Question

I am trying to author an extension method for a string that takes one argument and it appends the argument to the string’s value. Here is the behavior I want:

    public static void AddNumber(this string originalValue, string id)
    {
        List<string> ids = originalValue.Split(new char[] { ',' }, StringSplitOptions.RemoveEmptyEntries).ToString();
        ids.Add(id);
        string newValue = string.Join(",", ids);
        originalValue = newValue;
    }

Then I would like to use this as follows:

        string testing = "";
        testing.AddNumber("1"); // value should be 1
        testing.AddNumber("2"); // value should be 1,2
        testing.AddNumber("3"); // value should be 1,2,3

The issue is that I am seeing this:

        string testing = "";
        testing.AddNumber("1"); // value is ""
        testing.AddNumber("2"); // value is ""
        testing.AddNumber("3"); // value is ""

Now I have read the this! issue here on StackOverflow, and I am aware that I am doing a similar thing. I can’t replace the entire value of the string, I have to modify the contents of the string that is sent through… I just can’t find a way to modify it. I’ve tried modifying the character array and have had no luck. Any ideas?

Answer 1

Strings are immutable.
That’s fundamentally impossible.