C# in Depth

74 CHAPTER 3 Parameterized typing with genericslist.Add (second);return list;}...List list = MakeList ("Line 1", "Line 2");foreach (string x in list){Console.WriteLine (x);}The MakeList generic method only needs one type parameter (T). All it does is builda list containing the two parameters. It’s worth noting that we can use T as a type argumentwhen we create the List in the method, however. Just as when we were lookingat generic declarations, think of the implementation as (roughly speaking) replacing allof the places where it says T with string. When we call the method, we use the same syntaxwe’ve seen before. In case you were wondering, a generic method within a generictype doesn’t have to use the generic type’s type parameters—although most do.All OK so far? You should now have the hang of “simple” generics. There’s a bitmore complexity to come, I’m afraid, but if you’re happy with the fundamental ideaof generics, you’ve jumped the biggest hurdle. Don’t worry if it’s still a bit hazy—particularlywhen it comes to the open/closed/unbound/constructed terminology—butnow would be a good time to do some experimentation so you can see generics inaction before we go any further.The most important types to play with are List and Dictionary.A lot of the time you can get by just by instinct and experimentation, but if you wantmore details of these types, you can skip ahead to sections 3.5.1 and 3.5.2. Once you’reconfident using these types, you should find that you rarely want to use ArrayList orHashtable anymore.One thing you may find when you experiment is that it’s hard to only go part ofthe way. Once you make one part of an API generic, you often find that you need torework other code to either also be generic or to put in the casts required by the morestrongly typed method calls you have now. An alternative can be to have a stronglytyped implementation, using generic classes under the covers, but leaving a weaklytyped API for the moment. As time goes on, you’ll become more confident aboutwhen it’s appropriate to use generics.3.3 Beyond the basicsWhile the relatively simple uses of generics we’ve seen can get you a long way, thereare some more features available that can help you further. We’ll start off by examiningtype constraints, which allow you more control over which type arguments can bespecified. They are useful when creating your own generic types and methods, andyou’ll need to understand them in order to know what options are available whenusing the framework, too.We’ll then examine type inference —a handy compiler trick that means that whenyou’re using generic methods, you don’t always have to explicitly state the typeLicensed to Rhona Hadida