C# in Depth

102 CHAPTER 3 Parameterized typing with genericsLinked lists make it easy to insert another node into the chain—as long as youalready have a handle on the node representing the insertion position. All the listneeds to do is create a new node, and make the appropriate links between that nodeand the ones that will be before and after it. Lists storing all their data in a plain array(as List does) need to move all the entries that will come after the new one, whichcan be very expensive—and if the array runs out of spare capacity, the whole lot mustbe copied. Enumerating a linked list from start to end is also cheap—but randomaccess (fetching the fifth element, then the thousandth, then the second) is slowerthan using an array-backed list. Indeed, LinkedList doesn’t even provide a randomaccess method or indexer. Despite its name, it doesn’t implement IList.Linked lists are usually more expensive in terms of memory than their array-backedcousins due to the extra link node required for each value. However, they don’t havethe “wasted” space of the spare array capacity of List.The linked list implementation in .NET 2.0 is a relatively plain one—it doesn’t supportchaining two lists together to form a larger one, or splitting an existing one intotwo, for example. However, it can still be useful if you want fast insertions at both thestart and end of the list (or in between if you keep a reference to the appropriate node),and only need to read the values from start to end, or vice versa.Our final main section of the chapter looks at some of the limitations of genericsin C# and considers similar features in other languages.3.6 Limitations of generics in C# and other languagesThere is no doubt that generics contribute a great deal to C# in terms of expressiveness,type safety, and performance. The feature has been carefully designed to copewith most of the tasks that C++ programmers typically used templates for, but withoutsome of the accompanying disadvantages. However, this is not to say limitations don’texist. There are some problems that C++ templates solve with ease but that C# genericscan’t help with. Similarly, while generics in Java are generally less powerful than inC#, there are some concepts that can be expressed in Java but that don’t have a C#equivalent. This section will take you through some of the most commonly encounteredweaknesses, as well as briefly compare the C#/.NET implementation of genericswith C++ templates and Java generics.It’s important to stress that pointing out these snags does not imply that theyshould have been avoided in the first place. In particular, I’m in no way saying that Icould have done a better job! The language and platform designers have had to balancepower with complexity (and the small matter of achieving both design andimplementation within a reasonable timescale). It’s possible that future improvementswill either remove some of these issues or lessen their impact. Most likely, youwon’t encounter problems, and if you do, you’ll be able to work around them with theguidance given here.We’ll start with the answer to a question that almost everyone raises sooner or later:why can’t I convert a List to List?Licensed to Rhona Hadida