Covariance Analysis in Selected OOP Languages

This study aims to analyze covariance with non-generic parameters across seven renowned statically-typed object-oriented languages: C++, Eiffel, Java, C#, Scala, Kotlin, and Swift, presented in chronological order from oldest to newest. In the original examples, an attempt is made to apply covariance to two interconnected superclass/subclass pairs, specifically the Patient/HeartPatient and FoodForPatients / FoodForHeartPatients classes. Within a method of the Patient class, a parameter of the FoodForPatients class (or type) is introduced. We asked whether in the aforementioned languages, it is possible to create an overridden method in the HeartPatient subclass that utilizes the FoodForHeartPatients class in place of the FoodForPatients class. It is essential to emphasize that while the utilization of generic parameters and their covariance represents a viable solution, it is not considered the optimal one due to significant practical drawbacks.