C# in Depth

56 CHAPTER 2 Core foundations: building on C# 1a lot more sense. In C# 1, it didn’t matter whether or not two different event handlerslooked “quite similar”—you had to have a method with an exactly matching signaturein order to create a delegate instance. In C# 2, you may well find yourself able to usethe same method to handle many different kinds of events, particularly if the purposeof the method is fairly event independent, such as logging.C# 3 provides special syntax for instantiating delegate types, using lambda expressions.To demonstrate these, we’ll use a new delegate type. As part of the CLR gaininggenerics in .NET 2.0, generic delegate types became available and were used in a numberof API calls in generic collections. However, .NET 3.5 takes things a step further,introducing a group of generic delegate types called Func that all take a number ofparameters of specified types and return a value of another specified type. Listing 2.5gives an example of the use of a Func delegate type as well as lambda expressions.Listing 2.5Lambda expressions, which are like improved anonymous methodsFunc func = (x,y) => (x*y).ToString();Console.WriteLine (func(5, 20));Func is a delegate type that takes two integers and returns a string.The lambda expression in listing 2.5 specifies that the delegate instance (held infunc) should multiply the two integers together and call ToString(). The syntax ismuch more straightforward than that of anonymous methods, and there are otherbenefits in terms of the amount of type inference the compiler is prepared to performfor you. Lambda expressions are absolutely crucial to LINQ, and you should get readyto make them a core part of your language toolkit. They’re not restricted to workingwith LINQ, however—almost any use of anonymous methods from C# 2 can uselambda expressions in C# 3.To summarize, the new features related to delegates are as follows:■ Generics (generic delegate types)—C# 2■ Delegate instance creation expressions—C# 2■ Anonymous methods—C# 2■ Delegate covariance/contravariance—C# 2■ Lambda expressions—C# 3The use of generics extends well beyond delegates, of course—they’re one of the principleenhancements to the type system, which we’ll look at next.2.4.2 Features related to the type systemThe primary new feature in C# 2 regarding the type system is that of generics. Itlargely addresses the issues I raised in section 2.2.2 about strongly typed collections,although generic types are useful in a number of other situations too. As a feature, it’selegant, it solves a real problem, and despite a few wrinkles it generally works verywell. We’ve seen examples of this in quite a few places already, and it’s described fullyin the next chapter, so I won’t go into any more details here. It’ll be a brief reprieve,Licensed to Rhona Hadida