How do I replace the *first instance* of a string in .NET?

Question

I want to replace the first occurrence in a given string.

How can I accomplish this in .NET?

Answer 1

Taking the "first only" into account, perhaps:

int index = input.IndexOf("AA");
if (index >= 0) output = input.Substring(0, index) + "XQ" +
     input.Substring(index + 2);

?

Or more generally:

public static string ReplaceFirstInstance(this string source,
    string find, string replace)
{
    int index = source.IndexOf(find);
    return index < 0 ? source : source.Substring(0, index) + replace +
         source.Substring(index + find.Length);
}

Then:

string output = input.ReplaceFirstInstance("AA", "XQ");