[Kde-bindings] Bindings...

[Ashley Winters]

I managed to come up with an outline for what I plan with my particular
C interface for Qt/KDE.

First thing, prototype mangling is out the door. I'm going to cheat on
that one.

void QApplication::exec(int retcode = 0);

That will get two functions in C:

exec_1_wtS6
exec_2_LmeL

It's easy enough to sketch what those functions will look like.

extern "C"
void exec_1_wtS6(void *a1) {
    ((QApplication*)a1)->exec();
}

extern "C"
void exec_2_LmeL(void *a1, int a2) {
    ((QApplication*)a1)->exec(a2);
}

The format of the C functions names is interesting.

1. method_name
2. argument count
3. first 4 letters of the base64-encoded md5sum of the method prototype
being interfaced. Of course, all illegal characters are replaced with
'_'. Operators will get their gcc-standard names.

Fun, eh? No name mangling for me.

As for handling virtual functions, that's handled pretty simply too.

First, you need to get the global virtual function table for a class:

extern "C" void *virtual_get_QWidget();

Note: that's not the REAL virtual function table I'm using. Just a
parallel one. I'm not going that far off the deep end...

Then, for a language like C#, you would override a method using a
delegate pointer passed to a override_ prefixed method with the above
prototyping system. Like so:

// Overrides QWidget::setMask(const QBitmap &) with delegate
extern "C"
void override_setMask_2_piWT(void *vtable, void (*delegate)());

That delegate would get called with all the arguments passed to the
virtual function, with speed penalty.

For PerlQt, we would add a level of indirection. There would be a
separate function for marshalling the virtual function arguments, and
that function which marshalls the arguments would be passed to the
above function.

The XML file would contain the method signature used to generate the
MD5sum, as well as the 4-letter sum used for the method. This would
allow binary compatibility with client libraries between upgrades to
Qt/QtC, since the method names never change.

This isn't meant to be used by programmers, only by language bindings.

Also, the C library will keep a global table of pointers created, since
as far as I know every language binding needs that. In fact, the C
binding will need it as well, since I'm thinking about supporting
per-object virtual function tables! Whether I could do this without a
global speed penalty is another question...

Indeed, that means you could create singleton widgets like this in
PerlQt in the future:

$w = new Qt::Widget(this);   # vanilla widget, not a subclass!
$w->virtual->{mousePressEvent} = sub {
    my $e = shift;
    printf "You clicked at %dx%d\n", $e->x, $e->y;
}

Yes, I'm crazy. It's fun, though.

Ashley Winters

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