"identity is the basis for polymorphism in object-oriented programming."
In a purely functional object-oriented programming you don't need identity. But then that practice is almost indistinguishable from usual pure functional programming we have for at least 20 years with Haskell.
Forgive my insistence, but, what kind of problem does the ability to differentiate objects from one another solves? What kind of programs are made simpler by this ability?
Besides, I don't see how you would need identity in the sense of being structurally-equal-but-not-the-same for class based polymorphism. You could perfectly do this without any side effect, despite what the `final` keyword in Java might mean.
By "identity" Wikipedia probably means something like "you think I'm a Foo, which is right, but underneath, I'm a special kind of Foo: a Bar. By the way, there are others special kinds of Foo: the Baz, the Fiz, the Buz…". In other words, subtyping is the basis for polymorphism in OOP.
>Forgive my insistence, but, what kind of problem does the ability to differentiate objects from one another solves? What kind of programs are made simpler by this ability?
Oh, I don't know. I am not an expert in OO* at all.
All I know is that for something to be true OO it has to have objects with identities. I was told so. ;)
All I know about OO is Liskov substitution principle. Where it is unnecessary I tend to use State monad and immutable objects.
>subtyping is the basis for polymorphism in OOP.
Which can be solved by several means, interfaces and inheritance being two of them.
>Yes you can. Check out my language Babel-17
I failed to see how purely functional structured programming address the need of identity for objects.
Could you elaborate a little more?