C# in Depth

Extension methods in .NET 3.5263public static bool IsNullOrEmpty(this string text){return string.IsNullOrEmpty(text);}At first it seems odd to be able to call IsNullOrEmpty on a variable that is null withoutan exception being thrown, particularly if you’re familiar with it as a static method from.NET 2.0. In my view, code using the extension method is more easily understandable.For instance, if you read the expression if (name.IsNullOrEmpty()) out loud, it saysexactly what it’s doing. As always, experiment to see what works for you—but be awareof the possibility of other people using this technique if you’re debugging code. Don’tbe certain that an exception will be thrown on a method call unless you’re sure it’s notan extension method! Also note that you should think carefully before reusing an existingname for an extension method—the previous extension method could confusereaders who are only familiar with the static method from the framework.Now that we know the syntax and behavior of extension methods, we can have a lookat some examples of them, which are provided in .NET 3.5 as part of the framework.10.3 Extension methods in .NET 3.5The biggest use of extension methods in .NET 3.5 is in LINQ. Some LINQ providers havea few extension methods to help them along, but there are two classes that stand out,both of them appearing in the System.Linq namespace: Enumerable and Queryable.These contain many, many extension methods: most of the ones in Enumerable operateon IEnumerable and most of those in Queryable operate on IQueryable. We’llsee the purpose of IQueryable in chapter 12, but for the moment let’s concentrateon Enumerable.10.3.1 First steps with EnumerableEven just looking at Enumerable, we’re getting very close to LINQ now. Indeed, a lot ofthe time you don’t need full-blown query expressions to solve a problem. Enumerablehas a lot of methods in it, and the purpose of this section isn’t to cover all of them butto give you enough of a feel for them to let you go off and experiment. It’s a real joy tojust play with everything available in Enumerable—although this time it’s definitelyworth firing up Visual Studio 2008 for your experiments (rather than using Snippy) asIntelliSense is handy for this kind of activity.All the complete examples in this section deal with a simple situation: we start offwith a collection of integers and transform it in various ways. Obviously real-life situationsare likely to be somewhat more complicated, usually dealing with business-relatedtypes. At the end of this section, I’ll present a couple of examples of just the transformationside of things applied to possible business situations, with full source code availableon the book’s website—but that’s harder to play with than a straightforwardcollection of numbers. It’s worth considering some recent projects you’ve been workingon as we go, however—see if you can think of situations where you could have madeyour code simpler or more readable by using the kind of operations described here.Licensed to Rhona Hadida