"Model 2" prototype implementation

[Guillaume Martres]

On Friday 07 August 2015 16:09:14 Brian Goetz wrote:
> Most dispatch on Foo<any> receivers can proceed without indy; the
> prototype happens to use it for dispatching all calls on Foo<any>
> receivers, but this is neither necessary nor optimal.

Can you provide an example where it is necessary? I played a bit with the 
prototype but couldn't think of an example where it would.