Hello, I don't know Smalltalk well enough to give myself an answer about the following topic: When using design patterns, one benefit of writing interfaces and passing objects, that implement this interface, to methods is, that the reader instantly knows: okay, here the method A expects something that implements method B. Due to the nature of being a dynamically typed language, Smalltalk does not need interfaces. An exception object is thrown when a message is passed to an object that does not implement that method. But this message send could be deep inside the code. How do you show to the reader of your code your intention, that you are expecting, let's say for example, an iterator or an object that implements method X, Y and Z? Just with your method comments? Do you use UML? If so, how (without interfaces that point to the required methods)? Sorry, but I think my understanding of OOP is still to much influenced by C++ and Java based teachings... Thanks and best regards, Marc