Generic Interfaces

A generic interface is a contract parameterized by one or more types. IRepository<T> doesn't say "I store things," it says "I store things of type T," and the T shows up in every member that handles the data. The BCL is full of them (IEnumerable<T>, IComparer<T>, IEquatable<T>, and more), and your own code will be too once you start writing reusable services. This chapter covers how to declare a generic interface, the three ways to implement one, the awkward case of implementing the same generic interface for two different closed types on a single class, and a quick tour of the generic interfaces in the BCL you'll touch most often.