Question

Consider the following method example:

public static string[] ParseOptions()
{
    return Environment.GetCommandLineArgs();
}

What would I have to do to create an extension that would make ParseOptions() return all command line arguments in lower case?

I would like to be able to use the extension as follows:

var argArray = ParseOptions().MyExtToLower();

Note: I’m asking this to better understand how to create an extension for a method. I’m not actually interested in getting lower case command line arguments this way.

Answer 1

public static string[] MyExtToLower(this string[] source)
{
    for (int i = 0; i < source.Length; i++)
    {
        source[i] = source[i].ToLower();
    }
    return source;    
}

Notice the this keyword in the parameter list. That is what makes it possible to call the method like this:

var argArray = ParseOptions().MyExtToLower();

To be clear, you’re not actually adding an extension to a method here. What you are doing is adding an extension to the type that the method returns.