using System;

using System.Diagnostics;

public class Program

{

    public static void Main()

    {   

        Stopwatch s = Stopwatch.StartNew();

        s.Start();

        var hello = "Hello".AsSpan();

        var space = " ".AsSpan();

        var world = "World".AsSpan();

​

        // First allocate the buffer with the target size

        char[] buffer = new char[hello.Length + space.Length + world.Length];

        // "Convert" it to writable Span<char>

        var span = new Span<char>(buffer);

​

        // Then copy each span at the right position in the buffer

        int index = 0;

        hello.CopyTo(span.Slice(index, hello.Length));

        index += hello.Length;

​

        space.CopyTo(span.Slice(index, space.Length));

        index += space.Length;

​

        world.CopyTo(span.Slice(index, world.Length));

​

        // Finality get back the string

        string result = span.ToString();

        s.Stop();

        Console.WriteLine("Time elapsed (ns): {0}", s.Elapsed.TotalMilliseconds * 1000000);

    }

}