Hi,

typedef std::pair > mypair;

If I'm replacing 'mypair' with 'mystruct': struct mystruct { mystruct& operator=(const mystruct& other) { i = other.i; sv = other.sv; return *this; } int i; small_vector sv; }; Then I can compile it without C++11 support, but I've to implement the 'operator=' by hand, otherwise I'm still getting a compile error: dan@octa ~> g++ -Iboost_1_63_0/ small_vector_test_2.cpp In file included from boost_1_63_0/boost/container/small_vector.hpp:27:0, from small_vector_test_2.cpp:2: boost_1_63_0/boost/container/vector.hpp: In instantiation of ‘void boost::container::vector::assign(FwdIt, FwdIt, typename boost::move_detail::disable_if_or >, boost::move_detail::is_convertible, boost::container::container_detail::is_input_iterator<FwdIt> >::type*) [with FwdIt = boost::container::container_detail::vec_iterator; T = mystruct; Allocator = boost::container::small_vector_allocator; typename boost::move_detail::disable_if_or >, boost::move_detail::is_convertible, boost::container::container_detail::is_input_iterator<FwdIt> >::type = void]’: boost_1_63_0/boost/container/small_vector.hpp:563:7: required from ‘boost::container::small_vector::small_vector(const boost::container::small_vector&) [with T = mystruct; long unsigned int N = 8ul; Allocator = boost::container::new_allocator<mystruct>]’ /usr/include/c++/5/bits/stl_pair.h:113:31: required from ‘std::pair<_T1, _T2>::pair(const _T1&, const _T2&) [with _T1 = const int; _T2 = boost::container::small_vector]’ /usr/include/c++/5/bits/stl_map.h:487:23: required from ‘std::map<_Key, _Tp, _Compare, _Alloc>::mapped_type& std::map<_Key, _Tp, _Compare, _Alloc>::operator[](const key_type&) [with _Key = int; _Tp = boost::container::small_vector; _Compare = std::less<int>; _Alloc = std::allocator > >; std::map<_Key, _Tp, _Compare, _Alloc>::mapped_type = boost::container::small_vector; std::map<_Key, _Tp, _Compare, _Alloc>::key_type = int]’ small_vector_test_2.cpp:21:41: required from here boost_1_63_0/boost/container/vector.hpp:1261:15: error: binding ‘const mystruct’ to reference of type ‘mystruct&’ discards qualifiers *cur = *first; ^ small_vector_test_2.cpp:6:8: note: initializing argument 1 of ‘mystruct& mystruct::operator=(mystruct&)’ For whatever reasons the operator 'mystruct& mystruct::operator=(mystruct&)' is used, with a non const reference parameter, which can't work in this context. Looks like a bug? boost? gcc? Greetings, Daniel

On 31/12/2016 17:44, Daniel Trstenjak wrote:

Hi,

first the used versions: boost 1.63.0 gcc 5.4.0 20160609 Ubuntu 16.04.1

the example I've problems with is:

#include <map> #include

using boost::container::small_vector;

typedef std::pair > mypair;

typedef std::map mymap; typedef std::map > mymap2; typedef std::map, 8> > mymap3;

int main() { mymap m; mypair& sv = m[0];

mymap2 m2; small_vector& sv2 = m2[0];

mymap3 m3; small_vector, 8>& sv3 = m3[0]; }

In C++98 std::pair copy constructor is implicitly declared. Since small_vector declares operator= taking a non-const reference (as that's how move semantics are emulated), then std::pair's operator= takes a non-const pair argument: http://en.cppreference.com/w/cpp/language/copy_assignment#Implicitly-declare... So the problem you are facing it's a limitation of the move emulation library. When you define your own class holding a small_vector, you have the same problem. When you explicitly declare operator= taking a const reference the problem is solved. See: http://www.boost.org/doc/libs/1_63_0/doc/html/move/emulation_limitations.htm... and http://www.boost.org/doc/libs/1_63_0/doc/html/container/known_issues.html#co... Best, Ion