This chapter introduced generics. We discussed how generics ensure compile-time type safety by checking for type mismatches at compile time. You learned that the compiler will allow generic code to compile only if all operations performed on the type parameters in the generic code are supported for all types that could be used with the generic code. You also learned how to declare generic methods and classes using type parameters. We demonstrated how to use a type constraint to specify the requirements for a type parameter— a key component of compile-time type safety. We discussed several kinds of type constraints, including reference-type constraints, value-type constraints, class constraints, interface constraints and constructor constraints. We also discussed how to implement multiple type constraints for a type parameter. Finally, we showed how generics improve code reuse. In the next chapter, we demonstrate the .NET Framework Class Library’s collection classes, interfaces and algorithms. Collection classes are pre-built data structures that you can reuse in your apps, saving you time.