Polymorphism is not related to inheritance. In earlier object-oriented systems it was (and is), but only because they were trying all directions. It actually becomes clearer without inheritance and many modern systems introduce it as a separate concept of an interface.
For example, I am sending requests to an HTTP server. There are several authentication methods but when we look at request/method interaction they are similar. So it would be convenient to have standard interface here, something like 'auth.applyTo(request)'. Yet would it be a good idea to try making different 'Auth' methods to be subclasses of each other?
Or another example I'm currently working on: I have a typical search tree, say, AVL, but in my case I need to make references to cells in the tree because I will access it bottom-up. As the tree changes its geometry the data move between cells so I need to notify the data about the address change. This is simple: I merely provide a callback and the tree calls it with each new and changed cell address. I can store any object as long as it provides this callback interface. Does this mean I need to make all objects I am going to store in a tree to inherit some "TreeNotifiable" trait?
Polymorphism happens when we split a system into two components and plan interaction between them. Internals of a component do not matter, only the surface. Inheritance, on the other hand, is a way to share some common behavior of two components, so here the internals do matter. These are really two different concepts.
For example, I am sending requests to an HTTP server. There are several authentication methods but when we look at request/method interaction they are similar. So it would be convenient to have standard interface here, something like 'auth.applyTo(request)'. Yet would it be a good idea to try making different 'Auth' methods to be subclasses of each other?
Or another example I'm currently working on: I have a typical search tree, say, AVL, but in my case I need to make references to cells in the tree because I will access it bottom-up. As the tree changes its geometry the data move between cells so I need to notify the data about the address change. This is simple: I merely provide a callback and the tree calls it with each new and changed cell address. I can store any object as long as it provides this callback interface. Does this mean I need to make all objects I am going to store in a tree to inherit some "TreeNotifiable" trait?
Polymorphism happens when we split a system into two components and plan interaction between them. Internals of a component do not matter, only the surface. Inheritance, on the other hand, is a way to share some common behavior of two components, so here the internals do matter. These are really two different concepts.