C# 4 and .NET 4

8Delegates, lambdas, and events
WhaT ’ s in This ChaPTer
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Delegates
Lambda expressions
Events
Delegates are the .NET version of addresses to methods. Compare this to C++, where function
pointers are nothing more than a pointer to a memory location that are not type - safe. You have
no idea what a pointer is really pointing to, and items such as parameters and return types are not
known. This is completely different with .NET; delegates are type - safe classes that defi ne the return
types and types of parameters. The delegate class not only contains a reference to a method, but can
hold references to multiple methods.
Lambda expressions are directly related to delegates. When the parameter is a delegate type, you can
use a Lambda expression to implement a method that ’ s referenced from the delegate.
This chapter teaches you the basics of delegates and Lambda expressions, and shows you how to
implement methods called by delegates with Lambda expressions. It also demonstrates how .NET
uses delegates as the means of implementing events.
delegaTes
Delegates exist for situations in which you want to pass methods around to other methods. To see
what that means, consider this line of code:
int i = int.Parse("99");
You are so used to passing data to methods as parameters, as in this example, that you don ’ t
consciously think about it, and for this reason the idea of passing methods around instead of
data might sound a little strange. However, there are cases in which you have a method that does
something, and rather than operating on data, the method might need to do something that involves
invoking another method. To complicate things further, you do not know at compile time what this
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