network adapter driver error code 39 Some Delegate History: System.Delegate and System.MulticastDelegate in Visual Studio .NET

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Some Delegate History: System.Delegate and System.MulticastDelegate
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Even though the FCL defines the System.MulticastDelegate class, MulticastDelegate is actually derived from the System.Delegate class (also defined in the FCL), which itself is derived from System.Object. When originally designing the .NET Framework, Microsoft engineers felt the need to provide two different types of delegates: single cast and multicast. MulticastDelegate derived 294
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types would represent delegate objects that could be chained together, and Delegate derived types would represent objects that could not be chained together. The System.Delegate type was designed as the base type, and this class implemented all the functionality necessary to call back a wrapped method. The MulticastDelegate class was derived from the Delegate class and added the ability to create a linked list (or chain) of MulticastDelegate objects. When compiling source code, a compiler would check the delegate s signature and select the more appropriate of the two classes for the compiler generated delegate type s base class. For the curious, methods with a signature that indicated a non void return value would be derived from System.Delegate, and methods with a void return value would be derived from System.MulticastDelegate. This made sense because you can get the return value only from the last method called in a linked list chain. During the beta testing of the .NET Framework, it became clear that having the two different base types greatly confused developers. In addition, designing delegates this way placed arbitrary limitations on them. For example, many methods have return values that you can ignore in many situations. Because these methods would have a non void return value, they wouldn t be derived from the MulticastDelegate class, preventing them from being combined into a linked list. To reduce developer confusion, Microsoft s engineers wanted to merge the Delegate and MulticastDelegate classes together into a single class that allowed any delegate object to participate in a linked list chain. All compilers would generate delegate classes deriving from this one class. This change would reduce complexity and effort for the .NET Framework team, the CLR team, the compiler team, and for developers out in the field who are using delegates. Unfortunately, the idea of merging the Delegate and MulticastDelegate classes came along a bit late in the .NET Framework development cycle, and Microsoft was concerned about the potential bugs and testing hit that would occur if these changes were made. So in version 1 of the .NET Framework, these classes haven t been merged; in a future version of the .NET Framework, I expect that these two classes will be merged into a single class. Although Microsoft chose to delay the merging of these two classes in the FCL, they were able to modify all the Microsoft compilers. All the Microsoft compilers now generate delegate types derived from the MulticastDelegate class all the time. So when I said earlier in this chapter that all delegate types are derived from MulticastDelegate, I wasn t lying. Because of this change to the compiler, all instances of delegate types can be combined into a linked list chain regardless of the callback method s return value. You might be thinking, Why do I need to know about all this Well, here s why: As you start working more and more with delegates, you ll undoubtedly run across both the Delegate and MulticastDelegate types in the .NET Framework SDK documentation. I want you to understand the relationship between these two classes. In addition, even though all delegate types you create have MulticastDelegate as a base class, you ll occasionally manipulate your types using methods defined by the Delegate class instead of the MulticastDelegate class. For example, the Delegate class has static methods called Combine and Remove. (I explain what these methods do later.) The signatures for both these methods indicate that they take Delegate parameters. Because your delegate type is derived from MulticastDelegate, which is derived from Delegate, instances of your delegate type can be passed to the Combine and Remove methods.
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