Defender Extension Methods -- Resolution and Invoccation

[Neal Gafter]

Colin has a good point.  Unless the binary compatibility rules prevent you
from ever changing a defender method's implementation (which would be
horrible: the whole point of implementations is that they may be changed),
the compiler must require the programmer to resolve inheritance of multiple
defender methods, even when the implementation happens to be identical in
that particular version of the inherited interfaces.

I still don't see any compelling reasons for the separation.  Brian says
that this prevents the feature from forcing a paradigm shift on programmers,
but the separation appears to increase (rather than reduce) the conceptual
footprint of the feature and therefore the language.

On Wed, Aug 4, 2010 at 6:16 PM, Collin Fagan <collin.fagan at gmail.com> wrote:

> I know I've voiced this before but I'm not a fan of defender methods. I
> just
> don't see how this is not already multiple inheritance. Look I'm just your
> average Joe programmer but I don't understand how the statement "a class
> implementing two interfaces with two extension methods that collide is
> easier. They should have the same default." can possibly be true. If each
> interface provides a default how the heck is the programmer supposed to
> know
> which one will eclipse the other? Are you saying the default implementation
> needs to point to the same class/method? So when I use an interface from
> common.lang and one from java.util and there just happens to be a collision
> and they don't share the same default implementation only then am I going
> to
> be alerted by the compiler that something is wrong? What happens when the
> default changes? Does that mean at runtime there will be collsision that
> was
> not intended at compile time? Is the default actually part of the method
> signature? Will I get a method not found exception when there is a change?
> Will every API developer get 1 and only 1 shot at picking a default
> implementation?
>
> I'm sorry I'm really happy with the hard work people are putting into this.
> I'm just totally confused by defender methods.
>
> Collin
>
>
> On Wed, Aug 4, 2010 at 7:33 PM, Brian Goetz <brian.goetz at oracle.com>
> wrote:
>
> > On 8/4/2010 7:38 PM, Rémi Forax wrote:
> >
> > > I think the syntax of defender method has some technical merits:
> > > - solving the problem of a class implementing two interfaces with two
> > > extension methods
> > >     that collide is easier. They should have the same default.
> >
> > This one point alone should close down this discussion!
> >
> >
> >
> >
>
>