Both approaches have ups and downs. It's probably best not to call virtual methods from the constructor.
The reason C# (and Java too) do it this way is probably because of efficiency. Changing the vtable pointer (what C++ does) isn't possible in C#/Java because that would confuse the garbage collector. Additionally, in C++ member fields aren't implicitly initialized so they would probably contain junk if the constructor was able to call a virtual method that accesses them (before the base class constructor has a chance to initialize them). In C#/Java you don't have that problem, all fields are always initialized to zero/null/false before the constructor runs. Regards, Jeroen > > -----Original Message----- > From: Stephen Dunn [mailto:[EMAIL PROTECTED] > Sent: Thursday, June 19, 2003 15:59 > To: [EMAIL PROTECTED] > > Thanks to FxCop, I've just discovered quite a fundamental > difference between > C++ and C#. > > Check out the following code. > > class Base > { > public Base( ) > { > Method( ) ; > } > > public virtual void Method( ) > { > Console.Write("I'm the Base"); > } > } > > class Derived > : Base > { > public Derived( ) > { > Method( ) ; > } > > public override void Method() > { > Console.WriteLine("I'm the Derived"); > } > } > > Constructing a Derived object means a call is made to Base's > constructor > which calls Method; not Base's method (as in C++), but > Derived's Method. At > this point, Derive is only partially constructed. > When I stumbled over this in C++, I was surprised that the > base constructor > didn't call the derived method. I soon changed my mind when it was > explained to me that C++ is implemented this way as > unexpected results could > happen by called Derived's virtual method. > > Would anyone like to comment? Personally, I feel C++ is > correct in this > instance. > > Cheers, > > Steve >
