Why is this code trying to stuff a pair of - int and a class with a copy constructor not working?
int main() { std::map<int, A> m; A a; m.insert(std::make_pair(0, a)); return 0; } Class A:
A::A() = default; A::A(A &a) { //smth } Error text:
/home/wcobalt/Files/InstalledPrograms/clion-2018.2.4/bin/cmake/linux/bin/cmake --build /home/wcobalt/Files/test/cmake-build-debug --target test -- -j 2 Scanning dependencies of target test [ 66%] Building CXX object CMakeFiles/test.dir/A.cpp.o [ 66%] Building CXX object CMakeFiles/test.dir/main.cpp.o In file included from /usr/include/c++/7/bits/stl_algobase.h:64:0, from /usr/include/c++/7/bits/char_traits.h:39, from /usr/include/c++/7/ios:40, from /usr/include/c++/7/ostream:38, from /usr/include/c++/7/iostream:39, from /home/wcobalt/Files/test/main.cpp:1: /usr/include/c++/7/bits/stl_pair.h: In instantiation of 'struct std::pair<int, A>': /home/wcobalt/Files/test/main.cpp:11:33: required from here /usr/include/c++/7/bits/stl_pair.h:292:17: error: 'constexpr std::pair<_T1, _T2>::pair(const std::pair<_T1, _T2>&) [with _T1 = int; _T2 = A]' declared to take const reference, but implicit declaration would take non-const constexpr pair(const pair&) = default; ^~~~ /usr/include/c++/7/bits/stl_pair.h: In instantiation of 'struct std::pair<const int, A>': /usr/include/c++/7/type_traits:787:65: required by substitution of 'template<class _Tp, class> static std::true_type std::__do_is_destructible_impl::__test(int) [with _Tp = std::pair<const int, A>; <template-parameter-1-2> = <missing>]' /usr/include/c++/7/type_traits:798:35: required from 'struct std::__is_destructible_impl<std::pair<const int, A> >' /usr/include/c++/7/type_traits:809:12: required from 'struct std::__is_destructible_safe<std::pair<const int, A>, false, false>' /usr/include/c++/7/type_traits:824:12: required from 'struct std::is_destructible<std::pair<const int, A> >' /usr/include/c++/7/type_traits:143:12: [ skipping 2 instantiation contexts, use -ftemplate-backtrace-limit=0 to disable ] /usr/include/c++/7/type_traits:1070:12: required from 'struct std::__is_direct_constructible_new<std::pair<const int, A>, std::pair<int, A>&&>' /usr/include/c++/7/type_traits:1078:12: required from 'struct std::__is_direct_constructible<std::pair<const int, A>, std::pair<int, A>&&>' /usr/include/c++/7/type_traits:1118:12: required from 'struct std::__is_constructible_impl<std::pair<const int, A>, std::pair<int, A>&&>' /usr/include/c++/7/type_traits:1129:12: required from 'struct std::is_constructible<std::pair<const int, A>, std::pair<int, A>&&>' /usr/include/c++/7/bits/stl_map.h:805:32: required by substitution of 'template<class _Pair, class> std::pair<std::_Rb_tree_iterator<std::pair<const int, A> >, bool> std::map<int, A>::insert<_Pair, <template-parameter-1-2> >(_Pair&&) [with _Pair = std::pair<int, A>; <template-parameter-1-2> = <missing>]' /home/wcobalt/Files/test/main.cpp:11:34: required from here /usr/include/c++/7/bits/stl_pair.h:292:17: error: 'constexpr std::pair<_T1, _T2>::pair(const std::pair<_T1, _T2>&) [with _T1 = const int; _T2 = A]' declared to take const reference, but implicit declaration would take non-const /home/wcobalt/Files/test/main.cpp: In function 'int main()': /home/wcobalt/Files/test/main.cpp:11:34: error: no matching function for call to 'std::map<int, A>::insert(std::pair<int, A>)' m.insert(std::make_pair(0, a)); ^ In file included from /usr/include/c++/7/map:61:0, from /home/wcobalt/Files/test/main.cpp:2: /usr/include/c++/7/bits/stl_map.h:621:7: note: candidate: std::map<_Key, _Tp, _Compare, _Alloc>::insert_return_type std::map<_Key, _Tp, _Compare, _Alloc>::insert(std::map<_Key, _Tp, _Compare, _Alloc>::node_type&&) [with _Key = int; _Tp = A; _Compare = std::less<int>; _Alloc = std::allocator<std::pair<const int, A> >; std::map<_Key, _Tp, _Compare, _Alloc>::insert_return_type = std::_Node_insert_return<std::_Rb_tree_iterator<std::pair<const int, A> >, std::_Node_handle<int, std::pair<const int, A>, std::allocator<std::_Rb_tree_node<std::pair<const int, A> > > > >; std::map<_Key, _Tp, _Compare, _Alloc>::node_type = std::_Node_handle<int, std::pair<const int, A>, std::allocator<std::_Rb_tree_node<std::pair<const int, A> > > >] insert(node_type&& __nh) ^~~~~~ /usr/include/c++/7/bits/stl_map.h:621:7: note: no known conversion for argument 1 from 'std::pair<int, A>' to 'std::map<int, A>::node_type&& {aka std::_Node_handle<int, std::pair<const int, A>, std::allocator<std::_Rb_tree_node<std::pair<const int, A> > > >&&}' /usr/include/c++/7/bits/stl_map.h:626:7: note: candidate: std::map<_Key, _Tp, _Compare, _Alloc>::iterator std::map<_Key, _Tp, _Compare, _Alloc>::insert(std::map<_Key, _Tp, _Compare, _Alloc>::const_iterator, std::map<_Key, _Tp, _Compare, _Alloc>::node_type&&) [with _Key = int; _Tp = A; _Compare = std::less<int>; _Alloc = std::allocator<std::pair<const int, A> >; std::map<_Key, _Tp, _Compare, _Alloc>::iterator = std::_Rb_tree_iterator<std::pair<const int, A> >; std::map<_Key, _Tp, _Compare, _Alloc>::const_iterator = std::_Rb_tree_const_iterator<std::pair<const int, A> >; std::map<_Key, _Tp, _Compare, _Alloc>::node_type = std::_Node_handle<int, std::pair<const int, A>, std::allocator<std::_Rb_tree_node<std::pair<const int, A> > > >] insert(const_iterator __hint, node_type&& __nh) ^~~~~~ /usr/include/c++/7/bits/stl_map.h:626:7: note: candidate expects 2 arguments, 1 provided /usr/include/c++/7/bits/stl_map.h:795:7: note: candidate: std::pair<typename std::_Rb_tree<_Key, std::pair<const _Key, _Tp>, std::_Select1st<std::pair<const _Key, _Tp> >, _Compare, typename __gnu_cxx::__alloc_traits<_Alloc>::rebind<std::pair<const _Key, _Tp> >::other>::iterator, bool> std::map<_Key, _Tp, _Compare, _Alloc>::insert(const value_type&) [with _Key = int; _Tp = A; _Compare = std::less<int>; _Alloc = std::allocator<std::pair<const int, A> >; typename std::_Rb_tree<_Key, std::pair<const _Key, _Tp>, std::_Select1st<std::pair<const _Key, _Tp> >, _Compare, typename __gnu_cxx::__alloc_traits<_Alloc>::rebind<std::pair<const _Key, _Tp> >::other>::iterator = std::_Rb_tree_iterator<std::pair<const int, A> >; std::map<_Key, _Tp, _Compare, _Alloc>::value_type = std::pair<const int, A>] insert(const value_type& __x) ^~~~~~ /usr/include/c++/7/bits/stl_map.h:795:7: note: no known conversion for argument 1 from 'std::pair<int, A>' to 'const value_type& {aka const std::pair<const int, A>&}' /usr/include/c++/7/bits/stl_map.h:802:7: note: candidate: std::pair<typename std::_Rb_tree<_Key, std::pair<const _Key, _Tp>, std::_Select1st<std::pair<const _Key, _Tp> >, _Compare, typename __gnu_cxx::__alloc_traits<_Alloc>::rebind<std::pair<const _Key, _Tp> >::other>::iterator, bool> std::map<_Key, _Tp, _Compare, _Alloc>::insert(std::map<_Key, _Tp, _Compare, _Alloc>::value_type&&) [with _Key = int; _Tp = A; _Compare = std::less<int>; _Alloc = std::allocator<std::pair<const int, A> >; typename std::_Rb_tree<_Key, std::pair<const _Key, _Tp>, std::_Select1st<std::pair<const _Key, _Tp> >, _Compare, typename __gnu_cxx::__alloc_traits<_Alloc>::rebind<std::pair<const _Key, _Tp> >::other>::iterator = std::_Rb_tree_iterator<std::pair<const int, A> >; std::map<_Key, _Tp, _Compare, _Alloc>::value_type = std::pair<const int, A>] insert(value_type&& __x) ^~~~~~ /usr/include/c++/7/bits/stl_map.h:802:7: note: no known conversion for argument 1 from 'std::pair<int, A>' to 'std::map<int, A>::value_type&& {aka std::pair<const int, A>&&}' /usr/include/c++/7/bits/stl_map.h:809:2: note: candidate: template<class _Pair, class> std::pair<typename std::_Rb_tree<_Key, std::pair<const _Key, _Tp>, std::_Select1st<std::pair<const _Key, _Tp> >, _Compare, typename __gnu_cxx::__alloc_traits<_Alloc>::rebind<std::pair<const _Key, _Tp> >::other>::iterator, bool> std::map<_Key, _Tp, _Compare, _Alloc>::insert(_Pair&&) [with _Pair = _Pair; <template-parameter-2-2> = <template-parameter-1-2>; _Key = int; _Tp = A; _Compare = std::less<int>; _Alloc = std::allocator<std::pair<const int, A> >] insert(_Pair&& __x) ^~~~~~ /usr/include/c++/7/bits/stl_map.h:809:2: note: substitution of deduced template arguments resulted in errors seen above /usr/include/c++/7/bits/stl_map.h:823:7: note: candidate: void std::map<_Key, _Tp, _Compare, _Alloc>::insert(std::initializer_list<std::pair<const _Key, _Tp> >) [with _Key = int; _Tp = A; _Compare = std::less<int>; _Alloc = std::allocator<std::pair<const int, A> >] insert(std::initializer_list<value_type> __list) ^~~~~~ /usr/include/c++/7/bits/stl_map.h:823:7: note: no known conversion for argument 1 from 'std::pair<int, A>' to 'std::initializer_list<std::pair<const int, A> >' /usr/include/c++/7/bits/stl_map.h:853:7: note: candidate: std::map<_Key, _Tp, _Compare, _Alloc>::iterator std::map<_Key, _Tp, _Compare, _Alloc>::insert(std::map<_Key, _Tp, _Compare, _Alloc>::const_iterator, const value_type&) [with _Key = int; _Tp = A; _Compare = std::less<int>; _Alloc = std::allocator<std::pair<const int, A> >; std::map<_Key, _Tp, _Compare, _Alloc>::iterator = std::_Rb_tree_iterator<std::pair<const int, A> >; std::map<_Key, _Tp, _Compare, _Alloc>::const_iterator = std::_Rb_tree_const_iterator<std::pair<const int, A> >; std::map<_Key, _Tp, _Compare, _Alloc>::value_type = std::pair<const int, A>] insert(const_iterator __position, const value_type& __x) ^~~~~~ /usr/include/c++/7/bits/stl_map.h:853:7: note: candidate expects 2 arguments, 1 provided /usr/include/c++/7/bits/stl_map.h:863:7: note: candidate: std::map<_Key, _Tp, _Compare, _Alloc>::iterator std::map<_Key, _Tp, _Compare, _Alloc>::insert(std::map<_Key, _Tp, _Compare, _Alloc>::const_iterator, std::map<_Key, _Tp, _Compare, _Alloc>::value_type&&) [with _Key = int; _Tp = A; _Compare = std::less<int>; _Alloc = std::allocator<std::pair<const int, A> >; std::map<_Key, _Tp, _Compare, _Alloc>::iterator = std::_Rb_tree_iterator<std::pair<const int, A> >; std::map<_Key, _Tp, _Compare, _Alloc>::const_iterator = std::_Rb_tree_const_iterator<std::pair<const int, A> >; std::map<_Key, _Tp, _Compare, _Alloc>::value_type = std::pair<const int, A>] insert(const_iterator __position, value_type&& __x) ^~~~~~ /usr/include/c++/7/bits/stl_map.h:863:7: note: candidate expects 2 arguments, 1 provided /usr/include/c++/7/bits/stl_map.h:870:2: note: candidate: template<class _Pair, class> std::map<_Key, _Tp, _Compare, _Alloc>::iterator std::map<_Key, _Tp, _Compare, _Alloc>::insert(std::map<_Key, _Tp, _Compare, _Alloc>::const_iterator, _Pair&&) [with _Pair = _Pair; <template-parameter-2-2> = <template-parameter-1-2>; _Key = int; _Tp = A; _Compare = std::less<int>; _Alloc = std::allocator<std::pair<const int, A> >] insert(const_iterator __position, _Pair&& __x) ^~~~~~ /usr/include/c++/7/bits/stl_map.h:870:2: note: template argument deduction/substitution failed: /home/wcobalt/Files/test/main.cpp:11:34: note: candidate expects 2 arguments, 1 provided m.insert(std::make_pair(0, a)); ^ In file included from /usr/include/c++/7/map:61:0, from /home/wcobalt/Files/test/main.cpp:2: /usr/include/c++/7/bits/stl_map.h:886:2: note: candidate: template<class _InputIterator> void std::map<_Key, _Tp, _Compare, _Alloc>::insert(_InputIterator, _InputIterator) [with _InputIterator = _InputIterator; _Key = int; _Tp = A; _Compare = std::less<int>; _Alloc = std::allocator<std::pair<const int, A> >] insert(_InputIterator __first, _InputIterator __last) ^~~~~~ /usr/include/c++/7/bits/stl_map.h:886:2: note: template argument deduction/substitution failed: /home/wcobalt/Files/test/main.cpp:11:34: note: candidate expects 2 arguments, 1 provided m.insert(std::make_pair(0, a)); ^ CMakeFiles/test.dir/build.make:62: recipe for target 'CMakeFiles/test.dir/main.cpp.o' failed make[3]: *** [CMakeFiles/test.dir/main.cpp.o] Error 1 CMakeFiles/Makefile2:72: recipe for target 'CMakeFiles/test.dir/all' failed make[2]: *** [CMakeFiles/test.dir/all] Error 2 CMakeFiles/Makefile2:84: recipe for target 'CMakeFiles/test.dir/rule' failed make[1]: *** [CMakeFiles/test.dir/rule] Error 2 Makefile:118: recipe for target 'test' failed make: *** [test] Error 2 
