C# in Depth

Novel uses of nullable types133else{Console.WriteLine ("Couldn't parse");}You may well think there’s very little to distinguish the two versions here—they’re thesame number of lines, after all. However, I believe there’s a difference in emphasis. Thenullable version encapsulates the natural return value and the success or failure into asingle variable. It also separates the “doing” from the “testing,” which puts the emphasisin the right place in my opinion. Usually, if I call a method in the condition part of anif statement, that method’s primary purpose is to return a Boolean value. Here, thereturn value is in some ways less important than the output parameter. When you’rereading code, it’s easy to miss an output parameter in a method call and be left wonderingwhat’s actually doing all the work and magically giving the answer. With the nullableversion, this is more explicit—the result of the method has all the informationwe’re interested in. I’ve used this technique in a number of places (often with rathermore method parameters, at which point output parameters become even harder tospot) and believe it has improved the general feel of the code. Of course, this only worksfor value types.Another advantage of this pattern is that it can be used in conjunction with thenull coalescing operator—you can try to understand several pieces of input, stoppingat the first valid one. The normal TryXXX pattern allows this using the short-circuitingoperators, but the meaning isn’t nearly as clear when you use the same variable fortwo different output parameters in the same statement.The next pattern is an answer to a specific pain point—the irritation and fluff thatcan be present when writing multitiered comparisons.4.4.2 Painless comparisons with the null coalescing operatorI suspect you dislike writing the same code over and over again as much as I do. Refactoringcan often get rid of duplication, but there are some cases that resist refactoringsurprisingly effectively. Code for Equals and Compare often falls firmly into this categoryin my experience.Suppose you are writing an e-commerce site and have a list of products. You maywish to sort them by popularity (descending), then price, then name—so that the fivestar-ratedproducts come first, but the cheapest within those come before the moreexpensive ones. If there are multiple products with the same price, products beginningwith A are listed before products beginning with B. This isn’t a problem specificto e-commerce sites—sorting data by multiple criteria is a fairly common requirementin computing.Assuming we have a suitable Product type, we can write the comparison with codelike this in C# 1:public int Compare(Product first, Product second){// Reverse comparison of popularity to sort descendingint ret = second.Popularity.CompareTo(first.Popularity);Licensed to Rhona Hadida