./Machinarium/Classes/Geometry/Vector2.h:8:23: error: invalid covariant return type for ‘Vector2D<T> Vector2D<T>::add_by_number(T) [with T = int]’
8 | #define DVector(name) Vector ## name ## D
./Machinarium/Classes/Geometry/Vector2.cpp:36:36: note: in expansion of macro ‘DVector’
36 | template<typename T> DVector(2)<T> DVector(2)<T>::add_by_number(T value)
| ^~~~~~~
Как понять ошибку?