> provide mechanisms to avoid mutability e.g. data classes or keywords to make references constant.

So, functional programming?

> guarantees some sort of basic interface that all entities conform to e.g. being able to ask an entity to provide a hash code, or to carry out a comparison check with some other entity.

Isn't that terrible? You want to provide a generic interface to calculate a hash or perform comparison: Now the thing has to be an object! If it's a primitive type, you better wrap it in an object now. If it's an existing class, you have to extend it. It becomes an object of a different class.

Or, instead, you could just have type classes to let the same apply to anything whatsoever, as long as it's a type, without the need for it to be an object. Heck, in some cases, the type could be a function instead.