It's an OO-solution I'm after! Sure in this simple case I could add a
Process method to the Node class but what if I where to do something
more interesting in the Process method or the Node classes where not
under my control (CodeDom classes for instance)?
public class NodeProcessor {
private StringBuilder _sb = new StringBuilder();
void Process(Node node) {
if (node is BinaryNode) {
BinaryNode bnode = (BinaryNode)node;
Process(bnode.Left);
_sb.Append(bnode.Operator);
Process(bnode.Right);
}
else if (node is SetNode) {
SetNode snode = (SetNode)node;
bool first = true;
foreach (Node n in snode.Nodes) {
if (!first)
_sb.Append(",");
Process(n);
first = false;
}
}
else if (node is LiteralNode) {
LiteralNode lnode = (LiteralNode)node;
_sb.Append(lnode.Value);
}
// 10-15 other subclasses to handle
else if (...) { }
}
public string Result {
get { return _sb.ToString(); }
}
}
I could use the Visitor approach but that limits the control you have
while processing the node tree, for example the comma handling for the
SetNode processing.
Basically I'm after a solution that is maintainable, object-oriented and
fast :)
// Kristofer
-----Original Message-----
From: Discussion of advanced .NET topics.
[mailto:[EMAIL PROTECTED] On Behalf Of John Brett
Sent: den 17 juli 2006 18:10
To: [email protected]
Subject: Re: [ADVANCED-DOTNET] Multiple downcasts pattern
<snip>
> My problem is when you have a lot of subclasses to Node that you want
to
> process in different ways the second example gets very deeply nested
and
> hard to maintain. Is there a better way to deal with multiple
downcasts
> like this?
The example above is crying out for an object-oriented solution. Add an
abstract "Process" method to your base class, and lose all of the casts.
If you absolutely can't do that, then you could build an if/elseif tree
based
on node.GetType(), although even that's pretty poor practice unless you
absolutely can't use the OO approach.
John
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