This is exactly the problem you face in generic programming in C++ (and would have been fixed with concepts). You don't get to typecheck against the possible in

This is exactly the problem you face in generic programming in C++ (and would have been fixed with concepts). You don't get to typecheck against the possible interfaces some object implements, and you have to be very good at parsing compiler diagnostics - assuming your compiler reports good enough diagnostics to let you figure out the problem. I would gladly trade for the verboseness of making these relationships explicit if it let me typecheck and refactor with ease.