C# Delegates & Interfaces why?

Delagates are extremely useful. The event/delegate construct in C# provides a subtle addition to the callback schemes used in C/C++. In particular, each event you declare hold a list of delegates, instead of a single callback function. This makes it very easy for you to add a callback function without worrying if you'll override/replace another existing callback that needs to perform its functions.

In addition, in contrast to C++, delegates provide a clean method of allowing you to use member functions for your callbacks. This is a subtle, but huge improvement. In C++, each distinct classes member functions have a different signature. Depending on your pain threshold, some amount of template meta-programming can circumvent this limitation to some degree, but it's clumsy and awkward. Delegates make this simple.

As far as interface classes go, they're really nothing different than a class in C++ that defines all pure virtual functions. What is different is that C# doesn't allow multiple inheritance of classes, even abstract ones. They do this to protect you from the pitfalls of multiple inheritance. Really, it does lessen your flexibility in exchange for predictability. You can, however, derive a class from any number of interfaces as well as a single concrete class, if you desire. So basically, interfaces provide the only form of multiple inheritance in C#.

Hope that clears things up! =)

-John

So a single delegate can call multiple functions?

I think single event can dispatch to multiple objects. In C++ only functors with the help of templates can be treated as function pointers. Other methods need a command design pattern that you can then decide if multiple commands are allowed or not. Quake2 uses the command pattern for its commands albeit it does it thru normal function pointers. The culprit in C++ is ofcourse the crazyness of supplying an object that pointer to member is invoked on. That's the reason for command pattern for example. Basically a workaround for callbacks. I use callbacks to iterate over my containers as I don't bother to repeat the iteration code. I assume delegates are like command pattern.