Cursed.

Cursed.cs

using System.Runtime.CompilerServices;

Console.WriteLine("Hello, World!");

ConcreteWindow w = new();
Window<int> a = Unsafe.As<Window<int>>(w);
a.Show();
;

public interface IViewFor<T> { }

public class WindowBase
{
	public virtual void Show()
	{
	}
}

public sealed class Window<T> : WindowBase, IViewFor<T>
{
}

public class ConcreteWindow : WindowBase, IViewFor<int>
{
	public override void Show()
	{
		base.Show();
	}
}

Cursed2.cs

Window<int> b = ReinterpretCast<ConcreteWindow, Window<int>>(w);

static unsafe TDest ReinterpretCast<TSource, TDest>(TSource source)
{
	var sourceRef = __makeref(source);
	var dest = default(TDest);
	var destRef = __makeref(dest);
	*(nint*)&destRef = *(nint*)&sourceRef;
	return __refvalue(destRef, TDest);
}