Great post. I would go as far as claiming "don't really mess with inheritance until you have not internalized the principles of co- and contravariance". Might b

Great post. I would go as far as claiming "don't really mess with inheritance until you have not internalized the principles of co- and contravariance". Might be a bit extreme, but I see no way how you can safely navigate OOP without (see Java's famous problems with getting this wrong on container types...).