The example demonstrates the use of square brackets to extend the C # string.Format ()

extend_string_format.cs

using System;


public static class StringExtensions
{
    public static string Format(this string str, params object[] parameters)
    {
        return string.Format(str, parameters);
    }
    
    public static string FormatExt(this string str, params object[] parameters)
    {
        var result = System.Text.RegularExpressions.Regex.Replace(
            str,
            @"\[(\d+)\]",
            m => parameters[int.Parse(m.Groups[1].Value)].ToString());
        return result;
    }
}


// Example:
class Program
{
    static void Main()
    {
        
        var result = "my [1] name: {0}, my profile [0] link"
            .Format("Qwerty")
            .FormatExt("test", "new value");

        Console.WriteLine(result);
        
    }
}

Demo