[Kde-bindings] QtRuby virtual method callbacks

[Ashley Winters]

--- Richard Dale <Richard_Dale at tipitina.demon.co.uk> wrote:
> > mmh, but why?
> > "$" is for scalars, and I think that's what all languages will use
> for
> > marshalling "int&".
> > char** ought to be fed by the target language's equivalent of an
> array of
> > strings, so "?" looks right aswell...
> This is the code in qtruby.rb for references:
> 
> 			for arg in args
> 				if arg == nil or isObject(arg)
> 					method << "#"
> 				elsif isRef(arg)
> 					method << "?"
> 				else
> 					method << "$"
> 				end
> 			end
> 
> I 'made up' isRef() - there is no 'ref' in ruby as far as I know.

The case of nil/undef is handled specially by PerlQt's interface to
smoke. In that case, it could be a null string (undef $), null object
pointer (undef #) or a null array/other pointer (undef ?). In order to
fairly pick a matching prototype, all of these candidates are returned
from the matching function. Psuedo-code time:

If you will allow me to digress into psuedo-Perl for a moment:

@candidates = qw(functionName);

for my $arg (@args) {
    if($arg is undef) {   # psuedo, remember?
        @candidates = map { $_ . '$', $_ . '#', $_ . '?' } @candidates;
    } elsif($arg is scalar) {
        @candidates = map { $_ . '$' } @candidates;
    } elsif($arg is object) {
        @candidates = map { $_ . '#' } @candidates;
    } else {    # !nil and !scalar and !object
        @candidates = map { $_ . '?' } @candidates;
    }
}

# @candidates is now a list of prototypes which match the arguments
# passed by the program. sort them how you see fit...

And, for the specific case of the QApplication constructor, PerlQt
hijacks it and automatically passes the argc argument. It does this so
that PerlQt can read back in the argv after Qt muchs with it and
replace the perl @ARGV array with the proper values.

In the general case though, picture this:

void QFoo::foo(int&);

x = new QFoo
y = 1
x.foo(y)

Your smoke detector will generate a foo$ prototype since it's being
passed a scalar variable (y == 1), which is what smoke provides in the
case of int&. If you pass a nil variable to it, your smoke filter
(hehehe) will try to match the names foo$, foo#, and foo? as per my
above psuedo-code. Since my QFoo class does indeed have a foo$ and none
of the eithers, it matches and gets called.

Enough from me. Excellent work, Richard!

Ashley Winters

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