C# in Depth

98 CHAPTER 3 Parameterized typing with genericsListing 3.13 starts off by just creating a list of all the integers between 2 and 100 inclusiveB—nothing spectacular here, although once again I should point out thatthere’s no boxing involved. The delegate used in step C is a Predicate , andthe one used in D is an Action. One point to note is how simple the use ofRemoveAll is. Because you can’t change the contents of a collection while iteratingover it, the typical ways of removing multiple elements from a list have previously beenas follows:■ Iterate using the index in ascending order, decrementing the index variablewhenever you remove an element.■ Iterate using the index in descending order to avoid excessive copying.■ Create a new list of the elements to remove, and then iterate through the newlist, removing each element in turn from the old list.None of these is particularly satisfactory—the predicate approach is much neater, givingemphasis to what you want to achieve rather than how exactly it should happen. It’s agood idea to experiment with predicates a bit to get comfortable with them, particularlyif you’re likely to be using C# 3 in a production setting any time in the near future—thismore functional style of coding is going to be increasingly important over time.Next we’ll have a brief look at the methods that are present in ArrayList but notList, and consider why that might be the case.FEATURES “MISSING” FROM LISTA few methods in ArrayList have been shifted around a little—the static ReadOnlymethod is replaced by the AsReadOnly instance method, and TrimToSize is nearlyreplaced by TrimExcess (the difference is that TrimExcess won’t do anything if thesize and capacity are nearly the same anyway). There are a few genuinely “missing”pieces of functionality, however. These are listed, along with the suggestedworkaround, in table 3.3.Table 3.3Methods from ArrayList with no direct equivalent in ListArrayList methodWay of achieving similar effectAdapterCloneFixedSizeRepeatSetRangeSynchronizedNone providedlist.GetRange (0, list.Count) or new List(list)Nonefor loop or write a replacement generic methodfor loop or write a replacement generic methodSynchronizedCollectionThe Synchronized method was a bad idea in ArrayList to start with, in my view. Makingindividual calls to a collection doesn’t make the collection thread-safe, because somany operations (the most common is iterating over the collection) involve multipleLicensed to Rhona Hadida