[haXe] overloading parent with different type

[cornel]

thanks for your explanation, i guess i understand now.

cornel

On 4/9/06, Nicolas Cannasse <ncannasse at motion-twin.com> wrote:
> > hi all
> >
> > Nicolas,
> > Related to my older post, about qooxdoo: i wrote some code that would
> > create haxe interfaces out of qooxdoo classes, and i've encountered
> > the same problem:  there's a lot of methods that override methods with
> > the same name in the parent class. I'm not sure i understand why this
> > is an error.
> > For example, c++ has no problem with this code:
> >
> > class A{
> >       int f(){return 0;}
> > };
> >
> > class B:public A{
> >       std::string f(){return "hi";}
> > };
> >
> > Could you please elaborate a bit?
>
> I don't know any language that provide this kind of selection. That
> means that in your case B::f fully overload A::f, so the A::f is no
> longer accessible when you have a "B" instance.
>
> In general, selection is performed on the number/types of parameters.
> This can sometimes be tricky, especialy in presence of subtyping :
>
> class B extends A {
> }
>
> function f( a : A, b : B ) {
> }
>
> function f( b : B, a : A ) {
> }
>
>
> f( new B(), new B() );
>
> Which method to choose ?
>
> In haXe, you have an additional contraint, that is that for each call,
> the behavior should be the same whatever if you know or not the type of
> the arguments. Also, since objects are prototype-based, you can only
> have one method for a given name "f". That means that in order to
> correctly support method overloading, you need to generate one "generic"
> method that will do the runtime dispatching :
>
>
> function f( x, y ) {
>    if( Std.is(x,A) && Std.is(y,B) )
>         this.f__1(x,y);
>    else if( Std.is(x,B) && Std.is(y,A) )
>         this.f__2(x,y);
>    else
>         throw new TypeError();
>
> }
>
> Of course when at compile time you know the arguments type, you can
> select directly the method f__1 or f__2 and thus skip the dynamic
> dispatching.
>
> Nicolas
>
>
> --
> haXe - an open source web programming language
> http://haxe.org
>