Beginning C# 2008 Objects: From Concept to Code

6.3. Collections of Supertypes

We said earlier that arrays, as simple collections, contain items (either simple types or objects) that are all of the same type: all int(egers), for example, or all (references to) Student objects. However, the power of inheritance can be used to make arrays more versatile in the types of objects that they can hold.

If we declare an array to hold objects of a given type (for example, Person), we're free to insert objects explicitly declared to be of type Person or of any types derived from Person (for example, UndergraduateStudent, GraduateStudent, and Professor). This is because of the "is a" nature of inheritance; UndergraduateStudent, GraduateStudent, and Professor objects, as subclasses of Person, are simply ...