Just as info for other Nim-novices like me: It is even possible to call a method at compile time, using procCall and explicitly casting to the desired type. In my given example, it could be done like so: echo "compiletime procCall : " & $(procCall MyType(x).intSumDynamic(MyType(y)))
This is awesome, because it solves the original problem I was puzzling with while I encountered the behavior described in my initial post.