Re: function to resize a UML class object's extent?

[Cyrille Chepelov <chepelov calixo net>]

Le ven, nov 30, 2001, à 01:06:35 -0600, Lars Clausen a écrit:

> I was thinking of the vtable things, and AFAIR it doesn't really do
> inheritance.  If a sub'class' of Connection has a NULL in its vtable, it
> doesn't mean the superclass's function gets called.  Is there anything
> prohibiting the class constructor from copying functions from the
> superclass when the vtable has a NULL?

It's 100% manual ; you do what you want. Oh, I think I see what you really
mean: 

typedef struct { .... } A_ops;
typedef struct { A_ops* ops; .... } A;

typedef struct { A_ops a_ops; .... } B_ops;
typedef struct { A a; .... } B;

static B_ops B_vtable = { { a_op1,  
                            a_op2_overriden_by_b,
                            NULL, /* meaning, implicit a_op3 */
                          },
                          b_op1,
                          NULL, /* meaning, implicit b_op2 */
                          b_op3 };

void a_init(A* a) { 
   if (!(a->ops->op1)) a->ops->op1 = a_op1;
   if (!(a->ops->op2)) a->ops->op2 = a_op2;
   if (!(a->ops->op3)) a->ops->op3 = a_op3;
  
   /* init of the A objet itself */
}

void b_init(B* b) {
  A_ops* a_ops = &b->a.ops;
  B_ops* b_ops = (B_ops*)a_ops;
  A* a = &b->a;

  a_init(a);
  if (!b_ops->op1) b_ops->op1 = b_op1;
  if (!b_ops->op2) b_ops->op2 = b_op1;
  if (!b_ops->op3) b_ops->op3 = b_op1;
}

(of course, dia does things slightly differently)
I see nothing wrong with that (except a few nanoseconds at instance
construction). The day we allow C99 litterals, we'll be able to remove a lot
of clutter from the operations structures. However, how does this stuff
relate to GObject ? Isn't GObject supposed to provide these mechanisms
already ?

        -- Cyrille


> -Lars
>
> -- 
> Lars Clausen (http://shasta.cs.uiuc.edu/~lrclause)| Hårdgrim of Numenor
> "I do not agree with a word that you say, but I   |----------------------------
> will defend to the death your right to say it."   | Where are we going, and
>     --Evelyn Beatrice Hall paraphrasing Voltaire  | what's with the handbasket?
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-- 
Grumpf.