usages of virtual and new

As far as i see in c#,

virtual function are not just for polymorphism,

it is also for overriding the hiding method warning by the compiler

am i right ?

i will give an example :

class A
{
   public void func(int a)
     {
        ....
     }
}
class B:A
{
   public void func(int a)
     {
        ....
     }
}

now , im using B x = new B(); so the compiler will warn me for method in class B hides the one in A. so there is 2 solutions :

1) mark the one in B with the New keyword

2) make the one in 'A' virtual and the one in B - Overriding - this will clear the warning of hiding..

the only difference will be wit开发者_StackOverflow社区h Polymorphism A x = new B();

if there will be 'new' in class B - always the one from A will be called while if im using the virtual and not the new mechanism - the one from B will be called.

so virtual has 2 roles in .net : (please correct me if im wrong)

1) resolve the hiding warning (in non-Polymorphism enviroment)

2) and of course overriding the functions in yes-polymorphism enviroment.

please correct me if im wrong.

---

No, virtual methods are for polymorphism. Your "solution" #2 will change the behaviour of calling x.func() from calling the A implementation to calling the B implementation - i.e. making it polymorphic. Yes, it removes the warning - but it's no longer a "non-polymorphism environment" as you've made the behaviour polymorphic. Did you want to do that, or not? If you did, then virtual and override is the way to go. If you didn't, you should use new or rename the method.

I would strongly advise you to avoid using method hiding unless you really need to. Do you even need B to derive from A? If you want to give it another method with the same name but a different meaning, consider making them separate classes. Personally I steer away from inheritance unless there's a clear polymorphic relationship.

(Note that overriding and overloading are different concepts, by the way. You mean overriding here.)

---

The compiler warning is just that. It's a warning that your implementation of func() is probably incorrect, because it's hiding the member form the base class.

It's effect is to remove the warning, but that's not its reason. The reason is to make you double-check and confirm your intention.

---

Basically "New" keyword is used to overcome the warning of hiding method. while virtual key word is purely for the polymorphism it tells the compiler if override version of the method available then run that method other wise run virtual method.

Virtual overriding is also called runtime polymorphism.because it decides on runtime that what method will be run.

While "New" keyword remove the warning and only run child class method and hides the parent method ,so to over come this we use:

   public new void Method()
{
//Some code
Base.Method();

}

by using this we run parent method and unhide the parent class method