where t : multiple classes

Question

List<T> Foo<T>(Ilist list) 
where T : ??

is there any way to enforce T to be
one of few classes ?

eventually i want to do a switch on T..

thanks.

Answer 1

In this case, T could be a common base class or interface that you list objects share. You could have List<IFoo>, and the list could contain classes Foo, Bar, and Baz if they each implement the IFoo interface. Short of using inheritance, you would be stuck with a list of objects.

Answer 2

You can require that each class you want to allow into your list implements some interface ISomething and then create a List<ISomething>.

eventually i want to do a switch on T..

Instead of a switch on the type of the object it might be better to have a method in your interface and implement it differently for each class.

Answer 3

As far as I know, this is not possible. I would recommend deriving your limited set of classes from a common base class or interface.

Answer 4

Enforcing a type constraint in this way indicates that those several classes are related with common functionality.

You should implement a common Interface and then restrict the type to that Interface:

public interface IUseful
{
    public void UsefulMethod();
}

List<T> Foo<T>(IList list) where T : IUseful
{
    // You now have access to all common functionality defined in IUseful
}

The added benefit is that now you don't have to switch on T to implement different behaviors. You can have the children of IUseful implement their own behaviors and then call each on their own.

Answer 5

What is it do you want? After the colon, you may enumerate the types to which you constraint T to.

For multiple classes, perhaps implementing one generic interface and setting your constraint to it might do the trick.

Please look at this link for further details: Constraints on Type Parameters (C# Programming Guide)