C# in Depth

270 CHAPTER 10 Extension methodsIGrouping. There are many overloads of GroupBy, but I’ve used thesimplest one here and then selected just the key (the name of the developer) and thenumber of bugs assigned to them. After that we’ve just ordered the result to show thedevelopers with the most bugs first.One of the problems when looking at the Enumerable class can be working outexactly what’s going on—one of the overloads of GroupBy has four type parametersand five “normal” parameters (three of which are delegates), for instance. Don’tpanic, though—just follow the steps shown in chapter 3, assigning different types todifferent type parameters until you’ve got a concrete example of what the methodwould look like. That usually makes it a lot easier to understand what’s going on.We’ll use the example of defect tracking as our sample data when we look at queryexpressions in the next chapter.These examples aren’t particularly involved ones, but I hope you can see thepower of chaining method calls together, where each method takes an original collectionand returns another one in some form or other, whether by filtering out somevalues, ordering them, transforming each element, aggregating some values, or manyother options. In many cases, the resulting code can be read aloud and understoodimmediately—and in other situations it’s still usually a lot simpler than the equivalentcode would have been in previous versions of C#.Now that we’ve seen some of the extension methods provided for us, we’ll considerjust how and when it makes sense for you to write them yourself.10.4 Usage ideas and guidelinesLike implicit typing of local variables, extension methods are controversial. It wouldbe hard to claim that they make the overall aim of the code harder to understand inmany cases, but at the same time they do obscure the details of what method is gettingcalled. In the words of one of the lecturers at my university, “I’m hiding the truth inorder to show you a bigger truth”—if you believe that the most important aspect of thecode is its result, extension methods are great. If the implementation is more importantto you, then explicitly calling a static method is clearer. Effectively, it’s the differencebetween the “what” and the “how.”We’ve already looked at using extension methods for utility classes and methodchaining, but before we discuss the pros and cons further, it’s worth calling out a coupleof aspects of this that may not be obvious.10.4.1 “Extending the world” and making interfaces richerWes Dyer, a former developer on the C# compiler team, has a fantastic blog 2 coveringall kinds of subject matter. One of his posts about extension methods 3 particularlycaught my attention. It’s called “Extending the World,” and it talks about how2http://blogs.msdn.com/wesdyer3http://blogs.msdn.com/wesdyer/archive/2007/03/09/extending-the-world.aspxLicensed to Rhona Hadida