Re: [Boost-users] [container / move] return a container of non-copyable but movable from a function in C++03

Subject: Re: [Boost-users] [container / move] return a container of non-copyable but movable from a function in C++03
From: Adam Romanek (romanek.adam_at_[hidden])
Date: 2013-08-13 15:04:48

It turned out that copy-constructor is chosen over move-constructor when 
constructing nc_vector "v" in main().

That leads me to a question whether copy-constructor shouldn't be 
disable_if-ed in case the container's value_type is non-copyable?

Is there any way to work-around this issue?

WBR,
Adam Romanek

On 08/13/2013 04:59 PM, Gmail wrote:
> Ops. I meant I'd like to return a container of non-copyable but movable objects, as shown in the example.
>
> WBR,
> Adam Romanek
>
> Dnia 13 sie 2013 o godz. 16:09 Adam Romanek <romanek.adam_at_[hidden]> napisał(a):
>
>> Hi,
>>
>> I'd like to return a container of non-movables from a function in C++03 with no success.
>>
>> here is a sample code that does not compile for me:
>>
>> #include <boost/container/vector.hpp>
>> #include <boost/move/utility.hpp>
>>
>> class non_copyable {
>>   BOOST_MOVABLE_BUT_NOT_COPYABLE(non_copyable)
>>
>> public:
>>   non_copyable(){}
>>   non_copyable(BOOST_RV_REF(non_copyable)) {}
>>   non_copyable& operator=(BOOST_RV_REF(non_copyable)) { return *this; }
>> };
>>
>> typedef boost::container::vector<non_copyable> nc_vector;
>>
>> nc_vector create() {
>>   return nc_vector();
>> }
>>
>> int main () {
>>    nc_vector v(create());
>>    return 0;
>> }
>>
>> The compiler says:
>>
>> (...)
>> /home/A.Romanek/tmp/boost/boost_1_54_0/boost/preprocessor/iteration/detail/local.hpp:37:1: error: passing ‘const non_copyable’ as ‘this’ argument of ‘non_copyable::operator boost::rv<non_copyable>&()’ discards qualifiers [-fpermissive]
>> (...)
>>
>> See below for a full compiler output.
>>
>> I use Boost v1.54 and gcc (Ubuntu/Linaro 4.6.3-1ubuntu5) 4.6.3.
>>
>> Is it a bug?
>>
>> Here is the full compiler output:
>>
>> In file included from /home/A.Romanek/tmp/boost/boost_1_54_0/boost/container/allocator_traits.hpp:388:0,
>>                  from /home/A.Romanek/tmp/boost/boost_1_54_0/boost/container/detail/utilities.hpp:28,
>>                  from /home/A.Romanek/tmp/boost/boost_1_54_0/boost/container/vector.hpp:37,
>>                  from main.cpp:1:
>> /home/A.Romanek/tmp/boost/boost_1_54_0/boost/preprocessor/iteration/detail/local.hpp: In static member function ‘static void boost::container::allocator_traits<Alloc>::priv_construct_dispatch2(boost::false_type, Alloc&, T*, const P0&) [with T = non_copyable, P0 = non_copyable, Alloc = std::allocator<non_copyable>, boost::false_type = boost::integral_constant<bool, false>]’:
>> /home/A.Romanek/tmp/boost/boost_1_54_0/boost/preprocessor/iteration/detail/local.hpp:37:1:   instantiated from ‘static void boost::container::allocator_traits<Alloc>::priv_construct(boost::true_type, Alloc&, T*, const P0&) [with T = non_copyable, P0 = non_copyable, Alloc = std::allocator<non_copyable>, boost::true_type = boost::integral_constant<bool, true>]’
>> /home/A.Romanek/tmp/boost/boost_1_54_0/boost/preprocessor/iteration/detail/local.hpp:37:1:   instantiated from ‘static void boost::container::allocator_traits<Alloc>::construct(Alloc&, T*, const P0&) [with T = non_copyable, P0 = non_copyable, Alloc = std::allocator<non_copyable>]’
>> /home/A.Romanek/tmp/boost/boost_1_54_0/boost/container/detail/utilities.hpp:555:10:   instantiated from ‘typename boost::container::container_detail::disable_if_memcpy_copy_constructible<I, F, F>::type boost::container::uninitialized_copy_alloc_n(A&, I, typename std::iterator_traits<_II>::difference_type, F) [with A = std::allocator<non_copyable>, I = non_copyable*, F = non_copyable*, typename boost::container::container_detail::disable_if_memcpy_copy_constructible<I, F, F>::type = non_copyable*, typename std::iterator_traits<_II>::difference_type = int]’
>> /home/A.Romanek/tmp/boost/boost_1_54_0/boost/container/vector.hpp:734:7:   instantiated from ‘boost::container::vector<T, Allocator>::vector(const boost::container::vector<T, Allocator>&) [with T = non_copyable, Allocator = std::allocator<non_copyable>, boost::container::vector<T, Allocator> = boost::container::vector<non_copyable>]’
>> main.cpp:16:20:   instantiated from here
>> /home/A.Romanek/tmp/boost/boost_1_54_0/boost/preprocessor/iteration/detail/local.hpp:37:1: error: passing ‘const non_copyable’ as ‘this’ argument of ‘non_copyable::operator boost::rv<non_copyable>&()’ discards qualifiers [-fpermissive]
>>
>> WBR,
>> Adam Romanek
>>