Named Parameters in C#4.0
In the last example, we saw that the following call was invalid:
Process( "foo", myArrayList ); // Invalid!
But if the boolean ignoreWS is optional, why can't we just omit it? Well, one reason is for readability and maintainability, but primarily because it can become impossible to know what parameter you are specifying. If you had two parameters of the same type, or if one of the parameters was "object" or some other base class or interface, the compiler would not know which parameter you are sending. Imagine a method with ten optional parameters and you give it a single ArrayList. Since an ArrayList is also an object, an IList, and an IEnumerable, it is impossible to determine how to use it. Yes, the compiler could just pick the first valid option for each parameter (or a more complex system could be used), but this would become impossible for people to maintain and would cause countless programming mistakes.
Named parameters provide the solution:
ArrayList myArrayList = new ArrayList();
Process( "foo", true ); // valid, moreData omitted
Process( "foo", true, myArrayList ); // valid
Process( "foo", moreData: myArrayList); // valid, ignoreWS omitted
Process( "foo", moreData: myArrayList, ignoreWS: false ); // valid, but silly
As long as a parameter has a default value, it can be omitted, and you can just supply the parameters you want via their name. Note in the second line above, the 'true' value for ignoreWS did not have to be named since it is the next logical parameter.
