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Uses of Partial Methods

Given the restrictions that come with a partial method, most notably the fact that they must be

implicitly private and always return void, it is hard to see many useful applications of this new lan-

guage feature. Truth be told, out of all of the language features found with C# 2008, partial methods

will more likely than not be the least used among them.

In the current example, the VerifyDuplicates() method was marked as partial for illustrative

purposes; however, imagine that this method, if implemented, had to perform some very intensive

calculations.

By marking this method with the partial modifier, other class builders have the option of pro-

viding implementation details if they so choose. In this case, partial methods provide a cleaner

solution than using preprocessor directives, supplying “dummy” implementations to virtual meth-

ods or throwing NotImplementedException objects.

The most common use of this syntax is to define what are termed 

lightweight events. This tech-

nique enables class designers to provide method hooks, similar to event handlers, that developers

may choose to implement or not. As a naming convention, such lightweight event-handling meth-

ods take an On prefix, for example:

// CarLocator.EventHandler.cs

partial class CarLocator

{

public bool CarAvailableInZipCode(string zipCode)

{

...

OnZipCodeLookup(zipCode);

return true;

}

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