Why can't I put a delegate in an interface?

Question

Why can\'t I add a delegate to my interface?

Answer 1

As others have mentioned, you can only define delegates outside of the interface.

There is little to nothing wrong w/ using delegates. Personally I think that Func<int, double> is less desirable than using delegates:

1. You cannot name the arguments, so the argument meaning can be ambiguous

2. It is old news that Events are not thread safe, thus the following code is not ideal:

   if (MyFuncEvent != null)
   {
       MyFuncEvent(42, 42.42);
   }
   

   See: http://kristofverbiest.blogspot.com/2006/08/better-way-to-raise-events.html

   The safer code is:

   MyFuncEventHandler handler = MyFuncEvent;
   if (handler != null)
   {
       handler(42, 42.42);
   }
   

3. You have to duplicate the signature of the event if you want to save it to a variable (or you could use var, which I dislike). If you have lots of arguments then this could get very tedious (again, you could always be lazy and use var).

   Func<int, double, string, object, short, string, object> handler = MyFuncEvent;
   if (handler != null)
   {
       handler(42, 42.42, ...);
   }
   

Delegates save you from having to duplicate the signature of the method/event every time you want to assign it to a variable type.