All the dependencies of a unit are part of its API. You may not need to give them at every call, but you do need to give them atleast once. Whether the unit cal

All the dependencies of a unit are part of its API. You may not need to give them at every call, but you do need to give them atleast once. Whether the unit calls MissileLauncher::launch or not is in my opinion part of the external behavior of the unit.