Question

As is described at Microsoft Site ,String.Format arranges some String Variables into a single String and is another way how to concate string’s in c#.

string.Format("Name = {0} Surname = {1}",name,surname);

My question is how does this work ?
Is this method a Special method ,and can i create a method similar to this one which accepts at every {n} only an Integer .
Or is this method interpreted in a different way by compiler ,if yes than how does the compiler accesses this method .

If it’s possible i would like to see ,how does the compiler interpret this Method.

PS : How does it work ,when you can send as much parameters as you want to a method ?

[EDIT]
Does it mean ,that String.Format takes the first Parameter and filter’s into with a Regex or Whatever tool (Split etc) to get where {Number} is and places there a String token from second params portion ?

Answer 1

Sending a variable number of parameters to a method is done like this:

public static string MyStringFormat(string formatString, params object [] args)
{

}

You can now pass as many parameters as you like to this:

MyStringFormat("{0}{1}",42,"Hello World")
MyStringFormat("{0}{1}{2}",42,"Hello World",999.9)

Within the method, these arguments are simply an array (of object in this case).
here are the docs on the params keyword.

As for writing you own method to accept numeric input like Format does, this would be one way (using regular expressions):

 public static string MyStringFormat(string formatString, params object[] args)
    {
        var regex = new Regex("{([0-9]*)}");
        return regex.Replace(formatString,m =>
                           {
                               int index = int.Parse(m.Groups[1].Value);
                               if(index<args.Length)
                                  return args[index].ToString();
                               return String.Empty;
                           });
    }

Live example: http://rextester.com/rundotnet?code=OMZC13551