How can you use optional parameters in C#?

Question

^{Note: This question was asked at a time when C# did not yet support optional parameters (i.e. before C# 4).}

We're building a web API that's programmatically generated from a C# class. The class has method GetFooBar(int a, int b) and the API has a method GetFooBar taking query params like &a=foo &b=bar.

The classes needs to support optional parameters, which isn't supported in C# the language. What's the best approach?

Answer 1

An elegant and easy way which allows you to omit any parameters in any position, by taking advantage of nullable types is as follows:

public void PrintValues(int? a = null, int? b = null, float? c = null, string s = "")
{
    if(a.HasValue)
        Console.Write(a);
    else
        Console.Write("-");

    if(b.HasValue)
        Console.Write(b);
    else
        Console.Write("-");

    if(c.HasValue)
        Console.Write(c);
    else
        Console.Write("-");

    if(string.IsNullOrEmpty(s)) // Different check for strings
        Console.Write(s);
    else
        Console.Write("-");
}

Strings are already nullable types so they don't need the ?.

Once you have this method, the following calls are all valid:

PrintValues (1, 2, 2.2f);
PrintValues (1, c: 1.2f);
PrintValues(b:100);
PrintValues (c: 1.2f, s: "hello");
PrintValues();

When you define a method that way you have the freedom to set just the parameters you want by naming them. See the following link for more information on named and optional parameters:

Named and Optional Arguments (C# Programming Guide) @ MSDN