Both defect and trade-off. I can definitely see value in being able to pass an array of Dogs and treat it as an array of Animals, but it means that the array of

Both defect and trade-off. I can definitely see value in being able to pass an array of Dogs and treat it as an array of Animals, but it means that the array of Animals is not really an array of animals (because certain properties of a real array of Animals actually cause the code to break) and as a result the language is a little dirtier for it. Like, that's pretty horrible to be honest. What you really want in that instance is to be able to easily and explicitly cast the Dog[] to Animal[] before calling the method. A better language would make this easy instead. I think Java's Vector type can do it, so it surprises me that they allow that sort of type weirdness with arrays..