static void Main(string[] args)
{
DataTable dtA = new DataTable();
dtA.Columns.Add(new DataColumn("Col A", typeof(MyClass)));
dtA.Rows.Add(new MyClass(100));
DataTable dtB = dtA.Copy();
// both tables hold a reference to the same object...
((MyClass)dtA.Rows[0][0]).a = 3000;
// "3000" is displayed here for both
Console.WriteLine(((MyClass)dtA.Rows[0][0]).a);
Console.WriteLine(((MyClass)dtB.Rows[0][0]).a);
Console.WriteLine("Done...");
Console.ReadLine();
}