cast.cs

using System;

namespace Example
{
    class MainClass
    {
        static void Main()
        {
            Display(0);
            Display(new A(6));
            Display2(new A(6));
        }

        static void Display(object a)
        {
            Console.WriteLine("----------------");
            Console.WriteLine(a.GetType().FullName);

            reinterpret_cast<string>(a);

            Console.WriteLine(a.GetType().FullName);
            Console.WriteLine((string)a);
        }

        static void Display2(A a)
        {
            Console.WriteLine("+++++++++++++++++");
            Console.WriteLine(a.GetType().FullName);

            reinterpret_cast<B>(a);

            Console.WriteLine(a.GetType().FullName);
            var b = (B)(object)a;
            Console.WriteLine($"{b.M}{b.C}{b.W}{a.X()}");
        }

        //TODO: consider GC...
        unsafe static void reinterpret_cast<T>(object obj)
        {
            var tr = __makeref(obj);
            var typeHandle = **(IntPtr***)&tr;
            *typeHandle = typeof(T).TypeHandle.Value;
        }
    }

    class A
    {
        public int I;
        public readonly char M = 'T';
        public readonly char a = 'e';
        public readonly char r = 's';
        public readonly char c = 't';
        public readonly char i = ':';
        public readonly char n = ')';
        public A(int i)
        {
            I = i;
        }
        public /*virtual*/ string X() => "(some text)";
    }

    class B
    {
        public int I;
        public readonly char M = 'M';
        public readonly char C = 'C';
        public readonly char W = 'W';
        public B(int i)
        {
            I = i;
        }
        public /*virtual*/ string X() => "(XXXX XXXX)";
    }
}