Question

I’m trying to do a simple string generation based on pattern.
My idea was to use Regex to do simple replace.
I’ve started with simple method:

private static string parseTemplate(string template)
{
    return Regex.Replace(template, @"(\[d)((:)?([\d]+)?)\]", RandomDigit());
}

private static string RandomDigit()
{
    Random r = new Random();
    return r.Next(0, 9).ToString();
}

What this does for now is replacing groups like [d], [d:3] with what supposed to be random digit.
Unfortunately every group is replaced with the same digit, for example if I put test [d][d][d:3] my method will return test 222.
I would like to get different digit in every place, like test 361.

Second problem I have is way to handle length:

right now I must specify [d] for every digit I want, but it would be easier to specify [d:3] and get the same output.

I know that there is a project called Fare, but I would like to do this without this library

For now I only search for [d], but is this method will work fine there won’t be a problem to add other groups for example: [s] for special characters or any other type of patters.

Edit1

As it was suggested I changed Random to a static variable like so:

private static string parseTemplate(string template)
    {
        return Regex.Replace(template, @"(\[d)((:)?([\d]+)?)\]", RandomDigit());
    }

    private static Random r = new Random();

    private static string RandomDigit()
    {
        return r.Next(0, 9).ToString();
    }

Problem is that when I call my code like so:

Console.WriteLine(parseTemplate("test [d:2][d:][d]"));
Console.WriteLine(parseTemplate("test [d:2][d:][d]")); 

I get output like this

test 222
test 555

I would like output like this (for example):

test 265
test 962

I think that problem is with Regex.Replace which calls my RandomDigit only once.

Answer 1

Assumnig [d:3] means “three random digits”, the following MatchEvaluator uses the length (read from group 4) to generate a random digit string:

static string ReplaceSingleMatch(Match m)
{
    int length;
    if (!int.TryParse(m.Groups[1].Value, out length))
        length = 1;
    char[] chars = new char[length];
    for (int i = 0; i < chars.Length; i++)
        chars[i] = RandomDigit()[0];
    return new string(chars);
}

You can then call this as follows:

private static string parseTemplate(string template)
{
    return Regex.Replace(template, @"\[d(?::(\d+))?\]", ReplaceSingleMatch);
}

You might want to then change RandomDigit to return a single char rather than a string, or to take an int and return multiple characters.