C# in Depth

96 CHAPTER 3 Parameterized typing with genericsThe next section is much more down to earth than our investigations into reflectionand the bowels of the JIT. It covers the most common use of generics: the standardcollection classes.3.5 Generic collection classes in .NET 2.0Although this book is primarily about C# as a language, it would be foolish to ignore thefact that C# is almost always used within the .NET Framework, and that in order to usethe language effectively you’ll need to have a certain amount of knowledge of thelibraries too. I won’t be going into the details of ADO.NET, ASP.NET, and the like, butyou’re bound to use collections in almost any .NET program of any size. This sectionwill cover the core collections found in the System.Collections.Generic namespace.We’ll start in familiar territory with List.3.5.1 ListWe’ve already seen List several times. Broadly speaking, it’s the generic equivalentof the nongeneric ArrayList type, which has been a part of .NET from the wordgo. There are some new features, and a few operations in ArrayList didn’t make it toList. Most of the features that have been removed from List have also beenremoved from other collections, so we’ll cover them here and then just refer to themlater on when talking about the other collections. Many of the new features inList (beyond “being generic”) aren’t available in the other generic collections.The combination of these factors leads to our discussion of List being the longestin this section—but then it’s probably the most widely used collection in real-lifecode, too. When you think of using a list of data items in your code, List is thedefault choice.I won’t bore you with the most common operations (adding, removing, fetching,and replacing items) but will merely point out that List makes itself available in alarge number of situations using old APIs by implementing IList as well as IList.Enough of looking backward, though—let’s see what’s new.NEW FEATURES OF LISTThe new methods available within List are all powered by generics—in particular,generic delegates. This is part of a general trend toward using delegates more heavilyin the framework, which has been made simpler by the improvements in delegate syntaxavailable in C# 2. (There would have been little point in adding lots of delegatespecificfeatures into the framework with the syntax being as clunky as it was in C# 1.)We can now do the following:■ Convert each element of the list to a different type, resulting in a new list(ConvertAll).■ Check whether any of the elements in the list match a given predicate (Exists).■ Check whether all of the elements in the list match a given predicate(TrueForAll).■ Find the first, last, or all elements in the list matching a predicate (FindXXX).Licensed to Rhona Hadida