I've been noticing more and more that people use the 'as' keyword in C# to presumably do safe type casts. But enough is enough, it's not ideally the way to actually go about type conversions, nor does it have any benefits.
To start things of, the expression 'instance1 as SomeType' keyword is just the equivalent of '(instance1 is SomeType ? (SomeType)instance1 : null)' and the following code will throw an exception anyway, iff the type is not instance of SomeType... So why do you type cast this way?
[TestMethod]
public void Index()
{
// Setup
HomeController controller = new HomeController();
// Execute
ViewResult result = controller.Index() as ViewResult;
// Verify
ViewDataDictionary viewData =
result.ViewData as ViewDataDictionary;
Assert.AreEqual( "Home Page", viewData["Title"] );
}
The above example is from the ASP.NET MVC Framework, and while it's just a sample from the testing framework this code is bad. Because when the right-hand side 'controller.Index() as ViewResult' returns null (the return type was not of type ViewResult) and this code should, because this expression implies that type does not have to be ViewResult. There is no error handling code and the result is the NullReferenceException, which at this point is a side effect of some other code that failed.
Do you know the null coalescing operator? It's about the most useless thing in the language, or is it?
(controller.Index() as ViewResult) ?? new ViewResult()
Now, if you really want the program to crash in the event of such a failure you should NOT do this, nor should you yield null in the case of a type test failure. But if you want to actually type cast and in the case of a problem fall-back to some instance, you can use the above snippet.
Think about it. The example is really stupid because it fails to capture that an error could (or could not occur) as well as that if it would, the wrong error would be reported. But this snippet, it can actually make sense of a failed type test and rely on any other code to provide an instance of some type that doesn't have to stop execution of your program.
