Final answer:
In C# 8.0 and later, interfaces can include static methods, regular (non-abstract) methods, and static fields, offering more flexibility and facilitating the design of modular and reusable code.
Step-by-step explanation:
With C# 8.0 and later versions, interfaces in C# were expanded to support new features that were not available in earlier versions of the language. Specifically, you can now add static methods, regular (non-abstract) methods, and static fields to interfaces. These enhancements offer more flexibility and allow for rich interface definitions that can provide default implementations and utility functions which do not require an instance of a class that implements the interface. This helps in designing more modular and reusable code.
For example, prior to C# 8.0, interfaces could only contain declaration of methods, properties, events, and indexers without their implementation. Starting with C# 8.0, you can also include default implementations for interface members so that classes that implement the interface are not required to provide an implementation for those members. Static methods in interfaces allow for defining methods that can be called on the interface itself rather than on an instance of a class that implements the interface. Furthermore, static fields can be used to define static state that would be shared amongst all implementers of the interface.