As you’ve noted, impl AsRef<User> for User seems a little pointless since you can just do &user. You could do impl AsRef<String> for User or impl AsRef<u8> for User as alternatives to &user.email and &user.age but those examples are probably misuses of the trait. What does it mean to be able to convert a User … Read more
Some terminology: The kind * is sometimes called ground. You can think of it as 0th order. Any kind of the form * -> * -> … -> * with at least one arrow is first-order. A higher-order kind is one that has a “nested arrow on the left”, e.g., (* -> *) -> *. … Read more
Is polymorphism lost by allowing empty list handling? If so, how so, and why? Are there particular cases which would make this obvious? The free theorem for head states that f . head = head . $map f Applying this theorem to [] implies that f (head []) = head (map f []) = head … Read more
Polymorphism is one of the tenets of Object Oriented Programming (OOP). It is the practice of designing objects to share behaviors and to be able to override shared behaviors with specific ones. Polymorphism takes advantage of inheritance in order to make this happen. In OOP everything is considered to be modeled as an object. This … Read more