What Is A Separation Between Type And Class (Representation)?
For a short answer: Subtype Polymorphism, as opposed to Subclass Polymorphism, is the best answer in OO. Parametric polymorphism is a related concept where this is also true, but is of a different flavor (and usually requires object attributes by use. See also section 2.1). A type can be considered a set of values and a set of operations on those values. This can insure type-safe programming. However, the representation of types (classes in OO) can be separated from the notion of type allowing many representations per type while still maintaining reasonable type-safety. In many languages, a type has a single representation insuring all operations performed on that type are well defined (statically bound) and providing for efficiency by taking advantage of that representation wherever used. In many OO languages, subclassing and dynamic binding provides for greater flexibility by providing object specialization. However, in many OO languages classes are used for assignment compatibility
