Optional Parameters in C# 4.0
Some members of the C# community were discussing optional parameters and the implications for future versions when optional parameter values change. In short, you need to realize that changing the value of optional parameters in a public API is a change that is observable at client code. The ramifications vary greatly, from “no big” to “stop the world”. I’ll give a brief explanation of how the feature works, and what you need to watch for and how to separate reasonable caution from irrational fear from using a feature.
While most modern programming languages provide some way of declaring optional function parameters, C# doesn’t provide a way of directly doing so, despite the fact that VB.NET and .NET’s attribute system both support this functionality. This is a subject of some debate currently in the C# community. The C# development team’s position seems to boil down to the following: When provided, this feature is usually nothing more than dressing up method overloading with a little syntactic sugar.
When you get right down to it, their position makes some sense. A function with an optional parameter is in reality two different functions: one that assumes some default behavior if the optional parameter is omitted, and another that performs more specific behavior based on the value of the optional parameter if provided. But that doesn’t change the fact that using overloaded methods to provide optional parameter support feels a little clunky. It works, but you always wind up writing more code, and you pollute your object interface with the extra method signatures required to support all of your optional parameters. Let’s look at some alternatives.
