>Mike,
>
>>I would restate that slightly. The modules are not supposed to know so much about the other modules at runtime. The developer needs to know as much as possible to succeed at design time. Runtime composition helps tremendously as you've said.
>
>I think an O-O purist would say you don't need to see the implementation details of the class you are using at all. Use the documentation to know what methods to call when. But the actual code in those methods is hidden. This goes in line with the ability of the designer to change implementation as time goes on provided that the end result is still the same (or bug fixed so that it produces the correct result). To write client code that depends on the providers code causes a potentially hazardous coupling.
>
>Practically though we do end up needing to know more about the implementation detail than we should have to.

Yep. Some of those purists looked down from their Ivory Towers and got it wrong. Down in the real world, we need to know how things work so we can work with it. We don't just drive the car, we tune it up and customize it.