3. Question: Should I tell *unconditionally* in Boost.Test Jamfile in boost/libs/test/build that I want to pass -std=c++11/-std=c++0x depending on a version? If not, how do I test test_dataset target with this option? Also How do I disable for configurations which does not support it? 4. Issues with regression testers setup? If you look here: http://www.boost.org/development/tests/trunk/developer/test.html You will see that: a) clang linux columns are empty. Why is that? b) msvc-11.0 setup is broken because of: 'cl' is not recognized as an internal or external command, operable program or batch file. c) sun setup is broken because of: /bin/sh: line 2: CC: not found Can we fix these? 5. Portability for other compilers. I am not quite sure which is lowest version of gcc this feature works. Anyone who is interested in making it work with older/different compilers feel free to submit patches. Regards, Gennadiy

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Release branch closed
by Marshall Clow 08 Nov '12

08 Nov '12

Boosters, The release branch is now closed for all commits, except by explicit permission of release managers. -- The Release Managers, Beman Dawes Daniel James Eric Niebler Rene Rivera Vladimir Prus Marshall Clow

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[thread] warning in trunk
by Gennadiy Rozental 08 Nov '12

08 Nov '12

Hi, Can anyone clean this one: boost/thread/future.hpp(378) : warning C4913: user defined binary operator ',' exists but no overload could convert all operands, default built-in binary operator ',' used Gennadiy

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[OT] std::complex warts
by Neal Becker 08 Nov '12

08 Nov '12

std::complex doesn't seem to allow mixing of types in arithmetic operations. This is quite inconvenient for code that is generic on the base float type. For example: template<typename flt_t> flt_t some_function (std::complex<flt_t> z) { return 2. * z / 4.2 + ... } This will fail to compile when flt_t == float (but succeeds for double). casting every constant in a large computation is really not an acceptable option. Thoughts?

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[type_traits] is_convertible<int, int&> inconsistent result
by TONGARI 08 Nov '12

08 Nov '12

Hi, I'd expect boost::is_convertible<int, int&>::value to be false, so I was surprised that it gives me "true" under g++ 4.7.1. Switch to std::is_convertible<int, int&> or using clang instead gives me the expected "false". After some search, I found: https://svn.boost.org/trac/boost/ticket/7251 Any plan to fix it?

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[variant] static_visitor has no virtual destructor.
by Pierre Talbot 08 Nov '12

08 Nov '12

Hello, I have a compilation error with Boost (1.52) and g++ (4.7) with the flag -Weffc++: error: base class ‘class boost::static_visitor<std::basic_string<char> >’ has a non-virtual destructor [-Werror=effc++] And the static_visitor class is defined with a protected non-virtual destructor: template <typename R = ::boost::detail::static_visitor_default_return> class static_visitor : public detail::is_static_visitor_tag { public: // typedefs typedef R result_type; protected: // for use as base class only static_visitor() { } ~static_visitor() { } }; Is it normal ? And if it is, how to avoid this error ? Thank you for your help, Pierre Talbot.

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Adding an option to set the name of a boost::thread
by david.hagood＠gmail.com 07 Nov '12

07 Nov '12

Has any thought been given to allowing a name to be set on a boost::thread, such that (if the underlying implementation supports it) that name would show up in things like top and ps? In Linux, you can name a thread via the prctl() call and it will show up in top - dandy for debugging which of the bazillion threads in my app has decided to suck up all the CPU. I don't know if Windows supports such a call, and IMHO it would be acceptable if the call did nothing in such a case. Ideally, I'd want to see it as a property, something like: void boost::thread::set_name(std::string name) std::string boost::thread::get_name() const;

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[algorithm] Knuth-Morris-Pratt Search docs overly terse
by Jeff Flinn 07 Nov '12

07 Nov '12

I'm not sure if this is intentional but: http://www.boost.org/doc/libs/1_52_0/libs/algorithm/doc/html/the_boost_algo… contains only: Overview The header file 'knuth_morris_pratt.hpp' contains an an implementation of the Knuth-Morris-Pratt algorithm for searching sequences of values. I've created Ticket #7656. Jeff

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[functional] Interested in can_be_called<F, Sig> metafunction?
by TONGARI 07 Nov '12

07 Nov '12

Hi there, I've used this metafunction for some time, and it just fitted my need. Recently, I make up my mind to complete it, willing to put it in public. Synopsis -------------- can_be_called<F, Sig> F Any callable type to test, even member-function ptr. Sig The desired calling signature, function-type only. Example ------------- struct X; struct F { void operator()(); }; can_be_called<void(int), void(char)>::type // mpl::true_ can_be_called<int(), void()>::type // mpl::true_, return val can always be discarded can_be_called<int(), int&()>::type // mpl::false_, cannot return as reference can_be_called<void(int&), void(int)>::type // mpl::false_, cannot accept rvalue can_be_called<void(), void(*)()>::type // compile error, "void(*)()" not a function-type can_be_called<F, void()>::type // mpl::true_ can_be_called<F const, void()>::type // mpl::false_, F::operator() is non-const can_be_called<void(X::*)(), void()>::type // mpl::true_, only the signature part is concerned can_be_called<void(X::*)(), void(X*)>::type // mpl::false_, implicit 'this' arg not accounted Repository ---------------- https://github.com/jamboree/boost.functional test files provided, compile well on g++ 4.7.1 & clang 3.2 No docs are written (yet), if you're interested, please let me know and I'll prepare for review or something... Comments are welcome :)

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[1.52] PDF Documentation build available
by John Maddock 07 Nov '12

07 Nov '12

The PDF build of Boost docs is now available for 1.52 from: https://sourceforge.net/projects/boost/files/boost-docs/1.52.0/ John.

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[qvm] scalar_cast
by Nikolay Mladenov 07 Nov '12

07 Nov '12

Hi Emil, I am trying qvm in a small project that uses complex numbers and have expressions of the kind : cv3 = c1*rv3_1 + c2*rv3_2 (the v3's are vectors, the c's are complex and the r's are real). I wrote it as : cv3 = scalar_cast<complex>(rv3_1)*c1 + scalar_cast<complex>(rv3_2)*c2; but this seems to invoke 6 complex constructors (unnecessarily) I have not tested to see if the constructors will be optimized away, but it seems to me that if : v_traits<vector_scalar_cast_>::scalar_type == complex , bit v_traits<vector_scalar_cast_>::r/ir return real the expression will compile and no complex constructors will be invoked. It seems to me that there is a need for another kind of scalar_cast that just adapts the v_traits<>:scalar_type but leaves the r() and ir() unchanged Another question I have is if there is a reason why vector*scalar works but scalar*vector does not? Thanks in advance, Nikolay PS I can send patches if you'd like.

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[release][1.52.0] Release Notes
by Daniel James 06 Nov '12

06 Nov '12

Hello everyone, We're coming up to the beta release, so it's time to put together the release notes (although please don't feel you need to wait for me to start). As always you can send them to me, or if you want update them yourself in subversion. The files are at: https://svn.boost.org/svn/boost/website/public_html/live/feed/history/ The actual site won't get updated until I run the update script. You can see the release notes so far at: http://www.boost.org/users/history/version_1_52_0.html As usual, they're not finished yet, and some of the links might not work as the 1.52 documentation won't be uploaded until after the beta is released. thanks, Daniel

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[clang] Windows toolset support?
by Beman Dawes 06 Nov '12

06 Nov '12

Cygwin has been shipping clang for six months or so. Has anyone gotten the cygwin/clang distribution (or any other clang distribution) to build boost? What toolset did you use? What does your user-config.jam file look like? Do you run bjam/b2 from the Windows command line or the bash command line? Thanks, --Beman

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make_shared_array
by Peter Dimov 06 Nov '12

06 Nov '12

Hello, Glen Fernandes has kindly contributed an implementation of make_shared_array and allocate_shared_array. These are like make_shared and allocate_shared, except that they take a size_t argument N and allocate an array of N elements. Glen has made the functions return a shared_ptr, mostly because they are non-intrusive and it's not possible to return a shared_array without changes to shared_ptr and shared_array. But we can make such changes when we put the functions in Boost. So the question is, should we? It makes almost no sense to have a function called make_shared_array that does not, in fact, make a shared_array. On the other hand, Glen posits that some people may prefer to use shared_ptr instead of shared_array in their code for various reasons, one of which is that shared_array's default constructor can throw. Opinions?

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