Applying const to an object but not the container (D 2.0)

[Burton Radons]

I'm writing an XML class. There are two tests for this class, isAncestorOf and isDescendantOf, that are implemented in terms of one another. They're both const, and look like this:

class Node
{
	Node parentNode;
	/// ...

	/// Return whether this is an ancestor of the other node. A node is not an ancestor of itself, or of null.
	bool isAncestorOf (Node node) const
	{
		while (node) if ((node = node.parentNode) is this)
			return true;
		return false;
	}
	
	/// Return whether one of the parents of this node is the other. A node is not a descendant of itself, or of null.
	bool isDescendantOf (Node node) const
	{
		return node ? node.isAncestorOf (this) : false;
	}
}

The compiler doesn't like this, saying of the isDescendantOf essentially that "this" is const, but is being passed as mutable. However, if I make the argument const, then the assignment in the loop won't work because unlike "const (Struct) *", "const (Class)" applies both to the object and the container.

Is there a way around this aside from recursion?