string.cs

using System;
using System.Runtime.CompilerServices;
using static System.Console;

// No effect...
//[CompilationRelaxations(CompilationRelaxations.NoStringInterning)]

class Program
{
    const string kHello = "HelloWorld";

    class HelloWorld { }

    static void Main(string[] args)
    {
        var myStr = "HelloWorld";
        string x, y;

        AreEqual(myStr, kHello);
        AreEqual(myStr, ConstFunc());
        AreEqual(myStr, ConstAndConst());
        AreEqual(myStr, NameOf());

        AreEqual(myStr, x = ConstAndToString());
        AreEqual(myStr, y = string.Intern(x));  // Should be False after Ngen

        AreEqual(myStr, x = string.Format(myStr));
        AreEqual(myStr, y = string.Intern(x));  // Should be False after Ngen


        // Advanced: Inspect in the watch pane. They should have the same value,
        //           which points to the physical location of the interned literal.
        //
        // *(void**)&myStr
        // *(void**)&y
        //
        // Then open the memory pane (Ctrl+Alt+M, 1) and go to the given address.


        // String manipulation after the instance creation.
        x = new string(' ', myStr.Length);
        unsafe
        {
            fixed (char* pSrc = myStr)
            fixed (char* pDst = x)
            {
                var bytes = myStr.Length * sizeof(char);
                Buffer.MemoryCopy(pSrc, pDst, bytes, bytes);
            }
        }
        WriteLine(x);
        AreEqual(myStr, x);
        AreEqual(myStr, string.Intern(x));


        unsafe
        {
            fixed (char* pt = myStr)
                pt[0] = '@';
        }
        WriteLine(kHello);  // Attention please!  Constant is changed.


        // Modify the length to cause buffer overrun.
        unsafe
        {
            fixed (char* pt = myStr)
                ((int*)pt)[-1] = 100;
        }
        WriteLine(kHello);
    }

    static string ConstFunc() => "HelloWorld";
    static string ConstAndConst() => "Hello" + "World";
    static string ConstAndToString() => "Hello" + "World".ToString();
    static string NameOf() => nameof(HelloWorld);

    static void AreEqual(string s1, string s2) =>
        WriteLine(ReferenceEquals(s1, s2));
}