class Program
    {
        public static Random rand = new Random();

        private static string GetParam()
        {
            const string chars = "ABCDEFGHIJKLMNOPQRSTUVWXYZ";

            string paramName = string.Join
            (
                "",
                "@",
                chars[rand.Next(0, 25)],
                chars[rand.Next(0, 25)],
                chars[rand.Next(0, 25)],
                chars[rand.Next(0, 25)]
            );

            return paramName;
        }

        private static string GetParamName()
        {
            //const string chars = "ABCDEFGHIJKLMNOPQRSTUVWXYZ";
            ReadOnlySpan<char> chars = "ABCDEFGHIJKLMNOPQRSTUVWXYZ".AsSpan();

            string name = "@****";
            var readMemory = name.AsMemory(1);
            var memory = Unsafe.As<ReadOnlyMemory<char>, Memory<char>>(ref readMemory);

            memory.Span[0] = chars[rand.Next(0, 25)];
            memory.Span[1] = chars[rand.Next(0, 25)];
            memory.Span[2] = chars[rand.Next(0, 25)];
            memory.Span[3] = chars[rand.Next(0, 25)];

            return name;
        }

        public static void Main(string[] args)
        {
            Thread.Sleep(5000);
            Stopwatch stopwatch = new Stopwatch();
            stopwatch.Start();

            for (int i = 0; i < 100; i++)
            {
                string kek = GetParamName();
            }

            stopwatch.Stop();
            Console.WriteLine(stopwatch.ElapsedTicks);
            stopwatch.Restart();

            for (int i = 0; i < 100; i++)
            {
                string kek = GetParam();
            }

            stopwatch.Stop();
            Console.WriteLine(stopwatch.ElapsedTicks);

            Console.ReadKey();
        }
    }