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// This delegate can point to any method,

// taking two integers and returning an integer.

public delegate int BinaryOp(int x, int y);

When the C# compiler processes delegate types, it automatically generates a sealed class deriv-

ing from System.MulticastDelegate. This class (in conjunction with its base class, System.Delegate)

provides the necessary infrastructure for the delegate to hold onto a list of methods to be invoked at

a later time. For example, if you examine the BinaryOp delegate using ildasm.exe, you would find

the class shown in Figure 11-1.

As you can see, the compiler-generated BinaryOp class defines three public methods. Invoke()

is perhaps the core method, as it is used to invoke each method maintained by the delegate type in

a

synchronous manner, meaning the caller must wait for the call to complete before continuing on

its way. Strangely enough, the synchronous Invoke() method need not be called explicitly from your

C# code. As you will see in just a bit, Invoke() is called behind the scenes when you make use of the

appropriate C# syntax.

BeginInvoke() and EndInvoke() provide the ability to call the current method asynchronously

on a separate thread of execution. If you have a background in multithreading, you are aware that

one of the most common reasons developers create secondary threads of execution is to invoke

methods that require time to complete. Although the .NET base class libraries provide an entire

namespace devoted to multithreaded programming (System.Threading), delegates provide this

functionality out of the box.

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