8. Interfaces

Polymorphism is available in C# not only via inheritance (as discussed in Chapter 7) but also via interfaces. Unlike abstract classes, interfaces could not include any implementation—until C# 8.0. (But even in C# 8.0, it is questionable whether you should use this capability except for “versioning” and interfaces.) Like abstract classes, however, interfaces define a set of members that callers can rely on being implemented.

An illustration shows the various subjects involved in the interfaces. It is listed as follows: polymorphism, interface implementation, interface inheritance, extension methods on interfaces, and versioning. Interface implementation constitutes explicit and implicit.

By implementing an interface, a type defines its capabilities. The interface implementation relationship is a “can do” relationship. The type can do what the interface requires an implementing type to do. The ...

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