C# in Depth

266 CHAPTER 10 Extension methodsThat’s fine for instance methods, but extension methods allow static method calls tobe chained together. This is one of the primary reasons for extension methods existing.They’re useful for other utility classes, but their true power is revealed in this ability tochain static methods in a natural way. That’s why extension methods primarily showup in Enumerable and Queryable in .NET 3.5: LINQ is geared toward this approach todata processing, with information traveling through pipelines constructed of individualoperations chained together.NOTEEfficiency consideration: reordering method calls to avoid waste—I’m certainlynot a fan of micro-optimization without good cause, but it’s worth lookingat the ordering of the method calls in listing 10.8. We could haveadded the Where call after the Reverse call and achieved the same results.However, that would have wasted some effort—the Reverse call wouldhave had to work out where the even numbers should come in thesequence even though they will be discarded from the final result. In thiscase it’s not going to make much difference, but it can have a significanteffect on performance: if you can reduce the amount of wasted workwithout compromising readability, that’s a good thing. That doesn’tmean you should always put filters at the start of the pipeline, however;you need to think carefully about any reordering to make sure you’ll stillget the correct results.There are two obvious ways of writing the first part of listing 10.8 without using thefact that Reverse and Where are extension methods. One is to use a temporary variable,which keeps the structure intact:var collection = Enumerable.Range(0, 10);collection = Enumerable.Where(collection, x => x%2 != 0)collection = Enumerable.Reverse(collection);I hope you’ll agree that the meaning of the code is far less clear here than in listing 10.8.It gets even worse with the other option, which is to keep the “single statement” style:var collection = Enumerable.Reverse(Enumerable.Where(Enumerable.Range(0, 10),x => x%2 != 0));The method call order appears to be reversed, because the innermost method call(Range) will be performed first, then the others, with execution working its way outward.Let’s get back to our nice clean syntax but introduce another wrinkle—we’ll transform(or project) each element in our original collection, creating an anonymous typefor the result.10.3.3 Projections using the Select method and anonymous typesThe most important projection method in Enumerable is Select—it operates on anIEnumerable and projects it into an IEnumerable by way of aFunc, which is the transformation to use on each element, specifiedLicensed to Rhona Hadida