C# in Depth

134 CHAPTER 4 Saying nothing with nullable types}if (ret != 0){return ret;}ret = first.Price.CompareTo(second.Price);if (ret != 0){return ret;}return first.Name.CompareTo(second.Name);This assumes that we won’t be asked to compare null references, and that all of theproperties will return non-null references too. We could use some up-front null comparisonsand Comparer.Default to handle those cases, but that would make thecode even longer and more involved. The code could be shorter (and avoid returningfrom the middle of the method) by rearranging it slightly, but the fundamental “compare,check, compare, check” pattern would still be present, and it wouldn’t be asobvious that once we’ve got a nonzero answer, we’re done.Ah… now, that last sentence is reminiscent of something else: the null coalescingoperator. As we saw in section 4.3, if we have a lot of expressions separated by ?? thenthe operator will be repeatedly applied until it hits a non-null expression. Now all we’vegot to do is work out a way of returning null instead of zero from a comparison. This iseasy to do in a separate method, and that can also encapsulate the use of the defaultcomparer. We can even have an overload to use a specific comparer if we want. We’llalso deal with the case where either of the Product references we’re passed is null. First,let’s look at the class implementing our helper methods, as shown in listing 4.6.Listing 4.6Helper class for providing “partial comparisons”public static class PartialComparer{public static int? Compare(T first, T second){return Compare(Comparer.Default, first, second);}public static int? Compare(IComparer comparer,T first,T second){int ret = comparer.Compare(first, second);if (ret == 0){return null;}return ret;}public static int? ReferenceCompare(T first, T second)where T : classLicensed to Rhona Hadida