One of my colleagues enjoys explaining things a lot, and he does it very well. This comes up handy when I am missing something on a subject: I come to him, and he teaches me everything I have to know about the thing.
However, this also has a negative side. Sometimes, he starts explaining something that I already know, and continues with the explanation no matter what. Telling him something like: “Yeah, thanks, I already know all that; can we please go back to the original question?” has either no effect, or he barely responds: “Of course, I remember the original question, just let me explain [the subject] first.”
Here's how a recent conversation sounded like:
Me: do you think it would be better to use this approach rather than the one we considered originally? I'm not sure if the new one is clear enough; it doesn't look particularly readable...
Colleague: the benefit of the new approach is that it cleverly uses the polymorphic behavior of the classes. You know what polymorphism is, right?
Me: of course I do, it's when...
Colleague: it's when multiple types share the same interface, which makes it possible to use those types in the same way, as soon as the use only needs the members which are declared within the interface. One of the interesting aspects of it is parametric polymorphism. This is what translates into...
Me: into templates in C++ and generics in Java. I know. Speaking about the old and the new approaches...
Colleague: exactly, templates and generics. They allow you to use...
Me: I know what generics are...
Colleague: ... an object independently of its type, as soon as it extends a specific interface [...]
Those discussions sometimes take a long time, and are not very useful: I would rather prefer focusing on things I don't know, or don't know well. However, all my attempts to refocus the person failed.
I want to avoid to be rude to this person at all costs for both personal reasons and because he has valuable knowledge to share (personally, I find myself already quite rude to interrupt him, although he doesn't seem to notice or may be used to it).
Therefore, what is a polite way to focus his attention to the matters which are important to me, away from subjects I already know well?
Note: there is already a question here with a title looking a lot like mine. However, the specifics of the context of the other question and the reaction of the poster which was rather different than mine means that the answers don't apply much to my situation.
