Replace a key from string with some different values for every new found

Question

var myString = "$guid$! test $guid$, here another test string and then $guid$";

by using

myString.Replace("$guid$", Guid.NewGuid().ToString()))

the value for every found guid will be the same, how to change for every found new value?

Answer 1

You could use Regex.Replace:

var replaced = Regex.Replace(myString, @"\$guid\$", match => Guid.NewGuid().ToString());

The match evaluator will be called for every match and can easily return different replacements for each call

Answer 2

I create a tiny extension method that match the currents one

/// <summary>
/// Returns a new string in which all occurences of a specified string in this instance are replaced with a runtime determined string 
/// </summary>
/// <param name="oldValue">the string to be replaced</param>
/// <param name="newValue">the function used to replace the string called one time per occurence</param>
public static string Replace(this string text, string oldValue, Func<string> newValue)
{
    var replacedText = new StringBuilder();
    int pos = text.IndexOf(oldValue);
    while (pos >= 0)
    {
        var nv = newValue();
        replacedText.Append(text.Substring(0, pos) + nv);
        text = text.Substring(pos + oldValue.Length);
        pos = text.IndexOf(oldValue);
    }
    return replacedText + text;
}

I don't know why there is no existing C# function like this but it works nice.

I make a tiny unit test with your example (using NFluent) :

[TestMethod]
public void ReplaceTest()
{
    var i = 1;
    Check.That("$guid$! test $guid$, here another test string and then $guid$"
        .Replace("$guid$", () => (i++).ToString()))
        .IsEqualTo("1! test 2, here another test string and then 3");
}