Wholemy StringDirect is a joke

    // Debug:
    //
    // TestStringBuilderChars:   0.8   (ticks: 2833)
    // TestStringDirectChars:    25624 (ticks: 82820974)
    // TestOptimizedPerfChars:   0.5   (ticks: 1901)
    // TestStringBuilderStrings: 4     (ticks: 13111)
    // TestStringDirectStrings:  13.2  (ticks: 42725)
    // TestOptimizedMemStrings:  5.7   (ticks: 18480)
    //
    // Release:
    //
    // TestStringBuilderChars:   0.6   (ticks: 2085)
    // TestStringDirectChars:    6192  (ticks: 20014990)
    // TestOptimizedPerfChars:   0.5   (ticks: 1626)
    // TestStringBuilderStrings: 3.2   (ticks: 10524)
    // TestStringDirectStrings:  6.8   (ticks: 22054)
    // TestOptimizedMemStrings:  4.9   (ticks: 16034)

    public class Program
    {
        private readonly Random _rnd = new Random(0);
        private readonly List<string> _strings = Enumerable.Range(10000, 100).Select(i => i.ToString()).ToList();

        public static void Main () => new Program().Run();

        public void Run ()
        {
            Benchmark(TestStringBuilderChars, nameof(TestStringBuilderChars));
            Benchmark(TestStringDirectChars, nameof(TestStringDirectChars), 2);
            Benchmark(TestOptimizedPerfChars, nameof(TestOptimizedPerfChars));
            Benchmark(TestStringBuilderStrings, nameof(TestStringBuilderStrings));
            Benchmark(TestStringDirectStrings, nameof(TestStringDirectStrings));
            Benchmark(TestOptimizedMemStrings, nameof(TestOptimizedMemStrings));
            Console.WriteLine("Done!");
            Console.ReadLine();
        }

        public void TestStringBuilderChars ()
        {
            var sb = new StringBuilder();
            for (int i = 0; i < 100000; i++)
                sb.Append((char)(i % char.MaxValue));
            sb.ToString();
        }

        public void TestStringDirectChars ()
        {
            StringDirect sb = "";
            for (int i = 0; i < 100000; i++)
                sb += (char)(i % char.MaxValue);
            sb.ToString();
        }

        public void TestOptimizedPerfChars ()
        {
            char[] sb = new char[100000];
            for (int i = 0; i < sb.Length; i++)
                sb[i] = (char)(i % char.MaxValue);
            new string(sb);
        }

        public void TestStringBuilderStrings ()
        {
            var sb = new StringBuilder();
            for (int i = 0; i < 100000; i++)
                sb.Append(_strings[_rnd.Next(_strings.Count)]);
            sb.ToString();
        }

        public void TestStringDirectStrings ()
        {
            StringDirect sb = "";
            for (int i = 0; i < 100000; i++)
                sb += _strings[_rnd.Next(_strings.Count)];
            sb.ToString();
        }

        public void TestOptimizedMemStrings ()
        {
            var sb = new List<string>(100000);
            for (int i = 0; i < 100000; i++)
                sb.Add(_strings[_rnd.Next(_strings.Count)]);
            string.Concat(sb);
        }

        private void Benchmark (Action test, string name, int count = 10)
        {
            var sw = new Stopwatch();
            test();
            for (int i = 0; i < count; i++) {
                sw.Start();
                test();
                sw.Stop();
                Console.Write("+");
            }
            Console.WriteLine();
            Console.WriteLine($"{name}: {(double)sw.ElapsedMilliseconds / count} (ticks: {sw.ElapsedTicks / count})");
        }