What Are Generics

At its core, the term generics means parameterized types. Parameterized types are important because they enable you to create classes, structures, interfaces, methods, and delegates in which the type of data upon which they operate is specified as a parameter. Using generics, it is possible to create a single class, for example, that automatically works with different types of data. A class, structure, interface, method, or delegate that operates on a parameterized type is called generic, as in generic class or generic method.
It is important to understand that C# has always given you the ability to create generalized code by operating through references of type object. Because object is the base class of all other classes, an object reference can refer to any type of object. Thus, in pre-generics code, generalized code used object references to operate on a variety of different kinds of objects.
The problem was that it could not do so with type safety because casts were needed to convert between the object type and the actual type of the data. This was a potential source of errors because it was possible to accidentally use an incorrect cast. Generics avoid this problem by providing the type safety that was lacking. Generics also streamline the process because it is no longer necessary to employ casts to translate between object and the type of data that is actually being operated upon. Thus, generics expand your ability to re-use code, and let you do so safely and easily.