• Burton Radons <burton.radons gmail.com> May 23 2009
• div0 <div0 users.sourceforge.net> May 24 2009

Burton Radons <burton.radons gmail.com> writes:

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?

div0 <div0 users.sourceforge.net> writes:

Burton Radons wrote:
 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?


std.typecons.rebindable

a pointer with a nice wrapper basically.

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