C# in Depth

Static classes191}public static string Reverse(string input){char[] chars = input.ToCharArray();Array.Reverse(chars);return new string(chars);}All methodsare staticThe private constructor B may seem odd—why have it at all if it’s private and nevergoing to be used? The reason is that if you don’t supply any constructors for a class, theC# 1 compiler will always provide a default constructor that is public and parameterless. Inthis case, we don’t want any visible constructors, so we have to provide a private one.This pattern works reasonably well, but C# 2 makes it explicit and actively preventsthe type from being misused. First we’ll see what changes are needed to turn listing 7.3into a “proper” static class as defined in C# 2. As you can see from listing 7.4, very littleaction is required.Listing 7.4The same utility class as in listing 7.3 but converted into a C# 2 static classusing System;public static class StringHelper{public static string Reverse(string input){char[] chars = input.ToCharArray();Array.Reverse(chars);return new string(chars);}}We’ve used the static modifier in the class declaration this time instead of sealed,and we haven’t included a constructor at all—those are the only code differences. TheC# 2 compiler knows that a static class shouldn’t have any constructors, so it doesn’tprovide a default one. In fact, the compiler enforces a number of constraints on theclass definition:■ It can’t be declared as abstract or sealed, although it’s implicitly both.■ It can’t specify any implemented interfaces.■ It can’t specify a base type.■ It can’t include any nonstatic members, including constructors.■ It can’t include any operators.■ It can’t include any protected or protected internal members.It’s worth noting that although all the members have to be static, you’ve got to explicitlymake them static except for nested types and constants. Although nested types areimplicitly static members of the enclosing class, the nested type itself can be a nonstatictype if that’s required.The compiler not only puts constraints on the definition of static classes, though—it also guards against their misuse. As it knows that there can never be any instances ofLicensed to Rhona Hadida