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Source Code

The AutomaticProperties project can be found under the Chapter 13 subdirectory.

Understanding Extension Methods

The next C# 2008 language feature we will examine is the use of extension methods. As you know,

once a type is defined and compiled into a .NET assembly, its definition is, more or less, final. The

only way to add new members, update members, or remove members is to recode and recompile

the code base into an updated assembly (or take more drastic measures, such as using the

System.Reflection.Emit namespace to dynamically reshape a compiled type in memory).

Under C# 2008, it is now possible to define extension methods. In a nutshell, extension meth-

ods allow existing compiled types (specifically, classes, structures, or interface implementations) as

well as types currently being compiled (such as types in a project that contains extension methods)

to gain new functionality without needing to directly update the type being extended.

This technique can be quite helpful when you need to inject new functionality into types for

which you do not have an existing code base. It can also be quite helpful when you need to force a

type to support a set of members (in the interest of polymorphism), but cannot modify the original

type declaration. Using extension methods, you can add functionality to precompiled types while

providing the illusion these methods were there all along.