C# 4 and .NET 4

D e l e g a t e s ❘ 193
BubbleSorter.Sort(employees, Employee.CompareSalary);
}
}
}
foreach (var employee in employees)
{
Console.WriteLine(employee);
}
code snippet BubbleSorter/Program.cs
Running this code shows that the Employees are correctly sorted according to salary:
BubbleSorter
Elmer Fudd, $10,000.00
Bugs Bunny, $20,000.00
Foghorn Leghorn, $23,000.00
Daffy Duck, $25,000.00
RoadRunner, $50,000.00
Wile Coyote, $1,000,000.38
multicast delegates
So far, each of the delegates you have used wraps just one single method call. Calling the delegate amounts
to calling that method. If you want to call more than one method, you need to make an explicit call through
a delegate more than once. However, it is possible for a delegate to wrap more than one method. Such a
delegate is known as a multicast delegate. If a multicast delegate is called, it will successively call each
method in order. For this to make sense, the delegate signature should return a void ; otherwise, you would
only get the result of the last method that is invoked by the delegate.
With a void return type the Action < double > delegate can be used.
class Program
{
static void Main()
{
Action < double > operations = MathOperations.MultiplyByTwo;
operations += MathOperations.Square;
code snippet MulticastDelegates/Program.cs
In the earlier example, you wanted to store references to two methods, so you instantiated an array of
delegates. Here, you simply add both operations into the same multicast delegate. Multicast delegates
recognize the operators + and += . Alternatively, you can also expand the last two lines of the preceding
code, as in this snippet:
Action < double > operation1 = MathOperations.MultiplyByTwo;
Action < double > operation2 = MathOperations.Square;
Action < double > operations = operation1 + operation2;
Multicast delegates also recognize the operators – and - = to remove method calls from the delegate.
In terms of what ’ s going on under the hood, a multicast delegate is a class derived
from System.MulticastDelegate , which in turn is derived from System.Delegate .
System.MulticastDelegate , and has additional members to allow chaining of
method calls together into a list.
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