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

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

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