值类型问题

Question

Struct A : ICloneable { public Int32 x; public override String ToString() { return String.Format(”{0}”,x); } public object Clone() { return MemberwiseClone(); } } static void main() { A a; a.x = 100; Console.WriteLine(a.ToString()); Console.WriteLine(a.GetType()); A a2 = (A)a.Clone(); ICloneable c = a2; Ojbect o = c.Clone(); }因为A是值类型，编译器不会出现多态行为。看到这句话有个提问。关于编译器而言值类型编译器为什么不会出现多态行为？重写无用？