C# in Depth

190 CHAPTER 7 Concluding C# 2: the final featurescheaply later on, and may not even be required, you should leave the statement in thefirst form and avoid an unnecessary load in some cases.To be honest, unless you’re writing your own code generators, you’re more likely tobe implementing partial methods than declaring and calling them. If you’re only implementingthem, you don’t need to worry about the argument evaluation side of things.In summary, partial methods in C# 3 allow generated code to interact with handwrittencode in a rich manner without any performance penalties for situations where theinteraction is unnecessary. This is a natural continuation of the C# 2 partial types feature,which enables a much more productive relationship between code-generationtools and developers.Our next feature is entirely different, and is just a way of telling the compiler moreabout the intended nature of a type so that it can perform more checking on both thetype itself and any code using it.7.2 Static classesOur second new feature is in some ways completely unnecessary—it just makes thingstidier and a bit more elegant when you write utility classes.Everyone has utility classes. I haven’t seen a significant project in either Java or C#that didn’t have at least one class consisting solely of static methods. The classic exampleappearing in developer code is a type with string helper methods, doing anythingfrom escaping, reversing, smart replacing—you name it. An example from the Frameworkis the System.Math class. The key features of a utility class are as follows:■ All members are static (except a private constructor).■ The class derives directly from object.■ Typically there’s no state at all, unless there’s some caching or a singletoninvolved.■ There are no visible constructors.■ The class is sealed if the developer remembers to do so.The last two points are optional, and indeed if there are no visible constructors(including protected ones) then the class is effectively sealed anyway. Both of them helpmake the purpose of the class more obvious, however.Listing 7.3 gives an example of a C# 1 utility class—then we’ll see how C# 2improves matters.Listing 7.3A typical C# 1 utility classusing System;public sealed class StringHelper{private StringHelper(){}BSeals class toprevent derivationPrevents instantiationfrom other codeLicensed to Rhona Hadida