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Source Code

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

Understanding Partial Methods

Since the release of .NET 2.0, we have been able to build partial class definitions using the partial

keyword (see Chapter 5). Recall that this bit of syntax allows us to partition the full implementation

of a type across multiple code files (or other locations, such as in memory). As long as each aspect

of the partial type has the same fully qualified name, the end result is a single “normal” compiled

class type in the assembly being constructed.

C# 2008 widens the scope of the partial keyword in that it can now be applied on the method

level. In a nutshell, this allows you to prototype a method in one file, yet implement it in another

file. If you have a C++ background, this might remind you of the concept of a C++ header/imple-

mentation file; however, C# partial methods have a number of important restrictions:

• Partial methods can only be defined within a partial class.

• Partial methods must return void.

• Partial methods can be static or instance level.

• Partial methods can have arguments (including parameters modified by this, ref, or

params—but not with the out modifier).

• Partial methods are always implicitly private.

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Even stranger is the fact that a partial method may or may not be emitted into the compiled

assembly!