Re: [Chicken-users] Problems with pointers to c++ objects

[Felix Winkelmann]

On Thu, 29 Jul 2004 22:42:15 +0000, Petter Egesund <address@hidden>  
wrote:

> But I have problems with functions defined like this;
>
> QFont (const QString &, int pointSize, int weight, bool italic);
>
> They need the pointer to a created object, rather than the object itself.
>
> I have looked through the mailing list, but my failed attempt to create  
> a pointer to a font-object does not seem to work.
>
> Any clues on this one?


Yes, the problem here is that the FFI parser understands "Foo *",
where Foo is the name of a registered class and transforms it into
a foreign type specifier of the form (instance "Foo" <Foo>), which
is basically a specially handled type of pointer.
So the TinyCLOS wrapper for the QFont constructor wants a pointer (i.e.
a reference, because that's how Chicken passed references into Scheme)
but gets an instance.
So: "Foo &" is not properly recognized (even though the FFI handles
references). The solution is to have another foreign type
(instance-ref ...) that is treated as a specially handled reference
type.

I have cobbled something together that should work, but I have to do
some testing before I release it. I have only a rather old version
of Chicken here, so diffs will probably be not overly useful.

Anyway, that problem can be solved and I will provide a fix at
the start of next week.

BTW, this:

> (define the_font_name
>         (let ([a (make <QString> 'this a "Times")])
>         a))

should probably be

(define the_font_name
  (let ([a (make <QString> "Times")])
    a)


cheers,
felix