C# Inconsistent results using params keyword

Question

Given the following method:

static void ChangeArray(params string[] array) {

    for (int i = 0; i < array.Length; i++) 
        array[i] = array[i] + "s";
}

This works if I call it passing a array of strings:

string[] array = {"Michael", "Jordan"} // will become {"Michaels", "Jordans"}
ChangeArray(array);

But will not work if I call it using string arguments:

string Michael = "Michael";
string Jordan = "Jordan";
ChangeArray(Michael, Jordan); // This will NOT change the values of the variables

I understand that the compiler will wrap Michael and Jordan on an array, so shouldn't the results be the same on both cases?

Answer 1

Your second example is essentially:

string Michael = "Michael";
string Jordan = "Jordan";
{
    var tmp = new string[] {Michael, Jordan};
    ChangeArray(tmp);
}

so; actually, the values inside tmp were changed... but tmp was discarded afterwards, so you don't see anything. params does not emulate ref - it won't do a position-wise update back into the original variables. Or in code, it is not the following:

string Michael = "Michael";
string Jordan = "Jordan";
{
    var tmp = new string[] {Michael, Jordan};
    ChangeArray(tmp);
    Michael = tmp[0];
    Jordan = tmp[1];
}

If you need it to behave like that, then code it like that - or use instead an overload that takes ref parameters.