C# in Depth

Simple generics for everyday use73}...List integers = new List();integers.Add(1);integers.Add(2);integers.Add(3);integers.Add(4);Converter converter = TakeSquareRoot;BCreates andpopulates listof integersCCreates delegateinstanceList doubles;doubles = integers.ConvertAll(converter);foreach (double d in doubles){Console.WriteLine (d);}The creation and population of the list B is straightforward enough—it’s just a stronglytyped list of integers. C uses a feature of delegates (method group conversions), whichis new to C# 2 and which we’ll discuss in more detail in section 5.2. Although I don’t likeusing a feature before describing it fully, the line would just have been too long to fit onthe page with the full version. It does what you expect it to, though. At D we call thegeneric method, specifying the type argument for the method in the same way as we’veseen for generic types. We’ll see later (section 3.3.2) that you don’t always need to specifythe type argument—often the compiler can work it out itself, making the code that bitmore compact. We could have omitted it this time, but I wanted to show the full syntax.Writing out the list that has been returned is simple, and when you run the code you’llsee it print 1, 1.414..., 1.732..., and 2, as expected.So, what’s the point of all of this? We could have just used a foreach loop to gothrough the integers and printed out the square root immediately, of course, but it’snot at all uncommon to want to convert a list of one type to a list of another by performingsome logic on it. The code to do it manually is still simple, but it’s easier to read aversion that just does it in a single method call. That’s often the way with generic methods—theyoften do things that previously you’d have happily done “longhand” but thatare just simpler with a method call. Before generics, there could have been a similaroperation to ConvertAll on ArrayList converting from object to object, but it wouldhave been a lot less satisfactory. Anonymous methods (see section 5.4) also help here—if we hadn’t wanted to introduce an extra method, we could just have specified the conversion“inline.”Note that just because a method is generic doesn’t mean it has to be part of ageneric type. Listing 3.3 shows a generic method being declared and used within aperfectly normal class.DCalls genericmethod toconvert listListing 3.3Implementing a generic method in a nongeneric typestatic List MakeList (T first, T second){List list = new List();list.Add (first);Licensed to Rhona Hadida