RFC: SPL Comparator interface

Something that would be extremely useful is a comparator interface in
SPL, which could be used to easily implement sorting for objects.

Example:

class Foo implements Comparator
{
// is numeric for this example
public $bar;

//implements compare method from Comparator interface
public function compare($that)
{
	//simple example; will return < 1 if this is less
	//than that; zero if they're equal; > 1 if this is
	//greater than that
	return $this->bar - $that->bar;
}

}

Then, if I had an array of Foo objects, I could just call some kind of
spl_sort function on the array which would use my comparator to sort them.

I realize this can be kludged with usort(), but I think there should be
a better, OOP-ier way to do it.

I also realize that a similar effect could be achieved by defining an
SPL PriorityQueue-ish collection rather than an array, but I think there
ought to be a better way. Java has a Comparator interface which works
in much the same way, if that helps my case at all.

Jeremy