In file included from /in/driver/main.cpp:8:0:
/in/kdtree.hpp: In instantiation of 'KDTree<std::tuple<_Elements ...>, ValueType>& KDTree<std::tuple<_Elements ...>, ValueType>::operator=(const KDTree<std::tuple<_Elements ...>, ValueType>&) [with ValueType = std::__cxx11::basic_string<char>; KeyTypes = {int, int, int}]':
/in/driver/main.cpp:146:23:   required from here
/in/kdtree.hpp:490:41: error: 'copy_helper' was not declared in this scope
                 this->root = copy_helper(that.root,nullptr);
                              ~~~~~~~~~~~^~~~~~~~~~~~~~~~~~~
/in/kdtree.hpp:490:41: note: suggested alternative: 'delete_helper'
                 this->root = copy_helper(that.root,nullptr);
                              ~~~~~~~~~~~^~~~~~~~~~~~~~~~~~~
                              delete_helper