Re: anyone define port types?

[Jan Wedekind <jan@wedesoft.de>]

On Thu, 31 Mar 2016, Marko Rauhamaa wrote:

> Jan Wedekind <jan@wedesoft.de>:
>
>> On Wed, 30 Mar 2016, Marko Rauhamaa wrote:
>>> GOOPS' has the worst possible object model: objects are seen as mere
>>> data records. The concept of a "slot" is an anathema to OOP.
>>
>> Ok, I have updated the example to use accessor functions instead of
>> "slot-ref".
>
> (get-x) is only a fig leaf for (slot-ref). In general, no user of an <a>
> object should think the object holds a piece of information called x.
> Instead, you should be interacting with the abstract object <a>.
Well, actually (get-x) is a generic as well. I.e. it is polymorphic and 
does not have to be a simple accessor for a slot. I.e. the accessor syntax 
is just a shortcut for declaring a generic for accessing a slot 
separately:

(use-modules (oop goops))
(define-class <a> () (x #:init-keyword #:x))
(define-method (get-x (self <a>)) (slot-ref self 'x))

"get-x" can be defined differently for each class and its implementation 
can be doing something different than accessing a slot.

>
> Python people call it duck-typing.
>
> Java, Go et al use interfaces.
>
> Even C can do opaque structs.
>
> C++ suffers from "private" data members, and GOOPS strips away even that
> thin veil.

Here is an example using duck-typing with the generic "get-x":

(define-class <b> ())
(define-method (get-x (self <b>)) 123)
(define-method (use-duck-typing (x <object>)) (get-x x))
(use-duck-typing (make <a> #:x 3))
; => 3
(use-duck-typing (make <b>))
; => 123