The topic is the covariance of non-generic parameters in seven OOP languages: C++, Eiffel, Java, C#, Scala, Kotlin, Swift (the order is from oldest to youngest).
ABSTRACT
In the example, covariance is attempted to be applied to two related superclass/subclass pairs.
In this particular case these are the classes Animal/Cow and Animal_food/Cow_food.
In one procedure of the Animal class there is a parameter of the Animal_food class.
Can we (in the languages listed above) in the Cow subclass make an overridden procedure that uses the Cow_food class instead of the Animal_food class?
One language had this option from the beginning (late 80’s), but this feature allowed a runtime error, which was somewhat resolved only in 2014.
But there is another language (among the languages listed above) that makes this possible.
Note: the use of generic parameters (and their covariance) is not the “right” solution (it is a solution, but with major practical drawbacks).