The no-duplication principle: Member variables and function definitions should be distributed among class definitions to ensure that there is no duplication of identical code. Otherwise, duplicate copies are bound to become gratuitously different.
In the version of the program in
Segment 239, for example, the height
, width
, and
length
member variables and volume
member function reside in
the box
class, rather than in the box_car
, making those
member variables and member functions more generally available.