Implementing GtkTreeModel

Ok, so I'm trying to create my own class implementing GtkTreeModel to
make it much faster when dealing with thousands of rows. The problem I
have is there is a method called "foreach" that makes PHP blow a gasket
when I try to define it.

class TestTreeModel implements GtkTreeModel
{
	public function foreach($callback_func)
	{
		// do stuff
	}

	// all the other abstract methods are defined properly
}

This will return:

Parse error: syntax error, unexpected T_FOREACH, expecting T_STRING in
foo.php on line xx

Any idea on how to get around this? Thanks!

-Matt