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Contrasting Interface Types to Abstract Base Classes

Given your work in Chapter 6, the interface type may seem very similar to an abstract base class.

Recall that when a class is marked as abstract, it may define any number of abstract members to

provide a polymorphic interface to all derived types. However, even when a class type does define a

set of abstract members, it is also free to define any number of constructors, field data, nonabstract

members (with implementation), and so on. Interfaces, on the other hand, only contain abstract

members.

The polymorphic interface established by an abstract parent class suffers from one major limi-

tation in that only derived types support the members defined by the abstract parent. However, in

larger software systems, it is very common to develop multiple class hierarchies that have no com-

mon parent beyond System.Object. Given that abstract members in an abstract base class only

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apply to derived types, we have no way to configure types in different hierarchies to support the

same polymorphic interface. By way of an illustrative example, assume you have defined the follow-

ing abstract class:

abstract class CloneableType

{