ArrayFactory SAM type / toArray

[Brian Goetz]

In looking at the Collection API, there are two forms of toArray method, 
both of which are unfortunate:

   Object[] toArray() -- returns an Object[], not a T[]

   T[] toArray(T[]) -- reflective instantiation

Lambdas offer us a way out of this:

interface ArrayFactory<T> {
     T[] make(int n);
}

interface Collection<T> {
     T[] toArray(ArrayFactory<T> factory) default {
         return toArray(factory.make(size());
     }
}

The default is imperfect (though no worse than what clients typically 
do), and concrete implementations of Collection can do better.

Given that Stream has a toArray method, my preference would be to expose

   T[] toArray(ArrayFactory<T>)

possibly as the only toArray method.

We might be able to extend the constructor reference syntax to arrays: 
Foo[]::new.  If not, n -> new Foo[n] works fine.