What are the pros and cons of using interfaces in Delphi?

Question

I have used Delphi classes for a while now but never really got into using interfaces. I already have read a bit about them but want to learn more.

I would like to hear

Answer 1

All I can think of for now:

Pros:

• Clear separation between interface and implementation
• Reduced unit dependencies
• Multiple inheritance
• Reference counting (if desired, can be disabled)

Cons:

• Class and interface references cannot be mixed (at least with reference counting)
• Getter and setter functions required for all properties
• Reference counting does not work with circular references
• Debugging difficulties (thanks to gabr and Warren for pointing that out)