Re: But is it Object-Oriented?

>'many practicing programmers used to single-dispatching object-oriented
>languages complain that multi-methods just don't feel object-oriented.'
>...
>the extant generic-function-based approach to multiple-dispatching
>object oriented languages tends to encourage a function-oriented
>programming style at the expense of a data-abstraction-oriented
>programming style. 
>
There is not less data abstraction when you have multi-method than when 
you are restricted to mono-methods. In both cases, outside of the 
package defining a class, you can only use the operations that are 
public. You can also define new operations based on the existing ones. 
The difference is that with mono-methods you will need to resort to 
static methods, while multi-methods are more powerful (you can use 
dispatch) and are more elegant to use for clients (method calls look 
like they always do).

Take the typical exemple of data abstraction: stacks. A stack is 
something that supports the operations pop, push, and isEmpty. From the 
outside, you only know this, nothing about how it might be implemented 
internally.

In Java, you can write:

public class StackUtils {
  public static void clear(Stack s) {
    while (! s.isEmpty())
      s.pop();
  }
}

// Use: StackUtils.clear(myStack)

While in Nice you would write:

public void clear(Stack s) {
  while (! s.isEmpty())
    s.pop();
}

// Use: myStack.clear()

I don't see why the second would violate data-abstraction, if the first 
one doesn't. The fact is, neither does: they both simply use the public 
interface of stacks to define a new operation.

Daniel



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