§4.9.1.(a) Effect on sub-classes

The callin binding also effects instances of any type BSub that is a sub-type of B. If BSub overrides the bound base method bm, the overridden version is generally affected, too. However, if bm covariantly redefines the return type from its super version, the callin binding has to explicitly specify if the covariant sub-class version should be affected, too (see §4.9.3.(b)).