using System;

using System.Runtime.InteropServices;

public class Program

{

     public static string Marshal_Span(string Content)

    {

        Span<char> chars = MemoryMarshal.CreateSpan(ref MemoryMarshal.GetReference(Content.AsSpan()), Content.Length);

        for (int i = 0; i < chars.Length; i++)

        {

            if (chars[i] == ' ')

            {

                chars[i] = ',';

            }

        }

​

        return Content; 

    }

    public static void Main()

    {

        string Content =

        "Hello World! Add new line. Ok. Substring allocates a new string object on the heap and performs a full copy of the extracted text." +

        "String manipulation is a performance bottleneck for many programs. Many APIs that accept strings also have overloads that accept a ReadOnlySpan<System.Char> argument." +

        "When such overloads are available, you can improve performance by calling AsSpan instead of Substring.";

        Console.WriteLine(Marshal_Span(Content));

    }

}