[Dltk-dev] RE: Extending AST classes plus ASTNode.traverse template

["Doucette, Charles" <cdoucette@xxxxxxxxxxx>]

At least in this particular case, there are accessor methods that I can call to get the value of each child node.

Thus, I can implement my own version of traverseChildNodes by duplicating the code in the parent classes traverse method.

Ideally, I shouldn't have to do this.

Thanks,
Chuck 

-----Original Message-----
From: dltk-dev-bounces@xxxxxxxxxxx [mailto:dltk-dev-bounces@xxxxxxxxxxx] On Behalf Of Doucette, Charles
Sent: Tuesday, December 02, 2008 12:33 PM
To: DLTK Developer Discussions
Cc: Agranov, Gennady; George, Joseph; Murashova, Tatiana
Subject: [Dltk-dev] Extending AST classes plus ASTNode.traverse template

Our project includes classes which extend your AST classes.

The issue we just discovered is how you handle the visitor pattern.

Here's an example in the class MethodDeclaration:


	public void traverse(ASTVisitor visitor) throws Exception {

		if (visitor.visit(this)) {
			// Deocrators
			if (this.decorators != null) {
				if (this.decorators != null) {
					Iterator it = this.decorators.iterator();
					while (it.hasNext()) {
						Decorator dec = (Decorator) it.next();
						dec.traverse(visitor);
					}
				}
			}

			// Arguments
			if (this.arguments != null) {
				Iterator it = this.arguments.iterator();
				while (it.hasNext()) {
					Argument arg = (Argument) it.next();
					arg.traverse(visitor);
				}
			}

			// Body
			if (this.body != null) {
				this.body.traverse(visitor);
			}

			visitor.endvisit(this);
		}
	}

Our child class adds a few new child ASTNode objects. Here's an example class:

public class MyNode extends ASTNode {
}

public class MyMethodDeclaration extends MethodDeclaration {

private MyNode m_myNode;

	public void traverse(ASTVisitor visitor) throws Exception {

		if (visitor.visit(this)) {

			if (this.m_myNode != null) {
				this.m_myNode.traverse(visitor);
			}

			visitor.endvisit(this);
		}
	}
}

On the surface - this looks fine - except it never traverses the child nodes from the super class object.

How could it do that?

Ideally, you would add a method traverseChildNodes, like this:

	public traverseChildNodes(ASTVisitor visitor) throws Exception {
			// Deocrators
			if (this.decorators != null) {
				if (this.decorators != null) {
					Iterator it = this.decorators.iterator();
					while (it.hasNext()) {
						Decorator dec = (Decorator) it.next();
						dec.traverse(visitor);
					}
				}
			}

			// Arguments
			if (this.arguments != null) {
				Iterator it = this.arguments.iterator();
				while (it.hasNext()) {
					Argument arg = (Argument) it.next();
					arg.traverse(visitor);
				}
			}

			// Body
			if (this.body != null) {
				this.body.traverse(visitor);
			}
}

Then, I could add my own traverseChildNodes method:

	public traverseChildNodes(ASTVisitor visitor) throws Exception {
		super.traverseChildNodes(visitor);
		if (this.m_myNode != null) {
			this.m_myNode.traverse(visitor);
		}
	}

In the absence of this - could you make the data members of each ASTNode protected instead of private?

Thanks,
Chuck
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