AccessViolation.cs

using System.Runtime.InteropServices;

class Program
{
	[StructLayout(LayoutKind.Explicit)]
	struct Union
	{
		[FieldOffset(0)]
		public Foo foo;
		[FieldOffset(0)]
		public Bar bar;
	}

	class Foo { public Qux qux; }
	class Bar { public int integer; }
	class Qux { public int integer; }

	static void Main()
	{
		var foo = default(Union);
		foo.bar = new Bar { integer = 200_000 };
		foo.foo.qux.integer = 0; // AccessViolationException: Attempted to read or write protected memory.
	}
}