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Delegates, Events, and Lambdas

U

p to this point in the text, most of the applications you have developed added various bits of

code to Main(), which, in some way or another, sent requests to a given object. In Chapter 9, you

examined how the interface type can be used to build objects that can “talk back” to the entity that

created it. While callback interfaces can be used to configure objects that engage in two-way con-

versations, the .NET delegate type is the preferred manner to define and respond to callbacks under

the .NET platform.

Essentially, the .NET delegate type is a type-safe object that “points to” a method, or if you

wish, a list of methods, that can be invoked at a later time. Unlike a traditional C++ function pointer,

however, .NET delegates are classes that have built-in support for multicasting and asynchronous

method invocation.

Once you learn how to create and manipulate delegate types, you then investigate the C# event

keyword, which streamlines the process of working with delegate types. Along the way you will also

examine several delegate-and-event-centric language features of C#, including anonymous meth-

ods and method group conversions.

I wrap up this chapter by investigating a new C# 2008 language feature termed 

lambda expres-

sions. Using the new lambda operator (=>), it is now possible to specify a block of code statements

(and the parameters to pass to said code statements) wherever a strongly typed delegate is required.

As you will see, a lambda expression is little more than an anonymous method in disguise.