Visual Basic 2005: A Developer's Notebook

Build Typesafe Generic Classes

Programmers often face a difficult choice. On one hand, it's keenly important to build solutions that are as generic as possible, so that they can be reused in different scenarios. For example, why build a CustomerCollection class that accepts only objects of type Customer when you can build a generic Collection class that can be configured to accept objects of any type? On the other hand, performance and type safety considerations can make a generic solution less desirable. If you use a generic .NET Collection class to store Customer objects, for example, how can you be sure that someone won't accidentally insert another type of object into the collection, causing an insidious problem later on?

Note

Need to create a class that's flexible enough to work with any type of object, but able to restrict the objects it accepts in any given instance? With generics, VB has the perfect solution.

Visual Basic 2005 and .NET 2.0 provide a solution called generics. Generics are classes that are parameterized by type. In other words, generics allow you to create a class template that supports any type. When you instantiate that class, you specify the type you want to use, and from that point on, your object is "locked in" to the type you chose.

How do I do that?

An example of where the use of generics makes great sense is the System.Collections.ArrayList class. ArrayList is an all-purpose, dynamically self-sizing collection. It can hold ordinary .NET objects or ...