class TestDefault<T>
    {
        public T foo()
        {
            T t = null; //???
            return t;
        }
    }

class TestDefault<T>
    {
        public T foo()
        {
                return default(T);
        }
    }

 class Program
    {
        static void Main(string[] args)
        {
            TestDefault<int> t1 = new TestDefault<int>();
            int i = t1.foo();
            System.Diagnostics.Debug.Assert(i == 0);

            TestDefault<object> t2 = new TestDefault<object>();
            object o = t2.foo();
            System.Diagnostics.Debug.Assert(o == null);
        }
    }

class TestDefault<T>
    {
        public T foo()
        {
                return T.default;
        }
    }